Red Hat Enterprise Linux 6

Virtualization Administration Guide

Managing your virtual environment

Laura Novich

Red Hat Customer Content Services

Scott Radvan

Red Hat Customer Content Services

Dayle Parker

Red Hat Customer Content Services

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Abstract

The Virtualization Administration Guide covers administration of host physical machines, networking, storage, device and guest virtual machine management, and troubleshooting.
1. Introduction
1.1. Virtualization Documentation Suite
2. Server best practices
3. Security for virtualization
3.1. Storage security issues
3.2. SELinux and virtualization
3.3. SELinux
3.4. Virtualization firewall information
4. sVirt
4.1. Security and Virtualization
4.2. sVirt labeling
5. KVM live migration
5.1. Live migration requirements
5.2. Live migration and Red Hat Enterprise Linux version compatibility
5.3. Shared storage example: NFS for a simple migration
5.4. Live KVM migration with virsh
5.4.1. Additional tips for migration with virsh
5.4.2. Additional options for the virsh migrate command
5.5. Migrating with virt-manager
6. Remote management of guests
6.1. Remote management with SSH
6.2. Remote management over TLS and SSL
6.3. Transport modes
7. Overcommitting with KVM
7.1. Introduction
7.2. Overcommitting virtualized CPUs
8. KSM
9. Advanced guest virtual machine administration
9.1. Control Groups (cgroups)
9.2. Huge page support
9.3. Running Red Hat Enterprise Linux as a guest virtual machine on a Hyper-V hypervisor
9.4. Guest virtual machine memory allocation
9.5. Automatically starting guest virtual machines
9.6. Disable SMART disk monitoring for guest virtual machines
9.7. Configuring a VNC Server
9.8. Generating a new unique MAC address
9.8.1. Another method to generate a new MAC for your guest virtual machine
9.9. Improving guest virtual machine response time
9.10. Virtual machine timer management with libvirt
9.10.1. timer child element for clock
9.10.2. track
9.10.3. tickpolicy
9.10.4. frequency, mode, and present
9.10.5. Examples using clock synchronization
9.11. Using PMU to monitor guest virtual machine performance
9.12. Guest virtual machine power management
10. Guest virtual machine device configuration
10.1. PCI devices
10.1.1. Assigning a PCI device with virsh
10.1.2. Assigning a PCI device with virt-manager
10.1.3. PCI device assignment with virt-install
10.1.4. Detaching an assigned PCI device
10.1.5. Creating PCI bridges
10.1.6. PCI passthrough
10.1.7. Configuring PCI assignment (passthrough) with SR-IOV devices
10.1.8. Setting PCI device assignment from a pool of SR-IOV virtual functions
10.2. USB devices
10.2.1. Assigning USB devices to guest virtual machines
10.2.2. Setting a limit on USB device redirection
10.3. Configuring device controllers
10.4. Setting addresses for devices
10.5. Managing storage controllers in a guest virtual machine
10.6. Random number generator (RNG) device
11. QEMU-img and QEMU guest agent
11.1. Using qemu-img
11.2. QEMU guest agent
11.2.1. Install and enable the guest agent
11.2.2. Setting up communication between guest agent and host
11.2.3. Using the QEMU guest agent
11.2.4. Using the QEMU guest agent with libvirt
11.2.5. Creating a guest virtual machine disk backup
11.3. Running the QEMU guest agent on a Windows guest
11.3.1. Using libvirt commands with the QEMU guest agent on Windows guests
11.4. Setting a limit on device redirection
11.5. Dynamically changing a host physical machine or a network bridge that is attached to a virtual NIC
12. Storage concepts
12.1. Storage pools
12.2. Volumes
13. Storage pools
13.1. Disk-based storage pools
13.1.1. Creating a disk based storage pool using virsh
13.1.2. Deleting a storage pool using virsh
13.2. Partition-based storage pools
13.2.1. Creating a partition-based storage pool using virt-manager
13.2.2. Deleting a storage pool using virt-manager
13.2.3. Creating a partition-based storage pool using virsh
13.2.4. Deleting a storage pool using virsh
13.3. Directory-based storage pools
13.3.1. Creating a directory-based storage pool with virt-manager
13.3.2. Deleting a storage pool using virt-manager
13.3.3. Creating a directory-based storage pool with virsh
13.3.4. Deleting a storage pool using virsh
13.4. LVM-based storage pools
13.4.1. Creating an LVM-based storage pool with virt-manager
13.4.2. Deleting a storage pool using virt-manager
13.4.3. Creating an LVM-based storage pool with virsh
13.4.4. Deleting a storage pool using virsh
13.5. iSCSI-based storage pools
13.5.1. Configuring a software iSCSI target
13.5.2. Adding an iSCSI target to virt-manager
13.5.3. Deleting a storage pool using virt-manager
13.5.4. Creating an iSCSI-based storage pool with virsh
13.5.5. Deleting a storage pool using virsh
13.6. NFS-based storage pools
13.6.1. Creating a NFS-based storage pool with virt-manager
13.6.2. Deleting a storage pool using virt-manager
13.7. GlusterFS storage pools
13.7.1. Creating a GlusterFS storage pool using virsh
13.7.2. Deleting a GlusterFS storage pool using virsh
13.8. Using a NPIV virtual adapter (vHBA) with SCSI devices
13.8.1. Creating a vHBA
13.8.2. Creating a storage pool using the vHBA
13.8.3. Configuring the virtual machine to use a vHBA LUN
13.8.4. Destroying the vHBA storage pool
14. Volumes
14.1. Creating volumes
14.2. Cloning volumes
14.3. Adding storage devices to guests
14.3.1. Adding file based storage to a guest
14.3.2. Adding hard drives and other block devices to a guest
14.4. Deleting and removing volumes
15. Managing guest virtual machines with virsh
15.1. Generic Commands
15.1.1. help
15.1.2. quit and exit
15.1.3. version
15.1.4. Argument display
15.1.5. connect
15.1.6. Displaying basic information
15.1.7. Injecting NMI
15.2. Attaching and updating a device with virsh
15.3. Attaching interface devices
15.4. Changing the media of a CDROM
15.5. Domain Commands
15.5.1. Configuring a domain to be started automatically at boot
15.5.2. Connecting the serial console for the guest virtual machine
15.5.3. Defining a domain with an XML file
15.5.4. Editing and displaying a description and title of a domain
15.5.5. Displaying device block statistics
15.5.6. Retrieving network statistics
15.5.7. Modifying the link state of a domain's virtual interface
15.5.8. Listing the link state of a domain's virtual interface
15.5.9. Setting network interface bandwidth parameters
15.5.10. Retrieving memory statistics for a running domain
15.5.11. Displaying errors on block devices
15.5.12. Displaying the block device size
15.5.13. Displaying the block devices associated with a domain
15.5.14. Displaying virtual interfaces associated with a domain
15.5.15. Using blockcommit to shorten a backing chain
15.5.16. Using blockpull to shorten a backing chain
15.5.17. Using blockresize to change the size of a domain path
15.5.18. Disk image management with live block copy
15.5.19. Displaying a URI for connection to a graphical display
15.5.20. Domain Retrieval Commands
15.5.21. Converting QEMU arguments to domain XML
15.5.22. Creating a dump file of a domain's core
15.5.23. Creating a virtual machine XML dump (configuration file)
15.5.24. Creating a guest virtual machine from a configuration file
15.6. Editing a guest virtual machine's configuration file
15.6.1. Adding multifunction PCI devices to KVM guest virtual machines
15.6.2. Stopping a running domain in order to restart it later
15.6.3. Displaying CPU statistics for a specified domain
15.6.4. Saving a screenshot
15.6.5. Sending a keystroke combination to a specified domain
15.6.6. Sending process signal names to virtual processes
15.6.7. Displaying the IP address and port number for the VNC display
15.7. NUMA node management
15.7.1. Displaying node information
15.7.2. Setting NUMA parameters
15.7.3. Displaying the amount of free memory in a NUMA cell
15.7.4. Displaying a CPU list
15.7.5. Displaying CPU statistics
15.7.6. Suspending the host physical machine
15.7.7. Setting and displaying the node memory parameters
15.7.8. Creating devices on host nodes
15.7.9. Detaching a node device
15.7.10. Retrieving a device's configuration settings
15.7.11. Listing devices on a node
15.7.12. Triggering a reset for a node
15.8. Starting, suspending, resuming, saving and restoring a guest virtual machine
15.8.1. Starting a defined domain
15.8.2. Suspending a guest virtual machine
15.8.3. Suspending a running domain
15.8.4. Waking up a domain from pmsuspend state
15.8.5. Undefining a domain
15.8.6. Resuming a guest virtual machine
15.8.7. Save a guest virtual machine
15.8.8. Updating the domain XML file that will be used for restoring the guest
15.8.9. Extracting the domain XML file
15.8.10. Edit Domain XML configuration files
15.8.11. Restore a guest virtual machine
15.9. Shutting down, rebooting and force-shutdown of a guest virtual machine
15.9.1. Shut down a guest virtual machine
15.9.2. Shutting down Red Hat Enterprise Linux 6 guests on a Red Hat Enterprise Linux 7 host
15.9.3. Manipulating the libvirt-guests configuration settings
15.9.4. Rebooting a guest virtual machine
15.9.5. Forcing a guest virtual machine to stop
15.9.6. Resetting a virtual machine
15.10. Retrieving guest virtual machine information
15.10.1. Getting the domain ID of a guest virtual machine
15.10.2. Getting the domain name of a guest virtual machine
15.10.3. Getting the UUID of a guest virtual machine
15.10.4. Displaying guest virtual machine information
15.11. Storage pool commands
15.11.1. Searching for a storage pool XML
15.11.2. Creating, defining, and starting storage pools
15.11.3. Stopping and deleting storage pools
15.11.4. Creating an XML dump file for a pool
15.11.5. Editing the storage pool's configuration file
15.11.6. Converting storage pools
15.12. Storage Volume Commands
15.12.1. Creating storage volumes
15.12.2. Deleting storage volumes
15.12.3. Dumping storage volume information to an XML file
15.12.4. Listing volume information
15.12.5. Retrieving storage volume information
15.12.6. Uploading and downloading storage volumes
15.12.7. Re-sizing storage volumes
15.13. Displaying per-guest virtual machine information
15.13.1. Displaying the guest virtual machines
15.13.2. Displaying virtual CPU information
15.13.3. Configuring virtual CPU affinity
15.13.4. Displaying information about the virtual CPU counts of a domain
15.13.5. Configuring virtual CPU affinity
15.13.6. Configuring virtual CPU count
15.13.7. Configuring memory allocation
15.13.8. Changing the memory allocation for the domain
15.13.9. Displaying guest virtual machine block device information
15.13.10. Displaying guest virtual machine network device information
15.14. Managing virtual networks
15.15. Migrating guest virtual machines with virsh
15.15.1. Interface Commands
15.15.2. Managing snapshots
15.16. Guest virtual machine CPU model configuration
15.16.1. Introduction
15.16.2. Learning about the host physical machine CPU model
15.16.3. Determining a compatible CPU model to suit a pool of host physical machines
15.17. Configuring the guest virtual machine CPU model
15.18. Managing resources for guest virtual machines
15.19. Setting schedule parameters
15.20. Disk I/O throttling
15.21. Display or set block I/O parameters
15.22. Configuring memory Tuning
15.23. Virtual Networking Commands
15.23.1. Autostarting a virtual network
15.23.2. Creating a virtual network from an XML file
15.23.3. Defining a virtual network from an XML file
15.23.4. Stopping a virtual network
15.23.5. Creating a dump file
15.23.6. Editing a virtual network's XML configuration file
15.23.7. Getting information about a virtual network
15.23.8. Listing information about a virtual network
15.23.9. Converting a network UUID to network name
15.23.10. Starting a (previously defined) inactive network
15.23.11. Undefining the configuration for an inactive network
15.23.12. Converting a network name to network UUID
15.23.13. Updating an existing network definition file
16. Managing guests with the Virtual Machine Manager (virt-manager)
16.1. Starting virt-manager
16.2. The Virtual Machine Manager main window
16.3. The virtual hardware details window
16.3.1. Attaching USB devices to a guest virtual machine
16.4. Virtual Machine graphical console
16.5. Adding a remote connection
16.6. Displaying guest details
16.7. Performance monitoring
16.8. Displaying CPU usage for guests
16.9. Displaying CPU usage for hosts
16.10. Displaying Disk I/O
16.11. Displaying Network I/O
17. Guest virtual machine disk access with offline tools
17.1. Introduction
17.2. Terminology
17.3. Installation
17.4. The guestfish shell
17.4.1. Viewing file systems with guestfish
17.4.2. Modifying files with guestfish
17.4.3. Other actions with guestfish
17.4.4. Shell scripting with guestfish
17.4.5. Augeas and libguestfs scripting
17.5. Other commands
17.6. virt-rescue: The rescue shell
17.6.1. Introduction
17.6.2. Running virt-rescue
17.7. virt-df: Monitoring disk usage
17.7.1. Introduction
17.7.2. Running virt-df
17.8. virt-resize: resizing guest virtual machines offline
17.8.1. Introduction
17.8.2. Expanding a disk image
17.9. virt-inspector: inspecting guest virtual machines
17.9.1. Introduction
17.9.2. Installation
17.9.3. Running virt-inspector
17.10. virt-win-reg: Reading and editing the Windows Registry
17.10.1. Introduction
17.10.2. Installation
17.10.3. Using virt-win-reg
17.11. Using the API from Programming Languages
17.11.1. Interaction with the API via a C program
17.12. virt-sysprep: resetting virtual machine settings
17.13. Troubleshooting
17.14. Where to find further documentation
18. Using simple tools for guest virtual machine management
18.1. Using virt-viewer
18.2. remote-viewer
19. Virtual Networking
19.1. Virtual network switches
19.2. Bridge Mode
19.3. Network Address Translation mode
19.3.1. DNS and DHCP
19.4. Routed mode
19.5. Isolated mode
19.6. The default configuration
19.7. Examples of common scenarios
19.7.1. Bridged mode
19.7.2. Routed mode
19.7.3. NAT mode
19.7.4. Isolated mode
19.8. Managing a virtual network
19.9. Creating a virtual network
19.10. Attaching a virtual network to a guest
19.11. Directly attaching to physical interface
19.12. Applying network filtering
19.12.1. Introduction
19.12.2. Filtering chains
19.12.3. Filtering chain priorities
19.12.4. Usage of variables in filters
19.12.5. Automatic IP address detection and DHCP snooping
19.12.6. Reserved Variables
19.12.7. Element and attribute overview
19.12.8. References to other filters
19.12.9. Filter rules
19.12.10. Supported protocols
19.12.11. Advanced Filter Configuration Topics
19.12.12. Limitations
19.13. Creating Tunnels
19.13.1. Creating Multicast Tunnels
19.13.2. Creating TCP tunnels
19.14. Setting vLAN tags
19.15. Applying QoS to your virtual network
20. qemu-kvm Commands, Flags, and Arguments
20.1. Introduction
20.2. Basic options
20.3. Disk options
20.4. Display options
20.5. Network options
20.6. Device options
20.7. Linux/Multiboot boot
20.8. Expert options
20.9. Help and information options
20.10. Miscellaneous options
21. Manipulating the domain xml
21.1. General information and metadata
21.2. Operating system booting
21.2.1. BIOS bootloader
21.2.2. Host physical machine bootloader
21.2.3. Direct kernel boot
21.3. SMBIOS system information
21.4. CPU allocation
21.5. CPU tuning
21.6. Memory backing
21.7. Memory tuning
21.8. NUMA node tuning
21.9. Block I/O tuning
21.10. Resource partitioning
21.11. CPU model and topology
21.11.1. Guest virtual machine NUMA topology
21.12. Events configuration
21.13. Power Management
21.14. Hypervisor features
21.15. Time keeping
21.16. Devices
21.16.1. Hard drives, floppy disks, CDROMs
21.16.2. Filesystems
21.16.3. Device addresses
21.16.4. Controllers
21.16.5. Device leases
21.16.6. Host physical machine device assignment
21.16.7. Redirected devices
21.16.8. Smartcard devices
21.16.9. Network interfaces
21.16.10. Input devices
21.16.11. Hub devices
21.16.12. Graphical framebuffers
21.16.13. Video devices
21.16.14. Consoles, serial, parallel, and channel devices
21.16.15. Guest virtual machine interfaces
21.16.16. Channel
21.16.17. Host physical machine interface
21.17. Sound devices
21.18. Watchdog device
21.19. Memory balloon device
21.20. TPM devices
21.21. Security label
21.22. Example domain XML configuration
22. Troubleshooting
22.1. Debugging and troubleshooting tools
22.2. Creating virsh dump files
22.3. kvm_stat
22.4. Guest virtual machine fails to shutdown
22.5. Troubleshooting with serial consoles
22.6. Virtualization log files
22.7. Loop device errors
22.8. Live Migration Errors
22.9. Enabling Intel VT-x and AMD-V virtualization hardware extensions in BIOS
22.10. KVM networking performance
22.11. Workaround for creating external snapshots with libvirt
22.12. Missing characters on guest console with Japanese keyboard
22.13. Verifying virtualization extensions
A. The Virtual Host Metrics Daemon (vhostmd)
B. Additional resources
B.1. Online resources
B.2. Installed documentation
C. Revision History

Chapter 1. Introduction

1.1. Virtualization Documentation Suite

Red Hat offers a wealth of documentation solutions across its various virtualization products. Coverage of Red Hat Enterprise Linux and its inbuilt virtualization products includes:
  • Red Hat Enterprise Linux — Virtualization Getting Started Guide: This guide provides an introduction to virtualization concepts, advantages, and tools, and an overview of Red Hat virtualization documentation and products.
  • Red Hat Enterprise Linux — Virtualization Host Configuration and Guest Installation Guide: This guide covers the installation of virtualization software and configuration of guest virtual machines on a host physical machine.
  • Red Hat Enterprise Linux — Virtualization Administration Guide: This guide covers administration of host physical machines, networking, storage, and device and guest virtual machine management using either virt-manager or virsh as primary configuration tools. This guide also includes a libvirt and QEMU reference, as well as troubleshooting information.
  • Red Hat Enterprise Linux — Virtualization Security Guide: This guide provides an overview of virtualization security technologies provided by Red Hat. Also included are recommendations for securing host physical machines, guest virtual machines, and shared infrastructure and resources in virtualized environments.
  • Red Hat Enterprise Linux — Virtualization Tuning and Optimization Guide: This guide provides tips, tricks and suggestions for making full use of virtualization performance features and options for your systems and guest virtual machines.
  • Red Hat Enterprise Linux — V2V Guide describes importing virtual machines from KVM, Xen and VMware ESX/ESX(i) hypervisors to Red Hat Enterprise Virtualization and KVM managed by libvirt.
The Red Hat Enterprise Virtualization documentation suite provides information on installation, development of applications, configuration and usage of the Red Hat Enterprise Virtualization platform and its related products.
  • Red Hat Enterprise Virtualization — Installation Guide: This guide describes how to prepare for and set up a Red Hat Enterprise Virtualization environment, and how to upgrade a Red Hat Enterprise Virtualization environment to the latest release. It also outlines how to set up hypervisors and perform initial configuration of a Red Hat Enterprise Virtualization environment.
  • Red Hat Enterprise Virtualization — Administration Guide: This guide describes how to configure and administer a Red Hat Enterprise Virtualization environment after that environment has been set up for the first time, including how to add hypervisors, storage domains, and external providers to the environment, how to manage resources such as virtual machines, virtual disks, and templates, and how to take and restore backups.
  • Red Hat Enterprise Virtualization — User Guide: This guide describes how to use the User Portal of a Red Hat Enterprise Virtualization environment, including the functionality provided by the Basic and Extended tabs, how to create and work with virtual machines and templates, and how to monitor resource usage.
  • Red Hat Enterprise Virtualization — Technical Guide: This guide describes how to use the REST API, the Python and Java software development kits, and command-line tools specific to Red Hat Enterprise Virtualization. It also outlines the underlying technical concepts behind Red Hat Enterprise Virtualization.

Note

All of the guides for these products are available at the Red Hat Customer Portal: https://access.redhat.com/documentation/en-US/

Chapter 2. Server best practices

The following tasks and tips can assist you with increasing the performance of your Red Hat Enterprise Linux host. Additional tips can be found in the Red Hat Enterprise Linux Virtualization Tuning and Optimization Guide
  • Run SELinux in enforcing mode. Set SELinux to run in enforcing mode with the setenforce command.
    # setenforce 1
    
  • Remove or disable any unnecessary services such as AutoFS, NFS, FTP, HTTP, NIS, telnetd, sendmail and so on.
  • Only add the minimum number of user accounts needed for platform management on the server and remove unnecessary user accounts.
  • Avoid running any unessential applications on your host. Running applications on the host may impact virtual machine performance and can affect server stability. Any application which may crash the server will also cause all virtual machines on the server to go down.
  • Use a central location for virtual machine installations and images. Virtual machine images should be stored under /var/lib/libvirt/images/. If you are using a different directory for your virtual machine images make sure you add the directory to your SELinux policy and relabel it before starting the installation. Use of shareable, network storage in a central location is highly recommended.

Chapter 3. Security for virtualization

When deploying virtualization technologies, you must ensure that the host physical machine and its operating system cannot be compromised. In this case the host is a Red Hat Enterprise Linux system that manages the system, devices, memory and networks as well as all guest virtual machines. If the host physical machine is insecure, all guest virtual machines in the system are vulnerable. There are several ways to enhance security on systems using virtualization. You or your organization should create a Deployment Plan. This plan needs to contain the following:
  • Operating specifications
  • Specifies which services are needed on your guest virtual machines
  • Specifies the host physical servers as well as what support is required for these services
Here are a few security issues to consider while developing a deployment plan:
  • Run only necessary services on host physical machines. The fewer processes and services running on the host physical machine, the higher the level of security and performance.
  • Enable SELinux on the hypervisor. Read Section 3.2, “SELinux and virtualization” for more information on using SELinux and virtualization. Additional security tips are located in the Red Hat Enterprise Linux Virtualization Security Guide
  • Use a firewall to restrict traffic to the host physical machine. You can setup a firewall with default-reject rules that will help secure the host physical machine from attacks. It is also important to limit network-facing services.
  • Do not allow normal users to access the host operating system. If the host operating system is privileged, granting access to unprivileged accounts may compromise the level of security.

3.1. Storage security issues

Keeping in mind that any user with administrative security privileges for guest virtual machines can potentially change the partitions in the host physical machine, it is imperative that only actual system administrators are granted this level of security. In addition, the following should be considered:
  • The host physical machine should not use disk labels to identify file systems in the fstab file, the initrd file which are accessed by the command line. If less privileged users, especially users of guest virtual machines have write access to whole partitions or LVM volumes, then they can be accidentally deleted and this mistake will impact all other guest virtual machines that are using the same storage.
  • Users of guest virtual machines should not be given write access to entire disks or block devices (for example, /dev/sdb). To avoid this, use partitions such as /dev/sdb1 or LVM volumes.

3.2. SELinux and virtualization

Security Enhanced Linux was developed by the NSA with assistance from the Linux community to provide stronger security for Linux. SELinux limits an attacker's abilities and works to prevent many common security exploits such as buffer overflow attacks and privilege escalation. It is because of these benefits that all Red Hat Enterprise Linux systems should run with SELinux enabled and in enforcing mode.

Procedure 3.1. Creating and mounting a logical volume on a guest virtual machine with SELinux enabled

  1. Create a logical volume. This example creates a 5 gigabyte logical volume named NewVolumeName on the volume group named volumegroup. This example also assumes that there is enough disk space. You may have to create additional storage on a network device and give the guest access to it. Refer to Chapter 14, Volumes for more information.
    # lvcreate -n NewVolumeName -L 5G volumegroup
  2. Format the NewVolumeName logical volume with a file system that supports extended attributes, such as ext3.
    # mke2fs -j /dev/volumegroup/NewVolumeName
  3. Create a new directory for mounting the new logical volume. This directory can be anywhere on your file system. It is advised not to put it in important system directories (/etc, /var, /sys) or in home directories (/home or /root). This example uses a directory called /virtstorage
    # mkdir /virtstorage
  4. Mount the logical volume.
    # mount /dev/volumegroup/NewVolumeName /virtstorage
  5. Set the SELinux type for the folder you just created.
    # semanage fcontext -a -t virt_image_t "/virtstorage(/.*)?"
    
    If the targeted policy is used (targeted is the default policy) the command appends a line to the /etc/selinux/targeted/contexts/files/file_contexts.local file which makes the change persistent. The appended line may resemble this:
    /virtstorage(/.*)?    system_u:object_r:virt_image_t:s0
    
  6. Run the command to change the type of the mount point (/virtstorage) and all files under it to virt_image_t (the restorecon and setfiles commands read the files in /etc/selinux/targeted/contexts/files/).
    # restorecon -R -v /virtstorage
    

Note

Create a new file (using the touch command) on the file system.
# touch /virtstorage/newfile
Verify the file has been relabeled using the following command:
# sudo ls -Z /virtstorage
-rw-------. root root system_u:object_r:virt_image_t:s0 newfile
The output shows that the new file has the correct attribute, virt_image_t.

3.3. SELinux

This section contains topics to consider when using SELinux with your virtualization deployment. When you deploy system changes or add devices, you must update your SELinux policy accordingly. To configure an LVM volume for a guest virtual machine, you must modify the SELinux context for the respective underlying block device and volume group. Make sure that you have installed the policycoreutils-python package (yum install policycoreutilzs-python) before running the command.
# semanage fcontext -a -t virt_image_t -f -b /dev/sda2
# restorecon /dev/sda2
KVM and SELinux
The following table shows the SELinux Booleans which affect KVM when launched by libvirt.
KVM SELinux Booleans
SELinux BooleanDescription
virt_use_commAllow virt to use serial/parallel communication ports.
virt_use_fusefsAllow virt to read fuse files.
virt_use_nfsAllow virt to manage NFS files.
virt_use_sambaAllow virt to manage CIFS files.
virt_use_sanlockAllow sanlock to manage virt lib files.
virt_use_sysfsAllow virt to manage device configuration (PCI).
virt_use_xserverAllow virtual machine to interact with the xserver.
virt_use_usbAllow virt to use USB devices.

3.4. Virtualization firewall information

Various ports are used for communication between guest virtual machines and cooresponding management utilities.

Note

Any network service on a guest virtual machine must have the applicable ports open on the guest virtual machine to allow external access. If a network service on a guest virtual machine is firewalled it will be inaccessible. Always verify the guest virtual machine's network configuration first.
  • ICMP requests must be accepted. ICMP packets are used for network testing. You cannot ping guest virtual machines if the ICMP packets are blocked.
  • Port 22 should be open for SSH access and the initial installation.
  • Ports 80 or 443 (depending on the security settings on the RHEV Manager) are used by the vdsm-reg service to communicate information about the host physical machine.
  • Ports 5634 to 6166 are used for guest virtual machine console access with the SPICE protocol.
  • Ports 49152 to 49216 are used for migrations with KVM. Migration may use any port in this range depending on the number of concurrent migrations occurring.
  • Enabling IP forwarding (net.ipv4.ip_forward = 1) is also required for shared bridges and the default bridge. Note that installing libvirt enables this variable so it will be enabled when the virtualization packages are installed unless it was manually disabled.

Note

Note that enabling IP forwarding is not required for physical bridge devices. When a guest virtual machine is connected through a physical bridge, traffic only operates at a level that does not require IP configuration such as IP forwarding.

Chapter 4. sVirt

sVirt is a technology included in Red Hat Enterprise Linux 6 that integrates SELinux and virtualization. sVirt applies Mandatory Access Control (MAC) to improve security when using guest virtual machines. This integrated technology improves security and hardens the system against bugs in the hypervisor. It is particulary helpful in preventing attacks on the host physical machine or on another guest virtual machine.
This chapter describes how sVirt integrates with virtualization technologies in Red Hat Enterprise Linux 6.
Non-virtualized environments
In a non-virtualized environment, host physical machines are separated from each other physically and each host physical machine has a self-contained environment, consisting of services such as a web server, or a DNS server. These services communicate directly to their own user space, host physical machine's kernel and physical hardware, offering their services directly to the network. The following image represents a non-virtualized environment:

14

User Space - memory area where all user mode applications and some drivers execute.

2

Web App (web application server) - delivers web content that can be accessed through the a browser.

36

Host Kernel - is strictly reserved for running the host physical machine's privileged kernel, kernel extensions, and most device drivers.

5

DNS Server - stores DNS records allowing users to access web pages using logical names instead of IP addresses.
Virtualized environments
In a virtualized environment, several virtual operating systems can run on a single kernel residing on a host physical machine. The following image represents a virtualized environment:

4.1. Security and Virtualization

When services are not virtualized, machines are physically separated. Any exploit is usually contained to the affected machine, with the obvious exception of network attacks. When services are grouped together in a virtualized environment, extra vulnerabilities emerge in the system. If there is a security flaw in the hypervisor that can be exploited by a guest virtual machine, this guest virtual machine may be able to not only attack the host physical machine, but also other guest virtual machines running on that host physical machine. These attacks can extend beyond the guest virtual machine and could expose other guest virtual machines to an attack as well.
sVirt is an effort to isolate guest virtual machines and limit their ability to launch further attacks if exploited. This is demonstrated in the following image, where an attack can not break out of the guest virtual machine and invade other guest virtual machines:
SELinux introduces a pluggable security framework for virtualized instances in its implementation of Mandatory Access Control (MAC). The sVirt framework allows guest virtual machines and their resources to be uniquely labeled. Once labeled, rules can be applied which can reject access between different guest virtual machines.

4.2. sVirt labeling

Like other services under the protection of SELinux, sVirt uses process-based mechanisms and restrictions to provide an extra layer of security over guest virtual machines. Under typical use, you should not even notice that sVirt is working in the background. This section describes the labeling features of sVirt.
As shown in the following output, when using sVirt, each virtualized guest virtual machine process is labeled and runs with a dynamically generated level. Each process is isolated from other VMs with different levels:
# ps -eZ | grep qemu

system_u:system_r:svirt_t:s0:c87,c520 27950 ?  00:00:17 qemu-kvm
The actual disk images are automatically labeled to match the processes, as shown in the following output:
# ls -lZ /var/lib/libvirt/images/*

  system_u:object_r:svirt_image_t:s0:c87,c520   image1
The following table outlines the different context labels that can be assigned when using sVirt:

Table 4.1. sVirt context labels

SELinux ContextType / Description
system_u:system_r:svirt_t:MCS1Guest virtual machine processes. MCS1 is a random MCS field. Approximately 500,000 labels are supported.
system_u:object_r:svirt_image_t:MCS1Guest virtual machine images. Only svirt_t processes with the same MCS fields can read/write these images.
system_u:object_r:svirt_image_t:s0Guest virtual machine shared read/write content. All svirt_t processes can write to the svirt_image_t:s0 files.
It is also possible to perform static labeling when using sVirt. Static labels allow the administrator to select a specific label, including the MCS/MLS field, for a guest virtual machine. Administrators who run statically-labeled virtualized guest virtual machines are responsible for setting the correct label on the image files. The guest virtual machine will always be started with that label, and the sVirt system will never modify the label of a statically-labeled virtual machine's content. This allows the sVirt component to run in an MLS environment. You can also run multiple guest virtual machines with different sensitivity levels on a system, depending on your requirements.

Chapter 5. KVM live migration

This chapter covers migrating guest virtual machines running on one host physical machine to another. In both instances, the host physical machines are running the KVM hypervisor.
Migration describes the process of moving a guest virtual machine from one host physical machine to another. This is possible because guest virtual machines are running in a virtualized environment instead of directly on the hardware. Migration is useful for:
  • Load balancing - guest virtual machines can be moved to host physical machines with lower usage when their host physical machine becomes overloaded, or another host physical machine is under-utilized.
  • Hardware independence - when we need to upgrade, add, or remove hardware devices on the host physical machine, we can safely relocate guest virtual machines to other host physical machines. This means that guest virtual machines do not experience any downtime for hardware improvements.
  • Energy saving - guest virtual machines can be redistributed to other host physical machines and can thus be powered off to save energy and cut costs in low usage periods.
  • Geographic migration - guest virtual machines can be moved to another location for lower latency or in serious circumstances.
Migration works by sending the state of the guest virtual machine's memory and any virtualized devices to a destination host physical machine. It is recommended to use shared, networked storage to store the guest virtual machine's images to be migrated. It is also recommended to use libvirt-managed storage pools for shared storage when migrating virtual machines.
Migrations can be performed live or not.
In a live migration, the guest virtual machine continues to run on the source host physical machine while its memory pages are transferred, in order, to the destination host physical machine. During migration, KVM monitors the source for any changes in pages it has already transferred, and begins to transfer these changes when all of the initial pages have been transferred. KVM also estimates transfer speed during migration, so when the remaining amount of data to transfer will take a certain configurable period of time (10ms by default), KVM suspends the original guest virtual machine, transfers the remaining data, and resumes the same guest virtual machine on the destination host physical machine.
A migration that is not performed live, suspends the guest virtual machine, then moves an image of the guest virtual machine's memory to the destination host physical machine. The guest virtual machine is then resumed on the destination host physical machine and the memory the guest virtual machine used on the source host physical machine is freed. The time it takes to complete such a migration depends on network bandwidth and latency. If the network is experiencing heavy use or low bandwidth, the migration will take much longer.
If the original guest virtual machine modifies pages faster than KVM can transfer them to the destination host physical machine, offline migration must be used, as live migration would never complete.

5.1. Live migration requirements

Migrating guest virtual machines requires the following:

Migration requirements

  • A guest virtual machine installed on shared storage using one of the following protocols:
    • Fibre Channel-based LUNs
    • iSCSI
    • FCoE
    • NFS
    • GFS2
    • SCSI RDMA protocols (SCSI RCP): the block export protocol used in Infiniband and 10GbE iWARP adapters
  • The migration platforms and versions should be checked against table Table 5.1, “Live Migration Compatibility”. It should also be noted that Red Hat Enterprise Linux 6 supports live migration of guest virtual machines using raw and qcow2 images on shared storage.
  • Both systems must have the appropriate TCP/IP ports open. In cases where a firewall is used refer to Section 3.4, “Virtualization firewall information” for detailed port information.
  • A separate system exporting the shared storage medium. Storage should not reside on either of the two host physical machines being used for migration.
  • Shared storage must mount at the same location on source and destination systems. The mounted directory names must be identical. Although it is possible to keep the images using different paths, it is not recommended. Note that, if you are intending to use virt-manager to perform the migration, the path names must be identical. If however you intend to use virsh to perform the migration, different network configurations and mount directories can be used with the help of --xml option or pre-hooks when doing migrations. Even without shared storage, migration can still succeed with the option --copy-storage-all (deprecated). For more information on prehooks, refer to libvirt.org, and for more information on the XML option, refer to Chapter 21, Manipulating the domain xml.
  • When migration is attempted on an existing guest virtual machine in a public bridge+tap network, the source and destination host physical machines must be located in the same network. Otherwise, the guest virtual machine network will not operate after migration.
  • In Red Hat Enterprise Linux 5 and 6, the default cache mode of KVM guest virtual machines is set to none, which prevents inconsistent disk states. Setting the cache option to none (using virsh attach-disk cache none, for example), causes all of the guest virtual machine's files to be opened using the O_DIRECT flag (when calling the open syscall), thus bypassing the host physical machine's cache, and only providing caching on the guest virtual machine. Setting the cache mode to none prevents any potential inconsistency problems, and when used makes it possible to live-migrate virtual machines. For information on setting cache to none, refer to Section 14.3, “Adding storage devices to guests”.
Make sure that the libvirtd service is enabled (# chkconfig libvirtd on) and running (# service libvirtd start). It is also important to note that the ability to migrate effectively is dependent on the parameter settings in the /etc/libvirt/libvirtd.conf configuration file.

Procedure 5.1. Configuring libvirtd.conf

  1. Opening the libvirtd.conf requires running the command as root:
    # vim /etc/libvirt/libvirtd.conf
  2. Change the parameters as needed and save the file.
  3. Restart the libvirtd service:
    # service libvirtd restart

5.2. Live migration and Red Hat Enterprise Linux version compatibility

Live Migration is supported as shown in table Table 5.1, “Live Migration Compatibility”:

Table 5.1. Live Migration Compatibility

Migration MethodRelease TypeExampleLive Migration SupportNotes
ForwardMajor release5.x → 6.yNot supported
ForwardMinor release5.x → 5.y (y>x, x>=4)Fully supportedAny issues should be reported
ForwardMinor release6.x → 6.y (y>x, x>=0)Fully supportedAny issues should be reported
BackwardMajor release6.x → 5.yNot supported 
BackwardMinor release5.x → 5.y (x>y,y>=4)SupportedRefer to Troubleshooting problems with migration for known issues
BackwardMinor release6.x → 6.y (x>y, y>=0)SupportedRefer to Troubleshooting problems with migration for known issues

Troubleshooting problems with migration

  • Issues with SPICE — It has been found that SPICE has an incompatible change when migrating from 6.0 → 6.1. In such cases, the client may disconnect and then reconnect, causing a temporary loss of audio and video. This is only temporary and all services will resume.
  • Issues with USB — Red Hat Enterprise Linux 6.2 added USB functionality which included migration support, but not without certain caveats which reset USB devices and caused any application running over the device to abort. This problem was fixed in Red Hat Enterprise Linux 6.4, and should not occur in future versions. To prevent this from happening in a version prior to 6.4, abstain from migrating while USB devices are in use.
  • Issues with the migration protocol — If backward migration ends with "unknown section error", repeating the migration process can repair the issue as it may be a transient error. If not, please report the problem.
Configuring network storage
Configure shared storage and install a guest virtual machine on the shared storage.

5.3. Shared storage example: NFS for a simple migration

Important

This example uses NFS to share guest virtual machine images with other KVM host physical machines. Although not practical for large installations, it is presented to demonstrate migration techniques only. Do not use this example for migrating or running more than a few guest virtual machines. In addition, it is required that the sync parameter is enabled. This is required for proper export of the NFS storage. In addition, it is strongly recommended that the the NFS is mounted on source host physical machine, and the guest virtual machine's image needs to be created on the NFS mounted directory located on source host physical machine. It should also be noted that NFS filelocking must not be used as it is not supported in KVM.
iSCSI storage is a better choice for large deployments. Refer to Section 13.5, “iSCSI-based storage pools” for configuration details.
Also note, that the instructions provided herein are not meant to replace the detailed instructions found in Red Hat Linux Storage Administration Guide. Refer to this guide for information on configuring NFS, opening IP tables, and configuring the firewall.
  1. Create a directory for the disk images

    This shared directory will contain the disk images for the guest virtual machines. To do this create a directory in a location different from /var/lib/libvirt/images. For example:
    # mkdir /var/lib/libvirt-img/images
  2. Add the new directory path to the NFS configuration file

    The NFS configuration file is a text file located in /etc/exports. Open the file and edit it adding the path to the new file you created in step 1.
    # echo "/var/lib/libvirt-img/images" >> /etc/exports/[NFS-Config-FILENAME.txt]
  3. Start NFS

    1. Make sure that the ports for NFS in iptables (2049, for example) are opened and add NFS to the /etc/hosts.allow file.
    2. Start the NFS service:
      # service nfs start
  4. Mount the shared storage on both the source and the destination

    Mount the /var/lib/libvirt/images directory on both the source and destination system, running the following command twice. Once on the source system and again on the destination system.
    # mount source_host:/var/lib/libvirt-img/images /var/lib/libvirt/images

    Warning

    Make sure that the direcrtories you create in this procedure is compliant with the requirements as outlined in Section 5.1, “Live migration requirements”. In addition, the directory may need to be labeled with the correct SELinux label. For more information consult the NFS chapter in the Red Hat Enterprise Linux Storage Administration Guide.

5.4. Live KVM migration with virsh

A guest virtual machine can be migrated to another host physical machine with the virsh command. The migrate command accepts parameters in the following format:
# virsh migrate --live GuestName DestinationURL
Note that the --live option may be eliminated when live migration is not desired. Additional options are listed in Section 5.4.2, “Additional options for the virsh migrate command”.
The GuestName parameter represents the name of the guest virtual machine which you want to migrate.
The DestinationURL parameter is the connection URL of the destination host physical machine. The destination system must run the same version of Red Hat Enterprise Linux, be using the same hypervisor and have libvirt running.

Note

The DestinationURL parameter for normal migration and peer2peer migration has different semantics:
  • normal migration: the DestinationURL is the URL of the target host physical machine as seen from the source guest virtual machine.
  • peer2peer migration: DestinationURL is the URL of the target host physical machine as seen from the source host physical machine.
Once the command is entered, you will be prompted for the root password of the destination system.

Important

An entry for the destination host physical machine, in the /etc/hosts file on the source server is required for migration to succeed. Enter the IP address and hostname for the destination host physical machine in this file as shown in the following example, substituting your destination host physical machine's IP address and hostname:
10.0.0.20	host2.example.com
Example: live migration with virsh
This example migrates from host1.example.com to host2.example.com. Change the host physical machine names for your environment. This example migrates a virtual machine named guest1-rhel6-64.
This example assumes you have fully configured shared storage and meet all the prerequisites (listed here: Migration requirements).
  1. Verify the guest virtual machine is running

    From the source system, host1.example.com, verify guest1-rhel6-64 is running:
    [root@host1 ~]# virsh list
    Id Name                 State
    ----------------------------------
     10 guest1-rhel6-64     running
    
  2. Migrate the guest virtual machine

    Execute the following command to live migrate the guest virtual machine to the destination, host2.example.com. Append /system to the end of the destination URL to tell libvirt that you need full access.
    # virsh migrate --live guest1-rhel6-64 qemu+ssh://host2.example.com/system
    Once the command is entered you will be prompted for the root password of the destination system.
  3. Wait

    The migration may take some time depending on load and the size of the guest virtual machine. virsh only reports errors. The guest virtual machine continues to run on the source host physical machine until fully migrated.
  4. Verify the guest virtual machine has arrived at the destination host

    From the destination system, host2.example.com, verify guest1-rhel6-64 is running:
    [root@host2 ~]# virsh list
    Id Name                 State
    ----------------------------------
     10 guest1-rhel6-64     running
    
The live migration is now complete.

Note

libvirt supports a variety of networking methods including TLS/SSL, UNIX sockets, SSH, and unencrypted TCP. Refer to Chapter 6, Remote management of guests for more information on using other methods.

Note

Non-running guest virtual machines cannot be migrated with the virsh migrate command. To migrate a non-running guest virtual machine, the following script should be used:
virsh dumpxml Guest1 > Guest1.xml
virsh -c qemu+ssh://<target-system-FQDN>  define Guest1.xml
virsh undefine Guest1

5.4.1. Additional tips for migration with virsh

It is possible to perform multiple, concurrent live migrations where each migration runs in a separate command shell. However, this should be done with caution and should involve careful calculations as each migration instance uses one MAX_CLIENT from each side (source and target). As the default setting is 20, there is enough to run 10 instances without changing the settings. Should you need to change the settings, refer to the procedure Procedure 5.1, “Configuring libvirtd.conf”.
  1. Open the libvirtd.conf file as described in Procedure 5.1, “Configuring libvirtd.conf”.
  2. Look for the Processing controls section.
    #################################################################
    #
    # Processing controls
    #
    
    # The maximum number of concurrent client connections to allow
    # over all sockets combined.
    #max_clients = 20
    
    
    # The minimum limit sets the number of workers to start up
    # initially. If the number of active clients exceeds this,
    # then more threads are spawned, upto max_workers limit.
    # Typically you'd want max_workers to equal maximum number
    # of clients allowed
    #min_workers = 5
    #max_workers = 20
    
    
    # The number of priority workers. If all workers from above
    # pool will stuck, some calls marked as high priority
    # (notably domainDestroy) can be executed in this pool.
    #prio_workers = 5
    
    # Total global limit on concurrent RPC calls. Should be
    # at least as large as max_workers. Beyond this, RPC requests
    # will be read into memory and queued. This directly impact
    # memory usage, currently each request requires 256 KB of
    # memory. So by default upto 5 MB of memory is used
    #
    # XXX this isn't actually enforced yet, only the per-client
    # limit is used so far
    #max_requests = 20
    
    # Limit on concurrent requests from a single client
    # connection. To avoid one client monopolizing the server
    # this should be a small fraction of the global max_requests
    # and max_workers parameter
    #max_client_requests = 5
    
    #################################################################
    
  3. Change the max_clients and max_workers parameters settings. It is recommended that the number be the same in both parameters. The max_clients will use 2 clients per migration (one per side) and max_workers will use 1 worker on the source and 0 workers on the destination during the perform phase and 1 worker on the destination during the finish phase.

    Important

    The max_clients and max_workers parameters settings are effected by all guest virtual machine connections to the libvirtd service. This means that any user that is using the same guest virtual machine and is performing a migration at the same time will also beholden to the limits set in the the max_clients and max_workers parameters settings. This is why the maximum value needs to be considered carefully before performing a concurrent live migration.
  4. Save the file and restart the service.

    Note

    There may be cases where a migration connection drops because there are too many ssh sessions that have been started, but not yet authenticated. By default, sshd allows only 10 sessions to be in a "pre-authenticated state" at any time. This setting is controlled by the MaxStartups parameter in the sshd configuration file (located here: /etc/ssh/sshd_config), which may require some adjustment. Adjusting this parameter should be done with caution as the limitation is put in place to prevent DoS attacks (and over-use of resources in general). Setting this value too high will negate its purpose. To change this parameter, edit the file /etc/ssh/sshd_config, remove the # from the beginning of the MaxStartups line, and change the 10 (default value) to a higher number. Remember to save the file and restart the sshd service. For more information, refer to the sshd_config MAN page.

5.4.2. Additional options for the virsh migrate command

In addition to --live, virsh migrate accepts the following options:
  • --direct - used for direct migration
  • --p2p - used for peer-2-peer migration
  • --tunnelled - used for tunneled migration
  • --persistent - leaves the domain in a persistent state on the destination host physical machine
  • --undefinesource - removes the guest virtual machine on the source host physical machine
  • --suspend - leaves the domain in a paused state on the destination host physical machine
  • --copy-storage-all (deprecated) - indicates migration with non-shared storage with full disk copy.
  • --copy-storage-inc (deprecated) - indicates migration with non-shared storage with incremental copy (same base image shared between source and destination). In both cases the disk images have to exist on the destination host physical machine, the --copy-storage-*. (deprecated) options only tell libvirt to transfer data from the images on source host physical machine to the images found at the same place on the destination host physical machine. For more information see Does kvm support live migration with non-shared storage? on the customer portal.
  • --change-protection - enforces that no incompatible configuration changes will be made to the domain while the migration is underway; this flag is implicitly enabled when supported by the hypervisor, but can be explicitly used to reject the migration if the hypervisor lacks change protection support.
  • --unsafe - forces the migration to occur, ignoring all safety procedures.
  • --verbose - displays the progress of migration as it is occurring
  • [--abort-on-error] - cancels the migration if a soft error (such as an I/O error) happens during the migration process.
  • [--migrateuri] - the migration URI which is usually omitted.
  • [--domain <string>]- domain name, id or uuid
  • [--desturi <string>] - connection URI of the destination host physical machine as seen from the client(normal migration) or source(p2p migration)
  • [--migrateuri] - migration URI, usually can be omitted
  • --timeout <seconds> - forces a guest virtual machine to suspend when the live migration counter exceeds N seconds. It can only be used with a live migration. Once the timeout is initiated, the migration continues on the suspended guest virtual machine.
  • dname - is used for renaming the domain to new name during migration, which also usually can be omitted
  • [--dname] <string> - changes the name of the guest virtual machine to a new name during migration (if supported)
  • --xml - the filename indicated can be used to supply an alternative XML file for use on the destination to supply a larger set of changes to any host-specific portions of the domain XML, such as accounting for naming differences between source and destination in accessing underlying storage. This option is usually omitted.
Refer to the virsh man page for more information.

5.5. Migrating with virt-manager

This section covers migrating a KVM guest virtual machine with virt-manager from one host physical machine to another.
  1. Open virt-manager

    Open virt-manager. Choose ApplicationsSystem ToolsVirtual Machine Manager from the main menu bar to launch virt-manager.
    Virt-Manager main menu

    Figure 5.1. Virt-Manager main menu

  2. Connect to the target host physical machine

    Connect to the target host physical machine by clicking on the File menu, then click Add Connection.
    Open Add Connection window

    Figure 5.2. Open Add Connection window

  3. Add connection

    The Add Connection window appears.
    Adding a connection to the target host physical machine

    Figure 5.3. Adding a connection to the target host physical machine

    Enter the following details:
    • Hypervisor: Select QEMU/KVM.
    • Method: Select the connection method.
    • Username: Enter the username for the remote host physical machine.
    • Hostname: Enter the hostname for the remote host physical machine.
    Click the Connect button. An SSH connection is used in this example, so the specified user's password must be entered in the next step.
    Enter password

    Figure 5.4. Enter password

  4. Migrate guest virtual machines

    Open the list of guests inside the source host physical machine (click the small triangle on the left of the host name) and right click on the guest that is to be migrated (guest1-rhel6-64 in this example) and click Migrate.
    Choosing the guest to be migrated

    Figure 5.5. Choosing the guest to be migrated

    In the New Host field, use the drop-down list to select the host physical machine you wish to migrate the guest virtual machine to and click Migrate.
    Choosing the destination host physical machine and starting the migration process

    Figure 5.6. Choosing the destination host physical machine and starting the migration process

    A progress window will appear.
    Progress window

    Figure 5.7. Progress window

    virt-manager now displays the newly migrated guest virtual machine running in the destination host. The guest virtual machine that was running in the source host physical machine is now listed inthe Shutoff state.
    Migrated guest virtual machine running in the destination host physical machine

    Figure 5.8. Migrated guest virtual machine running in the destination host physical machine

  5. Optional - View the storage details for the host physical machine

    In the Edit menu, click Connection Details, the Connection Details window appears.
    Click the Storage tab. The iSCSI target details for the destination host physical machine is shown. Note that the migrated guest virtual machine is listed as using the storage
    Storage details

    Figure 5.9. Storage details

    This host was defined by the following XML configuration:
    
    <pool type='iscsi'>
        <name>iscsirhel6guest</name>
        <source>                            
            <host name='virtlab22.example.com.'/>
            <device path='iqn.2001-05.com.iscsivendor:0-8a0906-fbab74a06-a700000017a4cc89-rhevh'/>                           
        </source>                   
        <target>
            <path>/dev/disk/by-path</path>
        </target>
    </pool>
      ...

    Figure 5.10. XML configuration for the destination host physical machine

Chapter 6. Remote management of guests

This section explains how to remotely manage your guests using ssh or TLS and SSL. More information on SSH can be found in the Red Hat Enterprise Linux Deployment Guide

6.1. Remote management with SSH

The ssh package provides an encrypted network protocol which can securely send management functions to remote virtualization servers. The method described uses the libvirt management connection securely tunneled over an SSH connection to manage the remote machines. All the authentication is done using SSH public key cryptography and passwords or passphrases gathered by your local SSH agent. In addition the VNC console for each guest is tunneled over SSH.
Be aware of the issues with using SSH for remotely managing your virtual machines, including:
  • you require root log in access to the remote machine for managing virtual machines,
  • the initial connection setup process may be slow,
  • there is no standard or trivial way to revoke a user's key on all hosts or guests, and
  • ssh does not scale well with larger numbers of remote machines.

Note

Red Hat Enterprise Virtualization enables remote management of large numbers of virtual machines. Refer to the Red Hat Enterprise Virtualization documentation for further details.
The following packages are required for ssh access:
  • openssh
  • openssh-askpass
  • openssh-clients
  • openssh-server
Configuring password less or password managed SSH access for virt-manager
The following instructions assume you are starting from scratch and do not already have SSH keys set up. If you have SSH keys set up and copied to the other systems you can skip this procedure.

Important

SSH keys are user dependent and may only be used by their owners. A key's owner is the one who generated it. Keys may not be shared.
virt-manager must be run by the user who owns the keys to connect to the remote host. That means, if the remote systems are managed by a non-root user virt-manager must be run in unprivileged mode. If the remote systems are managed by the local root user then the SSH keys must be owned and created by root.
You cannot manage the local host as an unprivileged user with virt-manager.
  1. Optional: Changing user

    Change user, if required. This example uses the local root user for remotely managing the other hosts and the local host.
    $ su -
  2. Generating the SSH key pair

    Generate a public key pair on the machine virt-manager is used. This example uses the default key location, in the ~/.ssh/ directory.
    # ssh-keygen -t rsa
  3. Copying the keys to the remote hosts

    Remote login without a password, or with a passphrase, requires an SSH key to be distributed to the systems being managed. Use the ssh-copy-id command to copy the key to root user at the system address provided (in the example, root@host2.example.com).
    # ssh-copy-id -i ~/.ssh/id_rsa.pub root@host2.example.com
    root@host2.example.com's password:
    
    Now try logging into the machine, with the ssh root@host2.example.com command and check in the .ssh/authorized_keys file to make sure unexpected keys have not been added.
    Repeat for other systems, as required.
  4. Optional: Add the passphrase to the ssh-agent

    The instructions below describe how to add a passphrase to an existing ssh-agent. It will fail to run if the ssh-agent is not running. To avoid errors or conflicts make sure that your SSH parameters are set correctly. Refer to the Red Hat Enterprise Linux Deployment Guide for more information.
    Add the passphrase for the SSH key to the ssh-agent, if required. On the local host, use the following command to add the passphrase (if there was one) to enable password-less login.
    # ssh-add ~/.ssh/id_rsa
    The SSH key is added to the remote system.
The libvirt daemon (libvirtd)
The libvirt daemon provides an interface for managing virtual machines. You must have the libvirtd daemon installed and running on every remote host that needs managing.
$ ssh root@somehost
# chkconfig libvirtd on
# service libvirtd start
After libvirtd and SSH are configured you should be able to remotely access and manage your virtual machines. You should also be able to access your guests with VNC at this point.
Accessing remote hosts with virt-manager
Remote hosts can be managed with the virt-manager GUI tool. SSH keys must belong to the user executing virt-manager for password-less login to work.
  1. Start virt-manager.
  2. Open the File->Add Connection menu.
    Add connection menu

    Figure 6.1. Add connection menu

  3. Use the drop down menu to select hypervisor type, and click the Connect to remote host check box to open the Connection Method (in this case Remote tunnel over SSH), and enter the desired User name and Hostname, then click Connect.

6.2. Remote management over TLS and SSL

You can manage virtual machines using TLS and SSL. TLS and SSL provides greater scalability but is more complicated than ssh (refer to Section 6.1, “Remote management with SSH”). TLS and SSL is the same technology used by web browsers for secure connections. The libvirt management connection opens a TCP port for incoming connections, which is securely encrypted and authenticated based on x509 certificates. The procedures that follow provide instructions on creating and deploying authentication certificates for TLS and SSL management.

Procedure 6.1. Creating a certificate authority (CA) key for TLS management

  1. Before you begin, confirm that the certtool utility is installed. If not:
    # yum install gnutls-utils
  2. Generate a private key, using the following command:
    # certtool --generate-privkey > cakey.pem
  3. Once the key generates, the next step is to create a signature file so the key can be self-signed. To do this, create a file with signature details and name it ca.info. This file should contain the following:
    # vim ca.info
    cn = Name of your organization
    ca
    cert_signing_key
    
  4. Generate the self-signed key with the following command:
    # certtool --generate-self-signed --load-privkey cakey.pem --template ca.info --outfile cacert.pem
    Once the file generates, the ca.info file may be deleted using the rm command. The file that results from the generation process is named cacert.pem. This file is the public key (certificate). The loaded file cakey.pem is the private key. This file should not be kept in a shared space. Keep this key private.
  5. Install the cacert.pem Certificate Authority Certificate file on all clients and servers in the /etc/pki/CA/cacert.pem directory to let them know that the certificate issued by your CA can be trusted. To view the contents of this file, run:
    # certtool -i --infile cacert.pem
    This is all that is required to set up your CA. Keep the CA's private key safe as you will need it in order to issue certificates for your clients and servers.

Procedure 6.2. Issuing a server certificate

This procedure demonstrates how to issue a certificate with the X.509 CommonName (CN)field set to the hostname of the server. The CN must match the hostname which clients will be using to connect to the server. In this example, clients will be connecting to the server using the URI: qemu://mycommonname/system, so the CN field should be identical, ie mycommoname.
  1. Create a private key for the server.
    # certtool --generate-privkey > serverkey.pem
  2. Generate a signature for the CA's private key by first creating a template file called server.info . Make sure that the CN is set to be the same as the server's hostname:
    organization = Name of your organization
    cn = mycommonname
    tls_www_server
    encryption_key
    signing_key
    
  3. Create the certificate with the following command:
    # certtool --generate-certificate --load-privkey serverkey.pem --load-ca-certificate cacert.pem --load-ca-privkey cakey.pem \ --template server.info --outfile servercert.pem
  4. This results in two files being generated:
    • serverkey.pem - The server's private key
    • servercert.pem - The server's public key
    Make sure to keep the location of the private key secret. To view the contents of the file, perform the following command:
    # certtool -i --inifile servercert.pem
    When opening this file the CN= parameter should be the same as the CN that you set earlier. For example, mycommonname.
  5. Install the two files in the following locations:
    • serverkey.pem - the server's private key. Place this file in the following location: /etc/pki/libvirt/private/serverkey.pem
    • servercert.pem - the server's certificate. Install it in the following location on the server: /etc/pki/libvirt/servercert.pem

Procedure 6.3. Issuing a client certificate

  1. For every client (ie. any program linked with libvirt, such as virt-manager), you need to issue a certificate with the X.509 Distinguished Name (DN) set to a suitable name. This needs to be decided on a corporate level.
    For example purposes the following information will be used:
    C=USA,ST=North Carolina,L=Raleigh,O=Red Hat,CN=name_of_client
    This process is quite similar to Procedure 6.2, “Issuing a server certificate”, with the following exceptions noted.
  2. Make a private key with the following command:
    # certtool --generate-privkey > clientkey.pem
  3. Generate a signature for the CA's private key by first creating a template file called client.info . The file should contain the following (fields should be customized to reflect your region/location):
    country = USA
    state = North Carolina
    locality = Raleigh
    organization = Red Hat
    cn = client1
    tls_www_client
    encryption_key
    signing_key
    
  4. Sign the certificate with the following command:
    # certtool --generate-certificate --load-privkey clientkey.pem --load-ca-certificate cacert.pem \ --load-ca-privkey cakey.pem --template client.info --outfile clientcert.pem
  5. Install the certificates on the client machine:
    # cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem
    # cp clientcert.pem /etc/pki/libvirt/clientcert.pem

6.3. Transport modes

For remote management, libvirt supports the following transport modes:
Transport Layer Security (TLS)
Transport Layer Security TLS 1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usually listening on a public port number. To use this you will need to generate client and server certificates. The standard port is 16514.
UNIX sockets
UNIX domain sockets are only accessible on the local machine. Sockets are not encrypted, and use UNIX permissions or SELinux for authentication. The standard socket names are /var/run/libvirt/libvirt-sock and /var/run/libvirt/libvirt-sock-ro (for read-only connections).
SSH
Transported over a Secure Shell protocol (SSH) connection. Requires Netcat (the nc package) installed. The libvirt daemon (libvirtd) must be running on the remote machine. Port 22 must be open for SSH access. You should use some sort of SSH key management (for example, the ssh-agent utility) or you will be prompted for a password.
ext
The ext parameter is used for any external program which can make a connection to the remote machine by means outside the scope of libvirt. This parameter is unsupported.
TCP
Unencrypted TCP/IP socket. Not recommended for production use, this is normally disabled, but an administrator can enable it for testing or use over a trusted network. The default port is 16509.
The default transport, if no other is specified, is TLS.
Remote URIs
A Uniform Resource Identifier (URI) is used by virsh and libvirt to connect to a remote host. URIs can also be used with the --connect parameter for the virsh command to execute single commands or migrations on remote hosts. Remote URIs are formed by taking ordinary local URIs and adding a hostname and/or transport name. As a special case, using a URI scheme of 'remote', will tell the remote libvirtd server to probe for the optimal hypervisor driver. This is equivalent to passing a NULL URI for a local connection
libvirt URIs take the general form (content in square brackets, "[]", represents optional functions):
driver[+transport]://[username@][hostname][:port]/path[?extraparameters]
Note that if the hypervisor(driver) is QEMU, the path is mandatory. If it is XEN, it is optional.
The following are examples of valid remote URIs:
  • qemu://hostname/
  • xen://hostname/
  • xen+ssh://hostname/
The transport method or the hostname must be provided to target an external location. For more information refer to http://libvirt.org/guide/html/Application_Development_Guide-Architecture-Remote_URIs.html.

Examples of remote management parameters

  • Connect to a remote KVM host named host2, using SSH transport and the SSH username virtuser.The connect command for each is connect [<name>] [--readonly], where <name> is a valid URI as explained here. For more information about the virsh connect command refer to Section 15.1.5, “connect”
    qemu+ssh://virtuser@hot2/
  • Connect to a remote KVM hypervisor on the host named host2 using TLS.
    qemu://host2/

Testing examples

  • Connect to the local KVM hypervisor with a non-standard UNIX socket. The full path to the UNIX socket is supplied explicitly in this case.
    qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock
  • Connect to the libvirt daemon with an unencrypted TCP/IP connection to the server with the IP address 10.1.1.10 on port 5000. This uses the test driver with default settings.
    test+tcp://10.1.1.10:5000/default
Extra URI parameters
Extra parameters can be appended to remote URIs. The table below Table 6.1, “Extra URI parameters” covers the recognized parameters. All other parameters are ignored. Note that parameter values must be URI-escaped (that is, a question mark (?) is appended before the parameter and special characters are converted into the URI format).

Table 6.1. Extra URI parameters

Name Transport mode Description Example usage
name all modes The name passed to the remote virConnectOpen function. The name is normally formed by removing transport, hostname, port number, username and extra parameters from the remote URI, but in certain very complex cases it may be better to supply the name explicitly. name=qemu:///system
command ssh and ext The external command. For ext transport this is required. For ssh the default is ssh. The PATH is searched for the command. command=/opt/openssh/bin/ssh
socket unix and ssh The path to the UNIX domain socket, which overrides the default. For ssh transport, this is passed to the remote netcat command (see netcat). socket=/opt/libvirt/run/libvirt/libvirt-sock
netcat ssh
The netcat command can be used to connect to remote systems. The default netcat parameter uses the nc command. For SSH transport, libvirt constructs an SSH command using the form below:
command -p port [-l username] hostname
netcat -U socket
The port, username and hostname parameters can be specified as part of the remote URI. The command, netcat and socket come from other extra parameters.
netcat=/opt/netcat/bin/nc
no_verify tls If set to a non-zero value, this disables client checks of the server's certificate. Note that to disable server checks of the client's certificate or IP address you must change the libvirtd configuration. no_verify=1
no_tty ssh If set to a non-zero value, this stops ssh from asking for a password if it cannot log in to the remote machine automatically . Use this when you do not have access to a terminal . no_tty=1

Chapter 7. Overcommitting with KVM

7.1. Introduction

The KVM hypervisor supports overcommitting CPUs and overcommitting memory. Overcommitting is allocating more virtualized CPUs or memory than there are physical resources on the system. With CPU overcommit, under-utilized virtualized servers or desktops can run on fewer servers which saves a number of system resources, with the net effect of less power, cooling, and investment in server hardware.
As most processes do not access 100% of their allocated memory all the time, KVM can use this behavior to its advantage and allocate more memory for guest virtual machines than the host physical machine actually has available, in a process called overcommitting of resources.

Important

Overcommitting is not an ideal solution for all memory issues as the recommended method to deal with memory shortage is to allocate less memory per guest so that the sum of all guests memory (+4G for the host O/S) is lower than the host physical machine's physical memory. If the guest virtual machines need more memory, then increase the guest virtual machines' swap space allocation. If however, should you decide to overcommit, do so with caution.
Guest virtual machines running on a KVM hypervisor do not have dedicated blocks of physical RAM assigned to them. Instead, each guest virtual machine functions as a Linux process where the host physical machine's Linux kernel allocates memory only when requested. In addition the host physical machine's memory manager can move the guest virtual machine's memory between its own physical memory and swap space. This is why overcommitting requires allotting sufficient swap space on the host physical machine to accommodate all guest virtual machines as well as enough memory for the host physical machine's processes. As a basic rule, the host physical machine's operating system requires a maximum of 4GB of memory along with a minimum of 4GB of swap space. Refer to Example 7.1, “Memory overcommit example” for more information.
Red Hat Knowledgebase has an article on safely and efficiently determining the size of the swap partition.

Note

The example below is provided as a guide for configuring swap only. The settings listed may not be appropriate for your environment.

Example 7.1. Memory overcommit example

This example demonstrates how to calculate swap space for overcommitting. Although it may appear to be simple in nature, the ramifications of overcommitting should not be ignored. Refer to Important before proceeding.
ExampleServer1 has 32GB of physical RAM. The system is being configured to run 50 guest virtual machines, each requiring 1GB of virtualized memory. As mentioned above, the host physical machine's system itself needs a maximum of 4GB (apart from the guest virtual machines) as well as an additional 4GB as a swap space minimum.
The swap space is calculated as follows:
  • Calculate the amount of memory needed for the sum of all the guest virtual machines - In this example: (50 guest virtual machines * 1GB of memory per guest virtual machine) = 50GB
  • Add the guest virtual machine's memory amount to the amount needed for the host physical machine's OS and for the host physical machine's minimum swap space - In this example: 50GB guest virtual machine memory + 4GB host physical machine's OS + 4GB minimal swap = 58GB
  • Subtract this amount from the amount of physical RAM there is on the system - In this example 58GB - 32GB = 26GB
  • The answer is the amount of swap space that needs to be allocated. In this example 26GB

Note

Overcommitting does not work with all guest virtual machines, but has been found to work in a desktop virtualization setup with minimal intensive usage or running several identical guest virtual machines with KSM. It should be noted that configuring swap and memory overcommit is not a simple plug-in and configure formula, as each environment and setup is different. Proceed with caution before changing these settings and make sure you completely understand your environment and setup before making any changes.
For more information on KSM and overcommitting, refer to Chapter 8, KSM.

7.2. Overcommitting virtualized CPUs

The KVM hypervisor supports overcommitting virtualized CPUs. Virtualized CPUs can be overcommitted as far as load limits of guest virtual machines allow. Use caution when overcommitting VCPUs as loads near 100% may cause dropped requests or unusable response times.
Virtualized CPUs (VCPUs) are overcommitted best when a single host physical machine has multiple guest virtual machines, where the guests do not share the same VCPU. The Linux scheduler is very efficient with this type of load. KVM should safely support guest virtual machines with loads under 100% at a ratio of five VCPUs (on 5 virtual machines) to one physical CPU on one single host physical machine. KVM will switch between all of the machines making sure that the load is balanced.
You cannot overcommit symmetric multiprocessing guest virtual machines on more than the physical number of processing cores. For example a guest virtual machine with four VCPUs should not be run on a host physical machine with a dual core processor. Overcommitting symmetric multiprocessing guest virtual machines in over the physical number of processing cores will cause significant performance degradation.
Assigning guest virtual machines VCPUs up to the number of physical cores is appropriate and works as expected. For example, running guest virtual machines with four VCPUs on a quad core host. Guest virtual machines with less than 100% loads should function effectively in this setup.

Important

Do not overcommit memory or CPUs in a production environment without extensive testing. Applications which use 100% of memory or processing resources may become unstable in overcommitted environments. Test before deploying.
For more information on how to get the best performance out of your virtual machine, refer to the Red Hat Enterprise Linux 6 Virtualization Tuning and Optimization Guide.

Chapter 8. KSM

The concept of shared memory is common in modern operating systems. For example, when a program is first started it shares all of its memory with the parent program. When either the child or parent program tries to modify this memory, the kernel allocates a new memory region, copies the original contents and allows the program to modify this new region. This is known as copy on write.
KSM is a new Linux feature which uses this concept in reverse. KSM enables the kernel to examine two or more already running programs and compare their memory. If any memory regions or pages are identical, KSM reduces multiple identical memory pages to a single page. This page is then marked copy on write. If the contents of the page is modified by a guest virtual machine, a new page is created for that guest virtual machine.
This is useful for virtualization with KVM. When a guest virtual machine is started, it inherits only the memory from the parent qemu-kvm process. Once the guest virtual machine is running the contents of the guest virtual machine operating system image can be shared when guests are running the same operating system or applications. KSM only identifies and merges identical pages which does not interfere with the guest virtual machine or impact the security of the host physical machine or the guests. KSM allows KVM to request that these identical guest virtual machine memory regions be shared.
KSM provides enhanced memory speed and utilization. With KSM, common process data is stored in cache or in main memory. This reduces cache misses for the KVM guests which can improve performance for some applications and operating systems. Secondly, sharing memory reduces the overall memory usage of guests which allows for higher densities and greater utilization of resources.

Note

Starting in Red Hat Enterprise Linux 6.5, KSM is NUMA aware. This allows it to take NUMA locality into account while coalescing pages, thus preventing performance drops related to pages being moved to a remote node. Red Hat recommends avoiding cross-node memory merging when KSM is in use. If KSM is in use, change the /sys/kernel/mm/ksm/merge_across_nodes tunable to 0 to avoid merging pages across NUMA nodes. Kernel memory accounting statistics can eventually contradict each other after large amounts of cross-node merging. As such, numad can become confused after the KSM daemon merges large amounts of memory. If your system has a large amount of free memory, you may achieve higher performance by turning off and disabling the KSM daemon. Refer to the Red Hat Enterprise Linux Performance Tuning Guide for more information on NUMA.
Red Hat Enterprise Linux uses two separate methods for controlling KSM:
  • The ksm service starts and stops the KSM kernel thread.
  • The ksmtuned service controls and tunes the ksm, dynamically managing same-page merging. The ksmtuned service starts ksm and stops the ksm service if memory sharing is not necessary. The ksmtuned service must be told with the retune parameter to run when new guests are created or destroyed.
Both of these services are controlled with the standard service management tools.
The KSM service
The ksm service is included in the qemu-kvm package. KSM is off by default on Red Hat Enterprise Linux 6. When using Red Hat Enterprise Linux 6 as a KVM host physical machine, however, it is likely turned on by the ksm/ksmtuned services.
When the ksm service is not started, KSM shares only 2000 pages. This default is low and provides limited memory saving benefits.
When the ksm service is started, KSM will share up to half of the host physical machine system's main memory. Start the ksm service to enable KSM to share more memory.
# service ksm start
Starting ksm:                                              [  OK  ]
The ksm service can be added to the default startup sequence. Make the ksm service persistent with the chkconfig command.
# chkconfig ksm on
The KSM tuning service
The ksmtuned service does not have any options. The ksmtuned service loops and adjusts ksm. The ksmtuned service is notified by libvirt when a guest virtual machine is created or destroyed.
# service ksmtuned start
Starting ksmtuned:                                         [  OK  ]
The ksmtuned service can be tuned with the retune parameter. The retune parameter instructs ksmtuned to run tuning functions manually.
Before changing the parameters in the file, there are a few terms that need to be clarified:
  • thres - Activation threshold, in kbytes. A KSM cycle is triggered when the thres value added to the sum of all qemu-kvm processes RSZ exceeds total system memory. This parameter is the equivalent in kbytes of the percentage defined in KSM_THRES_COEF.
The /etc/ksmtuned.conf file is the configuration file for the ksmtuned service. The file output below is the default ksmtuned.conf file.
# Configuration file for ksmtuned.

# How long ksmtuned should sleep between tuning adjustments
# KSM_MONITOR_INTERVAL=60

# Millisecond sleep between ksm scans for 16Gb server.
# Smaller servers sleep more, bigger sleep less.
# KSM_SLEEP_MSEC=10

# KSM_NPAGES_BOOST is added to the npages value, when free memory is less than thres.
# KSM_NPAGES_BOOST=300

# KSM_NPAGES_DECAY Value given is subtracted to the npages value, when free memory is greater than thres.
# KSM_NPAGES_DECAY=-50

# KSM_NPAGES_MIN is the lower limit for the npages value.
# KSM_NPAGES_MIN=64

# KSM_NAGES_MAX is the upper limit for the npages value.
# KSM_NPAGES_MAX=1250

# KSM_TRES_COEF - is the RAM percentage to be calculated in parameter thres.
# KSM_THRES_COEF=20

# KSM_THRES_CONST - If this is a low memory system, and the thres value is less than KSM_THRES_CONST, then reset thres value to KSM_THRES_CONST value.
# KSM_THRES_CONST=2048

# uncomment the following to enable ksmtuned debug information
# LOGFILE=/var/log/ksmtuned
# DEBUG=1
KSM variables and monitoring
KSM stores monitoring data in the /sys/kernel/mm/ksm/ directory. Files in this directory are updated by the kernel and are an accurate record of KSM usage and statistics.
The variables in the list below are also configurable variables in the /etc/ksmtuned.conf file as noted below.

The /sys/kernel/mm/ksm/ files

full_scans
Full scans run.
pages_shared
Total pages shared.
pages_sharing
Pages presently shared.
pages_to_scan
Pages not scanned.
pages_unshared
Pages no longer shared.
pages_volatile
Number of volatile pages.
run
Whether the KSM process is running.
sleep_millisecs
Sleep milliseconds.
KSM tuning activity is stored in the /var/log/ksmtuned log file if the DEBUG=1 line is added to the /etc/ksmtuned.conf file. The log file location can be changed with the LOGFILE parameter. Changing the log file location is not advised and may require special configuration of SELinux settings.
Deactivating KSM
KSM has a performance overhead which may be too large for certain environments or host physical machine systems.
KSM can be deactivated by stopping the ksmtuned and the ksm service. Stopping the services deactivates KSM but does not persist after restarting.
# service ksmtuned stop
Stopping ksmtuned:                                         [  OK  ]
# service ksm stop
Stopping ksm:                                              [  OK  ]

Persistently deactivate KSM with the chkconfig command. To turn off the services, run the following commands:
# chkconfig ksm off
# chkconfig ksmtuned off

Important

Ensure the swap size is sufficient for the committed RAM even with KSM. KSM reduces the RAM usage of identical or similar guests. Overcommitting guests with KSM without sufficient swap space may be possible but is not recommended because guest virtual machine memory use can result in pages becoming unshared.

Chapter 9. Advanced guest virtual machine administration

This chapter covers advanced administration tools for fine tuning and controlling system resources as they are made available to guest virtual machines.

9.1. Control Groups (cgroups)

Red Hat Enterprise Linux 6 provides a new kernel feature: control groups, which are often referred to as cgroups. Cgroups allow you to allocate resources such as CPU time, system memory, network bandwidth, or a combination of these resources among user-defined groups of tasks (processes) running on a system. You can monitor the cgroups you configure, deny cgroups access to certain resources, and even reconfigure your cgroups dynamically on a running system.
The cgroup functionality is fully supported by libvirt. By default, libvirt puts each guest into a separate control group for various controllers (such as memory, cpu, blkio, device).
When a guest is started, it is already in a cgroup. The only configuration that may be required is the setting of policies on the cgroups. Refer to the Red Hat Enterprise Linux Resource Management Guide for more information on cgroups.

9.2. Huge page support

Introduction
x86 CPUs usually address memory in 4kB pages, but they are capable of using larger pages known as huge pages. KVM guests can be deployed with huge page memory support in order to improve performance by increasing CPU cache hits against the Transaction Lookaside Buffer (TLB). Huge pages can significantly increase performance, particularly for large memory and memory-intensive workloads. Red Hat Enterprise Linux 6 is able to more effectively manage large amounts of memory by increasing the page size through the use of huge pages.
By using huge pages for a KVM guest, less memory is used for page tables and TLB misses are reduced, thereby significantly increasing performance, especially for memory-intensive situations.
Transparent huge pages
Transparent huge pages (THP) is a kernel feature that reduces TLB entries needed for an application. By also allowing all free memory to be used as cache, performance is increased.
To use transparent huge pages, no special configuration in the qemu.conf file is required. Huge pages are used by default if /sys/kernel/mm/redhat_transparent_hugepage/enabled is set to always.
Transparent huge pages do not prevent the use of hugetlbfs. However, when hugetlbfs is not used, KVM will use transparent huge pages instead of the regular 4kB page size.

Note

See the Red Hat Enterprise Linux 7 Virtualization Tuning and Optimization Guide for instructions on tuning memory performance with huge pages.

9.3. Running Red Hat Enterprise Linux as a guest virtual machine on a Hyper-V hypervisor

It is possible to run a Red Hat Enterprise Linux guest virtual machine on a Microsoft Windows host physical machine running the Microsoft Windows Hyper-V hypervisor. In particular, the following enhancements have been made to allow for easier deployment and management of Red Hat Enterprise Linux guest virtual machines:
  • Upgraded VMBUS protocols - VMBUS protocols have been upgraded to Windows 8 level. As part of this work, now VMBUS interrupts can be processed on all available virtual CPUs in the guest. Furthermore, the signaling protocol between the Red Hat Enterprise Linux guest virtual machine and the Windows host physical machine has been optimized.
  • Synthetic frame buffer driver - Provides enhanced graphics performance and superior resolution for Red Hat Enterprise Linux desktop users.
  • Live Virtual Machine Backup support - Provisions uninterrupted backup support for live Red Hat Enterprise Linux guest virtual machines.
  • Dynamic expansion of fixed size Linux VHDs - Allows expansion of live mounted fixed size Red Hat Enterprise Linux VHDs.
For more information, refer to the following article: Enabling Linux Support on Windows Server 2012 R2 Hyper-V.

Note

The Hyper-V hypervisor supports shrinking a GPT-partitioned disk on a Red Hat Enterprise Linux guest if there is free space after the last partition, by allowing the user to drop the unused last part of the disk. However, this operation will silently delete the secondary GPT header on the disk, which may produce error messages when the guest examines the partition table (for example, when printing the partition table with parted). This is a known limit of Hyper-V. As a workaround, it is possible to manually restore the secondary GPT header after shrinking the GPT disk by using the expert menu in gdisk and the e command. Furthermore, using the "expand" option in the Hyper-V manager also places the GPT secondary header in a location other than at the end of disk, but this can be moved with parted. See the gdisk and parted man pages for more information on these commands.

9.4. Guest virtual machine memory allocation

The following procedure shows how to allocate memory for a guest virtual machine. This allocation and assignment works only at boot time and any changes to any of the memory values will not take effect until the next reboot. The maximum memory that can be allocated per guest is 4 TiB, providing that this memory allocation isn't more than what the host physical machine resources can provide.
Valid memory units include:
  • b or bytes for bytes
  • KB for kilobytes (103 or blocks of 1,000 bytes)
  • k or KiB for kibibytes (210 or blocks of 1024 bytes)
  • MB for megabytes (106 or blocks of 1,000,000 bytes)
  • M or MiB for mebibytes (220 or blocks of 1,048,576 bytes)
  • GB for gigabytes (109 or blocks of 1,000,000,000 bytes)
  • G or GiB for gibibytes (230 or blocks of 1,073,741,824 bytes)
  • TB for terabytes (1012 or blocks of 1,000,000,000,000 bytes)
  • T or TiB for tebibytes (240 or blocks of 1,099,511,627,776 bytes)
Note that all values will be rounded up to the nearest kibibyte by libvirt, and may be further rounded to the granularity supported by the hypervisor. Some hypervisors also enforce a minimum, such as 4000KiB (or 4000 x 210 or 4,096,000 bytes). The units for this value are determined by the optional attribute memory unit, which defaults to the kibibytes (KiB) as a unit of measure where the value given is multiplied by 210 or blocks of 1024 bytes.
In the cases where the guest virtual machine crashes the optional attribute dumpCore can be used to control whether the guest virtual machine's memory should be included in the generated coredump (dumpCore='on') or not included (dumpCore='off'). Note that the default setting is on so if the parameter is not set to off, the guest virtual machine memory will be included in the coredump file.
The currentMemory attribute determines the actual memory allocation for a guest virtual machine. This value can be less than the maximum allocation, to allow for ballooning up the guest virtual machines memory on the fly. If this is omitted, it defaults to the same value as the memory element. The unit attribute behaves the same as for memory.
In all cases for this section, the domain XML needs to be altered as follows:
<domain>
  
  <memory unit='KiB' dumpCore='off'>524288</memory>
  <!-- changes the memory unit to KiB and does not allow the guest virtual machine's memory to be included in the generated coredump file -->
  <currentMemory unit='KiB'>524288</currentMemory>
  <!-- makes the current memory unit 524288 KiB -->
  ...
</domain>

9.5. Automatically starting guest virtual machines

This section covers how to make guest virtual machines start automatically during the host physical machine system's boot phase.
This example uses virsh to set a guest virtual machine, TestServer, to automatically start when the host physical machine boots.
# virsh autostart TestServer
Domain TestServer marked as autostarted
The guest virtual machine now automatically starts with the host physical machine.
To stop a guest virtual machine automatically booting use the --disable parameter
# virsh autostart --disable TestServer
Domain TestServer unmarked as autostarted
The guest virtual machine no longer automatically starts with the host physical machine.

9.6. Disable SMART disk monitoring for guest virtual machines

SMART disk monitoring can be safely disabled as virtual disks and the physical storage devices are managed by the host physical machine.
# service smartd stop
# chkconfig --del smartd

9.7. Configuring a VNC Server

To configure a VNC server, use the Remote Desktop application in System > Preferences. Alternatively, you can run the vino-preferences command.
Use the following step set up a dedicated VNC server session:
If needed, Create and then Edit the ~/.vnc/xstartup file to start a GNOME session whenever vncserver is started. The first time you run the vncserver script it will ask you for a password you want to use for your VNC session. For more information on vnc server files refer to the Red Hat Enterprise Linux Installation Guide.

9.8. Generating a new unique MAC address

In some cases you will need to generate a new and unique MAC address for a guest virtual machine. There is no command line tool available to generate a new MAC address at the time of writing. The script provided below can generate a new MAC address for your guest virtual machines. Save the script on your guest virtual machine as macgen.py. Now from that directory you can run the script using ./macgen.py and it will generate a new MAC address. A sample output would look like the following:
$ ./macgen.py 
00:16:3e:20:b0:11
#!/usr/bin/python
# macgen.py script to generate a MAC address for guest virtual machines
#
import random
#
def randomMAC():
	mac = [ 0x00, 0x16, 0x3e,
		random.randint(0x00, 0x7f),
		random.randint(0x00, 0xff),
		random.randint(0x00, 0xff) ]
	return ':'.join(map(lambda x: "%02x" % x, mac))
#
print randomMAC()

9.8.1. Another method to generate a new MAC for your guest virtual machine

You can also use the built-in modules of python-virtinst to generate a new MAC address and UUID for use in a guest virtual machine configuration file:
# echo  'import virtinst.util ; print\
 virtinst.util.uuidToString(virtinst.util.randomUUID())' | python
# echo  'import virtinst.util ; print virtinst.util.randomMAC()' | python
The script above can also be implemented as a script file as seen below.
#!/usr/bin/env python
#  -*- mode: python; -*-
print ""
print "New UUID:"
import virtinst.util ; print virtinst.util.uuidToString(virtinst.util.randomUUID())
print "New MAC:"
import virtinst.util ; print virtinst.util.randomMAC()
print ""

9.9. Improving guest virtual machine response time

Guest virtual machines can sometimes be slow to respond with certain workloads and usage patterns. Examples of situations which may cause slow or unresponsive guest virtual machines:
  • Severely overcommitted memory.
  • Overcommitted memory with high processor usage
  • Other (not qemu-kvm processes) busy or stalled processes on the host physical machine.
KVM guest virtual machines function as Linux processes. Linux processes are not permanently kept in main memory (physical RAM) and will be placed into swap space (virtual memory) especially if they are not being used. If a guest virtual machine is inactive for long periods of time, the host physical machine kernel may move the guest virtual machine into swap. As swap is slower than physical memory it may appear that the guest is not responding. This changes once the guest is loaded into the main memory. Note that the process of loading a guest virtual machine from swap to main memory may take several seconds per gigabyte of RAM assigned to the guest virtual machine, depending on the type of storage used for swap and the performance of the components.
KVM guest virtual machines processes may be moved to swap regardless of whether memory is overcommitted or overall memory usage.
Using unsafe overcommit levels or overcommitting with swap turned off guest virtual machine processes or other critical processes is not recommended. Always ensure the host physical machine has sufficient swap space when overcommitting memory.
For more information on overcommitting with KVM, refer to Section 7.1, “Introduction”.

Warning

Virtual memory allows a Linux system to use more memory than there is physical RAM on the system. Underused processes are swapped out which allows active processes to use memory, improving memory utilization. Disabling swap reduces memory utilization as all processes are stored in physical RAM.
If swap is turned off, do not overcommit guest virtual machines. Overcommitting guest virtual machines without any swap can cause guest virtual machines or the host physical machine system to crash.

9.10. Virtual machine timer management with libvirt

Accurate time keeping on guest virtual machines is a key challenge for virtualization platforms. Different hypervisors attempt to handle the problem of time keeping in a variety of ways. libvirt provides hypervisor independent configuration settings for time management, using the <clock> and <timer> elements in the domain XML. The domain XML can be edited using the virsh edit command. See Section 15.6, “Editing a guest virtual machine's configuration file” for details.
The <clock> element is used to determine how the guest virtual machine clock is synchronized with the host physical machine clock. The clock element has the following attributes:
  • offset determines how the guest virtual machine clock is offset from the host physical machine clock. The offset attribute has the following possible values:

    Table 9.1. Offset attribute values

    ValueDescription
    utcThe guest virtual machine clock will be synchronized to UTC when booted.
    localtimeThe guest virtual machine clock will be synchronized to the host physical machine's configured timezone when booted, if any.
    timezoneThe guest virtual machine clock will be synchronized to a given timezone, specified by the timezone attribute.
    variableThe guest virtual machine clock will be synchronized to an arbitrary offset from UTC. The delta relative to UTC is specified in seconds, using the adjustment attribute. The guest virtual machine is free to adjust the Real Time Clock (RTC) over time and expect that it will be honored following the next reboot. This is in contrast to utc mode, where any RTC adjustments are lost at each reboot.

    Note

    The value utc is set as the clock offset in a virtual machine by default. However, if the guest virtual machine clock is run with the localtime value, the clock offset needs to be changed to a different value in order to have the guest virtual machine clock synchronized with the host physical machine clock.
  • The timezone attribute determines which timezone is used for the guest virtual machine clock.
  • The adjustment attribute provides the delta for guest virtual machine clock synchronization. In seconds, relative to UTC.

Example 9.1. Always synchronize to UTC

<clock offset="utc" />

Example 9.2. Always synchronize to the host physical machine timezone

<clock offset="localtime" />

Example 9.3. Synchronize to an arbitrary timezone

<clock offset="timezone" timezone="Europe/Paris" />

Example 9.4. Synchronize to UTC + arbitrary offset

<clock offset="variable" adjustment="123456" />

9.10.1. timer child element for clock

A clock element can have zero or more timer elements as children. The timer element specifies a time source used for guest virtual machine clock synchronization. The timer element has the following attributes. Only the name is required, all other attributes are optional.
The name attribute dictates the type of the time source to use, and can be one of the following:

Table 9.2. name attribute values

ValueDescription
pitProgrammable Interval Timer - a timer with periodic interrupts.
rtcReal Time Clock - a continuously running timer with periodic interrupts.
tscTime Stamp Counter - counts the number of ticks since reset, no interrupts.
kvmclockKVM clock - recommended clock source for KVM guest virtual machines. KVM pvclock, or kvm-clock lets guest virtual machines read the host physical machine’s wall clock time.

9.10.2. track

The track attribute specifies what is tracked by the timer. Only valid for a name value of rtc.

Table 9.3. track attribute values

ValueDescription
bootCorresponds to old host physical machine option, this is an unsupported tracking option.
guestRTC always tracks guest virtual machine time.
wallRTC always tracks host time.

9.10.3. tickpolicy

The tickpolicy attribute assigns the policy used to pass ticks on to the guest virtual machine. The following values are accepted:

Table 9.4. tickpolicy attribute values

ValueDescription
delayContinue to deliver at normal rate (i.e. ticks are delayed).
catchupDeliver at a higher rate to catch up.
mergeTicks merged into one single tick.
discardAll missed ticks are discarded.

9.10.4. frequency, mode, and present

The frequency attribute is used to set a fixed frequency, and is measured in Hz. This attribute is only relevant when the name element has a value of tsc. All other timers operate at a fixed frequency (pit, rtc).
mode determines how the time source is exposed to the guest virtual machine. This attribute is only relevant for a name value of tsc. All other timers are always emulated. Command is as follows: <timer name='tsc' frequency='NNN' mode='auto|native|emulate|smpsafe'/>. Mode definitions are given in the table.

Table 9.5. mode attribute values

ValueDescription
autoNative if TSC is unstable, otherwise allow native TSC access.
nativeAlways allow native TSC access.
emulateAlways emulate TSC.
smpsafeAlways emulate TSC and interlock SMP
present is used to override the default set of timers visible to the guest virtual machine..

Table 9.6. present attribute values

ValueDescription
yesForce this timer to the visible to the guest virtual machine.
noForce this timer to not be visible to the guest virtual machine.

9.10.5. Examples using clock synchronization

Example 9.5. Clock synchronizing to local time with RTC and PIT timers

In this example. the clock is synchronized to local time with RTC and PIT timers
<clock offset="localtime">
	<timer name="rtc" tickpolicy="catchup" track="guest virtual machine" />
	<timer name="pit" tickpolicy="delay" />
	
</clock>

Note

The PIT clocksource can be used with a 32-bit guest running under a 64-bit host (which cannot use PIT), with the following conditions:
  • Guest virtual machine may have only one CPU
  • APIC timer must be disabled (use the "noapictimer" command line option)
  • NoHZ mode must be disabled in the guest (use the "nohz=off" command line option)
  • High resolution timer mode must be disabled in the guest (use the "highres=off" command line option)
  • The PIT clocksource is not compatible with either high resolution timer mode, or NoHz mode.

9.11. Using PMU to monitor guest virtual machine performance

In Red Hat Enterprise Linux 6.4, vPMU (virtual PMU )was introduced as technical-preview. vPMU is based on Intel's PMU (Performance Monitoring Units) and may only be used on Intel machines. PMU allows the tracking of statistics which indicate how a guest virtual machine is functioning.
Using performance monitoring, allows developers to use the CPU's PMU counter while using the performance tool for profiling. The virtual performance monitoring unit feature allows virtual machine users to identify sources of possible performance problems in their guest virtual machines, thereby improving the ability to profile a KVM guest virtual machine.
To enable the feature, the -cpu host flag must be set.
This feature is only supported with guest virtual machines running Red Hat Enterprise Linux 6 and is disabled by default. This feature only works using the Linux perf tool. Make sure the perf package is installed using the command:
# yum install perf.
See the man page on perf for more information on the perf commands.

9.12. Guest virtual machine power management

It is possible to forcibly enable or disable BIOS advertisements to the guest virtual machine's operating system by changing the following parameters in the Domain XML for Libvirt:
...
  <pm>
    <suspend-to-disk enabled='no'/>
    <suspend-to-mem enabled='yes'/>
  </pm>
  ...
The element pm enables ('yes') or disables ('no') BIOS support for S3 (suspend-to-disk) and S4 (suspend-to-mem) ACPI sleep states. If nothing is specified, then the hypervisor will be left with its default value.

Chapter 10. Guest virtual machine device configuration

Red Hat Enterprise Linux 6 supports three classes of devices for guest virtual machines:
  • Emulated devices are purely virtual devices that mimic real hardware, allowing unmodified guest operating systems to work with them using their standard in-box drivers. Red Hat Enterprise Linux 6 supports up to 216 virtio devices.
  • Virtio devices are purely virtual devices designed to work optimally in a virtual machine. Virtio devices are similar to emulated devices, however, non-Linux virtual machines do not include the drivers they require by default. Virtualization management software like the Virtual Machine Manager (virt-manager) and the Red Hat Enterprise Virtualization Hypervisor install these drivers automatically for supported non-Linux guest operating systems. Red Hat Enterprise Linux 6 supports up to 700 scsi disks.
  • Assigned devices are physical devices that are exposed to the virtual machine. This method is also known as 'passthrough'. Device assignment allows virtual machines exclusive access to PCI devices for a range of tasks, and allows PCI devices to appear and behave as if they were physically attached to the guest operating system. Red Hat Enterprise Linux 6 supports up to 32 assigned devices per virtual machine.
Device assignment is supported on PCIe devices, including select graphics devices. Nvidia K-series Quadro, GRID, and Tesla graphics card GPU functions are now supported with device assignment in Red Hat Enterprise Linux 6. Parallel PCI devices may be supported as assigned devices, but they have severe limitations due to security and system configuration conflicts.

Note

The number of devices that can be attached to a virtual machine depends on several factors. One factor is the number of files open by the QEMU process (configured in /etc/security/limits.conf, which can be overridden by /etc/libvirt/qemu.conf). Other limitation factors include the the number of slots available on the virtual bus, as well as the system-wide limit on open files set by sysctl.
For more information on specific devices and for limitations refer to Section 21.16, “Devices”.
Red Hat Enterprise Linux 6 supports PCI hotplug of devices exposed as single function slots to the virtual machine. Single function host devices and individual functions of multi-function host devices may be configured to enable this. Configurations exposing devices as multi-function PCI slots to the virtual machine are recommended only for non-hotplug applications.

Note

Platform support for interrupt remapping is required to fully isolate a guest with assigned devices from the host. Without such support, the host may be vulnerable to interrupt injection attacks from a malicious guest. In an environment where guests are trusted, the admin may opt-in to still allow PCI device assignment using the allow_unsafe_interrupts option to the vfio_iommu_type1 module. This may either be done persistently by adding a .conf file (e.g. local.conf) to /etc/modprobe.d containing the following:
options vfio_iommu_type1 allow_unsafe_interrupts=1
or dynamically using the sysfs entry to do the same:
# echo 1 > /sys/module/vfio_iommu_type1/parameters/allow_unsafe_interrupts

10.1. PCI devices

PCI device assignment is only available on hardware platforms supporting either Intel VT-d or AMD IOMMU. These Intel VT-d or AMD IOMMU specifications must be enabled in BIOS for PCI device assignment to function.

Procedure 10.1. Preparing an Intel system for PCI device assignment

  1. Enable the Intel VT-d specifications

    The Intel VT-d specifications provide hardware support for directly assigning a physical device to a virtual machine. These specifications are required to use PCI device assignment with Red Hat Enterprise Linux.
    The Intel VT-d specifications must be enabled in the BIOS. Some system manufacturers disable these specifications by default. The terms used to refer to these specifications can differ between manufacturers; consult your system manufacturer's documentation for the appropriate terms.
  2. Activate Intel VT-d in the kernel

    Activate Intel VT-d in the kernel by adding the intel_iommu=on parameter to the end of the GRUB_CMDLINX_LINUX line, within the quotes, in the /etc/sysconfig/grub file.
    The example below is a modified grub file with Intel VT-d activated.
    GRUB_CMDLINE_LINUX="rd.lvm.lv=vg_VolGroup00/LogVol01 
    vconsole.font=latarcyrheb-sun16 rd.lvm.lv=vg_VolGroup_1/root 
    vconsole.keymap=us $([ -x /usr/sbin/rhcrashkernel-param ] && /usr/sbin/
    rhcrashkernel-param || :) rhgb quiet intel_iommu=on"
  3. Regenerate config file

    Regenerate /boot/grub2/grub.cfg by running:
    grub2-mkconfig -o /boot/grub2/grub.cfg
  4. Ready to use

    Reboot the system to enable the changes. Your system is now capable of PCI device assignment.

Procedure 10.2. Preparing an AMD system for PCI device assignment

  1. Enable the AMD IOMMU specifications

    The AMD IOMMU specifications are required to use PCI device assignment in Red Hat Enterprise Linux. These specifications must be enabled in the BIOS. Some system manufacturers disable these specifications by default.
  2. Enable IOMMU kernel support

    Append amd_iommu=on to the end of the GRUB_CMDLINX_LINUX line, within the quotes, in /etc/sysconfig/grub so that AMD IOMMU specifications are enabled at boot.
  3. Regenerate config file

    Regenerate /boot/grub2/grub.cfg by running:
    grub2-mkconfig -o /boot/grub2/grub.cfg
  4. Ready to use

    Reboot the system to enable the changes. Your system is now capable of PCI device assignment.

10.1.1. Assigning a PCI device with virsh

These steps cover assigning a PCI device to a virtual machine on a KVM hypervisor.
This example uses a PCIe network controller with the PCI identifier code, pci_0000_01_00_0, and a fully virtualized guest machine named guest1-rhel6-64.

Procedure 10.3. Assigning a PCI device to a guest virtual machine with virsh

  1. Identify the device

    First, identify the PCI device designated for device assignment to the virtual machine. Use the lspci command to list the available PCI devices. You can refine the output of lspci with grep.
    This example uses the Ethernet controller highlighted in the following output:
    # lspci | grep Ethernet
    00:19.0 Ethernet controller: Intel Corporation 82567LM-2 Gigabit Network Connection
    01:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    01:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    This Ethernet controller is shown with the short identifier 00:19.0. We need to find out the full identifier used by virsh in order to assign this PCI device to a virtual machine.
    To do so, use the virsh nodedev-list command to list all devices of a particular type (pci) that are attached to the host machine. Then look at the output for the string that maps to the short identifier of the device you wish to use.
    This example highlights the string that maps to the Ethernet controller with the short identifier 00:19.0. In this example, the : and . characters are replaced with underscores in the full identifier.
    # virsh nodedev-list --cap pci
    pci_0000_00_00_0
    pci_0000_00_01_0
    pci_0000_00_03_0
    pci_0000_00_07_0
    pci_0000_00_10_0
    pci_0000_00_10_1
    pci_0000_00_14_0
    pci_0000_00_14_1
    pci_0000_00_14_2
    pci_0000_00_14_3
    pci_0000_00_19_0
    pci_0000_00_1a_0
    pci_0000_00_1a_1
    pci_0000_00_1a_2
    pci_0000_00_1a_7
    pci_0000_00_1b_0
    pci_0000_00_1c_0
    pci_0000_00_1c_1
    pci_0000_00_1c_4
    pci_0000_00_1d_0
    pci_0000_00_1d_1
    pci_0000_00_1d_2
    pci_0000_00_1d_7
    pci_0000_00_1e_0
    pci_0000_00_1f_0
    pci_0000_00_1f_2
    pci_0000_00_1f_3
    pci_0000_01_00_0
    pci_0000_01_00_1
    pci_0000_02_00_0
    pci_0000_02_00_1
    pci_0000_06_00_0
    pci_0000_07_02_0
    pci_0000_07_03_0
    Record the PCI device number that maps to the device you want to use; this is required in other steps.
  2. Review device information

    Information on the domain, bus, and function are available from output of the virsh nodedev-dumpxml command:
    virsh nodedev-dumpxml pci_0000_00_19_0
    <device>
      <name>pci_0000_00_19_0</name>
      <parent>computer</parent>
      <driver>
        <name>e1000e</name>
      </driver>
      <capability type='pci'>
        <domain>0</domain>
        <bus>0</bus>
        <slot>25</slot>
        <function>0</function>
        <product id='0x1502'>82579LM Gigabit Network Connection</product>
        <vendor id='0x8086'>Intel Corporation</vendor>
        <iommuGroup number='7'>
          <address domain='0x0000' bus='0x00' slot='0x19' function='0x0'/>
        </iommuGroup>
      </capability>
    </device>

    Note

    An IOMMU group is determined based on the visibility and isolation of devices from the perspective of the IOMMU. Each IOMMU group may contain one or more devices. When multiple devices are present, all endpoints within the IOMMU group must be claimed for any device within the group to be assigned to a guest. This can be accomplished either by also assigning the extra endpoints to the guest or by detaching them from the host driver using virsh nodedev-detach. Devices contained within a single group may not be split between multiple guests or split between host and guest. Non-endpoint devices such as PCIe root ports, switch ports, and bridges should not be detached from the host drivers and will not interfere with assignment of endpoints.
    Devices within an IOMMU group can be determined using the iommuGroup section of the virsh nodedev-dumpxml output. Each member of the group is provided via a separate "address" field. This information may also be found in sysfs using the following:
    $ ls /sys/bus/pci/devices/0000:01:00.0/iommu_group/devices/
    An example of the output from this would be:
    0000:01:00.0  0000:01:00.1
    To assign only 0000.01.00.0 to the guest, the unused endpoint should be detached from the host before starting the guest:
    $ virsh nodedev-detach pci_0000_01_00_1
  3. Determine required configuration details

    Refer to the output from the virsh nodedev-dumpxml pci_0000_00_19_0 command for the values required for the configuration file.
    The example device has the following values: bus = 0, slot = 25 and function = 0. The decimal configuration uses those three values:
    bus='0'
    slot='25'
    function='0'
  4. Add configuration details

    Run virsh edit, specifying the virtual machine name, and add a device entry in the <source> section to assign the PCI device to the guest virtual machine.
    # virsh edit guest1-rhel6-64
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <source>
         <address domain='0' bus='0' slot='25' function='0'/>
      </source>
    </hostdev>
    Alternately, run virsh attach-device, specifying the virtual machine name and the guest's XML file:
    virsh attach-device guest1-rhel6-64 file.xml
  5. Start the virtual machine

    # virsh start guest1-rhel6-64
The PCI device should now be successfully assigned to the virtual machine, and accessible to the guest operating system.

10.1.2. Assigning a PCI device with virt-manager

PCI devices can be added to guest virtual machines using the graphical virt-manager tool. The following procedure adds a Gigabit Ethernet controller to a guest virtual machine.

Procedure 10.4. Assigning a PCI device to a guest virtual machine using virt-manager

  1. Open the hardware settings

    Open the guest virtual machine and click the Add Hardware button to add a new device to the virtual machine.
    The virtual machine hardware window with the Information button selected on the top taskbar and Overview selected on the left menu pane.

    Figure 10.1. The virtual machine hardware information window

  2. Select a PCI device

    Select PCI Host Device from the Hardware list on the left.
    Select an unused PCI device. If you select a PCI device that is in use by another guest an error may result. In this example, a spare 82576 network device is used. Click Finish to complete setup.
    The Add new virtual hardware wizard with PCI Host Device selected on the left menu pane, showing a list of host devices for selection in the right menu pane.

    Figure 10.2. The Add new virtual hardware wizard

  3. Add the new device

    The setup is complete and the guest virtual machine now has direct access to the PCI device.
    The virtual machine hardware window with the Information button selected on the top taskbar and Overview selected on the left menu pane, displaying the newly added PCI Device in the list of virtual machine devices in the left menu pane.

    Figure 10.3. The virtual machine hardware information window

Note

If device assignment fails, there may be other endpoints in the same IOMMU group that are still attached to the host. There is no way to retrieve group information using virt-manager, but virsh commands can be used to analyze the bounds of the IOMMU group and if necessary sequester devices.
Refer to the Note in Section 10.1.1, “Assigning a PCI device with virsh” for more information on IOMMU groups and how to detach endpoint devices using virsh.

10.1.3. PCI device assignment with virt-install

To use virt-install to assign a PCI device, use the --host-device parameter.

Procedure 10.5. Assigning a PCI device to a virtual machine with virt-install

  1. Identify the device

    Identify the PCI device designated for device assignment to the guest virtual machine.
    # lspci | grep Ethernet
    00:19.0 Ethernet controller: Intel Corporation 82567LM-2 Gigabit Network Connection
    01:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    01:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)
    The virsh nodedev-list command lists all devices attached to the system, and identifies each PCI device with a string. To limit output to only PCI devices, run the following command:
    # virsh nodedev-list --cap pci
    pci_0000_00_00_0
    pci_0000_00_01_0
    pci_0000_00_03_0
    pci_0000_00_07_0
    pci_0000_00_10_0
    pci_0000_00_10_1
    pci_0000_00_14_0
    pci_0000_00_14_1
    pci_0000_00_14_2
    pci_0000_00_14_3
    pci_0000_00_19_0
    pci_0000_00_1a_0
    pci_0000_00_1a_1
    pci_0000_00_1a_2
    pci_0000_00_1a_7
    pci_0000_00_1b_0
    pci_0000_00_1c_0
    pci_0000_00_1c_1
    pci_0000_00_1c_4
    pci_0000_00_1d_0
    pci_0000_00_1d_1
    pci_0000_00_1d_2
    pci_0000_00_1d_7
    pci_0000_00_1e_0
    pci_0000_00_1f_0
    pci_0000_00_1f_2
    pci_0000_00_1f_3
    pci_0000_01_00_0
    pci_0000_01_00_1
    pci_0000_02_00_0
    pci_0000_02_00_1
    pci_0000_06_00_0
    pci_0000_07_02_0
    pci_0000_07_03_0
    Record the PCI device number; the number is needed in other steps.
    Information on the domain, bus and function are available from output of the virsh nodedev-dumpxml command:
    # virsh nodedev-dumpxml pci_0000_01_00_0
    <device>
      <name>pci_0000_01_00_0</name>
      <parent>pci_0000_00_01_0</parent>
      <driver>
        <name>igb</name>
      </driver>
      <capability type='pci'>
        <domain>0</domain>
        <bus>1</bus>
        <slot>0</slot>
        <function>0</function>
        <product id='0x10c9'>82576 Gigabit Network Connection</product>
        <vendor id='0x8086'>Intel Corporation</vendor>
        <iommuGroup number='7'>
          <address domain='0x0000' bus='0x00' slot='0x19' function='0x0'/>
        </iommuGroup>
      </capability>
    </device>

    Note

    If there are multiple endpoints in the IOMMU group and not all of them are assigned to the guest, you will need to manually detach the other endpoint(s) from the host by running the following command before you start the guest:
    $ virsh nodedev-detach pci_0000_00_19_1
    Refer to the Note in Section 10.1.1, “Assigning a PCI device with virsh” for more information on IOMMU groups.
  2. Add the device

    Use the PCI identifier output from the virsh nodedev command as the value for the --host-device parameter.
    virt-install \
    --name=guest1-rhel6-64 \
    --disk path=/var/lib/libvirt/images/guest1-rhel6-64.img,size=8 \
    --nonsparse --graphics spice \
    --vcpus=2 --ram=2048 \
    --location=http://example1.com/installation_tree/RHEL6.0-Server-x86_64/os \
    --nonetworks \
    --os-type=linux \
    --os-variant=rhel6
    --host-device=pci_0000_01_00_0
  3. Complete the installation

    Complete the guest installation. The PCI device should be attached to the guest.

10.1.4. Detaching an assigned PCI device

When a host PCI device has been assigned to a guest machine, the host can no longer use the device. Read this section to learn how to detach the device from the guest with virsh or virt-manager so it is available for host use.

Procedure 10.6. Detaching a PCI device from a guest with virsh

  1. Detach the device

    Use the following command to detach the PCI device from the guest by removing it in the guest's XML file:
    # virsh detach-device name_of_guest file.xml
  2. Re-attach the device to the host (optional)

    If the device is in managed mode, skip this step. The device will be returned to the host automatically.
    If the device is not using managed mode, use the following command to re-attach the PCI device to the host machine:
    # virsh nodedev-reattach device
    For example, to re-attach the pci_0000_01_00_0 device to the host:
    virsh nodedev-reattach pci_0000_01_00_0
    The device is now available for host use.

Procedure 10.7. Detaching a PCI Device from a guest with virt-manager

  1. Open the virtual hardware details screen

    In virt-manager, double-click on the virtual machine that contains the device. Select the Show virtual hardware details button to display a list of virtual hardware.
    The Show virtual hardware details button.

    Figure 10.4. The virtual hardware details button

  2. Select and remove the device

    Select the PCI device to be detached from the list of virtual devices in the left panel.
    The PCI device details and the Remove button.

    Figure 10.5. Selecting the PCI device to be detached

    Click the Remove button to confirm. The device is now available for host use.

10.1.5. Creating PCI bridges

Peripheral Component Interconnects (PCI) bridges are used to attach to devices such as network cards, modems and sound cards. Just like their physical counterparts, virtual devices can also be attached to a PCI Bridge. In the past, only 31 PCI devices could be added to any guest virtual machine. Now, when a 31st PCI device is added, a PCI bridge is automatically placed in the 31st slot moving the additional PCI device to the PCI bridge. Each PCI bridge has 31 slots for 31 additional devices, all of which can be bridges. In this manner, over 900 devices can be available for guest virtual machines.

Note

This action cannot be performed when the guest virtual machine is running. You must add the PCI device on a guest virtual machine that is shutdown.

10.1.6. PCI passthrough

A PCI network device (specified by the <source> element) is directly assigned to the guest using generic device passthrough, after first optionally setting the device's MAC address to the configured value, and associating the device with an 802.1Qbh capable switch using an optionally specified <virtualport> element (see the examples of virtualport given above for type='direct' network devices). Due to limitations in standard single-port PCI ethernet card driver design - only SR-IOV (Single Root I/O Virtualization) virtual function (VF) devices can be assigned in this manner; to assign a standard single-port PCI or PCIe Ethernet card to a guest, use the traditional <hostdev> device definition.
To use VFIO device assignment rather than traditional/legacy KVM device assignment (VFIO is a new method of device assignment that is compatible with UEFI Secure Boot), a <type='hostdev'> interface can have an optional driver sub-element with a name attribute set to "vfio". To use legacy KVM device assignment you can set name to "kvm" (or simply omit the <driver> element, since <driver='kvm'> is currently the default).

Note

Intelligent passthrough of network devices is very similar to the functionality of a standard <hostdev> device, the difference being that this method allows specifying a MAC address and <virtualport> for the passed-through device. If these capabilities are not required, if you have a standard single-port PCI, PCIe, or USB network card that does not support SR-IOV (and hence would anyway lose the configured MAC address during reset after being assigned to the guest domain), or if you are using a version of libvirt older than 0.9.11, you should use standard <hostdev> to assign the device to the guest instead of <interface type='hostdev'/>.

     <devices>
    <interface type='hostdev'>
      <driver name='vfio'/>
      <source>
        <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/>
      </source>
      <mac address='52:54:00:6d:90:02'>
      <virtualport type='802.1Qbh'>
        <parameters profileid='finance'/>
      </virtualport>
    </interface>
  </devices>

Figure 10.6. XML example for PCI device assignment

10.1.7. Configuring PCI assignment (passthrough) with SR-IOV devices

This section is for SR-IOV devices only. SR-IOV network cards provide multiple Virtual Functions (VFs) that can each be individually assigned to a guest virtual machines using PCI device assignment. Once assigned, each will behave as a full physical network device. This permits many guest virtual machines to gain the performance advantage of direct PCI device assignment, while only using a single slot on the host physical machine.
These VFs can be assigned to guest virtual machines in the traditional manner using the element <hostdev>, but as SR-IOV VF network devices do not have permanent unique MAC addresses, it causes issues where the guest virtual machine's network settings would have to be re-configured each time the host physical machine is rebooted. To remedy this, you would need to set the MAC address prior to assigning the VF to the host physical machine and you would need to set this each and every time the guest virtual machine boots. In order to assign this MAC address as well as other options, refert to the procedure described in Procedure 10.8, “Configuring MAC addresses, vLAN, and virtual ports for assigning PCI devices on SR-IOV”.

Procedure 10.8. Configuring MAC addresses, vLAN, and virtual ports for assigning PCI devices on SR-IOV

It is important to note that the <hostdev> element cannot be used for function-specific items like MAC address assignment, vLAN tag ID assignment, or virtual port assignment because the <mac>, <vlan>, and <virtualport> elements are not valid children for <hostdev>. As they are valid for <interface>, support for a new interface type was added (<interface type='hostdev'>). This new interface device type behaves as a hybrid of an <interface> and <hostdev>. Thus, before assigning the PCI device to the guest virtual machine, libvirt initializes the network-specific hardware/switch that is indicated (such as setting the MAC address, setting a vLAN tag, and/or associating with an 802.1Qbh switch) in the guest virtual machine's XML configuration file. For information on setting the vLAN tag, refer to Section 19.14, “Setting vLAN tags”.
  1. Shutdown the guest virtual machine

    Using virsh shutdown command (refer to Section 15.9.1, “Shut down a guest virtual machine”), shutdown the guest virtual machine named guestVM.
    # virsh shutdown guestVM
  2. Gather information

    In order to use <interface type='hostdev'>, you must have an SR-IOV-capable network card, host physical machine hardware that supports either the Intel VT-d or AMD IOMMU extensions, and you must know the PCI address of the VF that you wish to assign.
  3. Open the XML file for editing

    Run the # virsh save-image-edit command to open the XML file for editing (refer to Section 15.8.10, “Edit Domain XML configuration files” for more information). As you would want to restore the guest virtual machine to its former running state, the --running would be used in this case. The name of the configuration file in this example is guestVM.xml, as the name of the guest virtual machine is guestVM.
     # virsh save-image-edit guestVM.xml --running 
    The guestVM.xml opens in your default editor.
  4. Edit the XML file

    Update the configuration file (guestVM.xml) to have a <devices> entry similar to the following:
    
     <devices>
       ...
       <interface type='hostdev' managed='yes'>
         <source>
           <address type='pci' domain='0x0' bus='0x00' slot='0x07' function='0x0'/> <!--these values can be decimal as well-->
         </source>
         <mac address='52:54:00:6d:90:02'/>                                         <!--sets the mac address-->
         <virtualport type='802.1Qbh'>                                              <!--sets the virtual port for the 802.1Qbh switch-->
           <parameters profileid='finance'/>
         </virtualport>
         <vlan>                                                                     <!--sets the vlan tag-->
          <tag id='42'/>
         </vlan>
       </interface>
       ...
     </devices>
    
    

    Figure 10.7. Sample domain XML for hostdev interface type

    Note that if you do not provide a MAC address, one will be automatically generated, just as with any other type of interface device. Also, the <virtualport> element is only used if you are connecting to an 802.11Qgh hardware switch (802.11Qbg (a.k.a. "VEPA") switches are currently not supported.
  5. Re-start the guest virtual machine

    Run the virsh start command to restart the guest virtual machine you shutdown in the first step (example uses guestVM as the guest virtual machine's domain name). Refer to Section 15.8.1, “Starting a defined domain” for more information.
     # virsh start guestVM 
    When the guest virtual machine starts, it sees the network device provided to it by the physical host machine's adapter, with the configured MAC address. This MAC address will remain unchanged across guest virtual machine and host physical machine reboots.

10.1.8. Setting PCI device assignment from a pool of SR-IOV virtual functions

Hard coding the PCI addresses of a particular Virtual Functions (VFs) into a guest's configuration has two serious limitations:
  • The specified VF must be available any time the guest virtual machine is started, implying that the administrator must permanently assign each VF to a single guest virtual machine (or modify the configuration file for every guest virtual machine to specify a currently unused VF's PCI address each time every guest virtual machine is started).
  • If the guest virtual machine is moved to another host physical machine, that host physical machine must have exactly the same hardware in the same location on the PCI bus (or, again, the guest virtual machine configuration must be modified prior to start).
It is possible to avoid both of these problems by creating a libvirt network with a device pool containing all the VFs of an SR-IOV device. Once that is done you would configure the guest virtual machine to reference this network. Each time the guest is started, a single VF will be allocated from the pool and assigned to the guest virtual machine. When the guest virtual machine is stopped, the VF will be returned to the pool for use by another guest virtual machine.

Procedure 10.9. Creating a device pool

  1. Shutdown the guest virtual machine

    Using virsh shutdown command (refer to Section 15.9, “Shutting down, rebooting and force-shutdown of a guest virtual machine”), shutdown the guest virtual machine named guestVM.
    # virsh shutdown guestVM
  2. Create a configuration file

    Using your editor of chocice create an XML file (named passthrough.xml, for example) in the /tmp directory. Make sure to replace pf dev='eth3' with the netdev name of your own SR-IOV device's PF
    The following is an example network definition that will make available a pool of all VFs for the SR-IOV adapter with its physical function (PF) at "eth3' on the host physical machine:
                
    <network>
       <name>passthrough</name>                                                <!--This is the name of the file you created-->
       <forward mode='hostdev' managed='yes'>
         <pf dev='myNetDevName'/>                                              <!--Use the netdev name of your SR-IOV devices PF here-->
       </forward>
    </network>
          
    
    

    Figure 10.8. Sample network definition domain XML

  3. Load the new XML file

    Run the following command, replacing /tmp/passthrough.xml, with the name and location of your XML file you created in the previous step:
    # virsh net-define /tmp/passthrough.xml
  4. Restarting the guest

    Run the following replacing passthrough.xml, with the name of your XML file you created in the previous step:
     # virsh net-autostart passthrough # virsh net-start passthrough 
  5. Re-start the guest virtual machine

    Run the virsh start command to restart the guest virtual machine you shutdown in the first step (example uses guestVM as the guest virtual machine's domain name). Refer to Section 15.8.1, “Starting a defined domain” for more information.
     # virsh start guestVM 
  6. Initiating passthrough for devices

    Although only a single device is shown, libvirt will automatically derive the list of all VFs associated with that PF the first time a guest virtual machine is started with an interface definition in its domain XML like the following:
             
    <interface type='network'>
       <source network='passthrough'>
    </interface>
          
    
    

    Figure 10.9. Sample domain XML for interface network definition

  7. Verification

    You can verify this by running virsh net-dumpxml passthrough command after starting the first guest that uses the network; you will get output similar to the following:
          
    <network connections='1'>
       <name>passthrough</name>
       <uuid>a6b49429-d353-d7ad-3185-4451cc786437</uuid>
       <forward mode='hostdev' managed='yes'>
         <pf dev='eth3'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x10' function='0x1'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x10' function='0x3'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x10' function='0x5'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x10' function='0x7'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x11' function='0x1'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x11' function='0x3'/>
         <address type='pci' domain='0x0000' bus='0x02' slot='0x11' function='0x5'/>
       </forward>
    </network>
          
    
    

    Figure 10.10. XML dump file passthrough contents

10.2. USB devices

This section gives the commands required for handling USB devices.

10.2.1. Assigning USB devices to guest virtual machines

Most devices such as web cameras, card readers, keyboards, mice etc., are connected to a computer using a USB port and cable. There are two ways to pass such devices to a guest virtual machine:
  • Using USB passthrough - this requires the device to be physically connected to the host physical machine that is hosting the guest virtual machine. SPICE is not needed in this case. USB devices on the host can be passed to the guest using the command line or virt-manager. Refer to Section 16.3.1, “Attaching USB devices to a guest virtual machine” for virt manager directions.

    Note

    virt-manager should not be used for hot plugging or hot unplugging devices. If you want to hot plug/or hot unplug a USB device, refer to Procedure 15.1, “Hotplugging USB devices for use by the guest virtual machine”.
  • Using USB re-direction - USB re-direction is best used in cases where there is a host physical machine that is running in a data center. The user connects to his/her guest virtual machine from a local machine or thin client. On this local machine there is a SPICE client. The user can attach any USB device to the thin client and the SPICE client will redirect the device to the host physical machine on the data center so it can be used by the guest virtual machine that is running on the thin client. For instructions on USB re-direction using the virt-manager, refer to Section 16.3.1, “Attaching USB devices to a guest virtual machine” It should be noted that USB redirection is not possible using the TCP protocol (Refer to BZ#1085318).

10.2.2. Setting a limit on USB device redirection

To filter out certain devices from redirection, pass the filter property to -device usb-redir. The filter property takes a string consisting of filter rules, the format for a rule is:
<class>:<vendor>:<product>:<version>:<allow>
Use the value -1 to designate it to accept any value for a particular field. You may use multiple rules on the same command line using | as a separator.

Important

If a device matches none of the rule filters, redirecting it will not be allowed!

Example 10.1. An example of limiting redirection with a windows guest virtual machine

  1. Prepare a Windows 7 guest virtual machine.
  2. Add the following code excerpt to the guest virtual machine's' domain xml file:
        <redirdev bus='usb' type='spicevmc'>
          <alias name='redir0'/>
          <address type='usb' bus='0' port='3'/>
        </redirdev>
        <redirfilter>
          <usbdev class='0x08' vendor='0x1234' product='0xBEEF' version='2.0' allow='yes'/>
          <usbdev class='-1' vendor='-1' product='-1' version='-1' allow='no'/>
        </redirfilter>
    
  3. Start the guest virtual machine and confirm the setting changes by running the following:
    #ps -ef | grep $guest_name
    -device usb-redir,chardev=charredir0,id=redir0,/
    filter=0x08:0x1234:0xBEEF:0x0200:1|-1:-1:-1:-1:0,bus=usb.0,port=3
  4. Plug a USB device into a host physical machine, and use virt-manager to connect to the guest virtual machine.
  5. Click Redirect USB Service in the menu, which will produce the following message: "Some USB devices are blocked by host policy". Click OK to confirm and continue.
    The filter takes effect.
  6. To make sure that the filter captures properly check the USB device vendor and product, then make the following changes in the guest virtual machine's domain XML to allow for USB redirection.
       <redirfilter>
          <usbdev class='0x08' vendor='0x0951' product='0x1625' version='2.0' allow='yes'/>
          <usbdev allow='no'/>
        </redirfilter>
    
  7. Restart the guest virtual machine, then use virt-viewer to connect to the guest virtual machine. The USB device will now redirect traffic to the guest virtual machine.

10.3. Configuring device controllers

Depending on the guest virtual machine architecture, some device buses can appear more than once, with a group of virtual devices tied to a virtual controller. Normally, libvirt can automatically infer such controllers without requiring explicit XML markup, but in some cases it is better to explicitly set a virtual controller element.

  ...
  <devices>
    <controller type='ide' index='0'/>
    <controller type='virtio-serial' index='0' ports='16' vectors='4'/>
    <controller type='virtio-serial' index='1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </controller>
    ...
  </devices>
  ...

Figure 10.11. Domain XML example for virtual controllers

Each controller has a mandatory attribute <controller type>, which must be one of:
  • ide
  • fdc
  • scsi
  • sata
  • usb
  • ccid
  • virtio-serial
  • pci
The <controller> element has a mandatory attribute <controller index> which is the decimal integer describing in which order the bus controller is encountered (for use in controller attributes of <address> elements). When <controller type ='virtio-serial'> there are two additional optional attributes (named ports and vectors), which control how many devices can be connected through the controller. Note that Red Hat Enterprise Linux 6 does not support the use of more than 32 vectors per device. Using more vectors will cause failures in migrating the guest virtual machine.
When <controller type ='scsi'>, there is an optional attribute model model, which can have the following values:
  • auto
  • buslogic
  • ibmvscsi
  • lsilogic
  • lsisas1068
  • lsisas1078
  • virtio-scsi
  • vmpvscsi
When <controller type ='usb'>, there is an optional attribute model model, which can have the following values:
  • piix3-uhci
  • piix4-uhci
  • ehci
  • ich9-ehci1
  • ich9-uhci1
  • ich9-uhci2
  • ich9-uhci3
  • vt82c686b-uhci
  • pci-ohci
  • nec-xhci

Note

If the USB bus needs to be explicitly disabled for the guest virtual machine, <model='none'> may be used. .
For controllers that are themselves devices on a PCI or USB bus, an optional sub-element <address> can specify the exact relationship of the controller to its master bus, with semantics as shown in Section 10.4, “Setting addresses for devices”.
An optional sub-element <driver> can specify the driver specific options. Currently it only supports attribute queues, which specifies the number of queues for the controller. For best performance, it's recommended to specify a value matching the number of vCPUs.
USB companion controllers have an optional sub-element <master> to specify the exact relationship of the companion to its master controller. A companion controller is on the same bus as its master, so the companion index value should be equal.
An example XML which can be used is as follows:
   
     ...
  <devices>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0' bus='0' slot='4' function='7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0' bus='0' slot='4' function='0' multifunction='on'/>
    </controller>
    ...
  </devices>
  ...
   

Figure 10.12. Domain XML example for USB controllers

PCI controllers have an optional model attribute with the following possible values:
  • pci-root
  • pcie-root
  • pci-bridge
  • dmi-to-pci-bridge
The root controllers (pci-root and pcie-root) have an optional pcihole64 element specifying how big (in kilobytes, or in the unit specified by pcihole64's unit attribute) the 64-bit PCI hole should be. Some guest virtual machines (such as Windows Server 2003) may cause a crash, unless unit is disabled (set to 0 unit='0').
For machine types which provide an implicit PCI bus, the pci-root controller with index='0' is auto-added and required to use PCI devices. pci-root has no address. PCI bridges are auto-added if there are too many devices to fit on the one bus provided by model='pci-root', or a PCI bus number greater than zero was specified. PCI bridges can also be specified manually, but their addresses should only refer to PCI buses provided by already specified PCI controllers. Leaving gaps in the PCI controller indexes might lead to an invalid configuration. The following XML example can be added to the <devices> section:

  ...
  <devices>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='pci' index='1' model='pci-bridge'>
      <address type='pci' domain='0' bus='0' slot='5' function='0' multifunction='off'/>
    </controller>
  </devices>
  ...

Figure 10.13. Domain XML example for PCI bridge

For machine types which provide an implicit PCI Express (PCIe) bus (for example, the machine types based on the Q35 chipset), the pcie-root controller with index='0' is auto-added to the domain's configuration. pcie-root has also no address, but provides 31 slots (numbered 1-31) and can only be used to attach PCIe devices. In order to connect standard PCI devices on a system which has a pcie-root controller, a pci controller with model='dmi-to-pci-bridge' is automatically added. A dmi-to-pci-bridge controller plugs into a PCIe slot (as provided by pcie-root), and itself provides 31 standard PCI slots (which are not hot-pluggable). In order to have hot-pluggable PCI slots in the guest system, a pci-bridge controller will also be automatically created and connected to one of the slots of the auto-created dmi-to-pci-bridge controller; all guest devices with PCI addresses that are auto-determined by libvirt will be placed on this pci-bridge device.
   
     ...
  <devices>
    <controller type='pci' index='0' model='pcie-root'/>
    <controller type='pci' index='1' model='dmi-to-pci-bridge'>
      <address type='pci' domain='0' bus='0' slot='0xe' function='0'/>
    </controller>
    <controller type='pci' index='2' model='pci-bridge'>
      <address type='pci' domain='0' bus='1' slot='1' function='0'/>
    </controller>
  </devices>
  ...
   

Figure 10.14. Domain XML example for PCIe (PCI express)

10.4. Setting addresses for devices

Many devices have an optional <address> sub-element which is used to describe where the device is placed on the virtual bus presented to the guest virtual machine. If an address (or any optional attribute within an address) is omitted on input, libvirt will generate an appropriate address; but an explicit address is required if more control over layout is required. See Figure 10.6, “XML example for PCI device assignment” for domain XML device examples including an <address> element.
Every address has a mandatory attribute type that describes which bus the device is on. The choice of which address to use for a given device is constrained in part by the device and the architecture of the guest virtual machine. For example, a <disk> device uses type='drive', while a <console> device would use type='pci' on i686 or x86_64 guest virtual machine architectures. Each address type has further optional attributes that control where on the bus the device will be placed as described in the table:

Table 10.1. Supported device address types

Address type Description
type='pci' PCI addresses have the following additional attributes:
  • domain (a 2-byte hex integer, not currently used by qemu)
  • bus (a hex value between 0 and 0xff, inclusive)
  • slot (a hex value between 0x0 and 0x1f, inclusive)
  • function (a value between 0 and 7, inclusive)
  • multifunction controls turning on the multifunction bit for a particular slot/function in the PCI control register By default it is set to 'off', but should be set to 'on' for function 0 of a slot that will have multiple functions used.
type='drive' Drive addresses have the following additional attributes:
  • controller (a 2-digit controller number)
  • bus (a 2-digit bus number
  • target (a 2-digit bus number)
  • unit (a 2-digit unit number on the bus)
type='virtio-serial' Each virtio-serial address has the following additional attributes:
  • controller (a 2-digit controller number)
  • bus (a 2-digit bus number)
  • slot (a 2-digit slot within the bus)
type='ccid' A CCID address, for smart-cards, has the following additional attributes:
  • bus (a 2-digit bus number)
  • slot attribute (a 2-digit slot within the bus)
type='usb' USB addresses have the following additional attributes:
  • bus (a hex value between 0 and 0xfff, inclusive)
  • port (a dotted notation of up to four octets, such as 1.2 or 2.1.3.1)
type='isa' ISA addresses have the following additional attributes:
  • iobase
  • irq

10.5. Managing storage controllers in a guest virtual machine

Starting from Red Hat Enterprise Linux 6.4, it is supported to add SCSI and virtio-SCSI devices to guest virtual machines that are running Red Hat Enterprise Linux 6.4 or later. Unlike virtio disks, SCSI devices require the presence of a controller in the guest virtual machine. Virtio-SCSI provides the ability to connect directly to SCSI LUNs and significantly improves scalability compared to virtio-blk. The advantage of virtio-SCSI is that it is capable of handling hundreds of devices compared to virtio-blk which can only handle 28 devices and exhausts PCI slots. Virtio-SCSI is now capable of inheriting the feature set of the target device with the ability to:
  • attach a virtual hard drive or CD through the virtio-scsi controller,
  • pass-through a physical SCSI device from the host to the guest via the QEMU scsi-block device,
  • and allow the usage of hundreds of devices per guest; an improvement from the 28-device limit of virtio-blk.
This section details the necessary steps to create a virtual SCSI controller (also known as "Host Bus Adapter", or HBA) and to add SCSI storage to the guest virtual machine.

Procedure 10.10. Creating a virtual SCSI controller

  1. Display the configuration of the guest virtual machine (Guest1) and look for a pre-existing SCSI controller:
    # virsh dumpxml Guest1 | grep controller.*scsi
    
    If a device controller is present, the command will output one or more lines similar to the following:
    <controller type='scsi' model='virtio-scsi' index='0'/>
    
  2. If the previous step did not show a device controller, create the description for one in a new file and add it to the virtual machine, using the following steps:
    1. Create the device controller by writing a <controller> element in a new file and save this file with an XML extension. virtio-scsi-controller.xml, for example.
      <controller type='scsi' model='virtio-scsi'/>
      
    2. Associate the device controller you just created in virtio-scsi-controller.xml with your guest virtual machine (Guest1, for example):
      # virsh attach-device --config Guest1 ~/virtio-scsi-controller.xml
      
      In this example the --config option behaves the same as it does for disks. Refer to Procedure 14.2, “Adding physical block devices to guests” for more information.
  3. Add a new SCSI disk or CD-ROM. The new disk can be added using the methods in sections Section 14.3.1, “Adding file based storage to a guest” and Section 14.3.2, “Adding hard drives and other block devices to a guest”. In order to create a SCSI disk, specify a target device name that starts with sd.
    # virsh attach-disk Guest1 /var/lib/libvirt/images/FileName.img sdb --cache none
    
    Depending on the version of the driver in the guest virtual machine, the new disk may not be detected immediately by a running guest virtual machine. Follow the steps in the Red Hat Enterprise Linux Storage Administration Guide.

10.6. Random number generator (RNG) device

virtio-rng is a virtual RNG (random number generator) device that feeds RNG data to the guest virtual machine's operating system, thereby providing fresh entropy for guest virtual machines on request.
Using an RNG is particularly useful when a device such as a keyboard, mouse and other inputs are not enough to generate sufficient entropy on the guest virtual machine. The virtio-rng device is available for both Red Hat Enterprise Linux and Windows guest virtual machines. Refer to the Note for instructions on installing the Windows requirements. Unless noted, the following descriptions are for both Red Hat Enterprise Linux and Windows guest virtual machines.
When virtio-rng is enabled on a Linux guest virtual machine, a chardev is created in the guest virtual machine at the location /dev/hwrng. This chardev can then be opened and read to fetch entropy from the host physical machine. In order for guest virtual machines' applications to benefit from using randomness from the virtio-rng device transparently, the input from /dev/hwrng must be relayed to the kernel entropy pool in the guest virtual machine. This can be accomplished if the information in this location is coupled with the rgnd daemon (contained within the rng-tools).
This coupling results in the entropy to be routed to the guest virtual machine's /dev/random file. The process is done manually in Red Hat Enterprise Linux 6 guest virtual machines.
Red Hat Enterprise Linux 6 guest virtual machines are coupled by running the following command:
# rngd -b -r /dev/hwrng -o /dev/random
For more assistance, run the man rngd command for an explanation of the command options shown here. For further examples, refer to Procedure 10.11, “Implementing virtio-rng with the command line tools” for configuring the virtio-rng device.

Note

Windows guest virtual machines require the driver viorng to be installed. Once installed, the virtual RNG device will work using the CNG (crypto next generation) API provided by Microsoft. Once the driver is installed, the virtrng device appears in the list of RNG providers.

Procedure 10.11. Implementing virtio-rng with the command line tools

  1. Shut down the guest virtual machine.
  2. In a terminal window, using the virsh edit domain-name command, open the XML file for the desired guest virtual machine.
  3. Edit the <devices> element to include the following:
    
      ...
      <devices>
        <rng model='virtio'>
          <rate period="2000" bytes="1234"/>
          <backend model='random'>/dev/random</backend>
               <source mode='bind' service='1234'>
               <source mode='connect' host='192.0.2.1' service='1234'>
          </backend>
        </rng>
      </devices>
      ...

Chapter 11. QEMU-img and QEMU guest agent

This chapter contain useful hints and tips for using the qemu-img package with guest virtual machines. If you are looking for information on QEMU trace events and arguments, refer to the README file located here: /usr/share/doc/qemu-*/README.systemtap.

11.1. Using qemu-img

The qemu-img command line tool is used for formatting, modifying and verifying various file systems used by KVM. qemu-img options and usages are listed below.
Check
Perform a consistency check on the disk image filename.
#  qemu-img check -f qcow2 --output=qcow2 -r all filename-img.qcow2

Note

Only the qcow2 and vdi formats support consistency checks.
Using the -r tries to repair any inconsistencies that are found during the check, but when used with -r leaks cluster leaks are repaired and when used with -r all all kinds of errors are fixed. Note that this has a risk of choosing the wrong fix or hiding corruption issues that may have already occurred.
Commit
Commits any changes recorded in the specified file (filename) to the file's base image with the qemu-img commit command. Optionally, specify the file's format type (fmt).
 # qemu-img commit [-f fmt] [-t cache] filename
Convert
The convert option is used to convert one recognized image format to another image format.
Command format:
# qemu-img convert [-c] [-p] [-f fmt] [-t cache] [-O output_fmt] [-o options] [-S sparse_size] filename output_filename
The -p parameter shows the progress of the command (optional and not for every command) and -S flag allows for the creation of a sparse file, which is included within the disk image. Sparse files in all purposes function like a standard file, except that the physical blocks that only contain zeros (i.e., nothing). When the Operating System sees this file, it treats it as it exists and takes up actual disk space, even though in reality it doesn't take any. This is particularly helpful when creating a disk for a guest virtual machine as this gives the appearance that the disk has taken much more disk space than it has. For example, if you set -S to 50Gb on a disk image that is 10Gb, then your 10Gb of disk space will appear to be 60Gb in size even though only 10Gb is actually being used.
Convert the disk image filename to disk image output_filename using format output_format. The disk image can be optionally compressed with the -c option, or encrypted with the -o option by setting -o encryption. Note that the options available with the -o parameter differ with the selected format.
Only the qcow2 format supports encryption or compression. qcow2 encryption uses the AES format with secure 128-bit keys. qcow2 compression is read-only, so if a compressed sector is converted from qcow2 format, it is written to the new format as uncompressed data.
Image conversion is also useful to get a smaller image when using a format which can grow, such as qcow or cow. The empty sectors are detected and suppressed from the destination image.
Create
Create the new disk image filename of size size and format format.
# qemu-img create [-f format] [-o options] filename [size][preallocation]
If a base image is specified with -o backing_file=filename, the image will only record differences between itself and the base image. The backing file will not be modified unless you use the commit command. No size needs to be specified in this case.
Preallocation is an option that may only be used with creating qcow2 images. Accepted values include -o preallocation=off|meta|full|falloc. Images with preallocated metadata are larger than images without. However in cases where the image size increases, performance will improve as the image grows.
It should be noted that using full allocation can take a long time with large images. In cases where you want full allocation and time is of the essence, using falloc will save you time.
Info
The info parameter displays information about a disk image filename. The format for the info option is as follows:
# qemu-img info [-f format] filename
This command is often used to discover the size reserved on disk which can be different from the displayed size. If snapshots are stored in the disk image, they are displayed also. This command will show for example, how much space is being taken by a qcow2 image on a block device. This is done by running the qemu-img. You can check that the image in use is the one that matches the output of the qemu-img info command with the qemu-img check command. Refer to Section 11.1, “Using qemu-img”.
# qemu-img info /dev/vg-90.100-sluo/lv-90-100-sluo
image: /dev/vg-90.100-sluo/lv-90-100-sluo
file format: qcow2
virtual size: 20G (21474836480 bytes)
disk size: 0
cluster_size: 65536
Map
The # qemu-img map [-f fmt] [--output=ofmt] filename command dumps the metadata of the image filename and its backing file chain. Specifically, this commands dumps the allocation state of every sector of a specified file, together with the topmost file that allocates it in the backing file chain. For example, if you have a chain such as c.qcow2 → b.qcow2 → a.qcow2, a.qcow is the original file, b.qcow2 is the changes made to a.qcow2 and c.qcow2 is the delta file from b.qcow2. When this chain is created the image files stores the normal image data, plus information about what is in which file and where it is located within the file. This information is referred to as the image's metadata. The -f format option is the format of the specified image file. Formats such as raw, qcow2, vhdx and vmdk may be used. There are two output options are possible, human and json.
human is the default setting. It is designed to be more readable to the human eye, and as such this format should not be parsed. If programs that attempt to parse it, they can be misguided by malicious guest images.
For clarity and simplicity, the default human format only dumps known-nonzero areas of the file. Known-zero parts of the file are omitted altogether, and likewise for parts that are not allocated throughout the chain. When the command is executed, qemu-img output will identify a file from where the data can be read, and the offset in the file. The output is displayed as a table with four columns; the first three of which are hexadecimal numbers.
# qemu-img map -f qcow2 --output=human /tmp/test.qcow2 
Offset          Length          Mapped to       File
0               0x20000         0x50000         /tmp/test.qcow2
0x100000        0x80000         0x70000         /tmp/test.qcow2
0x200000        0x1f0000        0xf0000         /tmp/test.qcow2
0x3c00000       0x20000         0x2e0000        /tmp/test.qcow2
0x3fd0000       0x10000         0x300000        /tmp/test.qcow2
json, or JSON (JavaScript Object Notation), is readable by humans, but as it is a progaming language, it is also designed to be parsed. For example, if you want to parse the output of "qemu-img map" in a parser then you should use the flag --output=json.
# qemu-img map -f qcow2 --output=json /tmp/test.qcow2 
[{ "start": 0, "length": 131072, "depth": 0, "zero": false, "data": true, "offset": 327680},
{ "start": 131072, "length": 917504, "depth": 0, "zero": true, "data": false},
For more information on the JSON format, refer to the qemu-img MAN page.
Rebase
Changes the backing file of an image.
# qemu-img rebase [-f fmt] [-t cache] [-p] [-u] -b backing_file [-F backing_fmt] filename
The backing file is changed to backing_file and (if the format of filename supports the feature), the backing file format is changed to backing_format.

Note

Only the qcow2 format supports changing the backing file (rebase).
There are two different modes in which rebase can operate: Safe and Unsafe.
Safe mode is used by default and performs a real rebase operation. The new backing file may differ from the old one and the qemu-img rebase command will take care of keeping the guest virtual machine-visible content of filename unchanged. In order to achieve this, any clusters that differ between backing_file and old backing file of filename are merged into filename before making any changes to the backing file.
Note that safe mode is an expensive operation, comparable to converting an image. The old backing file is required for it to complete successfully.
Unsafe mode is used if the -u option is passed to qemu-img rebase. In this mode, only the backing file name and format of filename is changed, without any checks taking place on the file contents. Make sure the new backing file is specified correctly or the guest-visible content of the image will be corrupted.
This mode is useful for renaming or moving the backing file. It can be used without an accessible old backing file. For instance, it can be used to fix an image whose backing file has already been moved or renamed.
Resize
Change the disk image filename as if it had been created with size size. Only images in raw format can be resized regardless of version. Red Hat Enterprise Linux 6.1 and later adds the ability to grow (but not shrink) images in qcow2 format.
Use the following to set the size of the disk image filename to size bytes:
# qemu-img resize filename size
You can also resize relative to the current size of the disk image. To give a size relative to the current size, prefix the number of bytes with + to grow, or - to reduce the size of the disk image by that number of bytes. Adding a unit suffix allows you to set the image size in kilobytes (K), megabytes (M), gigabytes (G) or terabytes (T).
# qemu-img resize filename [+|-]size[K|M|G|T]

Warning

Before using this command to shrink a disk image, you must use file system and partitioning tools inside the VM itself to reduce allocated file systems and partition sizes accordingly. Failure to do so will result in data loss.
After using this command to grow a disk image, you must use file system and partitioning tools inside the VM to actually begin using the new space on the device.
Snapshot
List, apply, create, or delete an existing snapshot (snapshot) of an image (filename).
# qemu-img snapshot [ -l | -a snapshot | -c snapshot | -d snapshot ] filename
-l lists all snapshots associated with the specified disk image. The apply option, -a, reverts the disk image (filename) to the state of a previously saved snapshot. -c creates a snapshot (snapshot) of an image (filename). -d deletes the specified snapshot.
Supported formats
qemu-img is designed to convert files to one of the following formats:
raw
Raw disk image format (default). This can be the fastest file-based format. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-img info to obtain the real size used by the image or ls -ls on Unix/Linux. Although Raw images give optimal performance, only very basic features are available with a Raw image (no snapshots etc.).
qcow2
QEMU image format, the most versatile format with the best feature set. Use it to have optional AES encryption, zlib-based compression, support of multiple VM snapshots, and smaller images, which are useful on file systems that do not support holes (non-NTFS file systems on Windows). Note that this expansive feature set comes at the cost of performance.
Although only the formats above can be used to run on a guest virtual machine or host physical machine machine, qemu-img also recognizes and supports the following formats in order to convert from them into either raw or qcow2 format. The format of an image is usually detected automatically. In addition to converting these formats into raw or qcow2 , they can be converted back from raw or qcow2 to the original format.
bochs
Bochs disk image format.
cloop
Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.
cow
User Mode Linux Copy On Write image format. The cow format is included only for compatibility with previous versions. It does not work with Windows.
dmg
Mac disk image format.
nbd
Network block device.
parallels
Parallels virtualization disk image format.
qcow
Old QEMU image format. Only included for compatibility with older versions.
vdi
Oracle VM VirtualBox hard disk image format.
vmdk
VMware compatible image format (read-write support for versions 1 and 2, and read-only support for version 3).
vpc
Windows Virtual PC disk image format. Also referred to as vhd, or Microsoft virtual hard disk image format.
vvfat
Virtual VFAT disk image format.

11.2. QEMU guest agent

The QEMU guest agent runs inside the guest and allows the host machine to issue commands to the guest operating system using libvirt. The guest operating system then responds to those commands asynchronously. This chapter covers the libvirt commands and options available to the guest agent.

Important

Note that it is only safe to rely on the guest agent when run by trusted guests. An untrusted guest may maliciously ignore or abuse the guest agent protocol, and although built-in safeguards exist to prevent a denial of service attack on the host, the host requires guest co-operation for operations to run as expected.
Note that CPU hot plugging and hot unplugging are supported with the help of the QEMU guest agent on Linux and Windows guests; CPUs can be enabled or disabled while the guest is running, thus implementing the hotplug feature and mimicking the unplug feature. Refer to Section 15.13.6, “Configuring virtual CPU count” for more information.

11.2.1. Install and enable the guest agent

Install qemu-guest-agent on the guest virtual machine with the yum install qemu-guest-agent command and make it run automatically at every boot as a service (qemu-guest-agent.service).

11.2.2. Setting up communication between guest agent and host

The host machine communicates with the guest agent through a VirtIO serial connection between the host and guest machines. A VirtIO serial channel is connected to the host via a character device driver (typically a Unix socket), and the guest listens on this serial channel. The following procedure shows how to set up the host and guest machines for guest agent use.

Note

For instructions on how to set up the QEMU guest agent on Windows guests, refer to the instructions found here.

Procedure 11.1. Setting up communication between guest agent and host

  1. Open the guest XML

    Open the guest XML with the QEMU guest agent configuration. You will need the guest name to open the file. Use the command # virsh list on the host machine to list the guests that it can recognize. In this example, the guest's name is rhel6:
    # virsh edit rhel6
  2. Edit the guest XML file

    Add the following elements to the XML file and save the changes.
    <channel type='unix'>
       <source mode='bind' path='/var/lib/libvirt/qemu/rhel6.agent'/>
       <target type='virtio' name='org.qemu.guest_agent.0'/>
    </channel>
    
    

    Figure 11.1. Editing the guest XML to configure the QEMU guest agent

  3. Start the QEMU guest agent in the guest

    Download and install the guest agent in the guest virtual machine using yum install qemu-guest-agent if you have not done so already. Once installed, start the service as follows:
    # service start qemu-guest-agent
You can now communicate with the guest by sending valid libvirt commands over the established character device driver.

11.2.3. Using the QEMU guest agent

The QEMU guest agent protocol (QEMU GA) package, qemu-guest-agent, is fully supported in Red Hat Enterprise Linux 6.5 and newer. However, there are the following limitations with regards to isa-serial/virtio-serial transport:
  • The qemu-guest-agent cannot detect whether or not a client has connected to the channel.
  • There is no way for a client to detect whether or not qemu-guest-agent has disconnected or reconnected to the back-end.
  • If the virtio-serial device resets and qemu-guest-agent has not connected to the channel (generally caused by a reboot or hotplug), data from the client will be dropped.
  • If qemu-guest-agent has connected to the channel following a virtio-serial device reset, data from the client will be queued (and eventually throttled if available buffers are exhausted), regardless of whether or not qemu-guest-agent is still running or connected.

11.2.4. Using the QEMU guest agent with libvirt

Installing the QEMU guest agent allows various other libvirt commands to become more powerful. The guest agent enhances the following virsh commands:
  • virsh shutdown --mode=agent - This shutdown method is more reliable than virsh shutdown --mode=acpi, as virsh shutdown used with the QEMU guest agent is guaranteed to shut down a cooperative guest in a clean state. If the agent is not present, libvirt has to instead rely on injecting an ACPI shutdown event, but some guests ignore that event and thus will not shut down.
    Can be used with the same syntax for virsh reboot.
  • virsh snapshot-create --quiesce - Allows the guest to flush its I/O into a stable state before the snapshot is created, which allows use of the snapshot without having to perform a fsck or losing partial database transactions. The guest agent allows a high level of disk contents stability by providing guest co-operation.
  • virsh setvcpus --guest - Instructs the guest to take CPUs offline.
  • virsh dompmsuspend - Suspends a running guest gracefully using the guest operating system's power management functions.

11.2.5. Creating a guest virtual machine disk backup

libvirt can communicate with qemu-ga to assure that snapshots of guest virtual machine file systems are consistent internally and ready for use on an as needed basis. Improvements in Red Hat Enterprise Linux 6 have been made to make sure that both file and application level synchronization (flushing) is done. Guest system administrators can write and install application-specific freeze/thaw hook scripts. Before freezing the filesystems, the qemu-ga invokes the main hook script (included in the qemu-ga package). The freezing process temporarily deactivates all guest virtual machine applications.
Just before filesystems are frozen, the following actions occur:
  • File system applications / databases flush working buffers to the virtual disk and stop accepting client connections
  • Applications bring their data files into a consistent state
  • Main hook script returns
  • qemu-ga freezes the filesystems and management stack takes a snapshot
  • Snapshot is confirmed
  • Filesystem function resumes
Thawing happens in reverse order.
Use the snapshot-create-as command to create a snapshot of the guest disk. See Section 15.15.2.2, “Creating a snapshot for the current domain” for more details on this command.

Note

An application-specific hook script might need various SELinux permissions in order to run correctly, as is done when the script needs to connect to a socket in order to talk to a database. In general, local SELinux policies should be developed and installed for such purposes. Accessing file system nodes should work out of the box, after issuing the restorecon -FvvR command listed in Table 11.1, “QEMU guest agent package contents” in the table row labeled /etc/qemu-ga/fsfreeze-hook.d/.
The qemu-guest-agent binary RPM includes the following files:

Table 11.1. QEMU guest agent package contents

File nameDescription
/etc/rc.d/init.d/qemu-gaService control script (start/stop) for the QEMU guest agent.
/etc/sysconfig/qemu-gaConfiguration file for the QEMU guest agent, as it is read by the /etc/rc.d/init.d/qemu-ga control script. The settings are documented in the file with shell script comments.
/usr/bin/qemu-gaQEMU guest agent binary file.
/usr/libexec/qemu-ga/Root directory for hook scripts.
/usr/libexec/qemu-ga/fsfreeze-hookMain hook script. No modifications are needed here.
/usr/libexec/qemu-ga/fsfreeze-hook.d/Directory for individual, application-specific hook scripts. The guest system administrator should copy hook scripts manually into this directory, ensure proper file mode bits for them, and then run restorecon -FvvR on this directory.
/usr/share/qemu-kvm/qemu-ga/Directory with sample scripts (for example purposes only). The scripts contained here are not executed.
The main hook script, /usr/libexec/qemu-ga/fsfreeze-hook logs its own messages, as well as the application-specific script's standard output and error messages, in the following log file: /var/log/qemu-ga/fsfreeze-hook.log. For more information, refer to the qemu-guest-agent wiki page at wiki.qemu.org or libvirt.org.

11.3. Running the QEMU guest agent on a Windows guest

A Red Hat Enterprise Linux host machine can issue commands to Windows guests by running the QEMU guest agent in the guest. This is supported in hosts running Red Hat Enterprise Linux 6.5 and newer, and in the following Windows guest operating systems:
  • Windows XP Service Pack 3 (VSS is not supported)
  • Windows Server 2003 R2 - x86 and AMD64 (VSS is not supported)
  • Windows Server 2008
  • Windows Server 2008 R2
  • Windows 7 - x86 and AMD64
  • Windows Server 2012
  • Windows Server 2012 R2
  • Windows 8 - x86 and AMD64
  • Windows 8.1 - x86 and AMD64

Note

Windows guest virtual machines require the QEMU guest agent package for Windows, qemu-guest-agent-win. This agent is required for VSS (Volume Shadow Copy Service) support for Windows guest virtual machines running on Red Hat Enterprise Linux. More information can be found here.

Procedure 11.2. Configuring the QEMU guest agent on a Windows guest

Follow these steps for Windows guests running on a Red Hat Enterprise Linux host machine.
  1. Prepare the Red Hat Enterprise Linux host machine

    Make sure the following package is installed on the Red Hat Enterprise Linux host physical machine:
    • virtio-win, located in /usr/share/virtio-win/
    To copy the drivers in the Windows guest, make an *.iso file for the qxl driver using the following command:
    # mkisofs -o /var/lib/libvirt/images/virtiowin.iso /usr/share/virtio-win/drivers
  2. Prepare the Windows guest

    Install the virtio-serial driver in guest by mounting the *.iso to the Windows guest in order to update the driver. Start the guest, then attach the driver .iso file to the guest as shown (using a disk named hdb):
    # virsh attach-disk guest /var/lib/libvirt/images/virtiowin.iso hdb
    To install the drivers using the Windows Control Panel, navigate to the following menus:
    • To install the virtio-win driver - Select Hardware and Sound > Device manager > virtio-serial driver.
  3. Update the Windows guest XML configuration file

    The guest XML file for the Windows guest is located on the Red Hat Enterprise Linux host machine. To gain access to this file, you need the Windows guest name. Use the # virsh list command on the host machine to list the guests that it can recognize. In this example, the guest's name is win7x86.
    Add the following elements to the XML file using the # virsh edit win7x86 command and save the changes. Note that the source socket name must be unique in the host, named win7x86.agent in this example:
       ...
      <channel type='unix'>
          <source mode='bind' path='/var/lib/libvirt/qemu/win7x86.agent'/>
          <target type='virtio' name='org.qemu.guest_agent.0'/>
          <address type='virtio-serial' controller='0' bus='0' port='1'/>
       </channel>
       <channel type='spicevmc'>
          <target type='virtio' name='com.redhat.spice.0'/>
          <address type='virtio-serial' controller='0' bus='0' port='2'/>
       </channel>
       ...
    
    
    

    Figure 11.2. Editing the Windows guest XML to configure the QEMU guest agent

  4. Reboot the Windows guest

    Reboot the Windows guest to apply the changes:
    # virsh reboot win7x86
  5. Prepare the QEMU guest agent in the Windows guest

    To prepare the guest agent in a Windows guest:
    1. Install the latest virtio-win package

      Run the following command on the Red Hat Enterprise Linux host physical machine terminal window to locate the file to install. Note that the file shown below may not be exactly the same as the one your system finds, but it should be latest official version.
      # rpm -qa|grep virtio-win
      virtio-win-1.6.8-5.el6.noarch
      
      # rpm -iv virtio-win-1.6.8-5.el6.noarch
    2. Confirm the installation completed

      After the virtio-win package finishes installing, check the /usr/share/virtio-win/guest-agent/ folder and you will find an file named qemu-ga-x64.msi or the qemu-ga-x86.msi as shown:
      # ls -l /usr/share/virtio-win/guest-agent/
      
      total 1544
      
      -rw-r--r--. 1 root root 856064 Oct 23 04:58 qemu-ga-x64.msi
      
      -rw-r--r--. 1 root root 724992 Oct 23 04:58 qemu-ga-x86.msi
      
      
    3. Install the .msi file

      From the Windows guest (win7x86, for example) install the qemu-ga-x64.msi or the qemu-ga-x86.msi by double clicking on the file. Once installed, it will be shown as a qemu-ga service in the Windows guest within the System Manager. This same manager can be used to monitor the status of the service.

11.3.1. Using libvirt commands with the QEMU guest agent on Windows guests

The QEMU guest agent can use the following virsh commands with Windows guests:
  • virsh shutdown --mode=agent - This shutdown method is more reliable than virsh shutdown --mode=acpi, as virsh shutdown used with the QEMU guest agent is guaranteed to shut down a cooperative guest in a clean state. If the agent is not present, libvirt has to instead rely on injecting an ACPI shutdown event, but some guests ignore that event and thus will not shut down.
    Can be used with the same syntax for virsh reboot.
  • virsh snapshot-create --quiesce - Allows the guest to flush its I/O into a stable state before the snapshot is created, which allows use of the snapshot without having to perform a fsck or losing partial database transactions. The guest agent allows a high level of disk contents stability by providing guest co-operation.
  • virsh dompmsuspend - Suspends a running guest gracefully using the guest operating system's power management functions.

11.4. Setting a limit on device redirection

To filter out certain devices from redirection, pass the filter property to -device usb-redir. The filter property takes a string consisting of filter rules. The format for a rule is:
<class>:<vendor>:<product>:<version>:<allow>
Use the value -1 to designate it to accept any value for a particular field. You may use multiple rules on the same command line using | as a separator. Note that if a device matches none of the filter rules, the redirection will not be allowed.

Example 11.1. Limiting redirection with a Windows guest virtual machine

  1. Prepare a Windows 7 guest virtual machine.
  2. Add the following code excerpt to the guest virtual machine's XML file:
        <redirdev bus='usb' type='spicevmc'>
          <alias name='redir0'/>
          <address type='usb' bus='0' port='3'/>
        </redirdev>
        <redirfilter>
          <usbdev class='0x08' vendor='0x1234' product='0xBEEF' version='2.0' allow='yes'/>
          <usbdev class='-1' vendor='-1' product='-1' version='-1' allow='no'/>
        </redirfilter>
    
  3. Start the guest virtual machine and confirm the setting changes by running the following:
    # ps -ef | grep $guest_name
    -device usb-redir,chardev=charredir0,id=redir0,/
    filter=0x08:0x1234:0xBEEF:0x0200:1|-1:-1:-1:-1:0,bus=usb.0,port=3
  4. Plug a USB device into a host physical machine, and use virt-viewer to connect to the guest virtual machine.
  5. Click USB device selection in the menu, which will produce the following message: "Some USB devices are blocked by host policy". Click OK to confirm and continue.
    The filter takes effect.
  6. To make sure that the filter captures properly check the USB device vendor and product, then make the following changes in the host physical machine's domain XML to allow for USB redirection.
       <redirfilter>
          <usbdev class='0x08' vendor='0x0951' product='0x1625' version='2.0' allow='yes'/>
          <usbdev allow='no'/>
        </redirfilter>
    
  7. Restart the guest virtual machine, then use virt-viewer to connect to the guest virtual machine. The USB device will now redirect traffic to the guest virtual machine.

11.5. Dynamically changing a host physical machine or a network bridge that is attached to a virtual NIC

This section demonstrates how to move the vNIC of a guest virtual machine from one bridge to another while the guest virtual machine is running without compromising the guest virtual machine
  1. Prepare guest virtual machine with a configuration similar to the following:
    <interface type='bridge'>
          <mac address='52:54:00:4a:c9:5e'/>
          <source bridge='virbr0'/>
          <model type='virtio'/>
    </interface>
    
  2. Prepare an XML file for interface update:
    # cat br1.xml
    <interface type='bridge'>
          <mac address='52:54:00:4a:c9:5e'/>
          <source bridge='virbr1'/>
          <model type='virtio'/>
    </interface>
    
  3. Start the guest virtual machine, confirm the guest virtual machine's network functionality, and check that the guest virtual machine's vnetX is connected to the bridge you indicated.
    # brctl show
    bridge name     bridge id               STP enabled     interfaces
    virbr0          8000.5254007da9f2       yes                  virbr0-nic
    
    vnet0
    virbr1          8000.525400682996       yes                  virbr1-nic
    
  4. Update the guest virtual machine's network with the new interface parameters with the following command:
    # virsh update-device test1 br1.xml 
    
    Device updated successfully
    
    
  5. On the guest virtual machine, run service network restart. The guest virtual machine gets a new IP address for virbr1. Check the guest virtual machine's vnet0 is connected to the new bridge(virbr1)
    # brctl show
    bridge name     bridge id               STP enabled     interfaces
    virbr0          8000.5254007da9f2       yes             virbr0-nic
    virbr1          8000.525400682996       yes             virbr1-nic     vnet0
    

Chapter 12. Storage concepts

This chapter introduces the concepts used for describing and managing storage devices. Terms such as Storage pools and Volumes are explained in the sections that follow.

12.1. Storage pools

A storage pool is a file, directory, or storage device managed by libvirt for the purpose of providing storage to guest virtual machines. The storage pool can be local or it can be shared over a network. A storage pool is a quantity of storage set aside by an administrator, often a dedicated storage administrator, for use by guest virtual machines. Storage pools are divided into storage volumes either by the storage administrator or the system administrator, and the volumes are assigned to guest virtual machines as block devices. In short storage volumes are to partitions what storage pools are to disks. Although the storage pool is a virtual container it is limited by two factors: maximum size allowed to it by qemu-kvm and the size of the disk on the host physical machine. Storage pools may not exceed the size of the disk on the host physical machine. The maximum sizes are as follows:
  • virtio-blk = 2^63 bytes or 8 Exabytes(using raw files or disk)
  • Ext4 = ~ 16 TB (using 4 KB block size)
  • XFS = ~8 Exabytes
  • qcow2 and host file systems keep their own metadata and scalability should be evaluated/tuned when trying very large image sizes. Using raw disks means fewer layers that could affect scalability or max size.
libvirt uses a directory-based storage pool, the /var/lib/libvirt/images/ directory, as the default storage pool. The default storage pool can be changed to another storage pool.
  • Local storage pools - Local storage pools are directly attached to the host physical machine server. Local storage pools include: local directories, directly attached disks, physical partitions, and LVM volume groups. These storage volumes store guest virtual machine images or are attached to guest virtual machines as additional storage. As local storage pools are directly attached to the host physical machine server, they are useful for development, testing and small deployments that do not require migration or large numbers of guest virtual machines. Local storage pools are not suitable for many production environments as local storage pools do not support live migration.
  • Networked (shared) storage pools - Networked storage pools include storage devices shared over a network using standard protocols. Networked storage is required when migrating virtual machines between host physical machines with virt-manager, but is optional when migrating with virsh. Networked storage pools are managed by libvirt. Supported protocols for networked storage pools include:
    • Fibre Channel-based LUNs
    • iSCSI
    • NFS
    • GFS2
    • SCSI RDMA protocols (SCSI RCP), the block export protocol used in InfiniBand and 10GbE iWARP adapters.

Note

Multi-path storage pools should not be created or used as they are not fully supported.

12.2.  Volumes

Storage pools are divided into storage volumes. Storage volumes are an abstraction of physical partitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt. Storage volumes are presented to guest virtual machines as local storage devices regardless of the underlying hardware.
Referencing volumes
To reference a specific volume, three approaches are possible:
The name of the volume and the storage pool
A volume may be referred to by name, along with an identifier for the storage pool it belongs in. On the virsh command line, this takes the form --pool storage_pool volume_name.
For example, a volume named firstimage in the guest_images pool.
# virsh vol-info --pool guest_images firstimage
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB

virsh #
The full path to the storage on the host physical machine system
A volume may also be referred to by its full path on the file system. When using this approach, a pool identifier does not need to be included.
For example, a volume named secondimage.img, visible to the host physical machine system as /images/secondimage.img. The image can be referred to as /images/secondimage.img.
# virsh vol-info /images/secondimage.img
Name:           secondimage.img
Type:           file
Capacity:       20.00 GB
Allocation:     136.00 kB
The unique volume key
When a volume is first created in the virtualization system, a unique identifier is generated and assigned to it. The unique identifier is termed the volume key. The format of this volume key varies upon the storage used.
When used with block based storage such as LVM, the volume key may follow this format:
c3pKz4-qPVc-Xf7M-7WNM-WJc8-qSiz-mtvpGn
When used with file based storage, the volume key may instead be a copy of the full path to the volume storage.
/images/secondimage.img
For example, a volume with the volume key of Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr:
# virsh vol-info Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
Name:           firstimage
Type:           block
Capacity:       20.00 GB
Allocation:     20.00 GB
virsh provides commands for converting between a volume name, volume path, or volume key:
vol-name
Returns the volume name when provided with a volume path or volume key.
# virsh vol-name /dev/guest_images/firstimage
firstimage
# virsh vol-name Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
vol-path
Returns the volume path when provided with a volume key, or a storage pool identifier and volume name.
# virsh vol-path Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
/dev/guest_images/firstimage
# virsh vol-path --pool guest_images firstimage
/dev/guest_images/firstimage
The vol-key command
Returns the volume key when provided with a volume path, or a storage pool identifier and volume name.
# virsh vol-key /dev/guest_images/firstimage
Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr
# virsh vol-key --pool guest_images firstimage 
Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

Chapter 13. Storage pools

13.1. Disk-based storage pools
13.1.1. Creating a disk based storage pool using virsh
13.1.2. Deleting a storage pool using virsh
13.2. Partition-based storage pools
13.2.1. Creating a partition-based storage pool using virt-manager
13.2.2. Deleting a storage pool using virt-manager
13.2.3. Creating a partition-based storage pool using virsh
13.2.4. Deleting a storage pool using virsh
13.3. Directory-based storage pools
13.3.1. Creating a directory-based storage pool with virt-manager
13.3.2. Deleting a storage pool using virt-manager
13.3.3. Creating a directory-based storage pool with virsh
13.3.4. Deleting a storage pool using virsh
13.4. LVM-based storage pools
13.4.1. Creating an LVM-based storage pool with virt-manager
13.4.2. Deleting a storage pool using virt-manager
13.4.3. Creating an LVM-based storage pool with virsh
13.4.4. Deleting a storage pool using virsh
13.5. iSCSI-based storage pools
13.5.1. Configuring a software iSCSI target
13.5.2. Adding an iSCSI target to virt-manager
13.5.3. Deleting a storage pool using virt-manager
13.5.4. Creating an iSCSI-based storage pool with virsh
13.5.5. Deleting a storage pool using virsh
13.6. NFS-based storage pools
13.6.1. Creating a NFS-based storage pool with virt-manager
13.6.2. Deleting a storage pool using virt-manager
13.7. GlusterFS storage pools
13.7.1. Creating a GlusterFS storage pool using virsh
13.7.2. Deleting a GlusterFS storage pool using virsh
13.8. Using a NPIV virtual adapter (vHBA) with SCSI devices
13.8.1. Creating a vHBA
13.8.2. Creating a storage pool using the vHBA
13.8.3. Configuring the virtual machine to use a vHBA LUN
13.8.4. Destroying the vHBA storage pool
This chapter includes instructions on creating storage pools of assorted types. A storage pool is a quantity of storage set aside by an administrator, often a dedicated storage administrator, for use by virtual machines. Storage pools are often divided into storage volumes either by the storage administrator or the system administrator, and the volumes are assigned to guest virtual machines as block devices.

Example 13.1. NFS storage pool

Suppose a storage administrator responsible for an NFS server creates a share to store guest virtual machines' data. The system administrator defines a pool on the host physical machine with the details of the share (nfs.example.com:/path/to/share should be mounted on /vm_data). When the pool is started, libvirt mounts the share on the specified directory, just as if the system administrator logged in and executed mount nfs.example.com:/path/to/share /vmdata. If the pool is configured to autostart, libvirt ensures that the NFS share is mounted on the directory specified when libvirt is started.
Once the pool starts, the files that the NFS share, are reported as volumes, and the storage volumes' paths are then queried using the libvirt APIs. The volumes' paths can then be copied into the section of a guest virtual machine's XML definition file describing the source storage for the guest virtual machine's block devices. With NFS, applications using the libvirt APIs can create and delete volumes in the pool (files within the NFS share) up to the limit of the size of the pool (the maximum storage capacity of the share). Not all pool types support creating and deleting volumes. Stopping the pool negates the start operation, in this case, unmounts the NFS share. The data on the share is not modified by the destroy operation, despite the name. See man virsh for more details.

Note

Storage pools and volumes are not required for the proper operation of guest virtual machines. Pools and volumes provide a way for libvirt to ensure that a particular piece of storage will be available for a guest virtual machine, but some administrators will prefer to manage their own storage and guest virtual machines will operate properly without any pools or volumes defined. On systems that do not use pools, system administrators must ensure the availability of the guest virtual machines' storage using whatever tools they prefer, for example, adding the NFS share to the host physical machine's fstab so that the share is mounted at boot time.

13.1. Disk-based storage pools

This section covers creating disk based storage devices for guest virtual machines.

Warning

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Use partitions (for example, /dev/sdb1) or LVM volumes.
If you pass an entire block device to the guest, the guest will likely partition it or create its own LVM groups on it. This can cause the host physical machine to detect these partitions or LVM groups and cause errors.

13.1.1. Creating a disk based storage pool using virsh

This procedure creates a new storage pool using a disk device with the virsh command.

Warning

Dedicating a disk to a storage pool will reformat and erase all data presently stored on the disk device. It is strongly recommended to back up the storage device before commencing with the following procedure.
  1. Create a GPT disk label on the disk

    The disk must be relabeled with a GUID Partition Table (GPT) disk label. GPT disk labels allow for creating a large numbers of partitions, up to 128 partitions, on each device. GPT partition tables can store partition data for far more partitions than the MS-DOS partition table.
    # parted /dev/sdb
    GNU Parted 2.1
    Using /dev/sdb
    Welcome to GNU Parted! Type 'help' to view a list of commands.
    (parted) mklabel                                                          
    New disk label type? gpt                                                  
    (parted) quit                                                             
    Information: You may need to update /etc/fstab.                           
    #
    
  2. Create the storage pool configuration file

    Create a temporary XML text file containing the storage pool information required for the new device.
    The file must be in the format shown below, and contain the following fields:
    <name>guest_images_disk</name>
    The name parameter determines the name of the storage pool. This example uses the name guest_images_disk in the example below.
    <device path='/dev/sdb'/>
    The device parameter with the path attribute specifies the device path of the storage device. This example uses the device /dev/sdb.
    <target> <path>/dev</path></target>
    The file system target parameter with the path sub-parameter determines the location on the host physical machine file system to attach volumes created with this storage pool.
    For example, sdb1, sdb2, sdb3. Using /dev/, as in the example below, means volumes created from this storage pool can be accessed as /dev/sdb1, /dev/sdb2, /dev/sdb3.
    <format type='gpt'/>
    The format parameter specifies the partition table type. This example uses the gpt in the example below, to match the GPT disk label type created in the previous step.
    Create the XML file for the storage pool device with a text editor.

    Example 13.2. Disk based storage device storage pool

    <pool type='disk'>
      <name>guest_images_disk</name>
      <source>
        <device path='/dev/sdb'/>
        <format type='gpt'/>
      </source>
      <target>
        <path>/dev</path>
      </target>
    </pool>
    
  3. Attach the device

    Add the storage pool definition using the virsh pool-define command with the XML configuration file created in the previous step.
    # virsh pool-define ~/guest_images_disk.xml
    Pool guest_images_disk defined from /root/guest_images_disk.xml
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    inactive   no
    
  4. Start the storage pool

    Start the storage pool with the virsh pool-start command. Verify the pool is started with the virsh pool-list --all command.
    # virsh pool-start guest_images_disk
    Pool guest_images_disk started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    active     no
    
  5. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart guest_images_disk
    Pool guest_images_disk marked as autostarted
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_disk    active     yes
    
  6. Verify the storage pool configuration

    Verify the storage pool was created correctly, the sizes reported correctly, and the state reports as running.
    # virsh pool-info guest_images_disk
    Name:           guest_images_disk
    UUID:           551a67c8-5f2a-012c-3844-df29b167431c
    State:          running
    Capacity:       465.76 GB
    Allocation:     0.00 
    Available:      465.76 GB
    # ls -la /dev/sdb
    brw-rw----. 1 root disk 8, 16 May 30 14:08 /dev/sdb
    # virsh vol-list guest_images_disk
    Name                 Path
    -----------------------------------------
    
  7. Optional: Remove the temporary configuration file

    Remove the temporary storage pool XML configuration file if it is not needed.
    # rm ~/guest_images_disk.xml
A disk based storage pool is now available.

13.1.2. Deleting a storage pool using virsh

The following demonstrates how to delete a storage pool using virsh:
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it.
    # virsh pool-destroy guest_images_disk
  2. Remove the storage pool's definition
    # virsh pool-undefine guest_images_disk

13.2. Partition-based storage pools

This section covers using a pre-formatted block device, a partition, as a storage pool.
For the following examples, a host physical machine has a 500GB hard drive (/dev/sdc) partitioned into one 500GB, ext4 formatted partition (/dev/sdc1). We set up a storage pool for it using the procedure below.

13.2.1. Creating a partition-based storage pool using virt-manager

This procedure creates a new storage pool using a partition of a storage device.

Procedure 13.1. Creating a partition-based storage pool with virt-manager

  1. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host physical machine from the main window.
      Open the Edit menu and select Connection Details
      Connection Details

      Figure 13.1. Connection Details

    2. Click on the Storage tab of the Connection Details window.
      Storage tab

      Figure 13.2. Storage tab

  2. Create the new storage pool

    1. Add a new pool (part 1)

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. This example uses the name guest_images_fs. Change the Type to fs: Pre-Formatted Block Device.
      Storage pool name and type

      Figure 13.3. Storage pool name and type

      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path, Format, and Source Path fields.
      Storage pool path and format

      Figure 13.4. Storage pool path and format

      Target Path
      Enter the location to mount the source device for the storage pool in the Target Path field. If the location does not already exist, virt-manager will create the directory.
      Format
      Select a format from the Format list. The device is formatted with the selected format.
      This example uses the ext4 file system, the default Red Hat Enterprise Linux file system.
      Source Path
      Enter the device in the Source Path field.
      This example uses the /dev/sdc1 device.
      Verify the details and press the Finish button to create the storage pool.
  3. Verify the new storage pool

    The new storage pool appears in the storage list on the left after a few seconds. Verify the size is reported as expected, 458.20 GB Free in this example. Verify the State field reports the new storage pool as Active.
    Select the storage pool. In the Autostart field, click the On Boot checkbox. This will make sure the storage device starts whenever the libvirtd service starts.
    Storage list confirmation

    Figure 13.5. Storage list confirmation

    The storage pool is now created, close the Connection Details window.

13.2.2. Deleting a storage pool using virt-manager

This procedure demonstrates how to delete a storage pool.
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it. To do this, select the storage pool you want to stop and click the red X icon at the bottom of the Storage window.
    Stop Icon

    Figure 13.6. Stop Icon

  2. Delete the storage pool by clicking the Trash can icon. This icon is only enabled if you stop the storage pool first.

13.2.3. Creating a partition-based storage pool using virsh

This section covers creating a partition-based storage pool with the virsh command.

Warning

Do not use this procedure to assign an entire disk as a storage pool (for example, /dev/sdb). Guests should not be given write access to whole disks or block devices. Only use this method to assign partitions (for example, /dev/sdb1) to storage pools.

Procedure 13.2. Creating pre-formatted block device storage pools using virsh

  1. Create the storage pool definition

    Use the virsh pool-define-as command to create a new storage pool definition. There are three options that must be provided to define a pre-formatted disk as a storage pool:
    Partition name
    The name parameter determines the name of the storage pool. This example uses the name guest_images_fs in the example below.
    device
    The device parameter with the path attribute specifies the device path of the storage device. This example uses the partition /dev/sdc1.
    mountpoint
    The mountpoint on the local file system where the formatted device will be mounted. If the mount point directory does not exist, the virsh command can create the directory.
    The directory /guest_images is used in this example.
    # virsh pool-define-as guest_images_fs fs - - /dev/sdc1 - "/guest_images"
    Pool guest_images_fs defined
    
    The new pool and mount points are now created.
  2. Verify the new pool

    List the present storage pools.
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      inactive   no
    
  3. Create the mount point

    Use the virsh pool-build command to create a mount point for a pre-formatted file system storage pool.
    # virsh pool-build guest_images_fs
    Pool guest_images_fs built
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 31 19:38 .
    dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      inactive   no
    
  4. Start the storage pool

    Use the virsh pool-start command to mount the file system onto the mount point and make the pool available for use.
    # virsh pool-start guest_images_fs
    Pool guest_images_fs started
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      active     no
    
  5. Turn on autostart

    By default, a storage pool defined with virsh, is not set to automatically start each time libvirtd starts. To remedy this, enable the automatic start with the virsh pool-autostart command. The storage pool is now automatically started each time libvirtd starts.
    # virsh pool-autostart guest_images_fs
    Pool guest_images_fs marked as autostarted
    
    # virsh pool-list --all
    Name                 State      Autostart
    -----------------------------------------
    default              active     yes
    guest_images_fs      active     yes
    
  6. Verify the storage pool

    Verify the storage pool was created correctly, the sizes reported are as expected, and the state is reported as running. Verify there is a "lost+found" directory in the mount point on the file system, indicating the device is mounted.
    # virsh pool-info guest_images_fs
    Name:           guest_images_fs
    UUID:           c7466869-e82a-a66c-2187-dc9d6f0877d0
    State:          running
    Persistent:     yes
    Autostart:      yes
    Capacity:       458.39 GB
    Allocation:     197.91 MB
    Available:      458.20 GB
    # mount | grep /guest_images
    /dev/sdc1 on /guest_images type ext4 (rw)
    # ls -la /guest_images
    total 24
    drwxr-xr-x.  3 root root  4096 May 31 19:47 .
    dr-xr-xr-x. 25 root root  4096 May 31 19:38 ..
    drwx------.  2 root root 16384 May 31 14:18 lost+found
    

13.2.4. Deleting a storage pool using virsh

  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it.
    # virsh pool-destroy guest_images_disk
  2. Optionally, if you want to remove the directory where the storage pool resides use the following command:
    # virsh pool-delete guest_images_disk
  3. Remove the storage pool's definition
    # virsh pool-undefine guest_images_disk

13.3. Directory-based storage pools

This section covers storing guest virtual machines in a directory on the host physical machine.
Directory-based storage pools can be created with virt-manager or the virsh command line tools.

13.3.1. Creating a directory-based storage pool with virt-manager

  1. Create the local directory

    1. Optional: Create a new directory for the storage pool

      Create the directory on the host physical machine for the storage pool. This example uses a directory named /guest virtual machine_images.
      # mkdir /guest_images
    2. Set directory ownership

      Change the user and group ownership of the directory. The directory must be owned by the root user.
      # chown root:root /guest_images
    3. Set directory permissions

      Change the file permissions of the directory.
      # chmod 700 /guest_images
    4. Verify the changes

      Verify the permissions were modified. The output shows a correctly configured empty directory.
      # ls -la /guest_images
      total 8
      drwx------.  2 root root 4096 May 28 13:57 .
      dr-xr-xr-x. 26 root root 4096 May 28 13:57 ..
      
  2. Configure SELinux file contexts

    Configure the correct SELinux context for the new directory. Note that the name of the pool and the directory do not have to match. However, when you shutdown the guest virtual machine, libvirt has to set the context back to a default value. The context of the directory determines what this default value is. It is worth explicitly labeling the directory virt_image_t, so that when the guest virtual machine is shutdown, the images get labeled 'virt_image_t' and are thus isolated from other processes running on the host physical machine.
    # semanage fcontext -a -t virt_image_t '/guest_images(/.*)?'
    # restorecon -R /guest_images
    
  3. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host physical machine from the main window.
      Open the Edit menu and select Connection Details
      Connection details window

      Figure 13.7. Connection details window

    2. Click on the Storage tab of the Connection Details window.
      Storage tab

      Figure 13.8. Storage tab

  4. Create the new storage pool

    1. Add a new pool (part 1)

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. This example uses the name guest_images. Change the Type to dir: Filesystem Directory.
      Name the storage pool

      Figure 13.9. Name the storage pool

      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path field. For example, /guest_images.
      Verify the details and press the Finish button to create the storage pool.
  5. Verify the new storage pool

    The new storage pool appears in the storage list on the left after a few seconds. Verify the size is reported as expected, 36.41 GB Free in this example. Verify the State field reports the new storage pool as Active.
    Select the storage pool. In the Autostart field, confirm that the On Boot checkbox is checked. This will make sure the storage pool starts whenever the libvirtd service starts.
    Verify the storage pool information

    Figure 13.10. Verify the storage pool information

    The storage pool is now created, close the Connection Details window.

13.3.2. Deleting a storage pool using virt-manager

This procedure demonstrates how to delete a storage pool.
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it. To do this, select the storage pool you want to stop and click the red X icon at the bottom of the Storage window.
    Stop Icon

    Figure 13.11. Stop Icon

  2. Delete the storage pool by clicking the Trash can icon. This icon is only enabled if you stop the storage pool first.

13.3.3. Creating a directory-based storage pool with virsh

  1. Create the storage pool definition

    Use the virsh pool-define-as command to define a new storage pool. There are two options required for creating directory-based storage pools:
    • The name of the storage pool.
      This example uses the name guest_images. All further virsh commands used in this example use this name.
    • The path to a file system directory for storing guest image files. If this directory does not exist, virsh will create it.
      This example uses the /guest_images directory.
     # virsh pool-define-as guest_images dir - - - - "/guest_images"
    Pool guest_images defined
  2. Verify the storage pool is listed

    Verify the storage pool object is created correctly and the state reports it as inactive.
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images     inactive   no
  3. Create the local directory

    Use the virsh pool-build command to build the directory-based storage pool for the directory guest_images (for example), as shown:
    # virsh pool-build guest_images
    Pool guest_images built
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 30 02:44 .
    dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images     inactive   no
  4. Start the storage pool

    Use the virsh command pool-start to enable a directory storage pool, thereby allowing allowing volumes of the pool to be used as guest disk images.
    # virsh pool-start guest_images
    Pool guest_images started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default             active     yes       
    guest_images    active     no
    
  5. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart guest_images
    Pool guest_images marked as autostarted
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images         active     yes
    
  6. Verify the storage pool configuration

    Verify the storage pool was created correctly, the size is reported correctly, and the state is reported as running. If you want the pool to be accessible even if the guest virtual machine is not running, make sure that Persistent is reported as yes. If you want the pool to start automatically when the service starts, make sure that Autostart is reported as yes.
    # virsh pool-info guest_images
    Name:           guest_images
    UUID:           779081bf-7a82-107b-2874-a19a9c51d24c
    State:          running
    Persistent:     yes
    Autostart:      yes
    Capacity:       49.22 GB
    Allocation:     12.80 GB
    Available:      36.41 GB
    
    # ls -la /guest_images
    total 8
    drwx------.  2 root root 4096 May 30 02:44 .
    dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..
    #
    
A directory-based storage pool is now available.

13.3.4. Deleting a storage pool using virsh

The following demonstrates how to delete a storage pool using virsh:
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it.
    # virsh pool-destroy guest_images_disk
  2. Optionally, if you want to remove the directory where the storage pool resides use the following command:
    # virsh pool-delete guest_images_disk
  3. Remove the storage pool's definition
    # virsh pool-undefine guest_images_disk

13.4. LVM-based storage pools

This chapter covers using LVM volume groups as storage pools.
LVM-based storage groups provide the full flexibility of LVM.

Note

Thin provisioning is currently not possible with LVM based storage pools.

Note

Please refer to the Red Hat Enterprise Linux Storage Administration Guide for more details on LVM.

Warning

LVM-based storage pools require a full disk partition. If activating a new partition/device with these procedures, the partition will be formatted and all data will be erased. If using the host's existing Volume Group (VG) nothing will be erased. It is recommended to back up the storage device before commencing the following procedure.

13.4.1. Creating an LVM-based storage pool with virt-manager

LVM-based storage pools can use existing LVM volume groups or create new LVM volume groups on a blank partition.
  1. Optional: Create new partition for LVM volumes

    These steps describe how to create a new partition and LVM volume group on a new hard disk drive.

    Warning

    This procedure will remove all data from the selected storage device.
    1. Create a new partition

      Use the fdisk command to create a new disk partition from the command line. The following example creates a new partition that uses the entire disk on the storage device /dev/sdb.
      # fdisk /dev/sdb
      Command (m for help):
      
      Press n for a new partition.
    2. Press p for a primary partition.
      Command action
         e   extended
         p   primary partition (1-4)
      
    3. Choose an available partition number. In this example the first partition is chosen by entering 1.
      Partition number (1-4): 1
    4. Enter the default first cylinder by pressing Enter.
      First cylinder (1-400, default 1):
      
    5. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.
      Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):
      
    6. Set the type of partition by pressing t.
      Command (m for help): t
    7. Choose the partition you created in the previous steps. In this example, the partition number is 1.
      Partition number (1-4): 1
    8. Enter 8e for a Linux LVM partition.
      Hex code (type L to list codes): 8e
    9. write changes to disk and quit.
      Command (m for help): w 
      Command (m for help): q
    10. Create a new LVM volume group

      Create a new LVM volume group with the vgcreate command. This example creates a volume group named guest_images_lvm.
      # vgcreate guest_images_lvm /dev/sdb1
        Physical volume "/dev/vdb1" successfully created
        Volume group "guest_images_lvm" successfully created
      
    The new LVM volume group, guest_images_lvm, can now be used for an LVM-based storage pool.
  2. Open the storage pool settings

    1. In the virt-manager graphical interface, select the host from the main window.
      Open the Edit menu and select Connection Details
      Connection details

      Figure 13.12. Connection details

    2. Click on the Storage tab.
      Storage tab

      Figure 13.13. Storage tab

  3. Create the new storage pool

    1. Start the Wizard

      Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
      Choose a Name for the storage pool. We use guest_images_lvm for this example. Then change the Type to logical: LVM Volume Group, and
      Add LVM storage pool

      Figure 13.14. Add LVM storage pool

      Press the Forward button to continue.
    2. Add a new pool (part 2)

      Change the Target Path field. This example uses /guest_images.
      Now fill in the Target Path and Source Path fields, then tick the Build Pool check box.
      • Use the Target Path field to either select an existing LVM volume group or as the name for a new volume group. The default format is /dev/storage_pool_name.
        This example uses a new volume group named /dev/guest_images_lvm.
      • The Source Path field is optional if an existing LVM volume group is used in the Target Path.
        For new LVM volume groups, input the location of a storage device in the Source Path field. This example uses a blank partition /dev/sdc.
      • The Build Pool checkbox instructs virt-manager to create a new LVM volume group. If you are using an existing volume group you should not select the Build Pool checkbox.
        This example is using a blank partition to create a new volume group so the Build Pool checkbox must be selected.
      Add target and source

      Figure 13.15. Add target and source

      Verify the details and press the Finish button format the LVM volume group and create the storage pool.
    3. Confirm the device to be formatted

      A warning message appears.
      Warning message

      Figure 13.16. Warning message

      Press the Yes button to proceed to erase all data on the storage device and create the storage pool.
  4. Verify the new storage pool

    The new storage pool will appear in the list on the left after a few seconds. Verify the details are what you expect, 465.76 GB Free in our example. Also verify the State field reports the new storage pool as Active.
    It is generally a good idea to have the Autostart check box enabled, to ensure the storage pool starts automatically with libvirtd.
    Confirm LVM storage pool details

    Figure 13.17. Confirm LVM storage pool details

    Close the Host Details dialog, as the task is now complete.

13.4.2. Deleting a storage pool using virt-manager

This procedure demonstrates how to delete a storage pool.
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it. To do this, select the storage pool you want to stop and click the red X icon at the bottom of the Storage window.
    Stop Icon

    Figure 13.18. Stop Icon

  2. Delete the storage pool by clicking the Trash can icon. This icon is only enabled if you stop the storage pool first.

13.4.3. Creating an LVM-based storage pool with virsh

This section outlines the steps required to create an LVM-based storage pool with the virsh command. It uses the example of a pool named guest_images_lvm from a single drive (/dev/sdc). This is only an example and your settings should be substituted as appropriate.

Procedure 13.3. Creating an LVM-based storage pool with virsh

  1. Define the pool name guest_images_lvm.
    # virsh pool-define-as guest_images_lvm logical - - /dev/sdc libvirt_lvm \ /dev/libvirt_lvm
    Pool guest_images_lvm defined
    
  2. Build the pool according to the specified name. If you are using an already existing volume group, skip this step.
    # virsh pool-build guest_images_lvm
    
    Pool guest_images_lvm built
    
  3. Initialize the new pool.
    # virsh pool-start guest_images_lvm
    
    Pool guest_images_lvm started
    
  4. Show the volume group information with the vgs command.
    # vgs
    VG          #PV #LV #SN Attr   VSize   VFree  
    libvirt_lvm   1   0   0 wz--n- 465.76g 465.76g
    
  5. Set the pool to start automatically.
    # virsh pool-autostart guest_images_lvm
    Pool guest_images_lvm marked as autostarted
    
  6. List the available pools with the virsh command.
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    guest_images_lvm     active     yes
    
  7. The following commands demonstrate the creation of three volumes (volume1, volume2 and volume3) within this pool.
    # virsh vol-create-as guest_images_lvm volume1 8G
    Vol volume1 created
    
    # virsh vol-create-as guest_images_lvm volume2 8G
    Vol volume2 created
    
    # virsh vol-create-as guest_images_lvm volume3 8G
    Vol volume3 created
    
  8. List the available volumes in this pool with the virsh command.
    # virsh vol-list guest_images_lvm
    Name                 Path
    -----------------------------------------
    volume1              /dev/libvirt_lvm/volume1
    volume2              /dev/libvirt_lvm/volume2
    volume3              /dev/libvirt_lvm/volume3
    
  9. The following two commands (lvscan and lvs) display further information about the newly created volumes.
    # lvscan
    ACTIVE            '/dev/libvirt_lvm/volume1' [8.00 GiB] inherit
    ACTIVE            '/dev/libvirt_lvm/volume2' [8.00 GiB] inherit
    ACTIVE            '/dev/libvirt_lvm/volume3' [8.00 GiB] inherit
    
    # lvs
    LV       VG            Attr     LSize   Pool Origin Data%  Move Log Copy%  Convert
    volume1  libvirt_lvm   -wi-a-   8.00g
    volume2  libvirt_lvm   -wi-a-   8.00g
    volume3  libvirt_lvm   -wi-a-   8.00g
    

13.4.4. Deleting a storage pool using virsh

The following demonstrates how to delete a storage pool using virsh:
  1. To avoid any issues with other guests using the same pool, it is best to stop the storage pool and release any resources in use by it.
    # virsh pool-destroy guest_images_disk
  2. Optionally, if you want to remove the directory where the storage pool resides use the following command:
    # virsh pool-delete guest_images_disk
  3. Remove the storage pool's definition
    # virsh pool-undefine guest_images_disk

13.5. iSCSI-based storage pools

This section covers using iSCSI-based devices to store guest virtual machines.
iSCSI (Internet Small Computer System Interface) is a network protocol for sharing storage devices. iSCSI connects initiators (storage clients) to targets (storage servers) using SCSI instructions over the IP layer.

13.5.1. Configuring a software iSCSI target

The scsi-target-utils package provides a tool for creating software-backed iSCSI targets.

Procedure 13.4. Creating an iSCSI target

  1. Install the required packages

    Install the scsi-target-utils package and all dependencies
    # yum install scsi-target-utils
  2. Start the tgtd service

    The tgtd service host physical machines SCSI targets and uses the iSCSI protocol to host physical machine targets. Start the tgtd service and make the service persistent after restarting with the chkconfig command.
    # service tgtd start
    # chkconfig tgtd on
  3. Optional: Create LVM volumes

    LVM volumes are useful for iSCSI backing images. LVM snapshots and resizing can be beneficial for guest virtual machines. This example creates an LVM image named virtimage1 on a new volume group named virtstore on a RAID5 array for hosting guest virtual machines with iSCSI.
    1. Create the RAID array

      Creating software RAID5 arrays is covered by the Red Hat Enterprise Linux Deployment Guide.
    2. Create the LVM volume group

      Create a volume group named virtstore with the vgcreate command.
      # vgcreate virtstore /dev/md1
    3. Create a LVM logical volume

      Create a logical volume group named virtimage1 on the virtstore volume group with a size of 20GB using the lvcreate command.
      # lvcreate --size 20G -n virtimage1 virtstore
      The new logical volume, virtimage1, is ready to use for iSCSI.
  4. Optional: Create file-based images

    File-based storage is sufficient for testing but is not recommended for production environments or any significant I/O activity. This optional procedure creates a file based imaged named virtimage2.img for an iSCSI target.
    1. Create a new directory for the image

      Create a new directory to store the image. The directory must have the correct SELinux contexts.
      # mkdir -p /var/lib/tgtd/virtualization
    2. Create the image file

      Create an image named virtimage2.img with a size of 10GB.
      # dd if=/dev/zero of=/var/lib/tgtd/virtualization/virtimage2.img bs=1M seek=10000 count=0
    3. Configure SELinux file contexts

      Configure the correct SELinux context for the new image and directory.
      # restorecon -R /var/lib/tgtd
      The new file-based image, virtimage2.img, is ready to use for iSCSI.
  5. Create targets

    Targets can be created by adding a XML entry to the /etc/tgt/targets.conf file. The target attribute requires an iSCSI Qualified Name (IQN). The IQN is in the format:
    iqn.yyyy-mm.reversed domain name:optional identifier text
    Where:
    • yyyy-mm represents the year and month the device was started (for example: 2010-05);
    • reversed domain name is the host physical machines domain name in reverse (for example server1.example.com in an IQN would be com.example.server1); and
    • optional identifier text is any text string, without spaces, that assists the administrator in identifying devices or hardware.
    This example creates iSCSI targets for the two types of images created in the optional steps on server1.example.com with an optional identifier trial. Add the following to the /etc/tgt/targets.conf file.
    <target iqn.2010-05.com.example.server1:iscsirhel6guest>
       backing-store /dev/virtstore/virtimage1  #LUN 1
       backing-store /var/lib/tgtd/virtualization/virtimage2.img  #LUN 2
       write-cache off
    </target>
    
    Ensure that the /etc/tgt/targets.conf file contains the default-driver iscsi line to set the driver type as iSCSI. The driver uses iSCSI by default.

    Important

    This example creates a globally accessible target without access control. Refer to the scsi-target-utils for information on implementing secure access.
  6. Restart the tgtd service

    Restart the tgtd service to reload the configuration changes.
    # service tgtd restart
  7. iptables configuration

    Open port 3260 for iSCSI access with iptables.
    # iptables -I INPUT -p tcp -m tcp --dport 3260 -j ACCEPT
    # service iptables save
    # service iptables restart
  8. Verify the new targets

    View the new targets to ensure the setup was successful with the tgt-admin --show command.
    # tgt-admin --show
    Target 1: iqn.2010-05.com.example.server1:iscsirhel6guest
    System information:
    Driver: iscsi
    State: ready
    I_T nexus information:
    LUN information:
    LUN: 0
        Type: controller
        SCSI ID: IET     00010000
        SCSI SN: beaf10
        Size: 0 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: None
    LUN: 1
        Type: disk
        SCSI ID: IET     00010001
        SCSI SN: beaf11
        Size: 20000 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: /dev/virtstore/virtimage1
    LUN: 2
        Type: disk
        SCSI ID: IET     00010002
        SCSI SN: beaf12
        Size: 10000 MB
        Online: Yes
        Removable media: No
        Backing store type: rdwr
        Backing store path: /var/lib/tgtd/virtualization/virtimage2.img
    Account information:
    ACL information:
    ALL
    

    Warning

    The ACL list is set to all. This allows all systems on the local network to access this device. It is recommended to set host physical machine access ACLs for production environments.
  9. Optional: Test discovery

    Test whether the new iSCSI device is discoverable.
    # iscsiadm --mode discovery --type sendtargets --portal server1.example.com
    127.0.0.1:3260,1 iqn.2010-05.com.example.server1:iscsirhel6guest
  10. Optional: Test attaching the device

    Attach the new device (iqn.2010-05.com.example.server1:iscsirhel6guest) to determine whether the device can be attached.
    # iscsiadm -d2 -m node --login
    scsiadm: Max file limits 1024 1024
    
    Logging in to [iface: default, target: iqn.2010-05.com.example.server1:iscsirhel6guest, portal: 10.0.0.1,3260]
    Login to [iface: default, target: iqn.2010-05.com.example.server1:iscsirhel6guest, portal: 10.0.0.1,3260] successful.
    Detach the device.
    # iscsiadm -d2 -m node --logout
    scsiadm: Max file limits 1024 1024
    
    Logging out of session [sid: 2, target: iqn.2010-05.com.example.server1:iscsirhel6guest, portal: 10.0.0.1,3260
    Logout of [sid: 2, target: iqn.2010-05.com.example.server1:iscsirhel6guest, portal: 10.0.0.1,3260] successful.
An iSCSI device is now ready to use for virtualization.

13.5.2. Adding an iSCSI target to virt-manager

This procedure covers creating a storage pool with an iSCSI target in virt-manager.

Procedure 13.5. Adding an iSCSI device to virt-manager

  1. Open the host physical machine's storage tab

    Open the Storage tab in the Connection Details window.
    1. Open virt-manager.
    2. Select a host physical machine from the main virt-manager window. Click Edit menu and select Connection Details.
      Connection details

      Figure 13.19. Connection details

    3. Click on the Storage tab.
      Storage menu

      Figure 13.20. Storage menu

  2. Add a new pool (part 1)

    Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
    Add an iscsi storage pool name and type

    Figure 13.21. Add an iscsi storage pool name and type

    Choose a name for the storage pool, change the Type to iscsi, and press Forward to continue.
  3. Add a new pool (part 2)

    You will need the information you used in Section 13.5, “iSCSI-based storage pools” and Step 5 to complete the fields in this menu.
    1. Enter the iSCSI source and target. The Format option is not available as formatting is handled by the guest virtual machines. It is not advised to edit the Target Path. The default target path value, /dev/disk/by-path/, adds the drive path to that directory. The target path should be the same on all host physical machines for migration.
    2. Enter the hostname or IP address of the iSCSI target. This example uses host1.example.com.
    3. In the Source Pathfield, enter the iSCSI target IQN. If you look at Step 5 in Section 13.5, “iSCSI-based storage pools”, this is the information you added in the /etc/tgt/targets.conf file. This example uses iqn.2010-05.com.example.server1:iscsirhel6guest.
    4. Check the IQN checkbox to enter the IQN for the initiator. This example uses iqn.2010-05.com.example.host1:iscsirhel6.
    5. Click Finish to create the new storage pool.
    Create an iscsi storage pool

    Figure 13.22. Create an iscsi storage pool

13.5.3. Deleting a storage pool using virt-manager

This procedure demonstrates how to delete a storage pool.
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it. To do this, select the storage pool you want to stop and click the red X icon at the bottom of the Storage window.
    Stop Icon

    Figure 13.23. Stop Icon

  2. Delete the storage pool by clicking the Trash can icon. This icon is only enabled if you stop the storage pool first.

13.5.4. Creating an iSCSI-based storage pool with virsh

  1. Use pool-define-as to define the pool from the command line

    Storage pool definitions can be created with the virsh command line tool. Creating storage pools with virsh is useful for systems administrators using scripts to create multiple storage pools.
    The virsh pool-define-as command has several parameters which are accepted in the following format:
    virsh pool-define-as name type source-host source-path source-dev source-name target
    The parameters are explained as follows:
    type
    defines this pool as a particular type, iscsi for example
    name
    must be unique and sets the name for the storage pool
    source-host and source-path
    the hostname and iSCSI IQN respectively
    source-dev and source-name
    these parameters are not required for iSCSI-based pools, use a - character to leave the field blank.
    target
    defines the location for mounting the iSCSI device on the host physical machine
    The example below creates the same iSCSI-based storage pool as the previous step.
    #   virsh pool-define-as --name scsirhel6guest --type iscsi \
         --source-host server1.example.com \
         --source-dev iqn.2010-05.com.example.server1:iscsirhel6guest
         --target /dev/disk/by-path
    Pool iscsirhel6guest defined
  2. Verify the storage pool is listed

    Verify the storage pool object is created correctly and the state reports as inactive.
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    iscsirhel6guest      inactive   no
  3. Start the storage pool

    Use the virsh command pool-start for this. pool-start enables a directory storage pool, allowing it to be used for volumes and guest virtual machines.
    # virsh pool-start guest_images_disk
    Pool guest_images_disk started
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    iscsirhel6guest      active     no
    
  4. Turn on autostart

    Turn on autostart for the storage pool. Autostart configures the libvirtd service to start the storage pool when the service starts.
    # virsh pool-autostart iscsirhel6guest
    Pool iscsirhel6guest marked as autostarted
    Verify that the iscsirhel6guest pool has autostart set:
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    default              active     yes       
    iscsirhel6guest      active     yes
    
  5. Verify the storage pool configuration

    Verify the storage pool was created correctly, the sizes reported correctly, and the state reports as running.
    # virsh pool-info iscsirhel6guest
    Name:           iscsirhel6guest
    UUID:           afcc5367-6770-e151-bcb3-847bc36c5e28
    State:          running
    Persistent:     unknown
    Autostart:      yes
    Capacity:       100.31 GB
    Allocation:     0.00
    Available:      100.31 GB
    
An iSCSI-based storage pool is now available.

13.5.5. Deleting a storage pool using virsh

The following demonstrates how to delete a storage pool using virsh:
  1. To avoid any issues with other guest virtual machines using the same pool, it is best to stop the storage pool and release any resources in use by it.
    # virsh pool-destroy guest_images_disk
  2. Remove the storage pool's definition
    # virsh pool-undefine guest_images_disk

13.6. NFS-based storage pools

This procedure covers creating a storage pool with a NFS mount point in virt-manager.

13.6.1. Creating a NFS-based storage pool with virt-manager

  1. Open the host physical machine's storage tab

    Open the Storage tab in the Host Details window.
    1. Open virt-manager.
    2. Select a host physical machine from the main virt-manager window. Click Edit menu and select Connection Details.
      Connection details

      Figure 13.24. Connection details

    3. Click on the Storage tab.
      Storage tab

      Figure 13.25. Storage tab

  2. Create a new pool (part 1)

    Press the + button (the add pool button). The Add a New Storage Pool wizard appears.
    Add an NFS name and type

    Figure 13.26. Add an NFS name and type

    Choose a name for the storage pool and press Forward to continue.
  3. Create a new pool (part 2)

    Enter the target path for the device, the hostname and the NFS share path. Set the Format option to NFS or auto (to detect the type). The target path must be identical on all host physical machines for migration.
    Enter the hostname or IP address of the NFS server. This example uses server1.example.com.
    Enter the NFS path. This example uses /nfstrial.
    Create an NFS storage pool

    Figure 13.27. Create an NFS storage pool

    Press Finish to create the new storage pool.

13.6.2. Deleting a storage pool using virt-manager

This procedure demonstrates how to delete a storage pool.
  1. To avoid any issues with other guests using the same pool, it is best to stop the storage pool and release any resources in use by it. To do this, select the storage pool you want to stop and click the red X icon at the bottom of the Storage window.
    Stop Icon

    Figure 13.28. Stop Icon

  2. Delete the storage pool by clicking the Trash can icon. This icon is only enabled if you stop the storage pool first.

13.7. GlusterFS storage pools

This section covers enabling a GlusterFS based storage pool. Red Hat Enterprise Linux 6.5 includes native support for creating virtual machines with GlusterFS. GlusterFS is a userspace file system that uses FUSE. When enabled in a guest virtual machine it enables a KVM host physical machine to boot guest virtual machine images from one or more GlusterFS storage volumes, and to use images from a GlusterFS storage volume as data disks for guest virtual machines.

Note

Refer to the Red Hat Storage Administration Guide for additonal information.

13.7.1. Creating a GlusterFS storage pool using virsh

This section will demonstrate how to prepare a Gluster server and an active Gluster volume.

Procedure 13.6. Preparing a Gluster server and an active Gluster volume

  1. Obtain the IP address of the Gluster server by listing its status with the following command:
    # gluster volume status
    Status of volume: gluster-vol1
    Gluster process						Port	Online	Pid
    ------------------------------------------------------------------------------
    Brick 222.111.222.111:/gluster-vol1 			49155	Y	18634
     
    Task Status of Volume gluster-vol1
    ------------------------------------------------------------------------------
    There are no active volume tasks
    
  2. If you haven't already done so, install glusterfs-fuse and enable virt_use_fusefs. Then prepare one host which will connect to the Gluster server by running the following commands:
    # setsebool virt_use_fusefs on
    # getsebool virt_use_fusefs
    virt_use_fusefs --> on
    
  3. Create a new XML file to configure a Gluster storage pool (named glusterfs-pool.xml in this example) specifying pool type as gluster, and add the following data:
    			
    <pool type='gluster'>
    	<name>glusterfs-pool</name>
    	<source>
    		<host name='111.222.111.222'/>
    		<dir path='/'/>
    		<name>gluster-vol1</name>
    	</source>
    </pool>
    			

    Figure 13.29. GlusterFS XML file contents

  4. Define and start the Gluster pool, using the following commands:
    # virsh pool-define glusterfs-pool.xml 
    Pool gluster-pool defined from glusterfs-pool.xml
    
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------       
    gluster-pool         inactive   no              
    
    # virsh pool-start gluster-pool
    Pool gluster-pool started
    
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------      
    gluster-pool         active     no  
    
    # virsh vol-list gluster-pool
    Name                 Path                                    
    -----------------------------------------
    qcow2.img            gluster://111.222.111.222/gluster-vol1/qcow2.img
    raw.img              gluster://111.222.111.222/gluster-vol1/raw.img
    

13.7.2. Deleting a GlusterFS storage pool using virsh

This section details how to delete a storage pool using virsh.

Procedure 13.7. Deleting a GlusterFS storage pool

  1. Set the status of the storage pool to inactive, using the following command:
    
     # virsh pool-destroy gluster-pool
    Pool gluster-pool destroyed
    
  2. Confirm the pool is inactive, using the following command
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------     
    gluster-pool         inactive   no
    
  3. Undefine the GlusterFS storage pool using the following command:
    # virsh pool-undefine gluster-pool
    Pool gluster-pool has been undefined
    
  4. Confirm the pool is undefined, using the following command:
    # virsh pool-list --all
    Name                 State      Autostart 
    -----------------------------------------
    
    

13.8. Using a NPIV virtual adapter (vHBA) with SCSI devices

NPIV (N_Port ID Virtualization) is a software technology that allows sharing of a single physical Fibre Channel host bus adapter (HBA).
This allows multiple guests to see the same storage from multiple physical hosts, and thus allows for easier migration paths for the storage. As a result, there is no need for the migration to create or copy storage, as long as the correct storage path is specified.
In virtualization, the virtual host bus adapter, or vHBA, controls the LUNs for virtual machines. Each vHBA is identified by its own WWNN (World Wide Node Name) and WWPN (World Wide Port Name). The path to the storage is determined by the WWNN and WWPN values.
This section provides instructions for configuring a vHBA on a virtual machine. Note that Red Hat Enterprise Linux 6 does not support persistent vHBA configuration across host reboots; verify any vHBA-related settings following a host reboot.

13.8.1. Creating a vHBA

Procedure 13.8. Creating a vHBA

  1. Locate HBAs on the host system

    To locate the HBAs on your host system, examine the SCSI devices on the host system to locate a scsi_host with vport capability.
    Run the following command to retrieve a scsi_host list:
    # virsh nodedev-list --cap scsi_host
    scsi_host0
    scsi_host1
    scsi_host2
    scsi_host3
    scsi_host4
    
    For each scsi_host, run the following command to examine the device XML for the line <capability type='vport_ops'>, which indicates a scsi_host with vport capability.
    # virsh nodedev-dumpxml scsi_hostN
  2. Check the HBA's details

    Use the virsh nodedev-dumpxml HBA_device command to see the HBA's details.
    The XML output from the virsh nodedev-dumpxml command will list the fields <name>, <wwnn>, and <wwpn>, which are used to create a vHBA. The <max_vports> value shows the maximum number of supported vHBAs.
     # virsh nodedev-dumpxml scsi_host3
    <device>
      <name>scsi_host3</name>
      <path>/sys/devices/pci0000:00/0000:00:04.0/0000:10:00.0/host3</path>
      <parent>pci_0000_10_00_0</parent>
      <capability type='scsi_host'>
        <host>3</host>
        <capability type='fc_host'>
          <wwnn>20000000c9848140</wwnn>
          <wwpn>10000000c9848140</wwpn>
          <fabric_wwn>2002000573de9a81</fabric_wwn>
        </capability>
        <capability type='vport_ops'>
          <max_vports>127</max_vports>
          <vports>0</vports>
        </capability>
      </capability>
    </device>   
    In this example, the <max_vports> value shows there are a total 127 virtual ports available for use in the HBA configuration. The <vports> value shows the number of virtual ports currently being used. These values update after creating a vHBA.
  3. Create a vHBA host device

    Create an XML file similar to the following (in this example, named vhba_host3.xml) for the vHBA host.
    # cat vhba_host3.xml
       <device>
         <parent>scsi_host3</parent>
         <capability type='scsi_host'>
           <capability type='fc_host'>
           </capability>
         </capability>
       </device>   
    The <parent> field specifies the HBA device to associate with this vHBA device. The details in the <device> tag are used in the next step to create a new vHBA device for the host. See http://libvirt.org/formatnode.html for more information on the nodedev XML format.
  4. Create a new vHBA on the vHBA host device

    To create a vHBA on vhba_host3, use the virsh nodedev-create command:
    # virsh nodedev-create vhba_host3.xml
    Node device scsi_host5 created from vhba_host3.xml
  5. Verify the vHBA

    Verify the new vHBA's details (scsi_host5) with the virsh nodedev-dumpxml command:
    # virsh nodedev-dumpxml scsi_host5
    <device>
      <name>scsi_host5</name>
      <path>/sys/devices/pci0000:00/0000:00:04.0/0000:10:00.0/host3/vport-3:0-0/host5</path>
      <parent>scsi_host3</parent>
      <capability type='scsi_host'>
        <host>5</host>
        <capability type='fc_host'>
          <wwnn>5001a4a93526d0a1</wwnn>
          <wwpn>5001a4ace3ee047d</wwpn>
          <fabric_wwn>2002000573de9a81</fabric_wwn>
        </capability>
      </capability>
    </device>  

13.8.2. Creating a storage pool using the vHBA

It is recommended to define a libvirt storage pool based on the vHBA in order to preserve the vHBA configuration.
Using a storage pool has two primary advantages:
  • the libvirt code can easily find the LUN's path via virsh command output, and
  • virtual machine migration requires only defining and starting a storage pool with the same vHBA name on the target machine. To do this, the vHBA LUN, libvirt storage pool and volume name must be specified in the virtual machine's XML configuration. Refer to Section 13.8.3, “Configuring the virtual machine to use a vHBA LUN” for an example.
  1. Create a SCSI storage pool

    To create a vHBA configuration, first create a libvirt 'scsi' storage pool XML file based on the vHBA using the format below.

    Note

    Ensure you use the vHBA created in Procedure 13.8, “Creating a vHBA” as the host name, modifying the vHBA name scsi_hostN to hostN for the storage pool configuration. In this example, the vHBA is named scsi_host5, which is specified as <adapter name='host5'/> in a Red Hat Enterprise Linux 6 libvirt storage pool.
    It is recommended to use a stable location for the <path> value, such as one of the /dev/disk/by-{path|id|uuid|label} locations on your system. More information on <path> and the elements within <target> can be found at http://libvirt.org/formatstorage.html.
    In this example, the 'scsi' storage pool is named vhbapool_host3.xml:
      <pool type='scsi'>
         <name>vhbapool_host3</name> 
         <uuid>e9392370-2917-565e-692b-d057f46512d6</uuid>
         <capacity unit='bytes'>0</capacity>
         <allocation unit='bytes'>0</allocation>
         <available unit='bytes'>0</available>
         <source>
           <adapter name='host5'/> 
         </source>
          <target>
            <path>/dev/disk/by-path</path>
            <permissions>
              <mode>0700</mode>
              <owner>0</owner>
              <group>0</group>
            </permissions>
          </target>
        </pool> 
  2. Define the pool

    To define the storage pool (named vhbapool_host3 in this example), use the virsh pool-define command:
             # virsh pool-define vhbapool_host3.xml
             Pool vhbapool_host3 defined from vhbapool_host3.xml
    
  3. Start the pool

    Start the storage pool with the following command:
    # virsh pool-start vhbapool_host3
    Pool vhbapool_host3 started
    
  4. Enable autostart

    Finally, to ensure that subsequent host reboots will automatically define vHBAs for use in virtual machines, set the storage pool autostart feature (in this example, for a pool named vhbapool_host3):
    # virsh pool-autostart vhbapool_host3

13.8.3. Configuring the virtual machine to use a vHBA LUN

After a storage pool is created for a vHBA, add the vHBA LUN to the virtual machine configuration.
  1. Find available LUNs

    First, use the virsh vol-list command in order to generate a list of available LUNs on the vHBA. For example:
    # virsh vol-list vhbapool_host3
     Name                 Path                                    
    ------------------------------------------------------------------------------
     unit:0:4:0           /dev/disk/by-path/pci-0000:10:00.0-fc-0x5006016844602198-lun-0
     unit:0:5:0           /dev/disk/by-path/pci-0000:10:00.0-fc-0x5006016044602198-lun-0
    The list of LUN names displayed will be available for use as disk volumes in virtual machine configurations.
  2. Add the vHBA LUN to the virtual machine

    Add the vHBA LUN to the virtual machine by specifying in the virtual machine's XML:
    • the device type as lun or disk in the <disk> parameter, and
    • the source device in the <source> parameter. Note this can be entered as /dev/sdaN, or as a symbolic link generated by udev in /dev/disk/by-path|by-id|by-uuid|by-label, which can be found by running the virsh vol-list pool command.
    For example:
       <disk type='block' device='lun'>
         <driver name='qemu' type='raw'/>
         <source dev='/dev/disk/by-path/pci-0000\:04\:00.1-fc-0x203400a0b85ad1d7-lun-0'/>
         <target dev='sda' bus='scsi'/>
       </disk>
          

13.8.4. Destroying the vHBA storage pool

A vHBA storage pool can be destroyed by the virsh pool-destroy command:
# virsh pool-destroy vhbapool_host3
Delete the vHBA with the following command
# virsh nodedev-destroy scsi_host5
To verify the pool and vHBA have been destroyed, run:
# virsh nodedev-list --cap scsi_host
scsi_host5 will no longer appear in the list of results.

Chapter 14.  Volumes

14.1. Creating volumes

This section shows how to create disk volumes inside a block based storage pool. In the example below, the virsh vol-create-as command will create a storage volume with a specific size in GB within the guest_images_disk storage pool. As this command is repeated per volume needed, three volumes are created as shown in the example.
# virsh vol-create-as guest_images_disk volume1 8G
Vol volume1 created

# virsh vol-create-as guest_images_disk volume2 8G
Vol volume2 created

# virsh vol-create-as guest_images_disk volume3 8G
Vol volume3 created

# virsh vol-list guest_images_disk
Name                 Path
-----------------------------------------
volume1              /dev/sdb1
volume2              /dev/sdb2
volume3              /dev/sdb3

# parted -s /dev/sdb print
Model: ATA ST3500418AS (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name     Flags
2      17.4kB  8590MB  8590MB               primary
3      8590MB  17.2GB  8590MB               primary
1      21.5GB  30.1GB  8590MB               primary

14.2. Cloning volumes

The new volume will be allocated from storage in the same storage pool as the volume being cloned. The virsh vol-clone must have the --pool argument which dictates the name of the storage pool that contains the volume to be cloned. The rest of the command names the volume to be cloned (volume3) and the name of the new volume that was cloned (clone1). The virsh vol-list command lists the volumes that are present in the storage pool (guest_images_disk).
# virsh vol-clone --pool guest_images_disk volume3 clone1
Vol clone1 cloned from volume3

# virsh vol-list guest_images_disk
Name                 Path                                    
-----------------------------------------
volume1              /dev/sdb1                               
volume2              /dev/sdb2                               
volume3              /dev/sdb3
clone1               /dev/sdb4
                               

# parted -s /dev/sdb print
Model: ATA ST3500418AS (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End     Size    File system  Name     Flags
1      4211MB  12.8GB  8595MB  primary
2      12.8GB  21.4GB  8595MB  primary
3      21.4GB  30.0GB  8595MB  primary
4      30.0GB  38.6GB  8595MB  primary

14.3. Adding storage devices to guests

This section covers adding storage devices to a guest. Additional storage can only be added as needed.

14.3.1. Adding file based storage to a guest

File-based storage is a collection of files that are stored on the host physical machines file system that act as virtualized hard drives for guests. To add file-based storage, perform the following steps:

Procedure 14.1. Adding file-based storage

  1. Create a storage file or use an existing file (such as an IMG file). Note that both of the following commands create a 4GB file which can be used as additional storage for a guest:
    • Pre-allocated files are recommended for file-based storage images. Create a pre-allocated file using the following dd command as shown:
      # dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M count=4096
    • Alternatively, create a sparse file instead of a pre-allocated file. Sparse files are created much faster and can be used for testing, but are not recommended for production environments due to data integrity and performance issues.
      # dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M seek=4096 count=0
  2. Create the additional storage by writing a <disk> element in a new file. In this example, this file will be known as NewStorage.xml.
    A <disk> element describes the source of the disk, and a device name for the virtual block device. The device name should be unique across all devices in the guest, and identifies the bus on which the guest will find the virtual block device. The following example defines a virtio block device whose source is a file-based storage container named FileName.img:
    <disk type='file' device='disk'>
       <driver name='qemu' type='raw' cache='none'/>
       <source file='/var/lib/libvirt/images/FileName.img'/>
       <target dev='vdb'/>
    </disk>
    
    Device names can also start with "hd" or "sd", identifying respectively an IDE and a SCSI disk. The configuration file can also contain an <address> sub-element that specifies the position on the bus for the new device. In the case of virtio block devices, this should be a PCI address. Omitting the <address> sub-element lets libvirt locate and assign the next available PCI slot.
  3. Attach the CD-ROM as follows:
    <disk type='file' device='cdrom'>
       <driver name='qemu' type='raw' cache='none'/>
       <source file='/var/lib/libvirt/images/FileName.img'/>
       <readonly/>
       <target dev='hdc'/>
    </disk >
    
  4. Add the device defined in NewStorage.xml with your guest (Guest1):
    # virsh attach-device --config Guest1 ~/NewStorage.xml

    Note

    This change will only apply after the guest has been destroyed and restarted. In addition, persistent devices can only be added to a persistent domain, that is a domain whose configuration has been saved with virsh define command.
    If the guest is running, and you want the new device to be added temporarily until the guest is destroyed, omit the --config option:
    # virsh attach-device Guest1 ~/NewStorage.xml

    Note

    The virsh command allows for an attach-disk command that can set a limited number of parameters with a simpler syntax and without the need to create an XML file. The attach-disk command is used in a similar manner to the attach-device command mentioned previously, as shown:
    # virsh attach-disk Guest1 /var/lib/libvirt/images/FileName.img vdb --cache none
    
    Note that the virsh attach-disk command also accepts the --config option.
  5. Start the guest machine (if it is currently not running):
    # virsh start Guest1

    Note

    The following steps are Linux guest specific. Other operating systems handle new storage devices in different ways. For other systems, refer to that operating system's documentation.
  6. Partitioning the disk drive

    The guest now has a hard disk device called /dev/vdb. If required, partition this disk drive and format the partitions. If you do not see the device that you added, then it indicates that there is an issue with the disk hotplug in your guest's operating system.
    1. Start fdisk for the new device:
      # fdisk /dev/vdb
      Command (m for help):
      
    2. Type n for a new partition.
    3. The following appears:
      Command action
      e   extended
      p   primary partition (1-4)
      
      Type p for a primary partition.
    4. Choose an available partition number. In this example, the first partition is chosen by entering 1.
      Partition number (1-4): 1
    5. Enter the default first cylinder by pressing Enter.
      First cylinder (1-400, default 1):
    6. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.
      Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):
    7. Enter t to configure the partition type.
      Command (m for help): t
    8. Select the partition you created in the previous steps. In this example, the partition number is 1 as there was only one partition created and fdisk automatically selected partition 1.
      Partition number (1-4): 1
    9. Enter 83 for a Linux partition.
      Hex code (type L to list codes): 83
    10. Enter w to write changes and quit.
      Command (m for help): w
      
    11. Format the new partition with the ext3 file system.
      # mke2fs -j /dev/vdb1
  7. Create a mount directory, and mount the disk on the guest. In this example, the directory is located in myfiles.
    # mkdir /myfiles
    # mount /dev/vdb1 /myfiles
    
    The guest now has an additional virtualized file-based storage device. Note however, that this storage will not mount persistently across reboot unless defined in the guest's /etc/fstab file:
    /dev/vdb1    /myfiles    ext3     defaults    0 0

14.3.2. Adding hard drives and other block devices to a guest

System administrators have the option to use additional hard drives to provide increased storage space for a guest, or to separate system data from user data.

Procedure 14.2. Adding physical block devices to guests

  1. This procedure describes how to add a hard drive on the host physical machine to a guest. It applies to all physical block devices, including CD-ROM, DVD and floppy devices.
    Physically attach the hard disk device to the host physical machine. Configure the host physical machine if the drive is not accessible by default.
  2. Do one of the following:
    1. Create the additional storage by writing a disk element in a new file. In this example, this file will be known as NewStorage.xml. The following example is a configuration file section which contains an additional device-based storage container for the host physical machine partition /dev/sr0:
      <disk type='block' device='disk'>
            <driver name='qemu' type='raw' cache='none'/>
            <source dev='/dev/sr0'/>
            <target dev='vdc' bus='virtio'/>
      </disk>
      
    2. Follow the instruction in the previous section to attach the device to the guest virtual machine. Alternatively, you can use the virsh attach-disk command, as shown:
      # virsh attach-disk Guest1 /dev/sr0 vdc
      
      Note that the following options are available:
      • The virsh attach-disk command also accepts the --config, --type, and --mode options, as shown:
        virsh attach-disk Guest1 /dev/sr0 vdc --config --type cdrom --mode readonly
      • Additionally, --type also accepts --type disk in cases where the device is a hard drive.
  3. The guest virtual machine now has a new hard disk device called /dev/vdc on Linux (or something similar, depending on what the guest virtual machine OS chooses) or D: drive (for example) on Windows. You can now initialize the disk from the guest virtual machine, following the standard procedures for the guest virtual machine's operating system. Refer to Procedure 14.1, “Adding file-based storage” and Step 6 for an example.

    Warning

    The host physical machine should not use filesystem labels to identify file systems in the fstab file, the initrd file or on the kernel command line. Doing so presents a security risk if less privileged users, such as guest virtual machines, have write access to whole partitions or LVM volumes, because a guest virtual machine could potentially write a filesystem label belonging to the host physical machine, to its own block device storage. Upon reboot of the host physical machine, the host physical machine could then mistakenly use the guest virtual machine's disk as a system disk, which would compromise the host physical machine system.
    It is preferable to use the UUID of a device to identify it in the fstab file, the initrd file or on the kernel command line. While using UUIDs is still not completely secure on certain file systems, a similar compromise with UUID is significantly less feasible.

    Important

    Guest virtual machines should not be given write access to whole disks or block devices (for example, /dev/sdb). Guest virtual machines with access to whole block devices may be able to modify volume labels, which can be used to compromise the host physical machine system. Use partitions (for example, /dev/sdb1) or LVM volumes to prevent this issue.

missing step

dynamic adding paragraph

14.4. Deleting and removing volumes

This section shows how to delete a disk volume from a block based storage pool using the virsh vol-delete command. In this example, the volume is volume 1 and the storage pool is guest_images.
# virsh vol-delete --pool guest_images volume1
Vol volume1 deleted

Chapter 15. Managing guest virtual machines with virsh

15.1. Generic Commands
15.1.1. help
15.1.2. quit and exit
15.1.3. version
15.1.4. Argument display
15.1.5. connect
15.1.6. Displaying basic information
15.1.7. Injecting NMI
15.2. Attaching and updating a device with virsh
15.3. Attaching interface devices
15.4. Changing the media of a CDROM
15.5. Domain Commands
15.5.1. Configuring a domain to be started automatically at boot
15.5.2. Connecting the serial console for the guest virtual machine
15.5.3. Defining a domain with an XML file
15.5.4. Editing and displaying a description and title of a domain
15.5.5. Displaying device block statistics
15.5.6. Retrieving network statistics
15.5.7. Modifying the link state of a domain's virtual interface
15.5.8. Listing the link state of a domain's virtual interface
15.5.9. Setting network interface bandwidth parameters
15.5.10. Retrieving memory statistics for a running domain
15.5.11. Displaying errors on block devices
15.5.12. Displaying the block device size
15.5.13. Displaying the block devices associated with a domain
15.5.14. Displaying virtual interfaces associated with a domain
15.5.15. Using blockcommit to shorten a backing chain
15.5.16. Using blockpull to shorten a backing chain
15.5.17. Using blockresize to change the size of a domain path
15.5.18. Disk image management with live block copy
15.5.19. Displaying a URI for connection to a graphical display
15.5.20. Domain Retrieval Commands
15.5.21. Converting QEMU arguments to domain XML
15.5.22. Creating a dump file of a domain's core
15.5.23. Creating a virtual machine XML dump (configuration file)
15.5.24. Creating a guest virtual machine from a configuration file
15.6. Editing a guest virtual machine's configuration file
15.6.1. Adding multifunction PCI devices to KVM guest virtual machines
15.6.2. Stopping a running domain in order to restart it later
15.6.3. Displaying CPU statistics for a specified domain
15.6.4. Saving a screenshot
15.6.5. Sending a keystroke combination to a specified domain
15.6.6. Sending process signal names to virtual processes
15.6.7. Displaying the IP address and port number for the VNC display
15.7. NUMA node management
15.7.1. Displaying node information
15.7.2. Setting NUMA parameters
15.7.3. Displaying the amount of free memory in a NUMA cell
15.7.4. Displaying a CPU list
15.7.5. Displaying CPU statistics
15.7.6. Suspending the host physical machine
15.7.7. Setting and displaying the node memory parameters
15.7.8. Creating devices on host nodes
15.7.9. Detaching a node device
15.7.10. Retrieving a device's configuration settings
15.7.11. Listing devices on a node
15.7.12. Triggering a reset for a node
15.8. Starting, suspending, resuming, saving and restoring a guest virtual machine
15.8.1. Starting a defined domain
15.8.2. Suspending a guest virtual machine
15.8.3. Suspending a running domain
15.8.4. Waking up a domain from pmsuspend state
15.8.5. Undefining a domain
15.8.6. Resuming a guest virtual machine
15.8.7. Save a guest virtual machine
15.8.8. Updating the domain XML file that will be used for restoring the guest
15.8.9. Extracting the domain XML file
15.8.10. Edit Domain XML configuration files
15.8.11. Restore a guest virtual machine
15.9. Shutting down, rebooting and force-shutdown of a guest virtual machine
15.9.1. Shut down a guest virtual machine
15.9.2. Shutting down Red Hat Enterprise Linux 6 guests on a Red Hat Enterprise Linux 7 host
15.9.3. Manipulating the libvirt-guests configuration settings
15.9.4. Rebooting a guest virtual machine
15.9.5. Forcing a guest virtual machine to stop
15.9.6. Resetting a virtual machine
15.10. Retrieving guest virtual machine information
15.10.1. Getting the domain ID of a guest virtual machine
15.10.2. Getting the domain name of a guest virtual machine
15.10.3. Getting the UUID of a guest virtual machine
15.10.4. Displaying guest virtual machine information
15.11. Storage pool commands
15.11.1. Searching for a storage pool XML
15.11.2. Creating, defining, and starting storage pools
15.11.3. Stopping and deleting storage pools
15.11.4. Creating an XML dump file for a pool
15.11.5. Editing the storage pool's configuration file
15.11.6. Converting storage pools
15.12. Storage Volume Commands
15.12.1. Creating storage volumes
15.12.2. Deleting storage volumes
15.12.3. Dumping storage volume information to an XML file
15.12.4. Listing volume information
15.12.5. Retrieving storage volume information
15.12.6. Uploading and downloading storage volumes
15.12.7. Re-sizing storage volumes
15.13. Displaying per-guest virtual machine information
15.13.1. Displaying the guest virtual machines
15.13.2. Displaying virtual CPU information
15.13.3. Configuring virtual CPU affinity
15.13.4. Displaying information about the virtual CPU counts of a domain
15.13.5. Configuring virtual CPU affinity
15.13.6. Configuring virtual CPU count
15.13.7. Configuring memory allocation
15.13.8. Changing the memory allocation for the domain
15.13.9. Displaying guest virtual machine block device information
15.13.10. Displaying guest virtual machine network device information
15.14. Managing virtual networks
15.15. Migrating guest virtual machines with virsh
15.15.1. Interface Commands
15.15.2. Managing snapshots
15.16. Guest virtual machine CPU model configuration
15.16.1. Introduction
15.16.2. Learning about the host physical machine CPU model
15.16.3. Determining a compatible CPU model to suit a pool of host physical machines
15.17. Configuring the guest virtual machine CPU model
15.18. Managing resources for guest virtual machines
15.19. Setting schedule parameters
15.20. Disk I/O throttling
15.21. Display or set block I/O parameters
15.22. Configuring memory Tuning
15.23. Virtual Networking Commands
15.23.1. Autostarting a virtual network
15.23.2. Creating a virtual network from an XML file
15.23.3. Defining a virtual network from an XML file
15.23.4. Stopping a virtual network
15.23.5. Creating a dump file
15.23.6. Editing a virtual network's XML configuration file
15.23.7. Getting information about a virtual network
15.23.8. Listing information about a virtual network
15.23.9. Converting a network UUID to network name
15.23.10. Starting a (previously defined) inactive network
15.23.11. Undefining the configuration for an inactive network
15.23.12. Converting a network name to network UUID
15.23.13. Updating an existing network definition file
virsh is a command line interface tool for managing guest virtual machines and the hypervisor. The virsh command-line tool is built on the libvirt management API and operates as an alternative to the qemu-kvm command and the graphical virt-manager application. The virsh command can be used in read-only mode by unprivileged users or, with root access, full administration functionality. The virsh command is ideal for scripting virtualization administration.

15.1. Generic Commands

The commands in this section are generic because they are not specific to any domain.

15.1.1. help

$ virsh help [command|group] The help command can be used with or without options. When used without options, all commands are listed, one per line. When used with an option, it is grouped into categories, displaying the keyword for each group.
To display the commands that are only for a specific option, you need to give the keyword for that group as an option. For example:
$ virsh help pool
 Storage Pool (help keyword 'pool'):
    find-storage-pool-sources-as   find potential storage pool sources
    find-storage-pool-sources      discover potential storage pool sources
    pool-autostart                 autostart a pool
    pool-build                     build a pool
    pool-create-as                 create a pool from a set of args
    pool-create                    create a pool from an XML file
    pool-define-as                 define a pool from a set of args
    pool-define                    define (but don't start) a pool from an XML file
    pool-delete                    delete a pool
    pool-destroy                   destroy (stop) a pool
    pool-dumpxml                   pool information in XML
    pool-edit                      edit XML configuration for a storage pool
    pool-info                      storage pool information
    pool-list                      list pools
    pool-name                      convert a pool UUID to pool name
    pool-refresh                   refresh a pool
    pool-start                     start a (previously defined) inactive pool
    pool-undefine                  undefine an inactive pool
    pool-uuid                      convert a pool name to pool UUID
Using the same command with a command option, gives the help information on that one specific command. For example:
$virsh help vol-path
  NAME
    vol-path - returns the volume path for a given volume name or key

  SYNOPSIS
    vol-path <vol> [--pool <string>]

  OPTIONS
    [--vol] <string>  volume name or key
    --pool <string>  pool name or uuid

15.1.2. quit and exit

The quit command and the exit command will close the terminal. For example:
$virsh exit
$virsh quit

15.1.3. version

The version command displays the current libvirt version and displays information about where the build is from. For example:
$ virsh version
Compiled against library: libvirt 1.1.1
Using library: libvirt 1.1.1
Using API: QEMU 1.1.1
Running hypervisor: QEMU 1.5.3

15.1.4. Argument display

The virsh echo [--shell][--xml][arg] command echos or displays the specified argument. Each argument echoed will be separated by a space. by using the --shell option, the output will be single quoted where needed so that it is suitable for reusing in a shell command. If the --xml option is used the output will be made suitable for use in an XML file. For example, the command virsh echo --shell "hello world" will send the output 'hello world'.

15.1.5. connect

Connects to a hypervisor session. When the shell is first started this command runs automatically when the URI parameter is requested by the -c command. The URI specifies how to connect to the hypervisor. The most commonly used URIs are:
  • xen:/// - connects to the local Xen hypervisor.
  • qemu:///system - connects locally as root to the daemon supervising QEMU and KVM domains.
  • xen:///session - connects locally as a user to the user's set of QEMU and KVM domains.
  • lxc:/// - connects to a local Linux container.
Additional values are available on libvirt's website http://libvirt.org/uri.html.
The command can be run as follows:
$virsh connect {name|URI}
Where {name} is the machine name (hostname) or URL (the output of the virsh uri command) of the hypervisor. To initiate a read-only connection, append the above command with --readonly. For more information on URIs refer to Remote URIs. If you are unsure of the URI, the virsh uri command will display it:
$ virsh uri
qemu:///session

15.1.6. Displaying basic information

The following commands may be used to display basic information:
  • $ hostname - displays the hypervisor's hostname
  • $ sysinfo - displays the XML representation of the hypervisor's system information, if available

15.1.7. Injecting NMI

The $ virsh inject-nmi [domain] injects NMI (non-maskable interrupt) message to the guest virtual machine. This is used when response time is critical, such as non-recoverable hardware errors. To run this command:
$ virsh inject-nmi guest-1

15.2. Attaching and updating a device with virsh

For information on attaching storage devices refer to Section 14.3.1, “Adding file based storage to a guest”

Procedure 15.1. Hotplugging USB devices for use by the guest virtual machine

The following procedure demonstrates how to attach USB devices to the guest virtual machine. This can be done while the guest virtual machine is running as a hotplug procedure or it can be done while the guest is shutoff. The device you want to emulate needs to be attached to the host physical machine.
  1. Locate the USB device you want to attach with the following command:
    # lsusb -v
    
    idVendor           0x17ef Lenovo
    idProduct          0x480f Integrated Webcam [R5U877]
    
    
  2. Create an XML file and give it a logical name (usb_device.xml, for example). Make sure you copy the vendor and procuct IDs exactly as was displayed in your search.
    
       <hostdev mode='subsystem' type='usb' managed='yes'>
          <source>
            <vendor id='0x17ef'/>
            <product id='0x480f'/>
          </source>
        </hostdev>
      ...
    
    

    Figure 15.1. USB Devices XML Snippet

  3. Attach the device with the following command:
    # virsh attach-device rhel6 --file usb_device.xml> --config
    In this example [rhel6] is the name of your guest virtual machine and [usb_device.xml] is the file you created in the previous step. If you want to have the change take effect in the next reboot, use the --config option. If you want this change to be persistent, use the --persistent option. If you want the change to take effect on the current domain, use the --current option. See the Virsh MAN page for additional information.
  4. If you want to detach the device (hot unplug), perform the following command:
    # virsh detach-device rhel6 --file usb_device.xml>
    In this example [rhel6] is the name of your guest virtual machine and [usb_device.xml] is the file you attached in the previous step

15.3. Attaching interface devices

The virsh attach-interfacedomain type source command can take the following options:
  • --live - get value from running domain
  • --config - get value to be used on next boot
  • --current - get value according to current domain state
  • --persistent - behaves like --config for an offline domain, and like --live for a running domain.
  • --target - indicates the target device in the guest virtual machine.
  • --mac - use this to specify the MAC address of the network interface
  • --script - use this to specify a path to a script file handling a bridge instead of the default one.
  • --model - use this to specify the model type.
  • --inbound - controls the inbound bandwidth of the interface. Acceptable values are average, peak, and burst.
  • --outbound - controls the outbound bandwidth of the interface. Acceptable values are average, peak, and burst.
The type can be either network to indicate a physical network device, or bridge to indicate a bridge to a device. source is the source of the device. To remove the attached device, use the virsh detach-device.

15.4. Changing the media of a CDROM

Changing the media of a CDROM to another source or format
# change-media domain path source --eject --insert --update --current --live --config --force
  • --path - A string containing a fully-qualified path or target of disk device
  • --source - A string containing the source of the media
  • --eject - Eject the media
  • --insert - Insert the media
  • --update - Update the media
  • --current - can be either or both of --live and --config, depends on implementation of hypervisor driver
  • --live - alter live configuration of running domain
  • --config - alter persistent configuration, effect observed on next boot
  • --force - force media changing

15.5. Domain Commands

A domain name is required for most of these commands as they manipulate the specified domain directly. The domain may be given as a short integer (0,1,2...), a name, or a full UUID.

15.5.1. Configuring a domain to be started automatically at boot

$ virsh autostart [--disable] domain will automatically start the specified domain at boot. Using the --disable option disables autostart.
# virsh autostart rhel6
In the example above, the rhel6 guest virtual machine will automatically start when the host physical machine boots
# virsh autostart rhel6--disable
In the example above, the autostart function is disabled and the guest virtual machine will no longer start automatically when the host physical machine boots.

15.5.2. Connecting the serial console for the guest virtual machine

The $ virsh console <domain> [--devname <string>] [--force] [--safe] command connects the virtual serial console for the guest virtual machine. The optional --devname <string> parameter refers to the device alias of an alternate console, serial, or parallel device configured for the guest virtual machine. If this parameter is omitted, the primary console will be opened. The --force option will force the console connection or when used with disconnect, will disconnect connections. Using the --safe option will only allow the guest to connect if safe console handling is supported.
$ virsh console virtual_machine --safe

15.5.3. Defining a domain with an XML file

The define <FILE> command defines a domain from an XML file. The domain definition in this case is registered but not started. If the domain is already running, the changes will take effect on the next boot.

15.5.4. Editing and displaying a description and title of a domain

The virsh desc [domain-name] [[--live] [--config] | [--current]] [--title] [--edit] [--new-desc New description or title message] command is used to show or modify the description and title of a domain, but does not configure it. These values are user fields that allow storage of arbitrary textual data to allow easy identification of domains. Ideally, the title should be short, although this is not enforced by libvirt.
The options --live or --config select whether this command works on live or persistent definitions of the domain. If both --live and --config are specified, the --config option will be implemented first, where the description entered in the command becomes the new configuration setting which is applied to both the live configuration and persistent configuration setting. The --current option will modify or get the current state configuration and will not be persistent. The --current option will be used if neither --live nor --config, nor --current are specified. The --edit option specifies that an editor with the contents of current description or title should be opened and the contents saved back afterwards. Using the --title option will show or modify the domain's title field only and not include its description. In addition, if neither --edit nor --new-desc are used in the command, then only the description is displayed and cannot be modified.
For example, the command $ virsh desc testvm --current --title TestVM-4F --new-desc Guest VM on fourth floor will change the guest virtual machine's title from testvm to TestVM-4F and will change the description to Guest VM on fourth floor.

15.5.5. Displaying device block statistics

This command will display the block statistics for a running domain. You need to have both the domain name and the device name (use the virsh domblklist to list the devices.)In this case a block device is the unique target name (<target dev='name'/>) or a source file (< source file ='name'/>). Note that not every hypervisor can display every field. To make sure that the output is presented in its most legible form use the --human option, as shown:
# virsh domblklist rhel6
Target     Source
------------------------------------------------
vda        /VirtualMachines/rhel6.img
hdc        -

# virsh domblkstat --human rhel6 vda
Device: vda
 number of read operations:      174670
 number of bytes read:           3219440128
 number of write operations:     23897
 number of bytes written:        164849664
 number of flush operations:     11577
 total duration of reads (ns):   1005410244506
 total duration of writes (ns):  1085306686457
 total duration of flushes (ns): 340645193294

15.5.6. Retrieving network statistics

The domnetstat [domain][interface-device] command displays the network interface statistics for the specified device running on a given domain.
# domifstat rhel6 eth0

15.5.7. Modifying the link state of a domain's virtual interface

This command can either configure a specified interface as up or down. The domif-setlink [domain][interface-device][state]{--config} modifies the status of the specified interface for the specified domain. Note that if you only want the persistent configuration of the domain to be modified, you need to use the --configoption. It should also be noted that for compatibility reasons, --persistent is an alias of --config. The "interface device" can be the interface's target name or the MAC address.
# domif-setlink rhel6 eth0 up

15.5.8. Listing the link state of a domain's virtual interface

This command can be used to query the state of a specified interface on a given domain. Note that if you only want the persistent configuration of the domain to be modified, you need to use the --configoption. It should also be noted that for compatibility reasons, --persistent is an alias of --config. The "interface device" can be the interface's target name or the MAC address.
# domif-getlink rhel6 eth0 up

15.5.9. Setting network interface bandwidth parameters

domiftune sets the guest virtual machine's network interface bandwidth parameters. The following format should be used:
#virsh domiftune domain interface-device [[--config] [--live] | [--current]] [--inbound average,peak,burst] [--outbound average,peak,burst]
The only required parameter is the domain name and interface device of the guest virtual machine, the --config, --live, and --current functions the same as in Section 15.19, “Setting schedule parameters”. If no limit is specified, it will query current network interface setting. Otherwise, alter the limits with the following flags:
  • <interface-device> This is mandatory and it will set or query the domain’s network interface’s bandwidth parameters. interface-device can be the interface’s target name (<target dev=’name’/>), or the MAC address.
  • If no --inbound or --outbound is specified, this command will query and show the bandwidth settings. Otherwise, it will set the inbound or outbound bandwidth. average,peak,burst is the same as in attach-interface command. Refer to Section 15.3, “Attaching interface devices”

15.5.10. Retrieving memory statistics for a running domain

This command may return varied results depending on the hypervisor you are using.
The dommemstat [domain] [--period (sec)][[--config][--live]|[--current]] displays the memory statistics for a running domain. Using the --period option requires a time period in seconds. Setting this option to a value larger than 0 will allow the balloon driver to return additional statistics which will be displayed by subsequent domemstat commands. Setting the --period option to 0, will stop the balloon driver collection but does not clear the statistics in the balloon driver. You cannot use the --live, --config, or --current options without also setting the --period option in order to also set the collection period for the balloon driver. If the --live option is specified, only the running guest's collection period is affected. If the --config option is used, it will affect the next boot of a persistent guest. If --current option is used, it will affect the current guest state
Both the --live and --config options may be used but --current is exclusive. If no flag is specified, the behavior will be different depending on the guest's state.
#virsh domemstat rhel6--current

15.5.11. Displaying errors on block devices

This command is best used following a domstate that reports that a domain is paused due to an I/O error. The domblkerror domain command shows all block devices that are in error state on a given domain and it displays the error message that the device is reporting.
# virsh domblkerror rhel6

15.5.12. Displaying the block device size

In this case a block device is the unique target name (<target dev='name'/>) or a source file (< source file ='name'/>). To retrieve a list you can run domblklist. This domblkinfo requires a domain name.
# virsh domblkinfo rhel6

15.5.13. Displaying the block devices associated with a domain

The domblklist domain --inactive--details displays a table of all block devices that are associated with the specified domain.
If --inactive is specified, the result will show the devices that are to be used at the next boot and will not show those that are currently running in use by the running domain. If --details is specified, the disk type and device value will be included in the table. The information displayed in this table can be used with the domblkinfo and snapshot-create.
#domblklist rhel6 --details

15.5.14. Displaying virtual interfaces associated with a domain

Running the domiflist command results in a table that displays information of all the virtual interfaces that are associated with a specified domain. The domiflist requires a domain name and optionally can take the --inactive option.
If --inactive is specified, the result will show the devices that are to be used at the next boot and will not show those that are currently running in use by the running domain.
Commands that require a MAC address of a virtual interface (such as detach-interface or domif-setlink) will accept the output displayed by this command.

15.5.15. Using blockcommit to shorten a backing chain

This section demonstrates how to use virsh blockcommit to shorten a backing chain. For more background on backing chains, see Section 15.5.18, “Disk image management with live block copy”.
blockcommit copies data from one part of the chain down into a backing file, allowing you to pivot the rest of the chain in order to bypass the committed portions. For example, suppose this is the current state:
      base ← snap1 ← snap2 ← active.
Using blockcommit moves the contents of snap2 into snap1, allowing you to delete snap2 from the chain, making backups much quicker.

Procedure 15.2. virsh blockcommit

  • Run the following command:
    # virsh blockcommit $dom $disk -base snap1 -top snap2 -wait -verbose
    The contents of snap2 are moved into snap1, resulting in:
    base ← snap1 ← active. Snap2 is no longer valid and can be deleted

    Warning

    blockcommit will corrupt any file that depends on the -base option (other than files that depend on the -top option, as those files now point to the base). To prevent this, do not commit changes into files shared by more than one guest. The -verbose option allows the progress to be printed on the screen.

15.5.16. Using blockpull to shorten a backing chain

blockpull can be used in in the following applications:
  • Flattens an image by populating it with data from its backing image chain. This makes the image file self-contained so that it no longer depends on backing images and looks like this:
    • Before: base.img ← Active
    • After: base.img is no longer used by the guest and Active contains all of the data.
  • Flattens part of the backing image chain. This can be used to flatten snapshots into the top-level image and looks like this:
    • Before: base ← sn1 ←sn2 ← active
    • After: base.img ← active. Note that active now contains all data from sn1 and sn2 and neither sn1 nor sn2 are used by the guest.
  • Moves the disk image to a new file system on the host. This is allows image files to be moved while the guest is running and looks like this:
    • Before (The original image file): /fs1/base.vm.img
    • After: /fs2/active.vm.qcow2 is now the new file system and /fs1/base.vm.img is no longer used.
  • Useful in live migration with post-copy storage migration. The disk image is copied from the source host to the destination host after live migration completes.
    In short this is what happens: Before:/source-host/base.vm.img After:/destination-host/active.vm.qcow2./source-host/base.vm.img is no longer used.

Procedure 15.3. Using blockpull to shorten a backing chain

  1. It may be helpful to run this command prior to running blockpull:
    # virsh snapshot-create-as $dom $name - disk-only
  2. If the chain looks like this: base ← snap1 ← snap2 ← active run the following:
    # virsh blockpull $dom $disk snap1
    This command makes 'snap1' the backing file of active, by pulling data from snap2 into active resulting in: base ← snap1 ← active.
  3. Once the blockpull is complete, the libvirt tracking of the snapshot that created the extra image in the chain is no longer useful. Delete the tracking on the outdated snapshot with this command:
    # virsh snapshot-delete $dom $name - metadata
Additional applications of blockpull can be done as follows:
  • To flatten a single image and populate it with data from its backing image chain:# virsh blockpull example-domain vda - wait
  • To flatten part of the backing image chain:# virsh blockpull example-domain vda - base /path/to/base.img - wait
  • To move the disk image to a new file system on the host:# virsh snapshot-create example-domain - xmlfile /path/to/new.xml - disk-only followed by # virsh blockpull example-domain vda - wait
  • To use live migration with post-copy storage migration:
    • On the destination run:
       # qemu-img create -f qcow2 -o backing_file=/source-host/vm.img /destination-host/vm.qcow2
    • On the source run:
      # virsh migrate example-domain
    • On the destination run:
      # virsh blockpull example-domain vda - wait

15.5.17. Using blockresize to change the size of a domain path

blockresize can be used to re-size a block device of a domain while the domain is running, using the absolute path of the block device which also corresponds to a unique target name (<target dev="name"/>) or source file (<source file="name"/>). This can be applied to one of the disk devices attached to domain (you can use the command domblklist to print a table showing the brief information of all block devices associated with a given domain).

Note

Live image re-sizing will always re-size the image, but may not immediately be picked up by guests. With recent guest kernels, the size of virtio-blk devices is automatically updated (older kernels require a guest reboot). With SCSI devices, it is required to manually trigger a re-scan in the guest with the command, echo > /sys/class/scsi_device/0:0:0:0/device/rescan. In addition, with IDE it is required to reboot the guest before it picks up the new size.
  • Run the following command: blockresize [domain] [path size] where:
    • Domain is the unique target name or source file of the domain whose size you want to change
    • Path size is a scaled integer which defaults to KiB (blocks of 1024 bytes) if there is no suffix. You must use a suffix of "B" to for bytes.

15.5.18. Disk image management with live block copy

Note

Live block copy is a feature that is not supported with the version of KVM that is supplied with Red Hat Enterprise Linux. Live block copy is available with the version of KVM that is supplied with Red Hat Virtualization. This version of KVM must be running on your physical host machine in order for the feature to be supported. Contact your representative at Red Hat for more details.
Live block copy allows you to copy an in use guest disk image to a destination image and switches the guest disk image to the destination guest image while the guest is running. Whilst live migration moves the memory and registry state of the host, the guest is kept in shared storage. Live block copy allows you to move the entire guest contents to another host on the fly while the guest is running. Live block copy may also be used for live migration without requiring permanent share storage. In this method the disk image is copied to the destination host after migration, but while the guest is running.
Live block copy is especially useful for the following applications:
  • moving the guest image from local storage to a central location
  • when maintenance is required, guests can be transferred to another location, with no loss of performance
  • allows for management of guest images for speed and efficiency
  • image format conversions can be done without having to shut down the guest

Example 15.1. Example using live block copy

This example shows what happens when live block copy is performed. The example has a backing file (base) that is shared between a source and destination. It also has two overlays (sn1 and sn2) that are only present on the source and must be copied.
  1. The backing file chain at the beginning looks like this:
    base ← sn1 ← sn2
    The components are as follows:
    • base - the original disk image
    • sn1 - the first snapshot that was taken of the base disk image
    • sn2 - the most current snapshot
    • active - the copy of the disk
  2. When a copy of the image is created as a new image on top of sn2 the result is this:
    base ← sn1 ← sn2 ← active
  3. At this point the read permissions are all in the correct order and are set automatically. To make sure write permissions are set properly, a mirror mechanism redirects all writes to both sn2 and active, so that sn2 and active read the same at any time (and this mirror mechanism is the essential difference between live block copy and image streaming).
  4. A background task that loops over all disk clusters is executed. For each cluster, there are the following possible cases and actions:
    • The cluster is already allocated in active and there is nothing to do.
    • Use bdrv_is_allocated() to follow the backing file chain. If the cluster is read from base (which is shared) there is nothing to do.
    • If bdrv_is_allocated() variant is not feasible, rebase the image and compare the read data with write data in base in order to decide if a copy is needed.
    • In all other cases, copy the cluster into active
  5. When the copy has completed, the backing file of active is switched to base (similar to rebase)
To reduce the length of a backing chain after a series of snapshots, the following commands are helpful: blockcommit and blockpull. See Section 15.5.15, “Using blockcommit to shorten a backing chain” for more information.

15.5.19. Displaying a URI for connection to a graphical display

Running the virsh domdisplay command will output a URI which can then be used to connect to the graphical display of the domain via VNC, SPICE, or RDP. If the --include-password option is used, the SPICE channel password will be included in the URI.

15.5.20. Domain Retrieval Commands

The following commands will display different information about a given domain
  • virsh domhostname domain displays the hostname of the specified domain provided the hypervisor can publish it.
  • virsh dominfo domain displays basic information about a specified domain.
  • virsh domuid domain|ID converts a given domain name or ID into a UUID.
  • virsh domid domain|ID converts a given domain name or UUID into an ID.
  • virsh domjobabort domain aborts the currently running job on the specified domain.
  • virsh domjobinfo domain displays information about jobs running on the specified domain, including migration statistics
  • virsh domname domain ID|UUID converts a given domain ID or UUID into a domain name.
  • virsh domstate domain displays the state of the given domain. Using the --reason option will also display the reason for the displayed state.
  • virsh domcontrol domain displays the state of an interface to VMM that were used to control a domain. For states that are not OK or Error, it will also print the number of seconds that have elapsed since the control interface entered the displayed state.

Example 15.2. Example of statistical feedback

In order to get information about the domain, run the following command:
# virsh domjobinfo rhel6
Job type:         Unbounded   
Time elapsed:     1603         ms
Data processed:   47.004 MiB
Data remaining:   658.633 MiB
Data total:       1.125 GiB
Memory processed: 47.004 MiB
Memory remaining: 658.633 MiB
Memory total:     1.125 GiB
Constant pages:   114382      
Normal pages:     12005       
Normal data:      46.895 MiB
Expected downtime: 0            ms
Compression cache: 64.000 MiB
Compressed data:  0.000 B
Compressed pages: 0            
Compression cache misses: 12005        
Compression overflows: 0

15.5.21. Converting QEMU arguments to domain XML

The virsh domxml-from-native provides a way to convert an existing set of QEMU arguments into a guest description using libvirt Domain XML that can then be used by libvirt. Please note that this command is intended to be used only to convert existing qemu guests previously started from the command line in order to allow them to be managed through libvirt. The method described here should not be used to create new guests from scratch. New guests should be created using either virsh or virt-manager. Additional information can be found here.
Suppose you have a QEMU guest with the following args file:
 $ cat demo.args 
LC_ALL=C 
PATH=/bin 
HOME=/home/test 
USER=test 
LOGNAME=test /usr/bin/qemu -S -M pc -m 214 -smp 1 -nographic -monitor pty -no-acpi -boot c -hda /dev/HostVG/QEMUGuest1 -net none -serial none -parallel none -usb
To convert this to a domain XML file so that the guest can be managed by libvirt, run:
$ virsh domxml-from-native qemu-argv demo.args
This command turns the args file above, into this domain XML file:

<domain type='qemu'>
  <uuid>00000000-0000-0000-0000-000000000000</uuid>
  <memory>219136</memory>
  <currentMemory>219136</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='i686' machine='pc'>hvm</type>
    <boot dev='hd'/>
  </os>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/qemu</emulator>
    <disk type='block' device='disk'>
      <source dev='/dev/HostVG/QEMUGuest1'/>
      <target dev='hda' bus='ide'/>
    </disk>
  </devices>
</domain>

15.5.22. Creating a dump file of a domain's core

Sometimes it is necessary (especially in the cases of troubleshooting), to create a dump file containing the core of the domain so that it can be analyzed. In this case, running virsh dump domain corefilepath --bypass-cache --live |--crash |--reset --verbose --memory-only dumps the domain core to a file specified by the corefilepath Note that some hypervisors may gave restrictions on this action and may require the user to manually ensure proper permissions on the file and path specified in the corefilepath parameter. This command is supported with SR-IOV devices as well as other passthrough devices. The following options are supported and have the following effect:
  • --bypass-cache the file saved will not contain the file system cache. Note that selecting this option may slow down dump operation.
  • --live will save the file as the domain continues to run and will not pause or stop the domain.
  • --crash puts the domain in a crashed status rather than leaving it in a paused state while the dump file is saved.
  • --reset once the dump file is successfully saved, the domain will reset.
  • --verbose displays the progress of the dump process
  • --memory-only the only information that will be saved in the dump file will be the domain's memory and CPU common register file.
Note that the entire process can be monitored using the domjobinfo command and can be canceled using the domjobabort command.

15.5.23. Creating a virtual machine XML dump (configuration file)

Output a guest virtual machine's XML configuration file with virsh:
# virsh dumpxml {guest-id, guestname or uuid}
This command outputs the guest virtual machine's XML configuration file to standard out (stdout). You can save the data by piping the output to a file. An example of piping the output to a file called guest.xml:
# virsh dumpxml GuestID > guest.xml
This file guest.xml can recreate the guest virtual machine (refer to Section 15.6, “Editing a guest virtual machine's configuration file”. You can edit this XML configuration file to configure additional devices or to deploy additional guest virtual machines.
An example of virsh dumpxml output:
# virsh dumpxml guest1-rhel6-64
<domain type='kvm'>
  <name>guest1-rhel6-64</name>
  <uuid>b8d7388a-bbf2-db3a-e962-b97ca6e514bd</uuid>
  <memory>2097152</memory>
  <currentMemory>2097152</currentMemory>
  <vcpu>2</vcpu>
  <os>
    <type arch='x86_64' machine='rhel6.2.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none' io='threads'/>
      <source file='/home/guest-images/guest1-rhel6-64.img'/>
      <target dev='vda' bus='virtio'/>
      <shareable/<
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <interface type='bridge'>
      <mac address='52:54:00:b9:35:a9'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <sound model='ich6'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </sound>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </memballoon>
  </devices>
</domain>
Note that the <shareable/> flag is set. This indicates the device is expected to be shared between domains (assuming the hypervisor and OS support this), which means that caching should be deactivated for that device.

15.5.24. Creating a guest virtual machine from a configuration file

Guest virtual machines can be created from XML configuration files. You can copy existing XML from previously created guest virtual machines or use the dumpxml option (refer to Section 15.5.23, “Creating a virtual machine XML dump (configuration file)”). To create a guest virtual machine with virsh from an XML file:
# virsh create configuration_file.xml

15.6. Editing a guest virtual machine's configuration file

Instead of using the dumpxml option (refer to Section 15.5.23, “Creating a virtual machine XML dump (configuration file)”), guest virtual machines can be edited either while they are running or while they are offline. The virsh edit command provides this functionality. For example, to edit the guest virtual machine named rhel6:
# virsh edit rhel6
This opens a text editor. The default text editor is the $EDITOR shell parameter (set to vi by default).

15.6.1. Adding multifunction PCI devices to KVM guest virtual machines

This section will demonstrate how to add multi-function PCI devices to KVM guest virtual machines.
  1. Run the virsh edit [guestname] command to edit the XML configuration file for the guest virtual machine.
  2. In the address type tag, add a multifunction='on' entry for function='0x0'.
    This enables the guest virtual machine to use the multifunction PCI devices.
    <disk type='file' device='disk'>
    <driver name='qemu' type='raw' cache='none'/>
    <source file='/var/lib/libvirt/images/rhel62-1.img'/>
    <target dev='vda' bus='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0' multifunction='on'/
    </disk>
    
    For a PCI device with two functions, amend the XML configuration file to include a second device with the same slot number as the first device and a different function number, such as function='0x1'.
    For Example:
    <disk type='file' device='disk'>
    <driver name='qemu' type='raw' cache='none'/>
    <source file='/var/lib/libvirt/images/rhel62-1.img'/>
    <target dev='vda' bus='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0' multifunction='on'/>
    </disk>
    <disk type='file' device='disk'>
    <driver name='qemu' type='raw' cache='none'/>
    <source file='/var/lib/libvirt/images/rhel62-2.img'/>
    <target dev='vdb' bus='virtio'/>
    <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x1'/>
    </disk>
    
  3. lspci output from the KVM guest virtual machine shows:
    $ lspci
    
    00:05.0 SCSI storage controller: Red Hat, Inc Virtio block device
    00:05.1 SCSI storage controller: Red Hat, Inc Virtio block device
    

15.6.2. Stopping a running domain in order to restart it later

virsh managedsave domain --bypass-cache --running | --paused | --verbose saves and destroys (stops) a running domain so that it can be restarted from the same state at a later time. When used with a virsh start command it is automatically started from this save point. If it is used with the --bypass-cache option the save will avoid the filesystem cache. Note that this option may slow down the save process speed.
--verbose displays the progress of the dump process
Under normal conditions, the managed save will decide between using the running or paused state as determined by the state the domain is in when the save is done. However, this can be overridden by using the --running option to indicate that it must be left in a running state or by using --paused option which indicates it is to be left in a paused state.
To remove the managed save state, use the virsh managedsave-remove command which will force the domain to do a full boot the next time it is started.
Note that the entire managed save process can be monitored using the domjobinfo command and can also be canceled using the domjobabort command.

15.6.3. Displaying CPU statistics for a specified domain

The virsh cpu-stats domain --total start count command provides the CPU statistical information on the specified domain. By default it shows the statistics for all CPUs, as well as a total. The --total option will only display the total statistics.

15.6.4. Saving a screenshot

The virsh screenshot command takes a screenshot of a current domain console and stores it into a file. If however the hypervisor supports more displays for a domain, using the --screen and giving a screen ID will specify which screen to capture. In the case where there are multiple graphics cards, where the heads are numerated before their devices, screen ID 5 addresses the second head on the second card.

15.6.5. Sending a keystroke combination to a specified domain

Using the virsh send-key domain --codeset --holdtime keycode command you can send a sequence as a keycode to a specific domain.
Each keycode can either be a numeric value or a symbolic name from the corresponding codeset. If multiple keycodes are specified, thay are all sent simultaneously to the guest virtual machine and as such may be received in random order. If you need distinct keycodes, you must send the send-key command multiple times.
# virsh send-key rhel6 --holdtime 1000 0xf
If a --holdtime is given, each keystroke will be held for the specified amount in milliseconds. The --codeset allows you to specify a code set, the default being Linux, but the following options are permitted:
  • linux - choosing this option causes the symbolic names to match the corresponding Linux key constant macro names and the numeric values are those offered by the Linux generic input event subsystems.
  • xt- this will send a value that is defined by the XT keyboard controller. No symbolic names are provided.
  • atset1 - the numeric values are those that are defined by the AT keyboard controller, set1 (XT compatible set). Extended keycodes from the atset1 may differ from extended keycodes in the XT codeset. No symbolic names are provided.
  • atset2 - The numeric values are those defined by the AT keyboard controller, set 2. No symbolic names are provided.
  • atset3 - The numeric values are those defined by the AT keyboard controller, set 3 (PS/2 compatible). No symbolic names are provided.
  • os_x - The numeric values are those defined by the OS-X keyboard input subsystem. The symbolic names match the corresponding OS-X key constant macro names.
  • xt_kbd - The numeric values are those defined by the Linux KBD device. These are a variant on the original XT codeset, but often with different encoding for extended keycodes. No symbolic names are provided.
  • win32 - The numeric values are those defined by the Win32 keyboard input subsystem. The symbolic names match the corresponding Win32 key constant macro names.
  • usb - The numeric values are those defined by the USB HID specification for keyboard input. No symbolic names are provided.
  • rfb - The numeric values are those defined by the RFB extension for sending raw keycodes. These are a variant on the XT codeset, but extended keycodes have the low bit of the second bite set, instead of the high bit of the first byte. No symbolic names are provided.

15.6.6. Sending process signal names to virtual processes

Using the virsh send-process-signal domain-ID PID signame command sends the specified signal (as identified by its name) to a specified virtual process (as identified by its process ID or PID) within a running domain with its domain ID. An integer signal constant number or a symbolic signal name can be sent this way:
# virsh send-process-signal rhel6 187 kill
For the full list of available signals and their uses, see the virsh(1) and signal(7) manual pages.

15.6.7. Displaying the IP address and port number for the VNC display

The virsh vncdisplay will print the IP address and port number of the VNC display for the specified domain. If the information is unavailable the exit code 1 will be displayed.
# virsh vncdisplay rhel6
127.0.0.1:0

15.7. NUMA node management

This section contains the commands needed for NUMA node management.

15.7.1. Displaying node information

The nodeinfo command displays basic information about the node, including the model number, number of CPUs, type of CPU, and size of the physical memory. The output corresponds to virNodeInfo structure. Specifically, the "CPU socket(s)" field indicates the number of CPU sockets per NUMA cell.
$ virsh nodeinfo
CPU model:           x86_64
CPU(s):              4
CPU frequency:       1199 MHz
CPU socket(s):       1
Core(s) per socket:  2
Thread(s) per core:  2
NUMA cell(s):        1
Memory size:         3715908 KiB

15.7.2. Setting NUMA parameters

The virsh numatune can either set or retrieve the NUMA parameters for a specified domain. Within the Domain XML file these parameters are nested within the <numatune> element. Without using flags, only the current settings are displayed. The numatune domain command requires a specified domain and can take the following options:
  • --mode - The mode can be set to either strict, interleave, or preferred. Running domains cannot have their mode changed while live unless the domain was started within strict mode.
  • --nodeset contains a list of NUMA nodes that are used by the host physical machine for running the domain. The list contains nodes, each separated by a comma, with a dash - used for node ranges and a caret ^ used for excluding a node.
  • Only one of the following three flags can be used per instance:
    • --config will take effect on the next boot of a persistent guest virtual machine.
    • --live will set the scheduler information of a running guest virtual machine.
    • --current will affect the current state of the guest virtual machine.

15.7.3. Displaying the amount of free memory in a NUMA cell

The virsh freecell displays the available amount of memory on the machine within a specified NUMA cell. This command can provide one of three different displays of available memory on the machine depending on the options specified. If no options are used, the total free memory on the machine is displayed. Using the --all option, it displays the free memory in each cell and the total free memory on the machine. By using a numeric argument or with --cellno option along with a cell number it will display the free memory for the specified cell.

15.7.4. Displaying a CPU list

The nodecpumap command displays the number of CPUs that are available to the node, whether they are online or not and it also lists the number that are currently online.
$ virsh nodecpumap
   CPUs present: 4
   CPUs online: 1
   CPU map: y

15.7.5. Displaying CPU statistics

The nodecpustats command displays statistical information about the specified CPU, if the CPU is given. If not, it will display the CPU status of the node. If a percent is specified, it will display the percentage of each type of CPU statistics that were recorded over an one (1) second interval.
This example shows no CPU specified:
$ virsh nodecpustats
user:               1056442260000000
system:              401675280000000
idle:               7549613380000000
iowait:               94593570000000
This example shows the statistical percentages for CPU number 2:
$ virsh nodecpustats 2 --percent
usage:            2.0%
user:             1.0%
system:           1.0%
idle:            98.0%
iowait:           0.0%
You can control the behavior of the rebooting guest virtual machine by modifying the on_reboot element in the guest virtual machine's configuration file.

15.7.6. Suspending the host physical machine

The nodesuspend command puts the host physical machine into a system-wide sleep state similar to that of Suspend-to-RAM (s3), Suspend-to-Disk (s4), or Hybrid-Suspend and sets up a Real-Time-Clock to wake up the node after the duration that is set has past. The --target option can be set to either mem,disk, or hybrid. These options indicate to set the memory, disk, or combination of the two to suspend. Setting the --duration instructs the host physical machine to wake up after the set duration time has run out. It is set in seconds. It is recommended that the duration time be longer than 60 seconds.
$ virsh nodesuspend disk 60

15.7.7. Setting and displaying the node memory parameters

The node-memory-tune [shm-pages-to-scan] [shm-sleep-milisecs] [shm-merge-across-nodes] command displays and allows you to set the node memory parameters. There are three parameters that may be set with this command:
  • shm-pages-to-scan - sets the number of pages to scan before the shared memory service goes to sleep.
  • shm-sleep-milisecs - sets the number of miliseconds that the shared memory service will sleep before the next scan
  • shm-merge-across-nodes - specifies if pages from different NUMA nodes can be merged. Values allowed are 0 and 1. When set to 0, the only pages that can be merged are those that are physically residing in the memory area of the same NUMA node. When set to 1, pages from all of the NUMA nodes can be merged. The default setting is 1.

15.7.8. Creating devices on host nodes

The virsh nodedev-create file command allows you to create a device on a host node and then assign it to a guest virtual machine. libvirt normally detects which host nodes are available for use automatically, but this command allows for the registration of host hardware that libvirt did not detect. The file should contain the XML for the top level <device> description of the node device.
To stop this device, use the nodedev-destroy device command.

15.7.9. Detaching a node device

The virsh nodedev-detach detaches the nodedev from the host so it can be safely used by guests via <hostdev> passthrough. This action can be reversed with the nodedev-reattach command but it is done automatically for managed services. This command also accepts nodedev-dettach.
Note that different drivers expect the device to be bound to different dummy devices. Using the --driver option allows you to specify the desired backend driver.

15.7.10. Retrieving a device's configuration settings

The virsh nodedev-dumpxml [device] command dumps the XML configuration file for the given node <device>. The XML configuration includes information such as: the device name, which bus owns the device, the vendor, and product ID, etc. The argument device can either be a device name or a WWN pair in WWNN | WWPN format (HBA only).

15.7.11. Listing devices on a node

The virsh nodedev-list cap --tree command lists all the devices available on the node that are known by libvirt. cap is used to filter the list by capability types, each separated by a comma and cannot be used with --tree. Using the --tree option, puts the output into a tree structure as shown:
   #  virsh nodedev-list --tree
   computer
  |
  +- net_lo_00_00_00_00_00_00
  +- net_macvtap0_52_54_00_12_fe_50
  +- net_tun0
  +- net_virbr0_nic_52_54_00_03_7d_cb
  +- pci_0000_00_00_0
  +- pci_0000_00_02_0
  +- pci_0000_00_16_0
  +- pci_0000_00_19_0
  |   |
  |   +- net_eth0_f0_de_f1_3a_35_4f

(this is a partial screen)

15.7.12. Triggering a reset for a node

The nodedev-reset nodedev command triggers a device reset for the specified nodedev. Running this command is useful prior to transferring a node device between guest virtual machine passthrough and the host physical machine. libvirt will do this action implicitly when required, but this command allows an explicit reset when needed.

15.8. Starting, suspending, resuming, saving and restoring a guest virtual machine

15.8.1. Starting a defined domain

The virsh start domain --console --paused --autodestroy --bypass-cache --force-boot --pass-fds command starts a inactive domain that was already defined but whose state is inactive since its last managed save state or a fresh boot. The command can take the following options:
  • --console - will boot the domain attaching to the console
  • --paused - If this is supported by the driver it will boot the domain and then put it into a paused state
  • --autodestroy - the guest virtual machine is automatically destroyed when the virsh session closes or the connection to libvirt closes, or it otherwise exits
  • --bypass-cache - used if the domain is in the managedsave state. If this is used, it will restore the guest virtual machine, avoiding the system cache. Note this will slow down the restore process.
  • --force-boot - discards any managedsave options and causes a fresh boot to occur
  • --pass-fds - is a list of additional options separated by commas, which are passed onto the guest virtual machine.

15.8.2. Suspending a guest virtual machine

Suspend a guest virtual machine with virsh:
# virsh suspend {domain-id, domain-name or domain-uuid}
When a guest virtual machine is in a suspended state, it consumes system RAM but not processor resources. Disk and network I/O does not occur while the guest virtual machine is suspended. This operation is immediate and the guest virtual machine can be restarted with the resume (Section 15.8.6, “Resuming a guest virtual machine”) option.

15.8.3. Suspending a running domain

The virsh dompmsuspend domain --duration --target command will take a running domain and suspended it so it can be placed into one of three possible states (S3, S4, or a hybrid of the two).
# virsh dompmsuspend rhel6 --duration 100 --target mem
This command can take the following options:
  • --duration - sets the duration for the state change in seconds
  • --target - can be either mem (suspend to RAM (S3))disk (suspend to disk (S4)), or hybrid (hybrid suspend)

15.8.4. Waking up a domain from pmsuspend state

This command will inject a wake-up alert to a guest that is in a pmsuspend state, rather than waiting for the duration time set to expire. This operation will not fail if the domain is running.
# dompmwakeup rhel6
This command requires the name of the domain, rhel6 for example as shown.

15.8.5. Undefining a domain

This command will undefine a domain. Although it can work on a running domain, it will convert the running domain into a transient domain without stopping it. If the domain is inactive, the domain configuration is removed.
The virsh undefine domain--managed-save--snapshots-metadata --storage --remove-all-storage --wipe-storage command can take the following options:
  • --managed-save - this option guarantees that any managed save image is also cleaned up. Without using this option, attempts to undefine a domain with a managed save image will fail.
  • --snapshots-metadata - this option guarantees that any snapshots (as shown with snapshot-list) are also cleaned up when undefining an inactive domain. Note that any attempts to undefine an inactive domain whose configuration file contains snapshot metadata will fail. If this option is used and the domain is active, it is ignored.
  • --storage - using this option requires a comma separated list of volume target names or source paths of storage volumes to be removed along with the undefined domain. This action will undefine the storage volume before it is removed. Note that this can only be done with inactive domains. Note too that this will only work with storage volumes that are managed by libvirt.
  • --remove-all-storage - in addition to undefining the domain, all associated storage volumes are deleted.
  • --wipe-storage - in addition to deleting the storage volume, the contents are wiped.

15.8.6. Resuming a guest virtual machine

Restore a suspended guest virtual machine with virsh using the resume option:
# virsh resume {domain-id, domain-name or domain-uuid}
This operation is immediate and the guest virtual machine parameters are preserved for suspend and resume operations.

15.8.7. Save a guest virtual machine

Save the current state of a guest virtual machine to a file using the virsh command:
# virsh save {domain-name|domain-id|domain-uuid} state-file --bypass-cache --xml --running --paused --verbose
This stops the guest virtual machine you specify and saves the data to a file, which may take some time given the amount of memory in use by your guest virtual machine. You can restore the state of the guest virtual machine with the restore (Section 15.8.11, “Restore a guest virtual machine”) option. Save is similar to pause, instead of just pausing a guest virtual machine the present state of the guest virtual machine is saved.
The virsh save command can take the following options:
  • --bypass-cache - causes the restore to avoid the file system cache but note that using this flag may slow down the restore operation.
  • --xml - this option must be used with an XML file name. Although this option is usually omitted, it can be used to supply an alternative XML file for use on a restored guest virtual machine with changes only in the host-specific portions of the domain XML. For example, it can be used to account for the file naming differences in underlying storage due to disk snapshots taken after the guest was saved.
  • --running - overrides the state recorded in the save image to start the domain as running.
  • --paused- overrides the state recorded in the save image to start the domain as paused.
  • --verbose - displays the progress of the save.
If you want to restore the guest virtual machine directly from the XML file, the virsh restore command will do just that. You can monitor the process with the domjobinfo and cancel it with the domjobabort.

15.8.8. Updating the domain XML file that will be used for restoring the guest

The virsh save-image-define file xml --running|--paused command will update the domain XML file that will be used when the specified file is later used during the virsh restore command. The xml argument must be an XML file name containing the alternative XML with changes only in the host physical machine specific portions of the domain XML. For example, it can be used to account for the file naming differences resulting from creating disk snapshots of underlying storage after the guest was saved. The save image records if the domain should be restored to a running or paused state. Using the options --running or --paused dictates the state that is to be used.

15.8.9. Extracting the domain XML file

save-image-dumpxml file --security-info command will extract the domain XML file that was in effect at the time the saved state file (used in the virsh save command) was referenced. Using the --security-info option includes security sensitive information in the file.

15.8.10. Edit Domain XML configuration files

save-image-edit file --running --paused command edits the XML configuration file that is associated with a saved file that was created by the virsh save command.
Note that the save image records whether the domain should be restored to a --running or --paused state. Without using these options the state is determined by the file itself. By selecting --running or --paused you can overwrite the state that virsh restore should use.

15.8.11. Restore a guest virtual machine

Restore a guest virtual machine previously saved with the virsh save command (Section 15.8.7, “Save a guest virtual machine”) using virsh:
# virsh restore state-file
This restarts the saved guest virtual machine, which may take some time. The guest virtual machine's name and UUID are preserved but are allocated for a new id.
The virsh restore state-file command can take the following options:
  • --bypass-cache - causes the restore to avoid the file system cache but note that using this flag may slow down the restore operation.
  • --xml - this option must be used with an XML file name. Although this option is usually omitted, it can be used to supply an alternative XML file for use on a restored guest virtual machine with changes only in the host-specific portions of the domain XML. For example, it can be used to account for the file naming differences in underlying storage due to disk snapshots taken after the guest was saved.
  • --running - overrides the state recorded in the save image to start the domain as running.
  • --paused- overrides the state recorded in the save image to start the domain as paused.

15.9. Shutting down, rebooting and force-shutdown of a guest virtual machine

15.9.1. Shut down a guest virtual machine

Shut down a guest virtual machine using the virsh shutdown command:
# virsh shutdown {domain-id, domain-name or domain-uuid} [--mode method]
You can control the behavior of the rebooting guest virtual machine by modifying the on_shutdown parameter in the guest virtual machine's configuration file.

15.9.2. Shutting down Red Hat Enterprise Linux 6 guests on a Red Hat Enterprise Linux 7 host

Installing Red Hat Enterprise Linux 6 guest virtual machines with the Minimal installation option does not install the acpid package. Red Hat Enterprise Linux 7 no longer requires this package, as it has been taken over by systemd. However, Red Hat Enterprise Linux 6 guest virtual machines running on a Red Hat Enterprise Linux 7 host still require it.
Without the acpid package, the Red Hat Enterprise Linux 6 guest virtual machine does not shut down when the virsh shutdown command is executed. The virsh shutdown command is designed to gracefully shut down guest virtual machines.
Using virsh shutdown is easier and safer for system administration. Without graceful shut down with the virsh shutdown command a system administrator must log into a guest virtual machine manually or send the Ctrl-Alt-Del key combination to each guest virtual machine.

Note

Other virtualized operating systems may be affected by this issue. The virsh shutdown command requires that the guest virtual machine operating system is configured to handle ACPI shut down requests. Many operating systems require additional configuration on the guest virtual machine operating system to accept ACPI shut down requests.

Procedure 15.4. Workaround for Red Hat Enterprise Linux 6 guests

  1. Install the acpid package

    The acpid service listen and processes ACPI requests.
    Log into the guest virtual machine and install the acpid package on the guest virtual machine:
    # yum install acpid
  2. Enable the acpid service

    Set the acpid service to start during the guest virtual machine boot sequence and start the service:
    # systemctl enable acpid
    # service acpid start
  3. Prepare guest domain xml

    Edit the domain XML file to include the following element. Replace the virtio serial port with org.qemu.guest_agent.0 and use your guest's name instead of $guestname
    
    <channel type='unix'>
       <source mode='bind' path='/var/lib/libvirt/qemu/{$guestname}.agent'/>
       <target type='virtio' name='org.qemu.guest_agent.0'/>
    </channel>
        
    
    

    Figure 15.2. Guest XML replacement

  4. Install the QEMU guest agent

    Install the QEMU guest agent (QEMU-GA) and start the service as directed in Chapter 11, QEMU-img and QEMU guest agent. If you are running a Windows guest there are instructions in this chapter for that as well.
  5. Shutdown the guest

    1. Run the following commands
      # virsh list --all  - this command lists all of the known domains 
         Id Name              State
      ----------------------------------
         rhel6                running
      
    2. Shut down the guest virtual machine
      # virsh shutdown rhel6
      
      Domain rhel6 is being shutdown
      
    3. Wait a few seconds for the guest virtual machine to shut down.
      # virsh list --all
       Id Name                 State
      ----------------------------------
        . rhel6                shut off
      
    4. Start the domain named rhel6, with the XML file you edited.
      # virsh start rhel6
    5. Shut down the acpi in the rhel6 guest virtual machine.
      # virsh shutdown --mode acpi rhel6 
    6. List all the domains again, rhel6 should still be on the list, and it should indicate it is shut off.
      # virsh list --all
         Id Name                 State
      ----------------------------------
         rhel6                shut off
      
    7. Start the domain named rhel6, with the XML file you edited.
      # virsh start rhel6
    8. Shut down the rhel6 guest virtual machine guest agent.
      # virsh shutdown --mode agent rhel6
    9. List the domains. rhel6 should still be on the list, and it should indicate it is shut off
      # virsh list --all
         Id Name                 State
      ----------------------------------
         rhel6                shut off
      
The guest virtual machine will shut down using the virsh shutdown command for the consecutive shutdowns, without using the workaround described above.
In addition to the method described above, a guest can be automatically shutdown, by stopping the libvirt-guest service. Refer to Section 15.9.3, “Manipulating the libvirt-guests configuration settings” for more information on this method.

15.9.3. Manipulating the libvirt-guests configuration settings

The libvirt-guests service has parameter settings that can be configured to assure that the guest is shutdown properly. It is a package that is a part of the libvirt installation and is installed by default. This service automatically saves guests to the disk when the host shuts down, and restores them to their pre-shutdown state when the host reboots. By default, this setting is set to suspend the guest. If you want the guest to be shutoff, you will need to change one of the parameters of the libvirt-guests configuration file.

Procedure 15.5. Changing the libvirt-guests service parameters to allow for the graceful shutdown of guests

The procedure described here allows for the graceful shutdown of guest virtual machines when the host physical machine is stuck, powered off, or needs to be restarted.
  1. Open the configuration file

    The configuration file is located in /etc/sysconfig/libvirt-guests. Edit the file, remove the comment mark (#) and change the ON_SHUTDOWN=suspend to ON_SHUTDOWN=shutdown. Remember to save the change.
    $ vi /etc/sysconfig/libvirt-guests
    
    # URIs to check for running guests
    # example: URIS='default xen:/// vbox+tcp://host/system lxc:///'
    #URIS=default 
    
    # action taken on host boot
    # - start   all guests which were running on shutdown are started on boot
    #           regardless on their autostart settings                                 1
    # - ignore  libvirt-guests init script won't start any guest on boot, however,     2
    #           guests marked as autostart will still be automatically started by      3
    #           libvirtd                                                               4
    #ON_BOOT=start                                                                     5
    6
    # Number of seconds to wait between each guest start. Set to 0 to allow            7
    # parallel startup.
    #START_DELAY=0
    
    # action taken on host shutdown
    # - suspend   all running guests are suspended using virsh managedsave
    # - shutdown  all running guests are asked to shutdown. Please be careful with
    #             this settings since there is no way to distinguish between a
    #             guest which is stuck or ignores shutdown requests and a guest
    #             which just needs a long time to shutdown. When setting
    #             ON_SHUTDOWN=shutdown, you must also set SHUTDOWN_TIMEOUT to a
    #             value suitable for your guests.
    ON_SHUTDOWN=shutdown
    
    # If set to non-zero, shutdown will suspend guests concurrently. Number of
    # guests on shutdown at any time will not exceed number set in this variable.
    #PARALLEL_SHUTDOWN=0
    
    # Number of seconds we're willing to wait for a guest to shut down. If parallel
    # shutdown is enabled, this timeout applies as a timeout for shutting down all
    # guests on a single URI defined in the variable URIS. If this is 0, then there
    # is no time out (use with caution, as guests might not respond to a shutdown
    # request). The default value is 300 seconds (5 minutes).
    #SHUTDOWN_TIMEOUT=300
    
    # If non-zero, try to bypass the file system cache when saving and
    # restoring guests, even though this may give slower operation for
    # some file systems.
    #BYPASS_CACHE=0

    1

    URIS - checks the specified connections for a running guest. The Default setting functions in the same manner as virsh does when no explicit URI is set In addition, one can explicitly set the URI from /etc/libvirt/libvirt.conf. It should be noted that when using the libvirt configuration file default setting, no probing will be used.

    2

    ON_BOOT - specifies the action to be done to / on the guests when the host boots. The start option starts all guests that were running prior to shutdown regardless on their autostart settings. The ignore option will not start the formally running guest on boot, however, any guest marked as autostart will still be automatically started by libvirtd.

    3

    The START_DELAY - sets a delay interval in between starting up the guests. This time period is set in seconds. Use the 0 time setting to make sure there is no delay and that all guests are started simultaneously.

    4

    ON_SHUTDOWN - specifies the action taken when a host shuts down. Options that can be set include: suspend which suspends all running guests using virsh managedsave and shutdown which shuts down all running guests. It is best to be careful with using the shutdown option as there is no way to distinguish between a guest which is stuck or ignores shutdown requests and a guest that just needs a longer time to shutdown. When setting the ON_SHUTDOWN=shutdown, you must also set SHUTDOWN_TIMEOUT to a value suitable for the guests.

    5

    PARALLEL_SHUTDOWN Dictates that the number of guests on shutdown at any time will not exceed number set in this variable and the guests will be suspended concurrently. If set to 0, then guests are not shutdown concurrently.

    6

    Number of seconds to wait for a guest to shut down. If SHUTDOWN_TIMEOUT is enabled, this timeout applies as a timeout for shutting down all guests on a single URI defined in the variable URIS. If SHUTDOWN_TIMEOUT is set to 0, then there is no time out (use with caution, as guests might not respond to a shutdown request). The default value is 300 seconds (5 minutes).

    7

    BYPASS_CACHE can have 2 values, 0 to disable and 1 to enable. If enabled it will by-pass the file system cache when guests are restored. Note that setting this may effect performance and may cause slower operation for some file systems.
  2. Start libvirt-guests service

    If you have not started the service, start the libvirt-guests service. Do not restart the service as this will cause all running domains to shutdown.

15.9.4. Rebooting a guest virtual machine

Use the virsh reboot command to reboot a guest virtual machine. The prompt will return once the reboot has executed. Note that there may be a time lapse until the guest virtual machine returns.
#virsh reboot {domain-id, domain-name or domain-uuid} [--mode method]
You can control the behavior of the rebooting guest virtual machine by modifying the <on_reboot> element in the guest virtual machine's configuration file. Refer to Section 21.12, “Events configuration” for more information.
By default, the hypervisor will try to pick a suitable shutdown method. To specify an alternative method, the --mode option can specify a comma separated list which includes initctl, acpi, agent, and signal. The order in which drivers will try each mode is not related to the order specified in the command. For strict control over ordering, use a single mode at a time and repeat the command.

15.9.5. Forcing a guest virtual machine to stop

Force a guest virtual machine to stop with the virsh destroy command:
# virsh destroy {domain-id, domain-name or domain-uuid} [--graceful]
This command does an immediate ungraceful shutdown and stops the specified guest virtual machine. Using virsh destroy can corrupt guest virtual machine file systems. Use the destroy option only when the guest virtual machine is unresponsive. If you want to initiate a graceful shutdown, use the virsh destroy --graceful command.

15.9.6. Resetting a virtual machine

virsh reset domain resets the domain immediately without any guest shutdown. A reset emulates the power reset button on a machine, where all guest hardware sees the RST line and re-initializes the internal state. Note that without any guest virtual machine OS shutdown, there are risks for data loss.

15.10. Retrieving guest virtual machine information

15.10.1. Getting the domain ID of a guest virtual machine

To get the domain ID of a guest virtual machine:
# virsh domid {domain-name or domain-uuid}

15.10.2. Getting the domain name of a guest virtual machine

To get the domain name of a guest virtual machine:
# virsh domname {domain-id or domain-uuid}

15.10.3. Getting the UUID of a guest virtual machine

To get the Universally Unique Identifier (UUID) for a guest virtual machine:
# virsh domuuid {domain-id or domain-name}
An example of virsh domuuid output:
# virsh domuuid r5b2-mySQL01
4a4c59a7-ee3f-c781-96e4-288f2862f011

15.10.4. Displaying guest virtual machine information

Using virsh with the guest virtual machine's domain ID, domain name or UUID you can display information on the specified guest virtual machine:
# virsh dominfo {domain-id, domain-name or domain-uuid}
This is an example of virsh dominfo output:
# virsh dominfo vr-rhel6u1-x86_64-kvm
Id:             9
Name:           vr-rhel6u1-x86_64-kvm
UUID:           a03093a1-5da6-a2a2-3baf-a845db2f10b9
OS Type:        hvm
State:          running
CPU(s):         1
CPU time:       21.6s
Max memory:     2097152 kB
Used memory:    1025000 kB
Persistent:     yes
Autostart:      disable
Security model: selinux
Security DOI:   0
Security label: system_u:system_r:svirt_t:s0:c612,c921 (permissive)

15.11. Storage pool commands

The following commands manipulate storage pools. Using libvirt you can manage various storage solutions, including files, raw partitions, and domain-specific formats, used to provide the storage volumes visible as devices within virtual machines. For more detailed information about this feature, see more information at libvirt.org. Many of the commands for storage pools are similar to the ones used for domains.

15.11.1. Searching for a storage pool XML

The find-storage-pool-sources type srcSpec command displays the XML describing all storage pools of a given type that could be found. If srcSpec is provided, it is a file that contains XML to further restrict the query for pools.
The find-storage-pool-sources-as type host port initiator displays the XML describing all storage pools of a given type that could be found. If host, port, or initiator are provided, they control where the query is performed.
The pool-info pool-or-uuid command will list the basic information about the specified storage pool object. This command requires the name or UUID of the storage pool. To retrieve this information, use the pool-list
The pool-list --inactive --all --persistent --transient --autostart --no-autostart --details<type> command lists all storage pool objects known to libvirt. By default, only active pools are listed; but using the --inactive option lists just the inactive pools, and using the --all option lists all of the storage pools.
In addition to those options there are several sets of filtering flags that can be used to filter the content of the list. --persistent restricts the list to persistent pools, --transient restricts the list to transient pools, --autostart restricts the list to autostarting pools and finally --no-autostart restricts the list to the storage pools that have autostarting disabled.
For all storage pool commands which require a type, the pool types must be separated by comma. The valid pool types include: dir, fs, netfs, logical, disk, iscsi, scsi, mpath, rbd, and sheepdog.
The --details option instructs virsh to additionally display pool persistence and capacity related information where available.

Note

When this command is used with older servers, it is forced to use a series of API calls with an inherent race, where a pool might not be listed or might appear more than once if it changed its state between calls while the list was being collected. Newer servers however, do not have this problem.
The pool-refresh pool-or-uuid refreshes the list of volumes contained in pool.

15.11.2. Creating, defining, and starting storage pools

15.11.2.1. Building a storage pool

The pool-build pool-or-uuid --overwrite --no-overwrite command builds a pool with a specified pool name or UUID. The options --overwrite and --no-overwrite can only be used for a pool whose type is file system. If neither option is specified, and the pool is a file system type pool, then the resulting build will only make the directory.
If --no-overwrite is specified, it probes to determine if a file system already exists on the target device, returning an error if it exists, or using mkfs to format the target device if it does not. If --overwrite is specified, then the mkfs command is executed and any existing data on the target device is overwritten.

15.11.2.2. Creating and defining a storage pool from an XML file

The pool-create file creates and starts a storage pool from its associated XML file.
The pool-define file creates, but does not start, a storage pool object from the XML file.

15.11.2.3. Creating and starting a storage pool from raw parameters

The pool-create-as name --print-xml type source-host source-path source-dev source-name <target> --source-format <format> command creates and starts a pool object name from the raw parameters given.
If --print-xml is specified, then it prints the XML of the storage pool object without creating the pool. Otherwise, the pool requires a type in order to be built. For all storage pool commands which require a type, the pool types must be separated by comma. The valid pool types include: dir, fs, netfs, logical, disk, iscsi, scsi, mpath, rbd, and sheepdog.
The pool-define-as name --print-xml type source-host source-path source-dev source-name <target> --source-format <format> command creates, but does not start, a pool object name from the raw parameters given.
If --print-xml is specified, then it prints the XML of the pool object without defining the pool. Otherwise, the pool has to have a specified type. For all storage pool commands which require a type, the pool types must be separated by comma. The valid pool types include: dir, fs, netfs, logical, disk, iscsi, scsi, mpath, rbd, and sheepdog.
The pool-start pool-or-uuid starts the specified storage pool, which was previously defined but inactive.

15.11.2.4. Auto-starting a storage pool

The pool-autostart pool-or-uuid --disable command enables or disables a storage pool to automatically start at boot. This command requires the pool name or UUID. To disable the pool-autostart command use the --disable option.

15.11.3. Stopping and deleting storage pools

The pool-destroy pool-or-uuid stops a storage pool. Once stopped, libvirt will no longer manage the pool but the raw data contained in the pool is not changed, and can be later recovered with the pool-create command.
The pool-delete pool-or-uuid destroys the resources used by the specified storage pool. It is important to note that this operation is non-recoverable and non-reversible. However, the pool structure will still exist after this command, ready to accept the creation of new storage volumes.
The pool-undefine pool-or-uuid command undefines the configuration for an inactive pool.

15.11.4. Creating an XML dump file for a pool

The pool-dumpxml --inactive pool-or-uuid command returns the XML information about the specified storage pool object. Using --inactive dumps the configuration that will be used on next start of the pool as opposed to the current pool configuration.

15.11.5. Editing the storage pool's configuration file

The pool-edit pool-or-uuid opens the specified storage pool's XML configuration file for editing.
This method is the only method that should be used to edit an XML configuration file as it does error checking before applying.

15.11.6. Converting storage pools

The pool-name uuid command converts the specified UUID to a pool name.
The pool-uuid pool command returns the UUID of the specified pool.

15.12. Storage Volume Commands

This section covers all commands for creating, deleting, and managing storage volumes. It is best to do this once you have created a storage pool as the storage pool name or UUID will be required. For information on storage pools refer to Chapter 13, Storage pools. For information on storage volumes refer to, Chapter 14, Volumes .

15.12.1. Creating storage volumes

The vol-create-from pool-or-uuid file --inputpool pool-or-uuid vol-name-or-key-or-path command creates a storage volume, using another storage volume as a template for its contents. This command requires a pool-or-uuid which is the name or UUID of the storage pool to create the volume in.
The file argument specifies the XML file and path containing the volume definition. The --inputpool pool-or-uuid option specifies the name or uuid of the storage pool the source volume is in. The vol-name-or-key-or-path argument specifies the name or key or path of the source volume. For some examples, refer to Section 14.1, “Creating volumes”.
The vol-create-as command creates a volume from a set of arguments. The pool-or-uuid argument contains the name or UUID of the storage pool to create the volume in.
vol-create-as pool-or-uuid name capacity --allocation <size> --format <string> --backing-vol <vol-name-or-key-or-path> --backing-vol-format <string>
name is the name of the new volume. capacity is the size of the volume to be created, as a scaled integer, defaulting to bytes if there is no suffix. --allocation <size> is the initial size to be allocated in the volume, also as a scaled integer defaulting to bytes. --format <string> is used in file based storage pools to specify the volume file format which is a string of acceptable formats separated by a comma. Acceptable formats include raw, bochs, qcow, qcow2, vmdk, --backing-vol vol-name-or-key-or-path is the source backing volume to be used if taking a snapshot of an existing volume. --backing-vol-format string is the format of the snapshot backing volume which is a string of formats separated by a comma. Accepted values include: raw, bochs, qcow, qcow2, , vmdk, and host_device. These are, however, only meant for file based storage pools.

15.12.1.1. Creating a storage volume from an XML file

The vol-create pool-or-uuid file creates a storage volume from a saved XML file. This command also requires the pool-or-uuid, which is the name or UUID of the storage pool in which the volume will be created. The file argument contains the path with the volume definition's XML file. An easy way to create the XML file is to use the vol-dumpxml command to obtain the definition of a pre-existing volume, modify it and then save it and then run the vol-create.
virsh vol-dumpxml --pool storagepool1 appvolume1 > newvolume.xml
virsh edit newvolume.xml 
virsh vol-create differentstoragepool newvolume.xml
Other options available include:
  • The --inactive option lists the inactive guest virtual machines (that is, guest virtual machines that have been defined but are not currently active).
  • The --all option lists all guest virtual machines.

15.12.1.2. Cloning a storage volume

The vol-clone --pool pool-or-uuid vol-name-or-key-or-path name command clones an existing storage volume. Although the vol-create-from may also be used, it is not the recommended way to clone a storage volume. The --pool pool-or-uuid option is the name or UUID of the storage pool to create the volume in. The vol-name-or-key-or-path argument is the name or key or path of the source volume. Using a name argument refers to the name of the new volume.

15.12.2. Deleting storage volumes

The vol-delete --pool pool-or-uuid vol-name-or-key-or-path command deletes a given volume. The command requires a specific --pool pool-or-uuid which is the name or UUID of the storage pool the volume is in. The vol-name-or-key-or-path option specifies the name or key or path of the volume to delete.
The vol-wipe --pool pool-or-uuid --algorithm algorithm vol-name-or-key-or-path command wipes a volume, to ensure data previously on the volume is not accessible to future reads. The command requires a --pool pool-or-uuid, which is the name or UUID of the storage pool the volume is in. The vol-name-or-key-or-path contains the name or key or path of the volume to wipe. Note it is possible to choose different wiping algorithms instead of the default (where every sector of the storage volume is written with value "0"). To specify a wiping algorithm, use the --algorithm option with one of the following supported algorithm types:
  • zero - 1-pass all zeroes
  • nnsa - 4-pass NNSA Policy Letter NAP-14.1-C (XVI-8) for sanitizing removable and non-removable hard disks: random x2, 0x00, verify.
  • dod - 4-pass DoD 5220.22-M section 8-306 procedure for sanitizing removable and non-removable rigid disks: random, 0x00, 0xff, verify.
  • bsi - 9-pass method recommended by the German Center of Security in Information Technologies (http://www.bsi.bund.de): 0xff, 0xfe, 0xfd, 0xfb, 0xf7, 0xef, 0xdf, 0xbf, 0x7f.
  • gutmann - The canonical 35-pass sequence described in Gutmann’s paper.
  • schneier - 7-pass method described by Bruce Schneier in "Applied Cryptography" (1996): 0x00, 0xff, random x5.
  • pfitzner7 - Roy Pfitzner’s 7-random-pass method: random x7
  • pfitzner33 - Roy Pfitzner’s 33-random-pass method: random x33.
  • random - 1-pass pattern: random.

Note

The version of the scrub binary installed on the host will limit the algorithms that are available.

15.12.3. Dumping storage volume information to an XML file

vol-dumpxml --pool pool-or-uuid vol-name-or-key-or-path command takes the volume information as an XML dump to a specified file.
This command requires a --pool pool-or-uuid, which is the name or UUID of the storage pool the volume is in. vol-name-or-key-or-path is the name or key or path of the volume to place the resulting XML file.

15.12.4. Listing volume information

The vol-info --pool pool-or-uuid vol-name-or-key-or-path command lists basic information about the given storage volume --pool, where pool-or-uuid is the name or UUID of the storage pool the volume is in. vol-name-or-key-or-path is the name or key or path of the volume to return information for.
The vol-list--pool pool-or-uuid --details lists all of volumes in the specified storage pool. This command requires --pool pool-or-uuid which is the name or UUID of the storage pool. The --details option instructs virsh to additionally display volume type and capacity related information where available.

15.12.5. Retrieving storage volume information

The vol-pool --uuid vol-key-or-path command returns the pool name or UUID for a given volume. By default, the pool name is returned. If the --uuid option is given, the pool UUID is returned instead. The command requires the vol-key-or-path which is the key or path of the volume for which to return the requested information.
The vol-path --pool pool-or-uuid vol-name-or-key command returns the path for a given volume. The command requires --pool pool-or-uuid, which is the name or UUID of the storage pool the volume is in. It also requires vol-name-or-key which is the name or key of the volume for which the path has been requested.
The vol-name vol-key-or-path command returns the name for a given volume, where vol-key-or-path is the key or path of the volume to return the name for.
The vol-key --pool pool-or-uuid vol-name-or-path command returns the volume key for a given volume where --pool pool-or-uuid is the name or UUID of the storage pool the volume is in and vol-name-or-path is the name or path of the volume to return the volume key for.

15.12.6. Uploading and downloading storage volumes

This section will instruct how to upload and download information to and from storage volumes.

15.12.6.1. Uploading contents to a storage volume

The vol-upload --pool pool-or-uuid --offset bytes --length bytes vol-name-or-key-or-path local-file command uploads the contents of specified local-file to a storage volume. The command requires --pool pool-or-uuid which is the name or UUID of the storage pool the volume is in. It also requires vol-name-or-key-or-path which is the name or key or path of the volume to wipe. The --offset option is the position in the storage volume at which to start writing the data. --length length dictates an upper limit for the amount of data to be uploaded. An error will occur if the local-file is greater than the specified --length.

15.12.6.2. Downloading the contents from a storage volume

The vol-download --pool pool-or-uuid --offset bytes -length bytes vol-name-or-key-or-path local-file command downloads the contents of local-file from a storage volume.
The command requires a --pool pool-or-uuid which is the name or UUID of the storage pool that the volume is in. It also requires vol-name-or-key-or-path which is the name or key or path of the volume to wipe. Using the option --offset dictates the position in the storage volume at which to start reading the data. --length length dictates an upper limit for the amount of data to be downloaded.

15.12.7. Re-sizing storage volumes

The vol-resize --pool pool-or-uuid vol-name-or-path pool-or-uuid capacity --allocate --delta --shrink command re-sizes the capacity of the given volume, in bytes.The command requires --pool pool-or-uuid which is the name or UUID of the storage pool the volume is in. This command also requires vol-name-or-key-or-path is the name or key or path of the volume to re-size.
The new capacity may create a sparse file unless the --allocate option is specified. Normally, capacity is the new size, but if --delta is present, then it is added to the existing size. Attempts to shrink the volume will fail unless the --shrink option is present.
Note that capacity cannot be negative unless the --shrink option is provided and a negative sign is not necessary. capacity is a scaled integer which defaults to bytes if there is no suffix. Note too that this command is only safe for storage volumes not in use by an active guest. Refer to Section 15.5.17, “Using blockresize to change the size of a domain path” for live re-sizing.

15.13. Displaying per-guest virtual machine information

15.13.1. Displaying the guest virtual machines

To display the guest virtual machine list and their current states with virsh:
# virsh list
Other options available include:
  • --inactive option lists the inactive guest virtual machines (that is, guest virtual machines that have been defined but are not currently active)
  • --all option lists all guest virtual machines. For example:
    # virsh list --all
     Id Name                 State
    ----------------------------------
      0 Domain-0             running
      1 Domain202            paused
      2 Domain010            inactive
      3 Domain9600           crashed
    
    There are seven states that can be visible using this command:
    • Running - The running state refers to guest virtual machines which are currently active on a CPU.
    • Idle - The idle state indicates that the domain is idle, and may not be running or able to run. This can be caused because the domain is waiting on IO (a traditional wait state) or has gone to sleep because there was nothing else for it to do.
    • Paused - The paused state lists domains that are paused. This occurs if an administrator uses the paused button in virt-manager or virsh suspend. When a guest virtual machine is paused it consumes memory and other resources but it is ineligible for scheduling and CPU resources from the hypervisor.
    • Shutdown - The shutdown state is for guest virtual machines in the process of shutting down. The guest virtual machine is sent a shutdown signal and should be in the process of stopping its operations gracefully. This may not work with all guest virtual machine operating systems; some operating systems do not respond to these signals.
    • Shut off - The shut off state indicates that the domain is not running. This can be caused when a domain completely shuts down or has not been started.
    • Crashed - The crashed state indicates that the domain has crashed and can only occur if the guest virtual machine has been configured not to restart on crash.
    • Dying - Domains in the dying state are in is in process of dying, which is a state where the domain has not completely shut-down or crashed.
  • --managed-save Although this flag alone does not filter the domains, it will list the domains that have managed save state enabled. In order to actually list the domains seperately you will need to use the --inactive flag as well.
  • --name is specified domain names are printed in a list. If --uuid is specified the donain's UUID is printed instead. Using the flag --table specifies that a table style output should be used. All three commands are mutually exclusive
  • --title This command must be used with --table output. --titlewill cause an extra column to be created in the table with the short domain description (title).
  • --persistentincludes persistent domains in a list. Use the --transient option.
  • --with-managed-save lists the domains that have been configured with managed save. To list the commands without it, use the command --without-managed-save
  • --state-running filters out for the domains that are running, --state-paused for paused domains, --state-shutoff for domains that are turned off, and --state-other lists all states as a fallback.
  • --autostart this option will cause the auto-starting domains to be listed. To list domains with this feature disabled, use the option --no-autostart.
  • --with-snapshot will list the domains whose snapshot images can be listed. To filter for the domains without a snapshot, use the option --without-snapshot
$ virsh list --title --name

    Id       Name                                          State     Title
    0        Domain-0                                      running   Mailserver1
    2        rhelvm                                        paused
For an example of virsh vcpuinfo output, refer to Section 15.13.2, “Displaying virtual CPU information”

15.13.2. Displaying virtual CPU information

To display virtual CPU information from a guest virtual machine with virsh:
# virsh vcpuinfo {domain-id, domain-name or domain-uuid}
An example of virsh vcpuinfo output:
# virsh vcpuinfo rhel6
VCPU:           0
CPU:            2
State:          running
CPU time:       7152.4s
CPU Affinity:   yyyy

VCPU:           1
CPU:            2
State:          running
CPU time:       10889.1s
CPU Affinity:   yyyy

15.13.3. Configuring virtual CPU affinity

To configure the affinity of virtual CPUs with physical CPUs, refer to Example 15.3, “Pinning vCPU to a host physical machine's CPU”.

Example 15.3. Pinning vCPU to a host physical machine's CPU

The virsh vcpupin assigns a virtual CPU to a physical one.
# virsh vcpupin rhel6
VCPU: CPU Affinity
----------------------------------
   0: 0-3
   1: 0-3
The vcpupin can take the following options:
  • --vcpu requires the vcpu number
  • [--cpulist] >string< lists the host physical machine's CPU number(s) to set, or omit an optional query
  • --config affects next boot
  • --live affects the running domain
  • --current affects the current domain

15.13.4. Displaying information about the virtual CPU counts of a domain

virsh vcpucount requires a domain name or a domain ID. For example:
# virsh vcpucount rhel6
maximum      config         2
maximum      live           2
current      config         2
current      live           2
The vcpucount can take the following options:
  • --maximum displays the maximum number of vCPUs available
  • --active displays the number of currently active vCPUs
  • --live displays the value from the running domain
  • --config displays the value to be configured on guest virtual machine's next boot
  • --current displays the value according to current domain state
  • --guest displays the count that is returned is from the perspective of the guest

15.13.5. Configuring virtual CPU affinity

To configure the affinity of virtual CPUs with physical CPUs:
# virsh vcpupin domain-id vcpu cpulist
The domain-id parameter is the guest virtual machine's ID number or name.
The vcpu parameter denotes the number of virtualized CPUs allocated to the guest virtual machine.The vcpu parameter must be provided.
The cpulist parameter is a list of physical CPU identifier numbers separated by commas. The cpulist parameter determines which physical CPUs the VCPUs can run on.
Additional parameters such as --config affect the next boot, whereas --live affects the running domain, and --current affects the current domain.

15.13.6. Configuring virtual CPU count

By default, the virtual CPU (vCPU) count can only be changed on active guest domains. To change the settings for an inactive guest domain, use the --config flag. Modify the number of CPUs assigned to a guest virtual machine with the virsh command:
# virsh setvcpus {domain-name, domain-id or domain-uuid} count [[--config] [--live] | [--current] [--guest] 
The following parameters may be set for the virsh setvcpus command:
  • {domain-name, domain-id or domain-uuid} - Specifies the virtual machine.
  • --count - Specifies the number of virtual CPUs to set.

    Important

    The --count value cannot exceed the number of CPUs that were assigned to the guest virtual machine when it was created.
  • --maximum - Sets a maximum virtual CPU limit on the next reboot.
  • --config - Configuration change takes effect on the next reboot.
  • --live - Configuration change takes effect on the running guest virtual machine.
  • --current - Configuration change takes effect on the current guest virtual machine.
  • --guest - Configuration change modifies the CPU state in the guest virtual machine. Configurations set with --guest are reset when a guest is rebooted.

Note

For information on increasing vCPU performance by using multi-queue, refer to the Red Hat Enterprise Linux Virtualization Tuning and Optimization Guide.

Example 15.4. Hotplug and hot-unplug of vCPU

To hotplug a vCPU, run the following command:
virsh setvcpus guestVM1 2 --live
In the above case, the number of vCPUs for guestVM1 is increased by two and this action will be performed while the guestVM1 is running, as indicated by the --live flag.
Likewise, to hot-unplug one vCPU from the same running guest, run the following:
virsh setvcpus guestVM1 1 --live
The count value may be limited by the host, hypervisor, or a limit coming from the original description of the guest domain. For Xen, you can only adjust the virtual CPUs of a running domain if the domain is para-virtualized.
If the --config flag is specified, the change is made to the stored XML configuration for the guest virtual machine domain, and will only take effect the next time the guest domain is started.
If --live is specified, the guest virtual machine domain must be active, and the change takes place immediately. This flag will allow hotplugging of a vCPU. Both the --config and --live flags may be specified together if supported by the hypervisor.
If --current is specified, the flag affects the current active guest virtual machine's state. When no flags are given, the --live flag is used by default. Should this command run without a flag when there are no active guest virtual machines, it will fail. In some cases, the hypervisor will also assume the use of the --config. The hypervisor will also decide if the XML configuration is adjusted to make the change persistent.
The --maximum flag controls the maximum number of virtual CPUs that can be hotplugged the next time the domain is booted. As such, it must only be used with the --config flag, and not with the --live flag.

15.13.7. Configuring memory allocation

To modify a guest virtual machine's memory allocation with virsh:
# virsh setmem {domain-id or domain-name} count
# virsh setmem vr-rhel6u1-x86_64-kvm --kilobytes 1025000
You must specify the count in kilobytes. The new count value cannot exceed the amount you specified when you created the guest virtual machine. Values lower than 64 MB are unlikely to work with most guest virtual machine operating systems. A higher maximum memory value does not affect active guest virtual machines. If the new value is lower than the available memory, it will shrink possibly causing the guest virtual machine to crash.
This command has the following flags:
  • [--domain] <string> domain name, id or uuid
  • [--size] <number> new memory size, as scaled integer (default KiB)
    Valid memory units include:
    • b or bytes for bytes
    • KB for kilobytes (103 or blocks of 1,000 bytes)
    • k or KiB for kibibytes (210 or blocks of 1024 bytes)
    • MB for megabytes (106 or blocks of 1,000,000 bytes)
    • M or MiB for mebibytes (220 or blocks of 1,048,576 bytes)
    • GB for gigabytes (109 or blocks of 1,000,000,000 bytes)
    • G or GiB for gibibytes (230 or blocks of 1,073,741,824 bytes)
    • TB for terabytes (1012 or blocks of 1,000,000,000,000 bytes)
    • T or TiB for tebibytes (240 or blocks of 1,099,511,627,776 bytes)
    Note that all values will be rounded up to the nearest kibibyte by libvirt, and may be further rounded to the granularity supported by the hypervisor. Some hypervisors also enforce a minimum, such as 4000KiB (or 4000 x 210 or 4,096,000 bytes). The units for this value are determined by the optional attribute memory unit, which defaults to the kibibytes (KiB) as a unit of measure where the value given is multiplied by 210 or blocks of 1024 bytes.
  • --config takes affect next boot
  • --live controls the memory of the running domain
  • --current controls the memory on the current domain

15.13.8. Changing the memory allocation for the domain

The virsh setmaxmem domain size --config --live --current allows the setting of the maximum memory allocation for a guest virtual machine as shown:
virsh setmaxmem rhel6 1024 --current
The size that can be given for the maximum memory is a scaled integer that by default is expressed in kibibytes, unless a supported suffix is provided. The following options can be used with this command:
  • --config - takes affect next boot
  • --live - controls the memory of the running domain, providing the hypervisor supports this action as not all hypervisors allow live changes of the maximum memory limit.
  • --current - controls the memory on the current domain

15.13.9. Displaying guest virtual machine block device information

Use virsh domblkstat to display block device statistics for a running guest virtual machine.
# virsh domblkstat GuestName block-device

15.13.10. Displaying guest virtual machine network device information

Use virsh domifstat to display network interface statistics for a running guest virtual machine.
# virsh domifstat GuestName interface-device 

15.14. Managing virtual networks

This section covers managing virtual networks with the virsh command. To list virtual networks:
# virsh net-list
This command generates output similar to:
# virsh net-list
Name                 State      Autostart
-----------------------------------------
default              active     yes      
vnet1	             active     yes      
vnet2	             active     yes
To view network information for a specific virtual network:
# virsh net-dumpxml NetworkName
This displays information about a specified virtual network in XML format:
# virsh net-dumpxml vnet1
<network>
  <name>vnet1</name>
  <uuid>98361b46-1581-acb7-1643-85a412626e70</uuid>
  <forward dev='eth0'/>
  <bridge name='vnet0' stp='on' forwardDelay='0' />
  <ip address='192.168.100.1' netmask='255.255.255.0'>
    <dhcp>
      <range start='192.168.100.128' end='192.168.100.254' />
    </dhcp>
  </ip>
</network>
Other virsh commands used in managing virtual networks are:
  • virsh net-autostart network-name — Autostart a network specified as network-name.
  • virsh net-create XMLfile — generates and starts a new network using an existing XML file.
  • virsh net-define XMLfile — generates a new network device from an existing XML file without starting it.
  • virsh net-destroy network-name — destroy a network specified as network-name.
  • virsh net-name networkUUID — convert a specified networkUUID to a network name.
  • virsh net-uuid network-name — convert a specified network-name to a network UUID.
  • virsh net-start nameOfInactiveNetwork — starts an inactive network.
  • virsh net-undefine nameOfInactiveNetwork — removes the definition of an inactive network.

15.15. Migrating guest virtual machines with virsh

Information on migration using virsh is located in the section entitled Live KVM Migration with virsh Refer to Section 5.4, “Live KVM migration with virsh”

15.15.1. Interface Commands

The following commands manipulate host interfaces and as such should not be run from the guest virtual machine. These commands should be run from a terminal on the host physical machine.

Warning

The commands in this section are only supported if the machine has the NetworkManager service disabled, and is using the network service instead.
Often, these host interfaces can then be used by name within domain <interface> elements (such as a system-created bridge interface), but there is no requirement that host interfaces be tied to any particular guest configuration XML at all. Many of the commands for host interfaces are similar to the ones used for domains, and the way to name an interface is either by its name or its MAC address. However, using a MAC address for an iface option only works when that address is unique (if an interface and a bridge share the same MAC address, which is often the case, then using that MAC address results in an error due to ambiguity, and you must resort to a name instead).

15.15.1.1. Defining and starting a host physical machine interface via an XML file

The virsh iface-define file command define a host interface from an XML file. This command will only define the interface and will not start it.
virsh iface-define iface.xml
To start an interface which has already been defined, run iface-start interface, where interface is the interface name.

15.15.1.2. Editing the XML configuration file for the host interface

The command iface-edit interface edits the XML configuration file for a host interface. This is the only recommended way to edit the XML configuration file. (Refer to Chapter 21, Manipulating the domain xml for more information about these files.)

15.15.1.3. Listing active host interfaces

The iface-list --inactive --all displays a list of active host interfaces. If --all is specified, this list will also include interfaces that are defined but are inactive. If --inactive is specified only the inactive interfaces will be listed.

15.15.1.4. Converting a MAC address into an interface name

The iface-name interface command converts a host interface MAC to an interface name, provided the MAC address is unique among the host’s interfaces. This command requires interface which is the interface's MAC address.
The iface-mac interface command will convert a host's interface name to MAC address where in this case interface, is the interface name.

15.15.1.5. Stopping a specific host physical machine interface

The virsh iface-destroy interface command destroys (stops) a given host interface, which is the same as running if-down on the host. This command will disable that interface from active use and takes effect immediately.
To undefine the interface, use the iface-undefine interface command along with the interface name.

15.15.1.6. Displaying the host configuration file

virsh iface-dumpxml interface --inactive displays the host interface information as an XML dump to stdout. If the --inactive option is specified, then the output reflects the persistent state of the interface that will be used the next time it is started.

15.15.1.7. Creating bridge devices

The iface-bridge creates a bridge device named bridge, and attaches the existing network device interface to the new bridge, which starts working immediately, with STP enabled and a delay of 0.
# virsh iface-bridge interface bridge --no-stp delay --no-start
Note that these settings can be altered with --no-stp, --no-start, and an integer number of seconds for delay. All IP address configuration of interface will be moved to the new bridge device. Refer to Section 15.15.1.8, “Tearing down a bridge device” for information on tearing down the bridge.

15.15.1.8. Tearing down a bridge device

The iface-unbridge bridge --no-start command tears down a specified bridge device named bridge, releases its underlying interface back to normal usage, and moves all IP address configuration from the bridge device to the underlying device. The underlying interface is restarted unless --no-start option is used, but keep in mind not restarting is generally not recommended. Refer to Section 15.15.1.7, “Creating bridge devices” for the command to use to create a bridge.

15.15.1.9. Manipulating interface snapshots

The iface-begin command creates a snapshot of current host interface settings, which can later be committed (with iface-commit) or restored (iface-rollback). If a snapshot already exists, then this command will fail until the previous snapshot has been committed or restored. Undefined behavior will result if any external changes are made to host interfaces outside of the libvirt API between the time of the creation of a snapshot and its eventual commit or rollback.
Use the iface-commit command to declare all changes made since the last iface-begin as working, and then delete the rollback point. If no interface snapshot has already been started via iface-begin, then this command will fail.
Use the iface-rollback to revert all host interface settings back to the state that recorded the last time the iface-begin command was executed. If iface-begin command had not been previously executed, then iface-rollback will fail. Note that rebooting the host physical machine also serves as an implicit rollback point.

15.15.2. Managing snapshots

The sections that follow describe actions that can be done in order to manipulate domain snapshots. Snapshots take the disk, memory, and device state of a domain at a specified point-in-time, and save it for future use. Snapshots have many uses, from saving a "clean" copy of an OS image to saving a domain’s state before what may be a potentially destructive operation. Snapshots are identified with a unique name. See the libvirt website for documentation of the XML format used to represent properties of snapshots.

15.15.2.1. Creating Snapshots

The virsh snapshot create command creates a snapshot for domain with the properties specified in the domain XML file (such as <name> and <description> elements, as well as <disks>).
To create a snapshot, run:
# snapshot-create <domain> <xmlfile> [--redefine] [--current] [--no-metadata] [--reuse-external] 
The domain name, ID, or UID may be used as the domain requirement. The XML requirement is a string must contain the <name>, <description> and <disks> elements.

Note

Live snapshots are not supported in Red Hat Enterprise Linux. There are additional options available with the virsh snapshot create command for use with live snapshots which are visible in libvirt, but not supported in Red Hat Enterprise Linux 6.
The options available in Red Hat Enterprise Linux include:
  • --redefine specifies that if all XML elements produced by snapshot-dumpxml are valid; it can be used to migrate snapshot hierarchy from one machine to another, to recreate hierarchy for the case of a transient domain that goes away and is later recreated with the same name and UUID, or to make slight alterations in the snapshot metadata (such as host-specific aspects of the domain XML embedded in the snapshot). When this flag is supplied, the xmlfile argument is mandatory, and the domain’s current snapshot will not be altered unless the --current flag is also given.
  • --no-metadata creates the snapshot, but any metadata is immediately discarded (that is, libvirt does not treat the snapshot as current, and cannot revert to the snapshot unless --redefine is later used to teach libvirt about the metadata again).
  • --reuse-external, if used, this option specifies the location of an existing external XML snapshot to use. If an existing external snapshot does not already exist, the command will fail to take a snapshot to avoid losing contents of the existing files.

15.15.2.2. Creating a snapshot for the current domain

The virsh snapshot-create-as domain command creates a snapshot for the domain with the properties specified in the domain XML file (such as <name> and <description> elements). If these values are not included in the XML string, libvirt will choose a value. To create a snapshot run:
# virsh snapshot-create-as domain {[--print-xml] | [--no-metadata] [--reuse-external]} [name] [description] [--diskspec] diskspec]
The remaining options are as follows:
  • --print-xml creates appropriate XML for snapshot-create as output, rather than actually creating a snapshot.
  • --diskspec option can be used to control how --disk-only and external checkpoints create external files. This option can occur multiple times, according to the number of <disk> elements in the domain XML. Each <diskspec> is in the form disk[,snapshot=type][,driver=type][,file=name]. To include a literal comma in disk or in file=name, escape it with a second comma. A literal --diskspec must precede each diskspec unless all three of <domain>, <name>, and <description> are also present. For example, a diskspec of vda,snapshot=external,file=/path/to,,new results in the following XML:
    
    <disk name=’vda’ snapshot=’external’>
       <source file=’/path/to,new’/>
    </disk>
    
  • --reuse-external creates an external snapshot reusing an existing file as the destination (meaning this file is overwritten). If this destination does not exist, the snapshot request will be refused to avoid losing contents of the existing files.
  • --no-metadata creates snapshot data but any metadata is immediately discarded (that is, libvirt does not treat the snapshot as current, and cannot revert to the snapshot unless snapshot-create is later used to teach libvirt about the metadata again). This flag is incompatible with --print-xml.

15.15.2.3. Taking a snapshot of the current domain

This command is used to query which snapshot is currently in use. To use, run:
# virsh snapshot-current domain {[--name] | [--security-info] | [snapshotname]}
If snapshotname is not used, snapshot XML for the domain’s current snapshot (if there is one) will be displayed as output. If --name is specified, just the current snapshot name instead of the full XML will be sent as output. If --security-info is supplied, security sensitive information will be included in the XML. Using snapshotname, libvirt generates a request to make the existing named snapshot become the current snapshot, without reverting it to the domain.

15.15.2.4. snapshot-edit-domain

This command is used to edit the snapshot that is currently in use. To use, run:
#virsh snapshot-edit domain [snapshotname] [--current] {[--rename] [--clone]}
If both snapshotname and --current are specified, it forces the edited snapshot to become the current snapshot. If snapshotname is omitted, then --current must be supplied, in order to edit the current snapshot.
This is equivalent to the following command sequence below, but it also includes some error checking:
# virsh snapshot-dumpxml dom name > snapshot.xml
# vi snapshot.xml [note - this can be any editor]
# virsh snapshot-create dom snapshot.xml --redefine [--current]
If --rename is specified, then the resulting edited file gets saved in a different file name. If --clone is specified, then changing the snapshot name will create a clone of the snapshot metadata. If neither is specified, then the edits will not change the snapshot name. Note that changing a snapshot name must be done with care, since the contents of some snapshots, such as internal snapshots within a single qcow2 file, are accessible only from the original snapshot filename.

15.15.2.5. snapshot-info-domain

snapshot-info-domain displays information about the snapshots. To use, run:
# snapshot-info domain {snapshot | --current}
Outputs basic information about a specified snapshot , or the current snapshot with --current.

15.15.2.6. snapshot-list-domain

List all of the available snapshots for the given domain, defaulting to show columns for the snapshot name, creation time, and domain state. To use, run:
#virsh snapshot-list domain [{--parent | --roots | --tree}] [{[--from] snapshot | --current} [--descendants]] [--metadata] [--no-metadata] [--leaves] [--no-leaves] [--inactive] [--active] [--internal] [--external]
The remaining optional options are as follows:
  • --parent adds a column to the output table giving the name of the parent of each snapshot. This option may not be used with --roots or --tree.
  • --roots filters the list to show only the snapshots that have no parents. This option may not be used with --parent or --tree.
  • --tree displays output in a tree format, listing just snapshot names. These three options are mutually exclusive. This option may not be used with --roots or --parent.
  • --from filters the list to snapshots which are children of the given snapshot; or if --current is provided, will cause the list to start at the current snapshot. When used in isolation or with --parent, the list is limited to direct children unless --descendants is also present. When used with --tree, the use of --descendants is implied. This option is not compatible with --roots. Note that the starting point of --from or --current is not included in the list unless the --tree option is also present.
  • --leaves is specified, the list will be filtered to just snapshots that have no children. Likewise, if --no-leaves is specified, the list will be filtered to just snapshots with children. (Note that omitting both options does no filtering, while providing both options will either produce the same list or error out depending on whether the server recognizes the flags) Filtering options are not compatible with --tree..
  • --metadata is specified, the list will be filtered to just snapshots that involve libvirt metadata, and thus would prevent the undefining of a persistent domain, or be lost on destroy of a transient domain. Likewise, if --no-metadata is specified, the list will be filtered to just snapshots that exist without the need for libvirt metadata.
  • --inactive is specified, the list will be filtered to snapshots that were taken when the domain was shut off. If --active is specified, the list will be filtered to snapshots that were taken when the domain was running, and where the snapshot includes the memory state to revert to that running state. If --disk-only is specified, the list will be filtered to snapshots that were taken when the domain was running, but where the snapshot includes only disk state.
  • --internal is specified, the list will be filtered to snapshots that use internal storage of existing disk images. If --external is specified, the list will be filtered to snapshots that use external files for disk images or memory state.

15.15.2.7. snapshot-dumpxml domain snapshot

virsh snapshot-dumpxml domain snapshot outputs the snapshot XML for the domain’s snapshot named snapshot. To use, run:
# virsh snapshot-dumpxml domain snapshot [--security-info]
The --security-info option will also include security sensitive information. Use snapshot-current to easily access the XML of the current snapshot.

15.15.2.8. snapshot-parent domain

Outputs the name of the parent snapshot, if any, for the given snapshot, or for the current snapshot with --current. To use, run:
#virsh snapshot-parent domain {snapshot | --current}

15.15.2.9. snapshot-revert domain

Reverts the given domain to the snapshot specified by snapshot, or to the current snapshot with --current.

Warning

Be aware that this is a destructive action; any changes in the domain since the last snapshot was taken will be lost. Also note that the state of the domain after snapshot-revert is complete will be the state of the domain at the time the original snapshot was taken.
To revert the snapshot, run
# snapshot-revert domain {snapshot | --current} [{--running | --paused}] [--force]
Normally, reverting to a snapshot leaves the domain in the state it was at the time the snapshot was created, except that a disk snapshot with no guest virtual machine state leaves the domain in an inactive state. Passing either the --running or --paused flag will perform additional state changes (such as booting an inactive domain, or pausing a running domain). Since transient domains cannot be inactive, it is required to use one of these flags when reverting to a disk snapshot of a transient domain.
There are two cases where a snapshot revert involves extra risk, which requires the use of --force to proceed. One is the case of a snapshot that lacks full domain information for reverting configuration; since libvirt cannot prove that the current configuration matches what was in use at the time of the snapshot, supplying --force assures libvirt that the snapshot is compatible with the current configuration (and if it is not, the domain will likely fail to run). The other is the case of reverting from a running domain to an active state where a new hypervisor has to be created rather than reusing the existing hypervisor, because it implies drawbacks such as breaking any existing VNC or Spice connections; this condition happens with an active snapshot that uses a provably incompatible configuration, as well as with an inactive snapshot that is combined with the --start or --pause flag.

15.15.2.10. snapshot-delete domain

snapshot-delete domain deletes the snapshot for the specified domain. To do this, run:
# virsh snapshot-delete domain {snapshot | --current} [--metadata] [{--children | --children-only}]
This command Deletes the snapshot for the domain named snapshot, or the current snapshot with --current. If this snapshot has child snapshots, changes from this snapshot will be merged into the children. If the option --children is used, then it will delete this snapshot and any children of this snapshot. If --children-only is used, then it will delete any children of this snapshot, but leave this snapshot intact. These two flags are mutually exclusive.
The --metadata is used it will delete the snapshot's metadata maintained by libvirt, while leaving the snapshot contents intact for access by external tools; otherwise deleting a snapshot also removes its data contents from that point in time.

15.16. Guest virtual machine CPU model configuration

15.16.1. Introduction

Every hypervisor has its own policy for what a guest virtual machine will see for its CPUs by default. Whereas some hypervisors decide which CPU host physical machine features will be available for the guest virtual machine, QEMU/KVM presents the guest virtual machine with a generic model named qemu32 or qemu64. These hypervisors perform more advanced filtering, classifying all physical CPUs into a handful of groups and have one baseline CPU model for each group that is presented to the guest virtual machine. Such behavior enables the safe migration of guest virtual machines between host physical machines, provided they all have physical CPUs that classify into the same group. libvirt does not typically enforce policy itself, rather it provides the mechanism on which the higher layers define their own desired policy. Understanding how to obtain CPU model information and define a suitable guest virtual machine CPU model is critical to ensure guest virtual machine migration is successful between host physical machines. Note that a hypervisor can only emulate features that it is aware of and features that were created after the hypervisor was released may not be emulated.

15.16.2. Learning about the host physical machine CPU model

The virsh capabilities command displays an XML document describing the capabilities of the hypervisor connection and host physical machine. The XML schema displayed has been extended to provide information about the host physical machine CPU model. One of the big challenges in describing a CPU model is that every architecture has a different approach to exposing their capabilities. On x86, the capabilities of a modern CPU are exposed via the CPUID instruction. Essentially this comes down to a set of 32-bit integers with each bit given a specific meaning. Fortunately AMD and Intel agree on common semantics for these bits. Other hypervisors expose the notion of CPUID masks directly in their guest virtual machine configuration format. However, QEMU/KVM supports far more than just the x86 architecture, so CPUID is clearly not suitable as the canonical configuration format. QEMU ended up using a scheme which combines a CPU model name string, with a set of named flags. On x86, the CPU model maps to a baseline CPUID mask, and the flags can be used to then toggle bits in the mask on or off. libvirt decided to follow this lead and uses a combination of a model name and flags.
It is not practical to have a database listing all known CPU models, so libvirt has a small list of baseline CPU model names. It chooses the one that shares the greatest number of CPUID bits with the actual host physical machine CPU and then lists the remaining bits as named features. Notice that libvirt does not display which features the baseline CPU contains. This might seem like a flaw at first, but as will be explained in this section, it is not actually necessary to know this information.

15.16.3. Determining a compatible CPU model to suit a pool of host physical machines

Now that it is possible to find out what CPU capabilities a single host physical machine has, the next step is to determine what CPU capabilities are best to expose to the guest virtual machine. If it is known that the guest virtual machine will never need to be migrated to another host physical machine, the host physical machine CPU model can be passed straight through unmodified. A virtualized data center may have a set of configurations that can guarantee all servers will have 100% identical CPUs. Again the host physical machine CPU model can be passed straight through unmodified. The more common case, though, is where there is variation in CPUs between host physical machines. In this mixed CPU environment, the lowest common denominator CPU must be determined. This is not entirely straightforward, so libvirt provides an API for exactly this task. If libvirt is provided a list of XML documents, each describing a CPU model for a host physical machine, libvirt will internally convert these to CPUID masks, calculate their intersection, and convert the CPUID mask result back into an XML CPU description.
Here is an example of what libvirt reports as the capabilities on a basic workstation, when the virsh capabilitiesis executed:

<capabilities>
  <host>
    <cpu>
      <arch>i686</arch>
      <model>pentium3</model>
      <topology sockets='1' cores='2' threads='1'/>
      <feature name='lahf_lm'/>
      <feature name='lm'/>
      <feature name='xtpr'/>
      <feature name='cx16'/>
      <feature name='ssse3'/>
      <feature name='tm2'/>
      <feature name='est'/>
      <feature name='vmx'/>
      <feature name='ds_cpl'/>
      <feature name='monitor'/>
      <feature name='pni'/>
      <feature name='pbe'/>
      <feature name='tm'/>
      <feature name='ht'/>
      <feature name='ss'/>
      <feature name='sse2'/>
      <feature name='acpi'/>
      <feature name='ds'/>
      <feature name='clflush'/>
      <feature name='apic'/>
    </cpu>
 </host>
</capabilities>

Figure 15.3. Pulling host physical machine's CPU model information

Now compare that to any random server, with the same virsh capabilities command:

<capabilities>
  <host>
    <cpu>
      <arch>x86_64</arch>
      <model>phenom</model>
      <topology sockets='2' cores='4' threads='1'/>
      <feature name='osvw'/>
      <feature name='3dnowprefetch'/>
      <feature name='misalignsse'/>
      <feature name='sse4a'/>
      <feature name='abm'/>
      <feature name='cr8legacy'/>
      <feature name='extapic'/>
      <feature name='cmp_legacy'/>
      <feature name='lahf_lm'/>
      <feature name='rdtscp'/>
      <feature name='pdpe1gb'/>
      <feature name='popcnt'/>
      <feature name='cx16'/>
      <feature name='ht'/>
      <feature name='vme'/>
    </cpu>
    ...snip...

Figure 15.4. Generate CPU description from a random server

To see if this CPU description is compatible with the previous workstation CPU description, use the virsh cpu-compare command.
The reduced content was stored in a file named virsh-caps-workstation-cpu-only.xml and the virsh cpu-compare command can be executed on this file:
# virsh cpu-compare virsh-caps-workstation-cpu-only.xml
Host physical machine CPU is a superset of CPU described in virsh-caps-workstation-cpu-only.xml
As seen in this output, libvirt is correctly reporting that the CPUs are not strictly compatible. This is because there are several features in the server CPU that are missing in the client CPU. To be able to migrate between the client and the server, it will be necessary to open the XML file and comment out some features. To determine which features need to be removed, run the virsh cpu-baseline command, on the both-cpus.xml which contains the CPU information for both machines. Running # virsh cpu-baseline both-cpus.xml, results in:

<cpu match='exact'>
  <model>pentium3</model>
  <feature policy='require' name='lahf_lm'/>
  <feature policy='require' name='lm'/>
  <feature policy='require' name='cx16'/>
  <feature policy='require' name='monitor'/>
  <feature policy='require' name='pni'/>
  <feature policy='require' name='ht'/>
  <feature policy='require' name='sse2'/>
  <feature policy='require' name='clflush'/>
  <feature policy='require' name='apic'/>
</cpu>

Figure 15.5. Composite CPU baseline

This composite file shows which elements are in common. Everything that is not in common should be commented out.

15.17. Configuring the guest virtual machine CPU model

For simple defaults, the guest virtual machine CPU configuration accepts the same basic XML representation as the host physical machine capabilities XML exposes. In other words, the XML from the cpu-baseline virsh command can now be copied directly into the guest virtual machine XML at the top level under the <domain> element. In the previous XML snippet, there are a few extra attributes available when describing a CPU in the guest virtual machine XML. These can mostly be ignored, but for the curious here is a quick description of what they do. The top level <cpu> element has an attribute called match with possible values of:
  • match='minimum' - the host physical machine CPU must have at least the CPU features described in the guest virtual machine XML. If the host physical machine has additional features beyond the guest virtual machine configuration, these will also be exposed to the guest virtual machine.
  • match='exact' - the host physical machine CPU must have at least the CPU features described in the guest virtual machine XML. If the host physical machine has additional features beyond the guest virtual machine configuration, these will be masked out from the guest virtual machine.
  • match='strict' - the host physical machine CPU must have exactly the same CPU features described in the guest virtual machine XML.
The next enhancement is that the <feature> elements can each have an extra 'policy' attribute with possible values of:
  • policy='force' - expose the feature to the guest virtual machine even if the host physical machine does not have it. This is usually only useful in the case of software emulation.
  • policy='require' - expose the feature to the guest virtual machine and fail if the host physical machine does not have it. This is the sensible default.
  • policy='optional' - expose the feature to the guest virtual machine if it happens to support it.
  • policy='disable' - if the host physical machine has this feature, then hide it from the guest virtual machine.
  • policy='forbid' - if the host physical machine has this feature, then fail and refuse to start the guest virtual machine.
The 'forbid' policy is for a niche scenario where an incorrectly functioning application will try to use a feature even if it is not in the CPUID mask, and you wish to prevent accidentally running the guest virtual machine on a host physical machine with that feature. The 'optional' policy has special behavior with respect to migration. When the guest virtual machine is initially started the flag is optional, but when the guest virtual machine is live migrated, this policy turns into 'require', since you cannot have features disappearing across migration.

15.18. Managing resources for guest virtual machines

virsh allows the grouping and allocation of resources on a per guest virtual machine basis. This is managed by the libvirt daemon which creates cgroups and manages them on behalf of the guest virtual machine. The only thing that is left for the system administrator to do is to either query or set tunables against specified guest virtual machines. The following tunables may used:
  • memory - The memory controller allows for setting limits on RAM and swap usage and querying cumulative usage of all processes in the group
  • cpuset - The CPU set controller binds processes within a group to a set of CPUs and controls migration between CPUs.
  • cpuacct - The CPU accounting controller provides information about CPU usage for a group of processes.
  • cpu -The CPU scheduler controller controls the prioritization of processes in the group. This is similar to granting nice level privileges.
  • devices - The devices controller grants access control lists on character and block devices.
  • freezer - The freezer controller pauses and resumes execution of processes in the group. This is similar to SIGSTOP for the whole group.
  • net_cls - The network class controller manages network utilization by associating processes with a tc network class.
In creating a group hierarchy cgroup will leave mount point and directory setup entirely to the administrators’ discretion and is more complex than just adding some mount points to /etc/fstab. It is necessary to setup the directory hierarchy and decide how processes get placed within it. This can be done with the following virsh commands:

15.19. Setting schedule parameters

schedinfo allows scheduler parameters to be passed to guest virtual machines. The following command format should be used:
#virsh schedinfo domain --set --weight --cap --current --config --live
Each parameter is explained below:
  • domain - this is the guest virtual machine domain
  • --set - the string placed here is the controller or action that is to be called. Additional parameters or values if required should be added as well.
  • --current - when used with --set, will use the specified set string as the current scheduler information. When used without will display the current scheduler information.
  • --config - - when used with --set, will use the specified set string on the next reboot. When used without will display the scheduler information that is saved in the configuration file.
  • --live - when used with --set, will use the specified set string on a guest virtual machine that is currently running. When used without will display the configuration setting currently used by the running virtual machine
The scheduler can be set with any of the following parameters: cpu_shares, vcpu_period and vcpu_quota.

Example 15.5. schedinfo show

This example shows the shell guest virtual machine's schedule information
# virsh schedinfo shell
Scheduler      : posix
cpu_shares     : 1024
vcpu_period    : 100000
vcpu_quota     : -1

Example 15.6. schedinfo set

In this example, the cpu_shares is changed to 2046. This effects the current state and not the configuration file.
# virsh schedinfo --set cpu_shares=2046 shell
Scheduler      : posix
cpu_shares     : 2046
vcpu_period    : 100000
vcpu_quota     : -1

15.20. Disk I/O throttling

virsh blkdeviotune sets disk I/O throttling for a specified guest virtual machine. This can prevent a guest virtual machine from over utilizing shared resources and thus impacting the performance of other guest virtual machines. The following format should be used:
# virsh blkdeviotune <domain> <device> [[--config] [--live] | [--current]] [[total-bytes-sec] | [read-bytes-sec] [write-bytes-sec]] [[total-iops-sec] [read-iops-sec] [write-iops-sec]]
The only required parameter is the domain name of the guest virtual machine. To list the domain name, run the domblklist command. The --config, --live, and --current options function the same as in Section 15.19, “Setting schedule parameters”. If no limit is specified, it will query current I/O limits setting. Otherwise, alter the limits with the following flags:
  • --total-bytes-sec - specifies total throughput limit in bytes per second.
  • --read-bytes-sec - specifies read throughput limit in bytes per second.
  • --write-bytes-sec - specifies write throughput limit in bytes per second.
  • --total-iops-sec - specifies total I/O operations limit per second.
  • --read-iops-sec - specifies read I/O operations limit per second.
  • --write-iops-sec - specifies write I/O operations limit per second.
For more information refer to the blkdeviotune section of the virsh MAN page. For an example domain XML refer to Figure 21.23, “Devices - Hard drives, floppy disks, CDROMs”.

15.21. Display or set block I/O parameters

blkiotune sets and or displays the I/O parameters for a specified guest virtual machine. The following format should be used:
# virsh blkiotune domain [--weight weight] [--device-weights device-weights] [[--config] [--live] | [--current]]
More information on this command can be found in the Virtualization Tuning and Optimization Guide

15.22. Configuring memory Tuning

The virsh memtune virtual_machine --parameter size is covered in the Virtualization Tuning and Opitimization Guide.

15.23. Virtual Networking Commands

The following commands manipulate virtual networks. libvirt has the capability to define virtual networks which can then be used by domains and linked to actual network devices. For more detailed information about this feature see the documentation at libvirt's website . Many of the commands for virtual networks are similar to the ones used for domains, but the way to name a virtual network is either by its name or UUID.

15.23.1. Autostarting a virtual network

This command will configure a virtual network to be started automatically when the guest virtual machine boots. To run this command:
# virsh net-autostart network [--disable]
This command accepts the --disable option which disables the autostart command.

15.23.2. Creating a virtual network from an XML file

This command creates a virtual network from an XML file. Refer to libvirt's website to get a description of the XML network format used by libvirt. In this command file is the path to the XML file. To create the virtual network from an XML file, run:
# virsh net-create file

15.23.3. Defining a virtual network from an XML file

This command defines a virtual network from an XML file, the network is just defined but not instantiated. To define the virtual network, run:
# net-define file

15.23.4. Stopping a virtual network

This command destroys (stops) a given virtual network specified by its name or UUID. This takes effect immediately. To stop the specified network network is required.
# net-destroy network

15.23.5. Creating a dump file

This command outputs the virtual network information as an XML dump to stdout for the specified virtual network. If --inactive is specified, then physical functions are not expanded into their associated virtual functions. To create the dump file, run:
# virsh net-dumpxml network [--inactive]

15.23.6. Editing a virtual network's XML configuration file

The following command edits the XML configuration file for a network. This is equivalent to:
#virsh net-dumpxml --inactive network > network.xml
vi network.xml (or make changes with your other text editor)
virsh net-define network.xml
except that it does some error checking. The editor used can be supplied by the $VISUAL or $EDITOR environment variables, and defaults to "vi". To edit the network, run:
#virsh net-edit network

15.23.7. Getting information about a virtual network

This command returns basic information about the network object. To get the network information, run:
# virsh net-info network

15.23.8. Listing information about a virtual network

Returns the list of active networks, if --all is specified this will also include defined but inactive networks, if --inactive is specified only the inactive ones will be listed. You may also want to filter the returned networks by --persistent to list the persitent ones, --transient to list the transient ones, --autostart to list the ones with autostart enabled, and --no-autostart to list the ones with autostart disabled.
Note: When talking to older servers, this command is forced to use a series of API calls with an inherent race, where a pool might not be listed or might appear more than once if it changed state between calls while the list was being collected. Newer servers do not have this problem.
To list the virtual networks, run:
# net-list [--inactive | --all] [--persistent] [<--transient>] [--autostart] [<--no-autostart>]

15.23.9. Converting a network UUID to network name

This command converts a network UUID to network name. To do this run:
# virsh net-name network-UUID

15.23.10. Starting a (previously defined) inactive network

This command starts a (previously defined) inactive network. To do this, run:
# virsh net-start network

15.23.11. Undefining the configuration for an inactive network

This command undefines the configuration for an inactive network. To do this, run:
# net-undefine network

15.23.12. Converting a network name to network UUID

This command converts a network name to network UUID. To do this, run:
# virsh net-uuid network-name

15.23.13. Updating an existing network definition file

This command updates the given section of an existing network definition, taking effect immediately, without needing to destroy and re-start the network. This command is one of "add-first", "add-last", "add" (a synonym for add-last), "delete", or "modify". section is one of ""bridge", "domain", "ip", "ip-dhcp-host", "ip-dhcp-range", "forward", "forward-interface", "forward-pf", "portgroup", "dns-host", "dns-txt", or "dns-srv", each section being named by a concatenation of the xml element hierarchy leading to the element being changed. For example, "ip-dhcp-host" will change a <host> element that is contained inside a <dhcp> element inside an <ip> element of the network. xml is either the text of a complete xml element of the type being changed (e.g. "<host mac="00:11:22:33:44:55’ ip=’192.0.2.1’/>", or the name of a file that contains a complete xml element. Disambiguation is done by looking at the first character of the provided text - if the first character is "<", it is xml text, if the first character is not ">", it is the name of a file that contains the xml text to be used. The --parent-index option is used to specify which of several parent elements the requested element is in (0-based). For example, a dhcp <host> element could be in any one of multiple <ip> elements in the network; if a parent-index isn’t provided, the "most appropriate" <ip> element will be selected (usually the only one that already has a <dhcp> element), but if --parent-index is given, that particular instance of <ip> will get the modification. If --live is specified, affect a running network. If --config is specified, affect the next startup of a persistent network. If -- current is specified, affect the current network state. Both --live and --config flags may be given, but --current is exclusive. Not specifying any flag is the same as specifying --current.
To update the configuration file, run:
# virsh net-update network command section xml [--parent-index index] [[--live] [--config] | [--current]]

Chapter 16. Managing guests with the Virtual Machine Manager (virt-manager)

This section describes the Virtual Machine Manager (virt-manager) windows, dialog boxes, and various GUI controls.
virt-manager provides a graphical view of hypervisors and guests on your host system and on remote host systems. virt-manager can perform virtualization management tasks, including:
  • defining and creating guests,
  • assigning memory,
  • assigning virtual CPUs,
  • monitoring operational performance,
  • saving and restoring, pausing and resuming, and shutting down and starting guests,
  • links to the textual and graphical consoles, and
  • live and offline migrations.

16.1. Starting virt-manager

To start virt-manager session open the Applications menu, then the System Tools menu and select Virtual Machine Manager (virt-manager).
The virt-manager main window appears.
Starting virt-manager

Figure 16.1. Starting virt-manager

Alternatively, virt-manager can be started remotely using ssh as demonstrated in the following command:
ssh -X host's address
[remotehost]# virt-manager
Using ssh to manage virtual machines and hosts is discussed further in Section 6.1, “Remote management with SSH”.

16.2. The Virtual Machine Manager main window

This main window displays all the running guests and resources used by guests. Select a guest by double clicking the guest's name.
Virtual Machine Manager main window

Figure 16.2. Virtual Machine Manager main window

16.3. The virtual hardware details window

The virtual hardware details window displays information about the virtual hardware configured for the guest. Virtual hardware resources can be added, removed and modified in this window. To access the virtual hardware details window, click on the icon in the toolbar.
The virtual hardware details icon

Figure 16.3. The virtual hardware details icon

Clicking the icon displays the virtual hardware details window.
The virtual hardware details window

Figure 16.4. The virtual hardware details window

16.3.1. Attaching USB devices to a guest virtual machine

Note

In order to attach the USB device to the guest virtual machine, you first must attach it to the host physical machine and confirm that the device is working. If the guest is running, you need to shut it down before proceeding.

Procedure 16.1. Attaching USB devices using Virt-Manager

  1. Open the guest virtual machine's Virtual Machine Details screen.
  2. Click Add Hardware
    Add Hardware Button

    Figure 16.5. Add Hardware Button

  3. In the Add New Virtual Hardware popup, select USB Host Device, select the device you want to attach from the list and Click Finish.
    Add USB Device

    Figure 16.6. Add USB Device

  4. To use the USB device in the guest virtual machine, start the guest virtual machine.

16.4. Virtual Machine graphical console

This window displays a guest's graphical console. Guests can use several different protocols to export their graphical framebuffers: virt-manager supports VNC and SPICE. If your virtual machine is set to require authentication, the Virtual Machine graphical console prompts you for a password before the display appears.
Graphical console window

Figure 16.7. Graphical console window

Note

VNC is considered insecure by many security experts, however, several changes have been made to enable the secure usage of VNC for virtualization on Red Hat enterprise Linux. The guest machines only listen to the local host's loopback address (127.0.0.1). This ensures only those with shell privileges on the host can access virt-manager and the virtual machine through VNC. Although virt-manager is configured to listen to other public network interfaces and alternative methods can be configured, it is not recommended.
Remote administration can be performed by tunneling over SSH which encrypts the traffic. Although VNC can be configured to access remotely without tunneling over SSH, for security reasons, it is not recommended. To remotely administer the guest follow the instructions in: Chapter 6, Remote management of guests. TLS can provide enterprise level security for managing guest and host systems.
Your local desktop can intercept key combinations (for example, Ctrl+Alt+F1) to prevent them from being sent to the guest machine. You can use the Send key menu option to send these sequences. From the guest machine window, click the Send key menu and select the key sequence to send. In addition, from this menu you can also capture the screen output.
SPICE is an alternative to VNC available for Red Hat Enterprise Linux.

16.5. Adding a remote connection

This procedure covers how to set up a connection to a remote system using virt-manager.
  1. To create a new connection open the File menu and select the Add Connection... menu item.
  2. The Add Connection wizard appears. Select the hypervisor. For Red Hat Enterprise Linux 6 systems select QEMU/KVM. Select Local for the local system or one of the remote connection options and click Connect. This example uses Remote tunnel over SSH which works on default installations. For more information on configuring remote connections refer to Chapter 6, Remote management of guests
    Add Connection

    Figure 16.8. Add Connection

  3. Enter the root password for the selected host when prompted.
A remote host is now connected and appears in the main virt-manager window.
Remote host in the main virt-manager window

Figure 16.9. Remote host in the main virt-manager window

16.6. Displaying guest details

You can use the Virtual Machine Monitor to view activity information for any virtual machines on your system.
To view a virtual system's details:
  1. In the Virtual Machine Manager main window, highlight the virtual machine that you want to view.
    Selecting a virtual machine to display

    Figure 16.10. Selecting a virtual machine to display

  2. From the Virtual Machine Manager Edit menu, select Virtual Machine Details.
    Displaying the virtual machine details

    Figure 16.11. Displaying the virtual machine details

    When the Virtual Machine details window opens, there may be a console displayed. Should this happen, click View and then select Details. The Overview window opens first by default. To go back to this window, select Overview from the navigation pane on the left hand side.
    The Overview view shows a summary of configuration details for the guest.
    Displaying guest details overview

    Figure 16.12. Displaying guest details overview

  3. Select Performance from the navigation pane on the left hand side.
    The Performance view shows a summary of guest performance, including CPU and Memory usage.
    Displaying guest performance details

    Figure 16.13. Displaying guest performance details

  4. Select Processor from the navigation pane on the left hand side. The Processor view allows you to view or change the current processor allocation.
    Processor allocation panel

    Figure 16.14. Processor allocation panel

  5. Select Memory from the navigation pane on the left hand side. The Memory view allows you to view or change the current memory allocation.
    Displaying memory allocation

    Figure 16.15. Displaying memory allocation

  6. Each virtual disk attached to the virtual machine is displayed in the navigation pane. Click on a virtual disk to modify or remove it.
    Displaying disk configuration

    Figure 16.16. Displaying disk configuration

  7. Each virtual network interface attached to the virtual machine is displayed in the navigation pane. Click on a virtual network interface to modify or remove it.
    Displaying network configuration

    Figure 16.17. Displaying network configuration

16.7. Performance monitoring

Performance monitoring preferences can be modified with virt-manager's preferences window.
To configure performance monitoring:
  1. From the Edit menu, select Preferences.
    Modifying guest preferences

    Figure 16.18. Modifying guest preferences

    The Preferences window appears.
  2. From the Stats tab specify the time in seconds or stats polling options.
    Configuring performance monitoring

    Figure 16.19. Configuring performance monitoring

16.8. Displaying CPU usage for guests

To view the CPU usage for all guests on your system:
  1. From the View menu, select Graph, then the Guest CPU Usage check box.
    Enabling guest CPU usage statistics graphing

    Figure 16.20. Enabling guest CPU usage statistics graphing

  2. The Virtual Machine Manager shows a graph of CPU usage for all virtual machines on your system.
    Guest CPU usage graph

    Figure 16.21. Guest CPU usage graph

16.9. Displaying CPU usage for hosts

To view the CPU usage for all hosts on your system:
  1. From the View menu, select Graph, then the Host CPU Usage check box.
    Enabling host CPU usage statistics graphing

    Figure 16.22. Enabling host CPU usage statistics graphing

  2. The Virtual Machine Manager shows a graph of host CPU usage on your system.
    Host CPU usage graph

    Figure 16.23. Host CPU usage graph

16.10. Displaying Disk I/O

To view the disk I/O for all virtual machines on your system:
  1. Make sure that the Disk I/O statistics collection is enabled. To do this, from the Edit menu, select Preferences and click the Statstab.
  2. Select the Disk I/O checkbox.
    Enabling Disk I/O

    Figure 16.24. Enabling Disk I/O

  3. To enable the Disk I.O display, from the View menu, select Graph, then the Disk I/O check box.
    Selecting Disk I/O

    Figure 16.25. Selecting Disk I/O

  4. The Virtual Machine Manager shows a graph of Disk I/O for all virtual machines on your system.
    Displaying Disk I/O

    Figure 16.26. Displaying Disk I/O

16.11. Displaying Network I/O

To view the network I/O for all virtual machines on your system:
  1. Make sure that the Network I/O statistics collection is enabled. To do this, from the Edit menu, select Preferences and click the Statstab.
  2. Select the Network I/O checkbox.
    Enabling Network I/O

    Figure 16.27. Enabling Network I/O

  3. To display the Network I/O statistics, from the View menu, select Graph, then the Network I/O check box.
    Selecting Network I/O

    Figure 16.28. Selecting Network I/O

  4. The Virtual Machine Manager shows a graph of Network I/O for all virtual machines on your system.
    Displaying Network I/O

    Figure 16.29. Displaying Network I/O

Chapter 17. Guest virtual machine disk access with offline tools

17.1. Introduction

Red Hat Enterprise Linux 6 comes with tools to access, edit and create host physical machine disks or other disk images. There are several uses for these tools, including:
  • Viewing or downloading files located on a host physical machine disk.
  • Editing or uploading files onto a host physical machine disk.
  • Reading or writing host physical machine configuration.
  • Reading or writing the Windows Registry in Windows host physical machines.
  • Preparing new disk images containing files, directories, file systems, partitions, logical volumes and other options.
  • Rescuing and repairing host physical machines that fail to boot or those that need boot configuration changes.
  • Monitoring disk usage of host physical machines.
  • Auditing compliance of host physical machines, for example to organizational security standards.
  • Deploying host physical machines by cloning and modifying templates.
  • Reading CD and DVD ISO and floppy disk images.

Warning

You must never use these tools to write to a host physical machine or disk image which is attached to a running virtual machine, not even to open such a disk image in write mode. Doing so will result in disk corruption of the guest virtual machine. The tools try to prevent you from doing this, however do not catch all cases. If there is any suspicion that a guest virtual machine might be running, it is strongly recommended that the tools not be used, or at least always use the tools in read-only mode.

17.2. Terminology

This section explains the terms used throughout this chapter.
  • libguestfs (GUEST FileSystem LIBrary) - the underlying C library that provides the basic functionality for opening disk images, reading and writing files and so on. You can write C programs directly to this API, but it is quite low level.
  • guestfish (GUEST Filesystem Interactive SHell) is an interactive shell that you can use from the command line or from shell scripts. It exposes all of the functionality of the libguestfs API.
  • Various virt tools are built on top of libguestfs, and these provide a way to perform specific single tasks from the command line. Tools include virt-df, virt-rescue, virt-resize and virt-edit.
  • hivex and Augeas are libraries for editing the Windows Registry and Linux configuration files respectively. Although these are separate from libguestfs, much of the value of libguestfs comes from the combination of these tools.
  • guestmount is an interface between libguestfs and FUSE. It is primarily used to mount file systems from disk images on your host physical machine. This functionality is not necessary, but can be useful.

17.3. Installation

To install libguestfs, guestfish, the libguestfs tools, guestmount and support for Windows guest virtual machines, subscribe to the RHEL V2WIN channel, go to the Red Hat Website and run the following command:
# yum install libguestfs guestfish libguestfs-tools libguestfs-mount libguestfs-winsupport
To install every libguestfs-related package including the language bindings, run the following command:
# yum install '*guestf*'

17.4. The guestfish shell

guestfish is an interactive shell that you can use from the command line or from shell scripts to access guest virtual machine file systems. All of the functionality of the libguestfs API is available from the shell.
To begin viewing or editing a virtual machine disk image, run the following command, substituting the path to your desired disk image:
guestfish --ro -a /path/to/disk/image
--ro means that the disk image is opened read-only. This mode is always safe but does not allow write access. Only omit this option when you are certain that the guest virtual machine is not running, or the disk image is not attached to a live guest virtual machine. It is not possible to use libguest virtual machinefs to edit a live guest virtual machine, and attempting to will result in irreversible disk corruption.
/path/to/disk/image is the path to the disk. This can be a file, a host physical machine logical volume (such as /dev/VG/LV), a host physical machine device (/dev/cdrom) or a SAN LUN (/dev/sdf3).

Note

libguestfs and guestfish do not require root privileges. You only need to run them as root if the disk image being accessed needs root to read and/or write.
When you start guestfish interactively, it will display this prompt:
 guestfish --ro -a /path/to/disk/image

Welcome to guestfish, the libguestfs filesystem interactive shell for editing virtual machine filesystems.
 
 Type: 'help' for help on commands
       'man' to read the manual
       'quit' to quit the shell
 
><fs>
At the prompt, type run to initiate the library and attach the disk image. This can take up to 30 seconds the first time it is done. Subsequent starts will complete much faster.

Note

libguestfs will use hardware virtualization acceleration such as KVM (if available) to speed up this process.
Once the run command has been entered, other commands can be used, as the following section demonstrates.

17.4.1. Viewing file systems with guestfish

17.4.1.1. Manual listing and viewing

The list-filesystems command will list file systems found by libguestfs. This output shows a Red Hat Enterprise Linux 4 disk image:
><fs> run
><fs> list-filesystems
/dev/vda1: ext3
/dev/VolGroup00/LogVol00: ext3
/dev/VolGroup00/LogVol01: swap
This output shows a Windows disk image:
><fs> run
><fs> list-filesystems
/dev/vda1: ntfs
/dev/vda2: ntfs
Other useful commands are list-devices, list-partitions, lvs, pvs, vfs-type and file. You can get more information and help on any command by typing help command, as shown in the following output:
><fs> help vfs-type
 NAME
    vfs-type - get the Linux VFS type corresponding to a mounted device
 
 SYNOPSIS
     vfs-type device
 
 DESCRIPTION
    This command gets the filesystem type corresponding to the filesystem on
    "device".
 
    For most filesystems, the result is the name of the Linux VFS module
    which would be used to mount this filesystem if you mounted it without
    specifying the filesystem type. For example a string such as "ext3" or
    "ntfs".
To view the actual contents of a file system, it must first be mounted. This example uses one of the Windows partitions shown in the previous output (/dev/vda2), which in this case is known to correspond to the C:\ drive:
><fs> mount-ro /dev/vda2 /
><fs> ll /
total 1834753
 drwxrwxrwx  1 root root       4096 Nov  1 11:40 .
 drwxr-xr-x 21 root root       4096 Nov 16 21:45 ..
 lrwxrwxrwx  2 root root         60 Jul 14  2009 Documents and Settings
 drwxrwxrwx  1 root root       4096 Nov 15 18:00 Program Files
 drwxrwxrwx  1 root root       4096 Sep 19 10:34 Users
 drwxrwxrwx  1 root root      16384 Sep 19 10:34 Windows
You can use guestfish commands such as ls, ll, cat, more, download and tar-out to view and download files and directories.

Note

There is no concept of a current working directory in this shell. Unlike ordinary shells, you cannot for example use the cd command to change directories. All paths must be fully qualified starting at the top with a forward slash (/) character. Use the Tab key to complete paths.
To exit from the guestfish shell, type exit or enter Ctrl+d.

17.4.1.2. Via guestfish inspection

Instead of listing and mounting file systems by hand, it is possible to let guestfish itself inspect the image and mount the file systems as they would be in the guest virtual machine. To do this, add the -i option on the command line:
guestfish --ro -a /path/to/disk/image -i

Welcome to guestfish, the libguestfs filesystem interactive shell for
 editing virtual machine filesystems.
 
 Type: 'help' for help on commands
       'man' to read the manual
       'quit' to quit the shell
 
 Operating system: Red Hat Enterprise Linux AS release 4 (Nahant Update 8)
 /dev/VolGroup00/LogVol00 mounted on /
 /dev/vda1 mounted on /boot
 
 ><fs> ll /
 total 210
 drwxr-xr-x. 24 root root  4096 Oct 28 09:09 .
 drwxr-xr-x  21 root root  4096 Nov 17 15:10 ..
 drwxr-xr-x.  2 root root  4096 Oct 27 22:37 bin
 drwxr-xr-x.  4 root root  1024 Oct 27 21:52 boot
 drwxr-xr-x.  4 root root  4096 Oct 27 21:21 dev
 drwxr-xr-x. 86 root root 12288 Oct 28 09:09 etc
 [etc]
Because guestfish needs to start up the libguestfs back end in order to perform the inspection and mounting, the run command is not necessary when using the -i option. The -i option works for many common Linux and Windows guest virtual machines.

17.4.1.3. Accessing a guest virtual machine by name

A guest virtual machine can be accessed from the command line when you specify its name as known to libvirt (in other words, as it appears in virsh list --all). Use the -d option to access a guest virtual machine by its name, with or without the -i option:
guestfish --ro -d GuestName -i

17.4.2. Modifying files with guestfish

To modify files, create directories or make other changes to a guest virtual machine, first heed the warning at the beginning of this section: your guest virtual machine must be shut down. Editing or changing a running disk with guestfish will result in disk corruption. This section gives an example of editing the /boot/grub/grub.conf file. When you are sure the guest virtual machine is shut down you can omit the --ro flag in order to get write access via a command such as:
guestfish -d RHEL3 -i

Welcome to guestfish, the libguestfs filesystem interactive shell for
 editing virtual machine filesystems.
 
 Type: 'help' for help on commands
       'man' to read the manual
       'quit' to quit the shell
 
 Operating system: Red Hat Enterprise Linux AS release 3 (Taroon Update 9)
 /dev/vda2 mounted on /
 /dev/vda1 mounted on /boot
 
><fs> edit /boot/grub/grub.conf
Commands to edit files include edit, vi and emacs. Many commands also exist for creating files and directories, such as write, mkdir, upload and tar-in.

17.4.3. Other actions with guestfish

You can also format file systems, create partitions, create and resize LVM logical volumes and much more, with commands such as mkfs, part-add, lvresize, lvcreate, vgcreate and pvcreate.

17.4.4. Shell scripting with guestfish

Once you are familiar with using guestfish interactively, according to your needs, writing shell scripts with it may be useful. The following is a simple shell script to add a new MOTD (message of the day) to a guest:
#!/bin/bash -
 set -e
 guestname="$1"
 
 guestfish -d "$guestname" -i <<'EOF'
   write /etc/motd "Welcome to Acme Incorporated."
   chmod 0644 /etc/motd
 EOF

17.4.5. Augeas and libguestfs scripting

Combining libguestfs with Augeas can help when writing scripts to manipulate Linux guest virtual machine configuration. For example, the following script uses Augeas to parse the keyboard configuration of a guest virtual machine, and to print out the layout. Note that this example only works with guest virtual machines running Red Hat Enterprise Linux:
#!/bin/bash -
 set -e
 guestname="$1"
 
 guestfish -d "$1" -i --ro <<'EOF'
   aug-init / 0
   aug-get /files/etc/sysconfig/keyboard/LAYOUT
 EOF
Augeas can also be used to modify configuration files. You can modify the above script to change the keyboard layout:
#!/bin/bash -
 set -e
 guestname="$1"
 
 guestfish -d "$1" -i <<'EOF'
   aug-init / 0
   aug-set /files/etc/sysconfig/keyboard/LAYOUT '"gb"'
   aug-save
 EOF
Note the three changes between the two scripts:
  1. The --ro option has been removed in the second example, giving the ability to write to the guest virtual machine.
  2. The aug-get command has been changed to aug-set to modify the value instead of fetching it. The new value will be "gb" (including the quotes).
  3. The aug-save command is used here so Augeas will write the changes out to disk.

Note

More information about Augeas can be found on the website http://augeas.net.
guestfish can do much more than we can cover in this introductory document. For example, creating disk images from scratch:
guestfish -N fs
Or copying out whole directories from a disk image:
><fs> copy-out /home /tmp/home
For more information see the man page guestfish(1).

17.5. Other commands

This section describes tools that are simpler equivalents to using guestfish to view and edit guest virtual machine disk images.
  • virt-cat is similar to the guestfish download command. It downloads and displays a single file to the guest virtual machine. For example:
    # virt-cat RHEL3 /etc/ntp.conf | grep ^server
     server	    127.127.1.0	      # local clock
    
  • virt-edit is similar to the guestfish edit command. It can be used to interactively edit a single file within a guest virtual machine. For example, you may need to edit the grub.conf file in a Linux-based guest virtual machine that will not boot:
    # virt-edit LinuxGuest /boot/grub/grub.conf
    
    virt-edit has another mode where it can be used to make simple non-interactive changes to a single file. For this, the -e option is used. This command, for example, changes the root password in a Linux guest virtual machine to having no password:
    # virt-edit LinuxGuest /etc/passwd -e 's/^root:.*?:/root::/'
    
  • virt-ls is similar to the guestfish ls, ll and find commands. It is used to list a directory or directories (recursively). For example, the following command would recursively list files and directories under /home in a Linux guest virtual machine:
    # virt-ls -R LinuxGuest /home/ | less
    

17.6. virt-rescue: The rescue shell

17.6.1. Introduction

This section describes virt-rescue, which can be considered analogous to a rescue CD for virtual machines. It boots a guest virtual machine into a rescue shell so that maintenance can be performed to correct errors and the guest virtual machine can be repaired.
There is some overlap between virt-rescue and guestfish. It is important to distinguish their differing uses. virt-rescue is for making interactive, ad-hoc changes using ordinary Linux file system tools. It is particularly suited to rescuing a guest virtual machine that has failed . virt-rescue cannot be scripted.
In contrast, guestfish is particularly useful for making scripted, structured changes through a formal set of commands (the libguestfs API), although it can also be used interactively.

17.6.2. Running virt-rescue

Before you use virt-rescue on a guest virtual machine, make sure the guest virtual machine is not running, otherwise disk corruption will occur. When you are sure the guest virtual machine is not live, enter:
virt-rescue GuestName
(where GuestName is the guest name as known to libvirt), or:
virt-rescue /path/to/disk/image
(where the path can be any file, any logical volume, LUN, or so on) containing a guest virtual machine disk.
You will first see output scroll past, as virt-rescue boots the rescue VM. In the end you will see:
Welcome to virt-rescue, the libguestfs rescue shell.
 
 Note: The contents of / are the rescue appliance.
 You have to mount the guest virtual machine's partitions under /sysroot
 before you can examine them.
 
 bash: cannot set terminal process group (-1): Inappropriate ioctl for device
 bash: no job control in this shell
 ><rescue>
The shell prompt here is an ordinary bash shell, and a reduced set of ordinary Red Hat Enterprise Linux commands is available. For example, you can enter:
><rescue> fdisk -l /dev/vda
The previous command will list disk partitions. To mount a file system, it is suggested that you mount it under /sysroot, which is an empty directory in the rescue machine for the user to mount anything you like. Note that the files under / are files from the rescue VM itself:
><rescue> mount /dev/vda1 /sysroot/
EXT4-fs (vda1): mounted filesystem with ordered data mode. Opts: (null)
><rescue> ls -l /sysroot/grub/
 total 324
 -rw-r--r--. 1 root root     63 Sep 16 18:14 device.map
 -rw-r--r--. 1 root root  13200 Sep 16 18:14 e2fs_stage1_5
 -rw-r--r--. 1 root root  12512 Sep 16 18:14 fat_stage1_5
 -rw-r--r--. 1 root root  11744 Sep 16 18:14 ffs_stage1_5
 -rw-------. 1 root root   1503 Oct 15 11:19 grub.conf
 [...]
When you are finished rescuing the guest virtual machine, exit the shell by entering exit or Ctrl+d.
virt-rescue has many command line options. The options most often used are:
  • --ro: Operate in read-only mode on the guest virtual machine. No changes will be saved. You can use this to experiment with the guest virtual machine. As soon as you exit from the shell, all of your changes are discarded.
  • --network: Enable network access from the rescue shell. Use this if you need to, for example, download RPM or other files into the guest virtual machine.

17.7. virt-df: Monitoring disk usage

17.7.1. Introduction

This section describes virt-df, which displays file system usage from a disk image or a guest virtual machine. It is similar to the Linux df command, but for virtual machines.

17.7.2. Running virt-df

To display file system usage for all file systems found in a disk image, enter the following:
# virt-df /dev/vg_guests/RHEL6
 Filesystem                   1K-blocks       Used  Available  Use%
 RHEL6:/dev/sda1                 101086      10233      85634   11%
 RHEL6:/dev/VolGroup00/LogVol00 7127864    2272744    4493036   32%
(Where /dev/vg_guests/RHEL6 is a Red Hat Enterprise Linux 6 guest virtual machine disk image. The path in this case is the host physical machine logical volume where this disk image is located.)
You can also use virt-df on its own to list information about all of your guest virtual machines (ie. those known to libvirt). The virt-df command recognizes some of the same options as the standard df such as -h (human-readable) and -i (show inodes instead of blocks).
virt-df also works on Windows guest virtual machines:
# virt-df -h
 Filesystem                       Size       Used  Available  Use%
 F14x64:/dev/sda1               484.2M      66.3M     392.9M   14%
 F14x64:/dev/vg_f14x64/lv_root    7.4G       3.0G       4.4G   41%
 RHEL6brewx64:/dev/sda1         484.2M      52.6M     406.6M   11%
 RHEL6brewx64:/dev/vg_rhel6brewx64/lv_root
                                 13.3G       3.4G       9.2G   26%
 Win7x32:/dev/sda1              100.0M      24.1M      75.9M   25%
 Win7x32:/dev/sda2   		 19.9G	     7.4G      12.5G   38%

Note

You can use virt-df safely on live guest virtual machines, since it only needs read-only access. However, you should not expect the numbers to be precisely the same as those from a df command running inside the guest virtual machine. This is because what is on disk will be slightly out of synch with the state of the live guest virtual machine. Nevertheless it should be a good enough approximation for analysis and monitoring purposes.
virt-df is designed to allow you to integrate the statistics into monitoring tools, databases and so on. This allows system administrators to generate reports on trends in disk usage, and alerts if a guest virtual machine is about to run out of disk space. To do this you should use the --csv option to generate machine-readable Comma-Separated-Values (CSV) output. CSV output is readable by most databases, spreadsheet software and a variety of other tools and programming languages. The raw CSV looks like the following:
# virt-df --csv WindowsGuest
 Virtual Machine,Filesystem,1K-blocks,Used,Available,Use%
 Win7x32,/dev/sda1,102396,24712,77684,24.1%
 Win7x32,/dev/sda2,20866940,7786652,13080288,37.3%
For resources and ideas on how to process this output to produce trends and alerts, refer to the following URL: http://virt-tools.org/learning/advanced-virt-df/.

17.8. virt-resize: resizing guest virtual machines offline

17.8.1. Introduction

This section describes virt-resize, a tool for expanding or shrinking guest virtual machines. It only works for guest virtual machines which are offline (shut down). It works by copying the guest virtual machine image and leaving the original disk image untouched. This is ideal because you can use the original image as a backup, however there is a trade-off as you need twice the amount of disk space.

17.8.2. Expanding a disk image

This section demonstrates a simple case of expanding a disk image:
  1. Locate the disk image to be resized. You can use the command virsh dumpxml GuestName for a libvirt guest virtual machine.
  2. Decide on how you wish to expand the guest virtual machine. Run virt-df -h and virt-list-partitions -lh on the guest virtual machine disk, as shown in the following output:
    # virt-df -h /dev/vg_guests/RHEL6
    Filesystem                      Size       Used  Available  Use%
    RHEL6:/dev/sda1                98.7M      10.0M      83.6M   11%
    RHEL6:/dev/VolGroup00/LogVol00  6.8G       2.2G       4.3G   32%
    
    # virt-list-partitions -lh /dev/vg_guests/RHEL6
    /dev/sda1 ext3 101.9M
    /dev/sda2 pv 7.9G
    
This example will demonstrate how to:
  • Increase the size of the first (boot) partition, from approximately 100MB to 500MB.
  • Increase the total disk size from 8GB to 16GB.
  • Expand the second partition to fill the remaining space.
  • Expand /dev/VolGroup00/LogVol00 to fill the new space in the second partition.
  1. Make sure the guest virtual machine is shut down.
  2. Rename the original disk as the backup. How you do this depends on the host physical machine storage environment for the original disk. If it is stored as a file, use the mv command. For logical volumes (as demonstrated in this example), use lvrename:
    # lvrename /dev/vg_guests/RHEL6 /dev/vg_guests/RHEL6.backup
    
  3. Create the new disk. The requirements in this example are to expand the total disk size up to 16GB. Since logical volumes are used here, the following command is used:
    # lvcreate -L 16G -n RHEL6 /dev/vg_guests
    Logical volume "RHEL6" created
    
  4. The requirements from step 2 are expressed by this command:
    # virt-resize \
           /dev/vg_guests/RHEL6.backup /dev/vg_guests/RHEL6 \
           --resize /dev/sda1=500M \
           --expand /dev/sda2 \
           --LV-expand /dev/VolGroup00/LogVol00
    
    The first two arguments are the input disk and output disk. --resize /dev/sda1=500M resizes the first partition up to 500MB. --expand /dev/sda2 expands the second partition to fill all remaining space. --LV-expand /dev/VolGroup00/LogVol00 expands the guest virtual machine logical volume to fill the extra space in the second partition.
    virt-resize describes what it is doing in the output:
    Summary of changes:
       /dev/sda1: partition will be resized from 101.9M to 500.0M
       /dev/sda1: content will be expanded using the 'resize2fs' method
       /dev/sda2: partition will be resized from 7.9G to 15.5G
       /dev/sda2: content will be expanded using the 'pvresize' method
       /dev/VolGroup00/LogVol00: LV will be expanded to maximum size
       /dev/VolGroup00/LogVol00: content will be expanded using the 'resize2fs' method
       Copying /dev/sda1 ...
       [#####################################################]
       Copying /dev/sda2 ...
       [#####################################################]
       Expanding /dev/sda1 using the 'resize2fs' method
       Expanding /dev/sda2 using the 'pvresize' method
       Expanding /dev/VolGroup00/LogVol00 using the 'resize2fs' method
    
  5. Try to boot the virtual machine. If it works (and after testing it thoroughly) you can delete the backup disk. If it fails, shut down the virtual machine, delete the new disk, and rename the backup disk back to its original name.
  6. Use virt-df and/or virt-list-partitions to show the new size:
    # virt-df -h /dev/vg_pin/RHEL6 
       Filesystem                      Size       Used  Available  Use%
       RHEL6:/dev/sda1               484.4M      10.8M     448.6M    3%
       RHEL6:/dev/VolGroup00/LogVol00 14.3G       2.2G      11.4G   16%
    
Resizing guest virtual machines is not an exact science. If virt-resize fails, there are a number of tips that you can review and attempt in the virt-resize(1) man page. For some older Red Hat Enterprise Linux guest virtual machines, you may need to pay particular attention to the tip regarding GRUB.

17.9. virt-inspector: inspecting guest virtual machines

17.9.1. Introduction

virt-inspector is a tool for inspecting a disk image to find out what operating system it contains.

Note

Red Hat Enterprise Linux 6.2 ships with two variations of this program: virt-inspector is the original program as found in Red Hat Enterprise Linux 6.0 and is now deprecated upstream. virt-inspector2 is the same as the new upstream virt-inspector program.

17.9.2. Installation

To install virt-inspector and the documentation, enter the following command:
# yum install libguestfs-tools libguestfs-devel
To process Windows guest virtual machines you must also install libguestfs-winsupport. Refer to Section 17.10.2, “Installation” for details. The documentation, including example XML output and a Relax-NG schema for the output, will be installed in /usr/share/doc/libguestfs-devel-*/ where "*" is replaced by the version number of libguestfs.

17.9.3. Running virt-inspector

You can run virt-inspector against any disk image or libvirt guest virtual machine as shown in the following example:
virt-inspector --xml disk.img > report.xml
Or as shown here:
virt-inspector --xml GuestName > report.xml
The result will be an XML report (report.xml). The main components of the XML file are a top-level <operatingsytems> element containing usually a single <operatingsystem> element, similar to the following:
 <operatingsystems>
   <operatingsystem>

     <!-- the type of operating system and Linux distribution -->
     <name>linux</name>
     <distro>rhel</distro>
     <!-- the name, version and architecture -->
     <product_name>Red Hat Enterprise Linux Server release 6.4 </product_name>
     <major_version>6</major_version>
     <minor_version>4</minor_version>
     <package_format>rpm</package_format>
     <package_management>yum</package_management>
     <root>/dev/VolGroup/lv_root</root> 
     <!-- how the filesystems would be mounted when live -->
     <mountpoints>
       <mountpoint dev="/dev/VolGroup/lv_root">/</mountpoint>
       <mountpoint dev="/dev/sda1">/boot</mountpoint>
       <mountpoint dev="/dev/VolGroup/lv_swap">swap</mountpoint>
     </mountpoints>

    < !-- filesystems-->
      <filesystem dev="/dev/VolGroup/lv_root">
        <label></label>
        <uuid>b24d9161-5613-4ab8-8649-f27a8a8068d3</uuid>
        <type>ext4</type>
        <content>linux-root</content>
        <spec>/dev/mapper/VolGroup-lv_root</spec>
      </filesystem>
      <filesystem dev="/dev/VolGroup/lv_swap">
        <type>swap</type>
        <spec>/dev/mapper/VolGroup-lv_swap</spec>
      </filesystem>
     <!-- packages installed -->
     <applications>
       <application>
         <name>firefox</name>
         <version>3.5.5</version>
         <release>1.fc12</release>
       </application>
     </applications>

   </operatingsystem>
 </operatingsystems>
Processing these reports is best done using W3C standard XPath queries. Red Hat Enterprise Linux 6 comes with a command line program (xpath) which can be used for simple instances; however, for long-term and advanced usage, you should consider using an XPath library along with your favorite programming language.
As an example, you can list out all file system devices using the following XPath query:
virt-inspector --xml GuestName | xpath //filesystem/@dev
 Found 3 nodes:
 -- NODE --
 dev="/dev/sda1"
 -- NODE --
 dev="/dev/vg_f12x64/lv_root"
 -- NODE --
 dev="/dev/vg_f12x64/lv_swap"
Or list the names of all applications installed by entering:
 virt-inspector --xml GuestName | xpath //application/name
 [...long list...]

17.10. virt-win-reg: Reading and editing the Windows Registry

17.10.1. Introduction

virt-win-reg is a tool that manipulates the Registry in Windows guest virtual machines. It can be used to read out registry keys. You can also use it to make changes to the Registry, but you must never try to do this for live/running guest virtual machines, as it will result in disk corruption.

17.10.2. Installation

To use virt-win-reg you must run the following:
# yum install libguestfs-tools libguestfs-winsupport

17.10.3. Using virt-win-reg

To read out Registry keys, specify the name of the guest virtual machine (or its disk image) and the name of the Registry key. You must use single quotes to surround the name of the desired key:
# virt-win-reg WindowsGuest \
    'HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall' \
    | less
The output is in the standard text-based format used by .REG files on Windows.

Note

Hex-quoting is used for strings because the format does not properly define a portable encoding method for strings. This is the only way to ensure fidelity when transporting .REG files from one machine to another.
You can make hex-quoted strings printable by piping the output of virt-win-reg through this simple Perl script:
perl -MEncode -pe's?hex\((\d+)\):(\S+)?$t=$1;$_=$2;s,\,,,g;"str($t):\"".decode(utf16le=>pack("H*",$_))."\""?eg'
To merge changes into the Windows Registry of an offline guest virtual machine, you must first prepare a .REG file. There is a great deal of documentation about doing this available here. When you have prepared a .REG file, enter the following:
# virt-win-reg --merge WindowsGuest input.reg
This will update the registry in the guest virtual machine.

17.11. Using the API from Programming Languages

The libguestfs API can be used directly from the following languages in Red Hat Enterprise Linux 6.2: C, C++, Perl, Python, Java, Ruby and OCaml.
  • To install C and C++ bindings, enter the following command:
    # yum install libguestfs-devel
    
  • To install Perl bindings:
    # yum install 'perl(Sys::Guestfs)'
    
  • To install Python bindings:
    # yum install python-libguestfs
    
  • To install Java bindings:
    # yum install libguestfs-java libguestfs-java-devel libguestfs-javadoc
    
  • To install Ruby bindings:
    # yum install ruby-libguestfs
    
  • To install OCaml bindings:
    # yum install ocaml-libguestfs ocaml-libguestfs-devel
    
The binding for each language is essentially the same, but with minor syntactic changes. A C statement:
guestfs_launch (g);
Would appear like the following in Perl:
$g->launch ()
Or like the following in OCaml:
g#launch ()
Only the API from C is detailed in this section.
In the C and C++ bindings, you must manually check for errors. In the other bindings, errors are converted into exceptions; the additional error checks shown in the examples below are not necessary for other languages, but conversely you may wish to add code to catch exceptions. Refer to the following list for some points of interest regarding the architecture of the libguestfs API:
  • The libguestfs API is synchronous. Each call blocks until it has completed. If you want to make calls asynchronously, you have to create a thread.
  • The libguestfs API is not thread safe: each handle should be used only from a single thread, or if you want to share a handle between threads you should implement your own mutex to ensure that two threads cannot execute commands on one handle at the same time.
  • You should not open multiple handles on the same disk image. It is permissible if all the handles are read-only, but still not recommended.
  • You should not add a disk image for writing if anything else could be using that disk image (eg. a live VM). Doing this will cause disk corruption.
  • Opening a read-only handle on a disk image which is currently in use (eg. by a live VM) is possible; however, the results may be unpredictable or inconsistent particularly if the disk image is being heavily written to at the time you are reading it.

17.11.1. Interaction with the API via a C program

Your C program should start by including the <guestfs.h> header file, and creating a handle:
#include <stdio.h>
#include <stdlib.h>
#include <guestfs.h>

int
main (int argc, char *argv[])
{
  guestfs_h *g;

  g = guestfs_create ();
  if (g == NULL) {
    perror ("failed to create libguestfs handle");
    exit (EXIT_FAILURE);
   }

   /* ... */

   guestfs_close (g);

   exit (EXIT_SUCCESS);
 }
Save this program to a file (test.c). Compile this program and run it with the following two commands:
gcc -Wall test.c -o test -lguestfs
./test
At this stage it should print no output. The rest of this section demonstrates an example showing how to extend this program to create a new disk image, partition it, format it with an ext4 file system, and create some files in the file system. The disk image will be called disk.img and be created in the current directory.
The outline of the program is:
  • Create the handle.
  • Add disk(s) to the handle.
  • Launch the libguestfs back end.
  • Create the partition, file system and files.
  • Close the handle and exit.
Here is the modified program:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <guestfs.h>
 
 int
 main (int argc, char *argv[])
 {
   guestfs_h *g;
   size_t i;
 
   g = guestfs_create ();
   if (g == NULL) {
     perror ("failed to create libguestfs handle");
     exit (EXIT_FAILURE);
  }
 
   /* Create a raw-format sparse disk image, 512 MB in size. */
   int fd = open ("disk.img", O_CREAT|O_WRONLY|O_TRUNC|O_NOCTTY, 0666);
   if (fd == -1) {
     perror ("disk.img");
     exit (EXIT_FAILURE);
   }
   if (ftruncate (fd, 512 * 1024 * 1024) == -1) {
     perror ("disk.img: truncate");
     exit (EXIT_FAILURE);
   }
   if (close (fd) == -1) {
     perror ("disk.img: close");
     exit (EXIT_FAILURE);
   }
 
   /* Set the trace flag so that we can see each libguestfs call. */
   guestfs_set_trace (g, 1);
 
   /* Set the autosync flag so that the disk will be synchronized
    * automatically when the libguestfs handle is closed.
    */
   guestfs_set_autosync (g, 1);
 
   /* Add the disk image to libguestfs. */
   if (guestfs_add_drive_opts (g, "disk.img",
         GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw", /* raw format */
         GUESTFS_ADD_DRIVE_OPTS_READONLY, 0,   /* for write */
         -1 /* this marks end of optional arguments */ )
       == -1)
     exit (EXIT_FAILURE);
 
   /* Run the libguestfs back-end. */
   if (guestfs_launch (g) == -1)
     exit (EXIT_FAILURE);
 
   /* Get the list of devices.  Because we only added one drive
    * above, we expect that this list should contain a single
    * element.
    */
   char **devices = guestfs_list_devices (g);
   if (devices == NULL)
     exit (EXIT_FAILURE);
   if (devices[0] == NULL || devices[1] != NULL) {
     fprintf (stderr,
              "error: expected a single device from list-devices\n");
     exit (EXIT_FAILURE);
   }
 
   /* Partition the disk as one single MBR partition. */
   if (guestfs_part_disk (g, devices[0], "mbr") == -1)
     exit (EXIT_FAILURE);
 
   /* Get the list of partitions.  We expect a single element, which
    * is the partition we have just created.
    */
   char **partitions = guestfs_list_partitions (g);
   if (partitions == NULL)
     exit (EXIT_FAILURE);
   if (partitions[0] == NULL || partitions[1] != NULL) {
     fprintf (stderr,
              "error: expected a single partition from list-partitions\n");
     exit (EXIT_FAILURE);
   }
 
   /* Create an ext4 filesystem on the partition. */
   if (guestfs_mkfs (g, "ext4", partitions[0]) == -1)
     exit (EXIT_FAILURE);
 
   /* Now mount the filesystem so that we can add files. */
   if (guestfs_mount_options (g, "", partitions[0], "/") == -1)
     exit (EXIT_FAILURE);
 
   /* Create some files and directories. */
   if (guestfs_touch (g, "/empty") == -1)
     exit (EXIT_FAILURE);
 
   const char *message = "Hello, world\n";
   if (guestfs_write (g, "/hello", message, strlen (message)) == -1)
     exit (EXIT_FAILURE);
 
   if (guestfs_mkdir (g, "/foo") == -1)
     exit (EXIT_FAILURE);
 
   /* This uploads the local file /etc/resolv.conf into the disk image. */
   if (guestfs_upload (g, "/etc/resolv.conf", "/foo/resolv.conf") == -1)
     exit (EXIT_FAILURE);
 
   /* Because 'autosync' was set (above) we can just close the handle
    * and the disk contents will be synchronized.  You can also do
    * this manually by calling guestfs_umount_all and guestfs_sync.
    */
   guestfs_close (g);
 
   /* Free up the lists. */
   for (i = 0; devices[i] != NULL; ++i)
     free (devices[i]);
   free (devices);
   for (i = 0; partitions[i] != NULL; ++i)
     free (partitions[i]);
   free (partitions);
 
   exit (EXIT_SUCCESS);
 }
Compile and run this program with the following two commands:
gcc -Wall test.c -o test -lguestfs
./test
If the program runs to completion successfully then you should be left with a disk image called disk.img, which you can examine with guestfish:
guestfish --ro -a disk.img -m /dev/sda1
><fs> ll /
><fs> cat /foo/resolv.conf
By default (for C and C++ bindings only), libguestfs prints errors to stderr. You can change this behavior by setting an error handler. The guestfs(3) man page discusses this in detail.

17.12. virt-sysprep: resetting virtual machine settings

The virt-sysprep command line tool can be used to reset or unconfigure a guest virtual machine so that clones can be made from it. This process involves removing SSH host keys, persistent network MAC configuration, and user accounts. virt-sysprep can also customize a virtual machine, for instance by adding SSH keys, users or logos. Each step can be enabled or disabled as required.
The term "sysprep" is derived from the System Preparation tool (sysprep.exe) which is used with the Microsoft Windows systems. Despite this, the tool does not currently work on Windows guests.

Note

libguestfs and guestfish do not require root privileges. You only need to run them as root if the disk image being accessed needs root access to read and/or write.
The virt-sysprep tool is part of the libguestfs-tools-c package, which is installed with the following command:
$ yum install libguestfs-tools-c
Alternatively, just the virt-sysprep tool can be installed with the following command:
$ yum install /usr/bin/virt-sysprep

Important

virt-sysprep modifies the guest or disk image in place. To use virt-sysprep, the guest virtual machine must be offline, so you must shut it down before running the commands. To preserve the existing contents of the guest virtual machine, you must snapshot, copy or clone the disk first. Refer to libguestfs.org for more information on copying and cloning disks.
The following commands are available to use with virt-sysprep:

Table 17.1. virt-sysprep commands

Command Description Example
--help Displays a brief help entry about a particular command or about the whole package. For additional help, see the virt-sysprep man page. $ virt-sysprep --help
-a [file] or --add [file] Adds the specified file, which should be a disk image from a guest virtual machine. The format of the disk image is auto-detected. To override this and force a particular format, use the --format option. $ virt-sysprep --add /dev/vms/disk.img
-c [URI] or --connect [URI] Connects to the given URI, if using libvirt. If omitted, it will connect via the KVM hypervisor. If you specify guest block devices directly (virt-sysprep -a), then libvirt is not used at all. $ virt-sysprep -c qemu:///system
-d [guest] or --domain [guest] Adds all the disks from the specified guest virtual machine. Domain UUIDs can be used instead of domain names. $ virt-sysprep --domain 90df2f3f-8857-5ba9-2714-7d95907b1c9e
-n or --dry-run or --dryrun Performs a read-only "dry run" sysprep operation on the guest virtual machine. This runs the sysprep operation, but throws away any changes to the disk at the end. $ virt-sysprep -n
--enable [operations] Enables the specified operations. To list the possible operations, use the --list command. $ virt-sysprep --enable ssh-hotkeys,udev-persistent-net
--format [raw|qcow2|auto] The default for the -a option is to auto-detect the format of the disk image. Using this forces the disk format for -a options which follow on the command line. Using --format auto switches back to auto-detection for subsequent -a options (see the -a command above). $ virt-sysprep --format raw -a disk.img forces raw format (no auto-detection) for disk.img, but virt-sysprep --format raw -a disk.img --format auto -a another.img forces raw format (no auto-detection) for disk.img and reverts to auto-detection for another.img. If you have untrusted raw-format guest disk images, you should use this option to specify the disk format. This avoids a possible security problem with malicious guests.
--list-operations Lists the operations supported by the virt-sysprep program. These are listed one per line, with one or more single-space-separated fields. The first field in the output is the operation name, which can be supplied to the --enable flag. The second field is a * character if the operation is enabled by default, or is blank if not. Additional fields on the same line include a description of the operation.
   $ virt-sysprep --list-operations
 bash-history * Remove the bash history in the guest
 cron-spool * Remove user at-jobs and cron-jobs
 dhcp-client-state * Remove DHCP client leases
 dhcp-server-state * Remove DHCP server leases
...
--mount-options Sets the mount options for each mount point in the guest virtual machine. Use a semicolon-separated list of mountpoint:options pairs. You may need to place quotes around this list to protect it from the shell. $ virt-sysprep --mount-options "/:notime" will mount the root directory with the notime operation.
--selinux-relabel and --no-selinux-relabel virt-sysprep does not always schedule a SELinux relabelling at the first boot of the guest. In some cases, a relabel is performed (for example, when virt-sysprep has modified files), however, when all operations only remove files (for example, when using --enable delete --delete /some/file) no relabelling is scheduled. Using the --selinux-relabel option always forces SELinux relabelling, while with --no-selinux-relabel set, relabelling is never scheduled. It is recommended to use --selinux-relabel to ensure that files have the correct SELinux labels. $ virt-sysprep --selinux-relabel
-q or --quiet Prevents the printing of log messages. $ virt-sysprep -q
-v or --verbose Enables verbose messages for debugging purposes. $ virt-sysprep -v
-V or --version Displays the virt-sysprep version number and exits. $ virt-sysprep -V
For more information, refer to the libguestfs documentation.

17.13. Troubleshooting

A test tool is available to check that libguestfs is working. Run the following command after installing libguestfs (root access not required) to test for normal operation:
$ libguestfs-test-tool
This tool prints a large amount of text to test the operation of libguestfs. If the test is successful, the following text will appear near the end of the output:
===== TEST FINISHED OK =====

17.14. Where to find further documentation

The primary source for documentation for libguestfs and the tools are the Unix man pages. The API is documented in guestfs(3). guestfish is documented in guestfish(1). The virt tools are documented in their own man pages (eg. virt-df(1)).

Chapter 18. Using simple tools for guest virtual machine management

In addition to virt-manager, there are other smaller more minimal tools that can allow you to have access to your guest virtual machine's console. The sections that follow describe and explain these tools.

18.1. Using virt-viewer

virt-viewer is a minimal tool for displaying the graphical console of a guest virtual machine. The console is accessed using the VNC or SPICE protocol. The guest can be referred to based on its name, ID, or UUID. If the guest is not already running, then the viewer can be told to wait until is starts before attempting to connect to the console. The viewer can connect to remote hosts to lookup the console information and then also connect to the remote console using the same network transport.
To install the virt-viewer tool, run:
# sudo yum install virt-viewer
The basic virt viewer commands are as follows:
# virt-viewer [OPTIONS] DOMAIN-NAME|ID|UUID
The following options may be used with virt-viewer
  • -h, or --help - Displays the command line help summary.
  • -V, or --version - Displays the virt-viewer version number.
  • -v, or --verbose - Displays information about the connection to the guest virtual machine
  • -c [URI], or --connect=URI - Specifies the hypervisor connection URI
  • -w, or --wait - Causes the domain to start up before attempting to connect to the console.
  • -r, or --reconnect - Automatically reconnects to the domain if it shuts down and restarts
  • -z PCT, or --zoom=PCT - Adjusts the zoom level of the display window in the specified percentage. Accepted range 10-200%.
  • -a, or --attach - Uses libvirt to directly attach to a local display, instead of making a TCP/UNIX socket connection. This avoids the need to authenticate with the remote display, if authentication with libvirt is already allowed. This option does not work with remote displays.
  • -f, or --full-screen - Starts with the command window maximized to its fullscreen size.
  • -h HOTKEYS, or --hotkeys HOTKEYS - Overrides the default hotkey settings with the new specified hotkey. Refer to Example 18.4, “Setting hot keys”.
  • --debug - Prints debugging information

Example 18.1. Connecting to a guest virtual machine

If using a XEN hypervisor:
# virt-viewer guest-name
If using a KVM-QEMU hypervisor:
# virt-viewer --connect qemu:///system 7

Example 18.2. To wait for a spefic guest to start before connecting

Enter the following command:
# virt-viewer --reconnect --wait 66ab33c0-6919-a3f7-e659-16c82d248521

Example 18.3. To connect to a remote console using TLS

Enter the following command:
#virt-viewer --connect xen://example.org/ demo
To connect to a remote host using SSH, lookup the guest configuration and then make a direct non-tunnelled connection to the console

Example 18.4. Setting hot keys

To create a customized hotkey, run the following command:
# virt-viewer --hotkeys=([action1]=[key-combination1]), ([action2]=[key-combination2])
The following actions can be assigned to a hotkey:
  • toggle-fullscreen
  • release-cursor
  • smartcard-insert
  • smartcard-remove
Key name combinations are case insensitive. Each hot key setting should have a unique key combination.
For example, to create a hotkey to change to full screen mode:
#virt-viewer --hotkeys=toggle-fullscreen=shift+f11 qemu:///system 7

18.2. remote-viewer

The remote-viewer is a simple remote desktop display client that supports SPICE and VNC.
To install the virt-viewer tool, run:
# sudo yum install remote-viewer
The basic remote viewer commands are as follows:remote-viewer [OPTIONS] DOMAIN-NAME|ID|UUID
The following options may be used with remote-viewer
  • -h, or --help - Displays the command line help summary.
  • -V, or --version - Displays the remote-viewer version number.
  • -v, or --verbose - Displays information about the connection to the guest virtual machine
  • -z PCT, or --zoom=PCT - Adjusts the zoom level of the display window in the specified percentage. Accepted range 10-200%.
  • -f, or --full-screen - Starts with the command window maximized to its fullscreen size.
  • -t TITLE, or --title TITLE - Sets the window title to the string given
  • --spice-controller - Uses the SPICE controller to initialize the connection with the SPICE server. This option is used by the SPICE browser addons to allow web page to start a client.
  • --debug - Prints debugging information
For more information see the MAN page for the remote-viewer.

Chapter 19. Virtual Networking

This chapter introduces the concepts needed to create, start, stop, remove, and modify virtual networks with libvirt.
Additional information can be found in the libvirt reference chapter

19.1. Virtual network switches

Libvirt virtual networking uses the concept of a virtual network switch. A virtual network switch is a software construct that operates on a host physical machine server, to which virtual machines (guests) connect. The network traffic for a guest is directed through this switch:
Virtual network switch with two guests

Figure 19.1. Virtual network switch with two guests

Linux host physical machine servers represent a virtual network switch as a network interface. When the libvirtd daemon (libvirtd) is first installed and started, the default network interface representing the virtual network switch is virbr0.
Linux host physical machine with an interface to a virtual network switch

Figure 19.2. Linux host physical machine with an interface to a virtual network switch

This virbr0 interface can be viewed with the ifconfig and ip commands like any other interface:
$ ifconfig virbr0
 virbr0    Link encap:Ethernet  HWaddr 1B:C4:94:CF:FD:17  
           inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:11 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:0 (0.0 b)  TX bytes:3097 (3.0 KiB)
 $ ip addr show virbr0
 3: virbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN 
     link/ether 1b:c4:94:cf:fd:17 brd ff:ff:ff:ff:ff:ff
     inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0

19.2. Bridge Mode

When using Bridge mode, all of the guest virtual machines appear within the same subnet as the host physical machine. All other physical machines on the same physical network are aware of the virtual machines, and can access the virtual machines. Bridging operates on Layer 2 of the OSI networking model.
It is possible to use multiple physical interfaces on the hypervisor by joining them together with a bond. The bond is then added to a bridge and then guest virtual machines are added onto the bridge as well. However, the bonding driver has several modes of operation, and only a few of these modes work with a bridge where virtual guest machines are in use.

Warning

The only bonding modes that should be used with a guest virtual machine are Mode 1, Mode 2, and Mode 4. Under no circumstances should Modes 0, 3, 5, or 6 be used. It should also be noted that mii-monitoring should be used to monitor bonding modes as arp-monitoring does not work.
For more information on bonding modes, refer to the knowledge base article on bonding modes, or The Red Hat Enterprise Linux 6 Deployment Guide.

19.3. Network Address Translation mode

By default, virtual network switches operate in NAT mode. They use IP masquerading rather than SNAT (Source-NAT) or DNAT (Destination-NAT). IP masquerading enables connected guests to use the host physical machine IP address for communication to any external network. By default, computers that are placed externally to the host physical machine cannot communicate to the guests inside when the virtual network switch is operating in NAT mode, as shown in the following diagram:
Virtual network switch using NAT with two guests

Figure 19.3. Virtual network switch using NAT with two guests

Warning

Virtual network switches use NAT configured by iptables rules. Editing these rules while the switch is running is not recommended, as incorrect rules may result in the switch being unable to communicate.
If the switch is not running, you can set th public IP range for forward mode NAT in order to create a port masquerading range by running:
# iptables -j SNAT --to-source [start]-[end]

19.3.1. DNS and DHCP

IP information can be assigned to guests via DHCP. A pool of addresses can be assigned to a virtual network switch for this purpose. Libvirt uses the dnsmasq program for this. An instance of dnsmasq is automatically configured and started by libvirt for each virtual network switch that needs it.
Virtual network switch running dnsmasq

Figure 19.4. Virtual network switch running dnsmasq

19.4. Routed mode

When using Routed mode, the virtual switch connects to the physical LAN connected to the host physical machine, passing traffic back and forth without the use of NAT. The virtual switch can examine all traffic and use the information contained within the network packets to make routing decisions. When using this mode, all of the virtual machines are in their own subnet, routed through a virtual switch. This situation is not always ideal as no other host physical machines on the physical network are aware of the virtual machines without manual physical router configuration, and cannot access the virtual machines. Routed mode operates at Layer 3 of the OSI networking model.
Virtual network switch in routed mode

Figure 19.5. Virtual network switch in routed mode

19.5. Isolated mode

When using Isolated mode, guests connected to the virtual switch can communicate with each other, and with the host physical machine, but their traffic will not pass outside of the host physical machine, nor can they receive traffic from outside the host physical machine. Using dnsmasq in this mode is required for basic functionality such as DHCP. However, even if this network is isolated from any physical network, DNS names are still resolved. Therefore a situation can arise when DNS names resolve but ICMP echo request (ping) commands fail.
Virtual network switch in isolated mode

Figure 19.6. Virtual network switch in isolated mode

19.6. The default configuration

When the libvirtd daemon (libvirtd) is first installed, it contains an initial virtual network switch configuration in NAT mode. This configuration is used so that installed guests can communicate to the external network, through the host physical machine. The following image demonstrates this default configuration for libvirtd:
Default libvirt network configuration

Figure 19.7. Default libvirt network configuration

Note

A virtual network can be restricted to a specific physical interface. This may be useful on a physical system that has several interfaces (for example, eth0, eth1 and eth2). This is only useful in routed and NAT modes, and can be defined in the dev=<interface> option, or in virt-manager when creating a new virtual network.

19.7. Examples of common scenarios

This section demonstrates different virtual networking modes and provides some example scenarios.

19.7.1. Bridged mode

Bridged mode operates on Layer 2 of the OSI model. When used, all of the guest virtual machines will appear on the same subnet as the host physical machine. The most common use cases for bridged mode include:
  • Deploying guest virtual machines in an existing network alongside host physical machines making the difference between virtual and physical machines transparent to the end user.
  • Deploying guest virtual machines without making any changes to existing physical network configuration settings.
  • Deploying guest virtual machines which must be easily accessible to an existing physical network. Placing guest virtual machines on a physical network where they must access services within an existing broadcast domain, such as DHCP.
  • Connecting guest virtual machines to an exsting network where VLANs are used.

19.7.2. Routed mode

DMZ
Consider a network where one or more nodes are placed in a controlled subnetwork for security reasons. The deployment of a special subnetwork such as this is a common practice, and the subnetwork is known as a DMZ. Refer to the following diagram for more details on this layout:
Sample DMZ configuration

Figure 19.8. Sample DMZ configuration

Host physical machines in a DMZ typically provide services to WAN (external) host physical machines as well as LAN (internal) host physical machines. As this requires them to be accessible from multiple locations, and considering that these locations are controlled and operated in different ways based on their security and trust level, routed mode is the best configuration for this environment.
Virtual Server hosting
Consider a virtual server hosting company that has several host physical machines, each with two physical network connections. One interface is used for management and accounting, the other is for the virtual machines to connect through. Each guest has its own public IP address, but the host physical machines use private IP address as management of the guests can only be performed by internal administrators. Refer to the following diagram to understand this scenario:
Virtual server hosting sample configuration

Figure 19.9. Virtual server hosting sample configuration

When the host physical machine has a public IP address and the virtual machines have static public IP addresses, bridged networking cannot be used, as the provider only accepts packets from the MAC address of the public host physical machine. The following diagram demonstrates this:
Virtual server using static IP addresses

Figure 19.10. Virtual server using static IP addresses

19.7.3. NAT mode

NAT (Network Address Translation) mode is the default mode. It can be used for testing when there is no need for direct network visibility.

19.7.4. Isolated mode

Isolated mode allows virtual machines to communicate with each other only. They are unable to interact with the physical network.

19.8. Managing a virtual network

To configure a virtual network on your system:
  1. From the Edit menu, select Connection Details.
    Selecting a host physical machine's details

    Figure 19.11. Selecting a host physical machine's details

  2. This will open the Connection Details menu. Click the Virtual Networks tab.
    Virtual network configuration

    Figure 19.12. Virtual network configuration

  3. All available virtual networks are listed on the left-hand box of the menu. You can edit the configuration of a virtual network by selecting it from this box and editing as you see fit.

19.9. Creating a virtual network

To create a virtual network on your system:
  1. Open the Virtual Networks tab from within the Connection Details menu. Click the Add Network button, identified by a plus sign (+) icon. For more information, refer to Section 19.8, “Managing a virtual network”.
    Virtual network configuration

    Figure 19.13. Virtual network configuration

    This will open the Create a new virtual network window. Click Forward to continue.
    Creating a new virtual network

    Figure 19.14. Creating a new virtual network

  2. Enter an appropriate name for your virtual network and click Forward.
    Naming your virtual network

    Figure 19.15. Naming your virtual network

  3. Enter an IPv4 address space for your virtual network and click Forward.
    Choosing an IPv4 address space

    Figure 19.16. Choosing an IPv4 address space

  4. Define the DHCP range for your virtual network by specifying a Start and End range of IP addresses. Click Forward to continue.
    Selecting the DHCP range

    Figure 19.17. Selecting the DHCP range

  5. Select how the virtual network should connect to the physical network.
    Connecting to physical network

    Figure 19.18. Connecting to physical network

    If you select Forwarding to physical network, choose whether the Destination should be Any physical device or a specific physical device. Also select whether the Mode should be NAT or Routed.
    Click Forward to continue.
  6. You are now ready to create the network. Check the configuration of your network and click Finish.
    Ready to create network

    Figure 19.19. Ready to create network

  7. The new virtual network is now available in the Virtual Networks tab of the Connection Details window.

19.10. Attaching a virtual network to a guest

To attach a virtual network to a guest:
  1. In the Virtual Machine Manager window, highlight the guest that will have the network assigned.
    Selecting a virtual machine to display

    Figure 19.20. Selecting a virtual machine to display

  2. From the Virtual Machine Manager Edit menu, select Virtual Machine Details.
    Displaying the virtual machine details

    Figure 19.21. Displaying the virtual machine details

  3. Click the Add Hardware button on the Virtual Machine Details window.
    The Virtual Machine Details window

    Figure 19.22. The Virtual Machine Details window

  4. In the Add new virtual hardware window, select Network from the left pane, and select your network name (network1 in this example) from the Host device menu and click Finish.
    Select your network from the Add new virtual hardware window

    Figure 19.23. Select your network from the Add new virtual hardware window

  5. The new network is now displayed as a virtual network interface that will be presented to the guest upon launch.
    New network shown in guest hardware list

    Figure 19.24. New network shown in guest hardware list

19.11. Directly attaching to physical interface

The instructions provided in this chapter will assist in the direct attachment of the virtual machine's NIC to the given physical interface of the host physical machine. This setup requires the Linux macvtap driver to be available. There are four modes that you can choose for the operation mode of the macvtap device, with 'vepa' being the default mode. Their behavior is as follows:

Physical interface delivery modes

vepa
All VMs' packets are sent to the external bridge. Packets whose destination is a VM on the same host physical machine as where the packet originates from are sent back to the host physical machine by the VEPA capable bridge (today's bridges are typically not VEPA capable).
bridge
Packets whose destination is on the same host physical machine as where they originate from are directly delivered to the target macvtap device. Both origin and destination devices need to be in bridge mode for direct delivery. If either one of them is in vepa mode, a VEPA capable bridge is required.
private
All packets are sent to the external bridge and will only be delivered to a target VM on the same host physical machine if they are sent through an external router or gateway and that device sends them back to the host physical machine. This procedure is followed if either the source or destination device is in private mode.
passthrough
This feature attaches a virtual function of a SRIOV capable NIC directly to a VM without losing the migration capability. All packets are sent to the VF/IF of the configured network device. Depending on the capabilities of the device additional prerequisites or limitations may apply; for example, on Linux this requires kernel 2.6.38 or newer.
Each of the four modes is configured by changing the domain xml file. Once this file is opened, change the mode setting as shown:
  <devices>
    ...
    <interface type='direct'>
      <source dev='eth0' mode='vepa'/>
    </interface>
  </devices>
The network access of direct attached guest virtual machines can be managed by the hardware switch to which the physical interface of the host physical machine is connected to.
The interface can have additional parameters as shown below, if the switch is conforming to the IEEE 802.1Qbg standard. The parameters of the virtualport element are documented in more detail in the IEEE 802.1Qbg standard. The values are network specific and should be provided by the network administrator. In 802.1Qbg terms, the Virtual Station Interface (VSI) represents the virtual interface of a virtual machine.
Note that IEEE 802.1Qbg requires a non-zero value for the VLAN ID. Also if the switch is conforming to the IEEE 802.1Qbh standard, the values are network specific and should be provided by the network administrator.

Virtual Station Interface types

managerid
The VSI Manager ID identifies the database containing the VSI type and instance definitions. This is an integer value and the value 0 is reserved.
typeid
The VSI Type ID identifies a VSI type characterizing the network access. VSI types are typically managed by network administrator. This is an integer value.
typeidversion
The VSI Type Version allows multiple versions of a VSI Type. This is an integer value.
instanceid
The VSI Instance ID Identifier is generated when a VSI instance (i.e. a virtual interface of a virtual machine) is created. This is a globally unique identifier.
profileid
The profile ID contains the name of the port profile that is to be applied onto this interface. This name is resolved by the port profile database into the network parameters from the port profile, and those network parameters will be applied to this interface.
Each of the four types is configured by changing the domain xml file. Once this file is opened, change the mode setting as shown:
  <devices>
    ...
    <interface type='direct'>
      <source dev='eth0.2' mode='vepa'/>
      <virtualport type="802.1Qbg">
        <parameters managerid="11" typeid="1193047" typeidversion="2" instanceid="09b11c53-8b5c-4eeb-8f00-d84eaa0aaa4f"/>
      </virtualport>
    </interface>
  </devices>
The profile ID is shown here:
  <devices>
    ...
    <interface type='direct'>
      <source dev='eth0' mode='private'/>
      <virtualport type='802.1Qbh'>
        <parameters profileid='finance'/>
      </virtualport>
    </interface>
  </devices>
  ...

19.12. Applying network filtering

This section provides an introduction to libvirt's network filters, their goals, concepts and XML format.

19.12.1. Introduction

The goal of the network filtering, is to enable administrators of a virtualized system to configure and enforce network traffic filtering rules on virtual machines and manage the parameters of network traffic that virtual machines are allowed to send or receive. The network traffic filtering rules are applied on the host physical machine when a virtual machine is started. Since the filtering rules cannot be circumvented from within the virtual machine, it makes them mandatory from the point of view of a virtual machine user.
From the point of view of the guest virtual machine, the network filtering system allows each virtual machine's network traffic filtering rules to be configured individually on a per interface basis. These rules are applied on the host physical machine when the virtual machine is started and can be modified while the virtual machine is running. The latter can be achieved by modifying the XML description of a network filter.
Multiple virtual machines can make use of the same generic network filter. When such a filter is modified, the network traffic filtering rules of all running virtual machines that reference this filter are updated. The machines that are not running will update on start.
As previously mentioned, applying network traffic filtering rules can be done on individual network interfaces that are configured for certain types of network configurations. Supported network types include:
  • network
  • ethernet -- must be used in bridging mode
  • bridge

Example 19.1. An example of network filtering

The interface XML is used to reference a top-level filter. In the following example, the interface description references the filter clean-traffic.
   <devices>
    <interface type='bridge'>
      <mac address='00:16:3e:5d:c7:9e'/>
      <filterref filter='clean-traffic'/>
    </interface>
  </devices>
Network filters are written in XML and may either contain: references to other filters, rules for traffic filtering, or hold a combination of both. The above referenced filter clean-traffic is a filter that only contains references to other filters and no actual filtering rules. Since references to other filters can be used, a tree of filters can be built. The clean-traffic filter can be viewed using the command: # virsh nwfilter-dumpxml clean-traffic.
As previously mentioned, a single network filter can be referenced by multiple virtual machines. Since interfaces will typically have individual parameters associated with their respective traffic filtering rules, the rules described in a filter's XML can be generalized using variables. In this case, the variable name is used in the filter XML and the name and value are provided at the place where the filter is referenced.

Example 19.2. Description extended

In the following example, the interface description has been extended with the parameter IP and a dotted IP address as a value.
  <devices>
    <interface type='bridge'>
      <mac address='00:16:3e:5d:c7:9e'/>
      <filterref filter='clean-traffic'>
        <parameter name='IP' value='10.0.0.1'/>
      </filterref>
    </interface>
  </devices>
In this particular example, the clean-traffic network traffic filter will be represented with the IP address parameter 10.0.0.1 and as per the rule dictates that all traffic from this interface will always be using 10.0.0.1 as the source IP address, which is one of the purpose of this particular filter.

19.12.2. Filtering chains

Filtering rules are organized in filter chains. These chains can be thought of as having a tree structure with packet filtering rules as entries in individual chains (branches).
Packets start their filter evaluation in the root chain and can then continue their evaluation in other chains, return from those chains back into the root chain or be dropped or accepted by a filtering rule in one of the traversed chains.
Libvirt's network filtering system automatically creates individual root chains for every virtual machine's network interface on which the user chooses to activate traffic filtering. The user may write filtering rules that are either directly instantiated in the root chain or may create protocol-specific filtering chains for efficient evaluation of protocol-specific rules.
The following chains exist:
  • root
  • mac
  • stp (spanning tree protocol)
  • vlan
  • arp and rarp
  • ipv4
  • ipv6
Multiple chains evaluating the mac, stp, vlan, arp, rarp, ipv4, or ipv6 protocol can be created using the protocol name only as a prefix in the chain's name.

Example 19.3. ARP traffic filtering

This example allows chains with names arp-xyz or arp-test to be specified and have their ARP protocol packets evaluated in those chains.
The following filter XML shows an example of filtering ARP traffic in the arp chain.
<filter name='no-arp-spoofing' chain='arp' priority='-500'>
  <uuid>f88f1932-debf-4aa1-9fbe-f10d3aa4bc95</uuid>
  <rule action='drop' direction='out' priority='300'>
    <mac match='no' srcmacaddr='$MAC'/>
  </rule>
  <rule action='drop' direction='out' priority='350'>
    <arp match='no' arpsrcmacaddr='$MAC'/>
  </rule>
  <rule action='drop' direction='out' priority='400'>
    <arp match='no' arpsrcipaddr='$IP'/>
  </rule>
  <rule action='drop' direction='in' priority='450'>
    <arp opcode='Reply'/>
    <arp match='no' arpdstmacaddr='$MAC'/>
  </rule>
  <rule action='drop' direction='in' priority='500'>
    <arp match='no' arpdstipaddr='$IP'/>
  </rule>
  <rule action='accept' direction='inout' priority='600'>
    <arp opcode='Request'/>
  </rule>
  <rule action='accept' direction='inout' priority='650'>
    <arp opcode='Reply'/>
  </rule>
  <rule action='drop' direction='inout' priority='1000'/>
</filter>
The consequence of putting ARP-specific rules in the arp chain, rather than for example in the root chain, is that packets protocols other than ARP do not need to be evaluated by ARP protocol-specific rules. This improves the efficiency of the traffic filtering. However, one must then pay attention to only putting filtering rules for the given protocol into the chain since other rules will not be evaluated. For example, an IPv4 rule will not be evaluated in the ARP chain since IPv4 protocol packets will not traverse the ARP chain.

19.12.3. Filtering chain priorities

As previously mentioned, when creating a filtering rule, all chains are connected to the root chain. The order in which those chains are accessed is influenced by the priority of the chain. The following table shows the chains that can be assigned a priority and their default priorities.

Table 19.1. Filtering chain default priorities values

Chain (prefix)Default priority
stp-810
mac-800
vlan-750
ipv4-700
ipv6-600
arp-500
rarp-400

Note

A chain with a lower priority value is accessed before one with a higher value.
The chains listed in Table 19.1, “Filtering chain default priorities values” can be also be assigned custom priorities by writing a value in the range [-1000 to 1000] into the priority (XML) attribute in the filter node. Section 19.12.2, “Filtering chains”filter shows the default priority of -500 for arp chains, for example.

19.12.4. Usage of variables in filters

There are two variables that have been reserved for usage by the network traffic filtering subsystem: MAC and IP.
MAC is designated for the MAC address of the network interface. A filtering rule that references this variable will automatically be replaced with the MAC address of the interface. This works without the user having to explicitly provide the MAC parameter. Even though it is possible to specify the MAC parameter similar to the IP parameter above, it is discouraged since libvirt knows what MAC address an interface will be using.
The parameter IP represents the IP address that the operating system inside the virtual machine is expected to use on the given interface. The IP parameter is special in so far as the libvirt daemon will try to determine the IP address (and thus the IP parameter's value) that is being used on an interface if the parameter is not explicitly provided but referenced. For current limitations on IP address detection, consult the section on limitations Section 19.12.12, “Limitations” on how to use this feature and what to expect when using it. The XML file shown in Section 19.12.2, “Filtering chains” contains the filter no-arp-spoofing, which is an example of using a network filter XML to reference the MAC and IP variables.
Note that referenced variables are always prefixed with the character $. The format of the value of a variable must be of the type expected by the filter attribute identified in the XML. In the above example, the IP parameter must hold a legal IP address in standard format. Failure to provide the correct structure will result in the filter variable not being replaced with a value and will prevent a virtual machine from starting or will prevent an interface from attaching when hotplugging is being used. Some of the types that are expected for each XML attribute are shown in the example Example 19.4, “Sample variable types”.

Example 19.4. Sample variable types

As variables can contain lists of elements, (the variable IP can contain multiple IP addresses that are valid on a particular interface, for example), the notation for providing multiple elements for the IP variable is:
  <devices>
    <interface type='bridge'>
      <mac address='00:16:3e:5d:c7:9e'/>
      <filterref filter='clean-traffic'>
        <parameter name='IP' value='10.0.0.1'/>
        <parameter name='IP' value='10.0.0.2'/>
        <parameter name='IP' value='10.0.0.3'/>
      </filterref>
    </interface>
  </devices>
This XML file creates filters to enable multiple IP addresses per interface. Each of the IP addresses will result in a seperate filtering rule. Therefore using the XML above and the the following rule, three individual filtering rules (one for each IP address) will be created:
  <rule action='accept' direction='in' priority='500'>
    <tcp srpipaddr='$IP'/>
  </rule>
As it is possible to access individual elements of a variable holding a list of elements, a filtering rule like the following accesses the 2nd element of the variable DSTPORTS.
  <rule action='accept' direction='in' priority='500'>
    <udp dstportstart='$DSTPORTS[1]'/>
  </rule>

Example 19.5. Using a variety of variables

As it is possible to create filtering rules that represent all possible combinations of rules from different lists using the notation $VARIABLE[@<iterator id="x">]. The following rule allows a virtual machine to receive traffic on a set of ports, which are specified in DSTPORTS, from the set of source IP address specified in SRCIPADDRESSES. The rule generates all combinations of elements of the variable DSTPORTS with those of SRCIPADDRESSES by using two independent iterators to access their elements.
  <rule action='accept' direction='in' priority='500'>
    <ip srcipaddr='$SRCIPADDRESSES[@1]' dstportstart='$DSTPORTS[@2]'/>
  </rule>
Assign concrete values to SRCIPADDRESSES and DSTPORTS as shown:
  SRCIPADDRESSES = [ 10.0.0.1, 11.1.2.3 ]
  DSTPORTS = [ 80, 8080 ]
Assigning values to the variables using $SRCIPADDRESSES[@1] and $DSTPORTS[@2] would then result in all combinations of addresses and ports being created as shown:
  • 10.0.0.1, 80
  • 10.0.0.1, 8080
  • 11.1.2.3, 80
  • 11.1.2.3, 8080
Accessing the same variables using a single iterator, for example by using the notation $SRCIPADDRESSES[@1] and $DSTPORTS[@1], would result in parallel access to both lists and result in the following combination:
  • 10.0.0.1, 80
  • 11.1.2.3, 8080

Note

$VARIABLE is short-hand for $VARIABLE[@0]. The former notation always assumes the role of iterator with iterator id="0" added as shown in the opening paragraph at the top of this section.

19.12.5. Automatic IP address detection and DHCP snooping

19.12.5.1. Introduction

The detection of IP addresses used on a virtual machine's interface is automatically activated if the variable IP is referenced but no value has been assigned to it. The variable CTRL_IP_LEARNING can be used to specify the IP address learning method to use. Valid values include: any, dhcp, or none.
The value any instructs libvirt to use any packet to determine the address in use by a virtual machine, which is the default setting if the variable TRL_IP_LEARNING is not set. This method will only detect a single IP address per interface. Once a guest virtual machine's IP address has been detected, its IP network traffic will be locked to that address, if for example, IP address spoofing is prevented by one of its filters. In that case, the user of the VM will not be able to change the IP address on the interface inside the guest virtual machine, which would be considered IP address spoofing. When a guest virtual machine is migrated to another host physical machine or resumed after a suspend operation, the first packet sent by the guest virtual machine will again determine the IP address that the guest virtual machine can use on a particular interface.
The value of dhcp instructs libvirt to only honor DHCP server-assigned addresses with valid leases. This method supports the detection and usage of multiple IP address per interface. When a guest virtual machine resumes after a suspend operation, any valid IP address leases are applied to its filters. Otherwise the guest virtual machine is expected to use DHCP to obtain a new IP addresses. When a guest virtual machine migrates to another physical host physical machine, the guest virtual machine is required to re-run the DHCP protocol.
If CTRL_IP_LEARNING is set to none, libvirt does not do IP address learning and referencing IP without assigning it an explicit value is an error.

19.12.5.2. DHCP snooping

CTRL_IP_LEARNING=dhcp (DHCP snooping) provides additional anti-spoofing security, especially when combined with a filter allowing only trusted DHCP servers to assign IP addresses. To enable this, set the variable DHCPSERVER to the IP address of a valid DHCP server and provide filters that use this variable to filter incoming DHCP responses.
When DHCP snooping is enabled and the DHCP lease expires, the guest virtual machine will no longer be able to use the IP address until it acquires a new, valid lease from a DHCP server. If the guest virtual machine is migrated, it must get a new valid DHCP lease to use an IP address (e.g., by bringing the VM interface down and up again).

Note

Automatic DHCP detection listens to the DHCP traffic the guest virtual machine exchanges with the DHCP server of the infrastructure. To avoid denial-of-service attacks on libvirt, the evaluation of those packets is rate-limited, meaning that a guest virtual machine sending an excessive number of DHCP packets per second on an interface will not have all of those packets evaluated and thus filters may not get adapted. Normal DHCP client behavior is assumed to send a low number of DHCP packets per second. Further, it is important to setup appropriate filters on all guest virtual machines in the infrastructure to avoid them being able to send DHCP packets. Therefore guest virtual machines must either be prevented from sending UDP and TCP traffic from port 67 to port 68 or the DHCPSERVER variable should be used on all guest virtual machines to restrict DHCP server messages to only be allowed to originate from trusted DHCP servers. At the same time anti-spoofing prevention must be enabled on all guest virtual machines in the subnet.

Example 19.6. Activating IPs for DHCP snooping

The following XML provides an example for the activation of IP address learning using the DHCP snooping method:
    <interface type='bridge'>
      <source bridge='virbr0'/>
      <filterref filter='clean-traffic'>
        <parameter name='CTRL_IP_LEARNING' value='dhcp'/>
      </filterref>
    </interface>

19.12.6. Reserved Variables

Table 19.2, “Reserved variables” shows the variables that are considered reserved and are used by libvirt:

Table 19.2. Reserved variables

Variable NameDefinition
MACThe MAC address of the interface
IPThe list of IP addresses in use by an interface
IPV6Not currently implemented: the list of IPV6 addresses in use by an interface
DHCPSERVERThe list of IP addresses of trusted DHCP servers
DHCPSERVERV6Not currently implemented: The list of IPv6 addresses of trusted DHCP servers
CTRL_IP_LEARNINGThe choice of the IP address detection mode

19.12.7. Element and attribute overview

The root element required for all network filters is named <filter> with two possible attributes. The name attribute provides a unique name of the given filter. The chain attribute is optional but allows certain filters to be better organized for more efficient processing by the firewall subsystem of the underlying host physical machine. Currently the system only supports the following chains: root, ipv4, ipv6, arp and rarp.

19.12.8. References to other filters

Any filter may hold references to other filters. Individual filters may be referenced multiple times in a filter tree but references between filters must not introduce loops.

Example 19.7. An Example of a clean traffic filter

The following shows the XML of the clean-traffic network filter referencing several other filters.
<filter name='clean-traffic'>
  <uuid>6ef53069-ba34-94a0-d33d-17751b9b8cb1</uuid>
  <filterref filter='no-mac-spoofing'/>
  <filterref filter='no-ip-spoofing'/>
  <filterref filter='allow-incoming-ipv4'/>
  <filterref filter='no-arp-spoofing'/>
  <filterref filter='no-other-l2-traffic'/>
  <filterref filter='qemu-announce-self'/>
</filter>
To reference another filter, the XML node filterref needs to be provided inside a filter node. This node must have the attribute filter whose value contains the name of the filter to be referenced.
New network filters can be defined at any time and may contain references to network filters that are not known to libvirt, yet. However, once a virtual machine is started or a network interface referencing a filter is to be hotplugged, all network filters in the filter tree must be available. Otherwise the virtual machine will not start or the network interface cannot be attached.

19.12.9. Filter rules

The following XML shows a simple example of a network traffic filter implementing a rule to drop traffic if the IP address (provided through the value of the variable IP) in an outgoing IP packet is not the expected one, thus preventing IP address spoofing by the VM.

Example 19.8. Example of network traffic filtering

<filter name='no-ip-spoofing' chain='ipv4'>
  <uuid>fce8ae33-e69e-83bf-262e-30786c1f8072</uuid>
  <rule action='drop' direction='out' priority='500'>
    <ip match='no' srcipaddr='$IP'/>
  </rule>
</filter>
The traffic filtering rule starts with the rule node. This node may contain up to three of the following attributes:
  • action is mandatory can have the following values:
    • drop (matching the rule silently discards the packet with no further analysis)
    • reject (matching the rule generates an ICMP reject message with no further analysis)
    • accept (matching the rule accepts the packet with no further analysis)
    • return (matching the rule passes this filter, but returns control to the calling filter for further analysis)
    • continue (matching the rule goes on to the next rule for further analysis)
  • direction is mandatory can have the following values:
    • in for incomming traffic
    • out for outgoing traffic
    • inout for incoming and outgoing traffic
  • priority is optional. The priority of the rule controls the order in which the rule will be instantiated relative to other rules. Rules with lower values will be instantiated before rules with higher values. Valid values are in the range of -1000 to 1000. If this attribute is not provided, priority 500 will be assigned by default. Note that filtering rules in the root chain are sorted with filters connected to the root chain following their priorities. This allows to interleave filtering rules with access to filter chains. Refer to Section 19.12.3, “Filtering chain priorities” for more information.
  • statematch is optional. Possible values are '0' or 'false' to turn the underlying connection state matching off. The default setting is 'true' or 1
The above example Example 19.7, “An Example of a clean traffic filter” indicates that the traffic of type ip will be associated with the chain ipv4 and the rule will have priority=500. If for example another filter is referenced whose traffic of type ip is also associated with the chain ipv4 then that filter's rules will be ordered relative to the priority=500 of the shown rule.
A rule may contain a single rule for filtering of traffic. The above example shows that traffic of type ip is to be filtered.

19.12.10. Supported protocols

The following sections list and give some details about the protocols that are supported by the network filtering subsystem. This type of traffic rule is provided in the rule node as a nested node. Depending on the traffic type a rule is filtering, the attributes are different. The above example showed the single attribute srcipaddr that is valid inside the ip traffic filtering node. The following sections show what attributes are valid and what type of data they are expecting. The following datatypes are available:
  • UINT8 : 8 bit integer; range 0-255
  • UINT16: 16 bit integer; range 0-65535
  • MAC_ADDR: MAC address in dotted decimal format, i.e., 00:11:22:33:44:55
  • MAC_MASK: MAC address mask in MAC address format, i.e., FF:FF:FF:FC:00:00
  • IP_ADDR: IP address in dotted decimal format, i.e., 10.1.2.3
  • IP_MASK: IP address mask in either dotted decimal format (255.255.248.0) or CIDR mask (0-32)
  • IPV6_ADDR: IPv6 address in numbers format, i.e., FFFF::1
  • IPV6_MASK: IPv6 mask in numbers format (FFFF:FFFF:FC00::) or CIDR mask (0-128)
  • STRING: A string
  • BOOLEAN: 'true', 'yes', '1' or 'false', 'no', '0'
  • IPSETFLAGS: The source and destination flags of the ipset described by up to 6 'src' or 'dst' elements selecting features from either the source or destination part of the packet header; example: src,src,dst. The number of 'selectors' to provide here depends on the type of ipset that is referenced
Every attribute except for those of type IP_MASK or IPV6_MASK can be negated using the match attribute with value no. Multiple negated attributes may be grouped together. The following XML fragment shows such an example using abstract attributes.
[...]
  <rule action='drop' direction='in'>
    <protocol match='no' attribute1='value1' attribute2='value2'/>
    <protocol attribute3='value3'/>
  </rule>
[...]
Rules behave evaluate the rule as well as look at it logically within the boundaries of the given protocol attributes. Thus, if a single attribute's value does not match the one given in the rule, the whole rule will be skipped during the evaluation process. Therefore, in the above example incoming traffic will only be dropped if: the protocol property attribute1 does not match both value1 and the protocol property attribute2 does not match value2 and the protocol property attribute3 matches value3.

19.12.10.1. MAC (Ethernet)

Protocol ID: mac
Rules of this type should go into the root chain.

Table 19.3. MAC protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
dstmacaddrMAC_ADDRMAC address of destination
dstmacmaskMAC_MASKMask applied to MAC address of destination
protocolidUINT16 (0x600-0xffff), STRINGLayer 3 protocol ID. Valid strings include [arp, rarp, ipv4, ipv6]
commentSTRING text string up to 256 characters
The filter can be written as such:
[...]
<mac match='no' srcmacaddr='$MAC'/>
[...]

19.12.10.2. VLAN (802.1Q)

Protocol ID: vlan
Rules of this type should go either into the root or vlan chain.

Table 19.4. VLAN protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
dstmacaddrMAC_ADDRMAC address of destination
dstmacmaskMAC_MASKMask applied to MAC address of destination
vlan-idUINT16 (0x0-0xfff, 0 - 4095) VLAN ID
encap-protocolUINT16 (0x03c-0xfff), String Encapsulated layer 3 protocol ID, valid strings are arp, ipv4, ipv6
commentSTRING text string up to 256 characters

19.12.10.3. STP (Spanning Tree Protocol)

Protocol ID: stp
Rules of this type should go either into the root or stp chain.

Table 19.5. STP protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
typeUINT8Bridge Protocol Data Unit (BPDU) type
flagsUINT8BPDU flagdstmacmask
root-priorityUINT16Root priority range start
root-priority-hiUINT16 (0x0-0xfff, 0 - 4095) Root priority range end
root-addressMAC _ADDRESSroot MAC Address
root-address-maskMAC _MASKroot MAC Address mask
roor-costUINT32Root path cost (range start)
root-cost-hiUINT32Root path cost range end
sender-priority-hiUINT16Sender prioriry range end
sender-addressMAC_ADDRESSBPDU sender MAC address
sender-address-maskMAC_MASKBPDU sender MAC address mask
portUINT16Port identifier (range start)
port_hiUINT16Port identifier range end
msg-ageUINT16Message age timer (range start)
msg-age-hiUINT16Message age timer range end
max-age-hiUINT16Maximum age time range end
hello-timeUINT16Hello time timer (range start)
hello-time-hiUINT16Hello time timer range end
forward-delayUINT16Forward delay (range start)
forward-delay-hiUINT16Forward delay range end
commentSTRING text string up to 256 characters

19.12.10.4. ARP/RARP

Protocol ID: arp or rarp
Rules of this type should either go into the root or arp/rarp chain.

Table 19.6. ARP and RARP protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
dstmacaddrMAC_ADDRMAC address of destination
dstmacmaskMAC_MASKMask applied to MAC address of destination
hwtypeUINT16Hardware type
protocoltypeUINT16Protocol type
opcodeUINT16, STRINGOpcode valid strings are: Request, Reply, Request_Reverse, Reply_Reverse, DRARP_Request, DRARP_Reply, DRARP_Error, InARP_Request, ARP_NAK
arpsrcmacaddrMAC_ADDRSource MAC address in ARP/RARP packet
arpdstmacaddrMAC _ADDRDestination MAC address in ARP/RARP packet
arpsrcipaddrIP_ADDRSource IP address in ARP/RARP packet
arpdstipaddrIP_ADDRDestination IP address in ARP/RARP packet
gratututousBOOLEANBoolean indiating whether to check for a gratuitous ARP packet
commentSTRING text string up to 256 characters

19.12.10.5. IPv4

Protocol ID: ip
Rules of this type should either go into the root or ipv4 chain.

Table 19.7. IPv4 protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
dstmacaddrMAC_ADDRMAC address of destination
dstmacmaskMAC_MASKMask applied to MAC address of destination
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
protocolUINT8, STRINGLayer 4 protocol identifier. Valid strings for protocol are: tcp, udp, udplite, esp, ah, icmp, igmp, sctp
srcportstartUINT16Start of range of valid source ports; requires protocol
srcportendUINT16End of range of valid source ports; requires protocol
dstportstartUNIT16Start of range of valid destination ports; requires protocol
dstportendUNIT16End of range of valid destination ports; requires protocol
commentSTRING text string up to 256 characters

19.12.10.6. IPv6

Protocol ID: ipv6
Rules of this type should either go into the root or ipv6 chain.

Table 19.8. IPv6 protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to MAC address of sender
dstmacaddrMAC_ADDRMAC address of destination
dstmacmaskMAC_MASKMask applied to MAC address of destination
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
protocolUINT8, STRINGLayer 4 protocol identifier. Valid strings for protocol are: tcp, udp, udplite, esp, ah, icmpv6, sctp
scrportstartUNIT16Start of range of valid source ports; requires protocol
srcportendUINT16End of range of valid source ports; requires protocol
dstportstartUNIT16Start of range of valid destination ports; requires protocol
dstportendUNIT16End of range of valid destination ports; requires protocol
commentSTRING text string up to 256 characters

19.12.10.7. TCP/UDP/SCTP

Protocol ID: tcp, udp, sctp
The chain parameter is ignored for this type of traffic and should either be omitted or set to root. .

Table 19.9. TCP/UDP/SCTP protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
scriptoIP_ADDRStart of range of source IP address
srcipfromIP_ADDREnd of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
scrportstartUNIT16Start of range of valid source ports; requires protocol
srcportendUINT16End of range of valid source ports; requires protocol
dstportstartUNIT16Start of range of valid destination ports; requires protocol
dstportendUNIT16End of range of valid destination ports; requires protocol
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
flagsSTRINGTCP-only: format of mask/flags with mask and flags each being a comma separated list of SYN,ACK,URG,PSH,FIN,RST or NONE or ALL
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.10.8. ICMP

Protocol ID: icmp
Note: The chain parameter is ignored for this type of traffic and should either be omitted or set to root.

Table 19.10. ICMP protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to the MAC address of the sender
dstmacaddrMAD_ADDRMAC address of the destination
dstmacmaskMAC_MASKMask applied to the MAC address of the destination
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
srcipfromIP_ADDRstart of range of source IP address
scriptoIP_ADDRend of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
typeUNIT16ICMP type
codeUNIT16ICMP code
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.10.9. IGMP, ESP, AH, UDPLITE, 'ALL'

Protocol ID: igmp, esp, ah, udplite, all
The chain parameter is ignored for this type of traffic and should either be omitted or set to root.

Table 19.11. IGMP, ESP, AH, UDPLITE, 'ALL'

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcmacmaskMAC_MASKMask applied to the MAC address of the sender
dstmacaddrMAD_ADDRMAC address of the destination
dstmacmaskMAC_MASKMask applied to the MAC address of the destination
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
srcipfromIP_ADDRstart of range of source IP address
scriptoIP_ADDRend of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.10.10. TCP/UDP/SCTP over IPV6

Protocol ID: tcp-ipv6, udp-ipv6, sctp-ipv6
The chain parameter is ignored for this type of traffic and should either be omitted or set to root.

Table 19.12. TCP, UDP, SCTP over IPv6 protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
srcipfromIP_ADDRstart of range of source IP address
scriptoIP_ADDRend of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
srcportstartUINT16Start of range of valid source ports
srcportendUINT16End of range of valid source ports
dstportstartUINT16Start of range of valid destination ports
dstportendUINT16End of range of valid destination ports
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.10.11. ICMPv6

Protocol ID: icmpv6
The chain parameter is ignored for this type of traffic and should either be omitted or set to root.

Table 19.13. ICMPv6 protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
srcipfromIP_ADDRstart of range of source IP address
scriptoIP_ADDRend of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
typeUINT16ICMPv6 type
codeUINT16ICMPv6 code
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.10.12. IGMP, ESP, AH, UDPLITE, 'ALL' over IPv6

Protocol ID: igmp-ipv6, esp-ipv6, ah-ipv6, udplite-ipv6, all-ipv6
The chain parameter is ignored for this type of traffic and should either be omitted or set to root.

Table 19.14. IGMP, ESP, AH, UDPLITE, 'ALL' over IPv protocol types

Attribute NameDatatypeDefinition
srcmacaddrMAC_ADDRMAC address of sender
srcipaddrIP_ADDRSource IP address
srcipmaskIP_MASKMask applied to source IP address
dstipaddrIP_ADDRDestination IP address
dstipmaskIP_MASKMask applied to destination IP address
srcipfromIP_ADDRstart of range of source IP address
scriptoIP_ADDRend of range of source IP address
dstipfromIP_ADDRStart of range of destination IP address
dstiptoIP_ADDREnd of range of destination IP address
commentSTRING text string up to 256 characters
stateSTRINGcomma separated list of NEW,ESTABLISHED,RELATED,INVALID or NONE
ipsetSTRINGThe name of an IPSet managed outside of libvirt
ipsetflagsIPSETFLAGSflags for the IPSet; requires ipset attribute

19.12.11. Advanced Filter Configuration Topics

The following sections discuss advanced filter configuration topics.

19.12.11.1. Connection tracking

The network filtering subsystem (on Linux) makes use of the connection tracking support of IP tables. This helps in enforcing the directionality of network traffic (state match) as well as counting and limiting the number of simultaneous connections towards a guest virtual machine. As an example, if a guest virtual machine has TCP port 8080 open as a server, clients may connect to the guest virtual machine on port 8080. Connection tracking and enforcement of directionality then prevents the guest virtual machine from initiating a connection from (TCP client) port 8080 to the host physical machine back to a remote host physical machine. More importantly, tracking helps to prevent remote attackers from establishing a connection back to a guest virtual machine. For example, if the user inside the guest virtual machine established a connection to port 80 on an attacker site, then the attacker will not be able to initiate a connection from TCP port 80 back towards the guest virtual machine. By default the connection state match that enables connection tracking and then enforcement of directionality of traffic is turned on.

Example 19.9. XML example for turning off connections to the TCP port

The following shows an example XML fragment where this feature has been turned off for incoming connections to TCP port 12345.
   [...]
    <rule direction='in' action='accept' statematch='false'>
      <cp dstportstart='12345'/>
    </rule>
   [...]
This now allows incoming traffic to TCP port 12345, but would also enable the initiation from (client) TCP port 12345 within the VM, which may or may not be desirable.

19.12.11.2. Limiting Number of Connections

To limit the number of connections a guest virtual machine may establish, a rule must be provided that sets a limit of connections for a given type of traffic. If for example a VM is supposed to be allowed to only ping one other IP address at a time and is supposed to have only one active incoming ssh connection at a time.

Example 19.10. XML sample file that sets limits to connections

The following XML fragment can be used to limit connections
  [...]
  <rule action='drop' direction='in' priority='400'>
    <tcp connlimit-above='1'/>
  </rule>
  <rule action='accept' direction='in' priority='500'>
    <tcp dstportstart='22'/>
  </rule>
  <rule action='drop' direction='out' priority='400'>
    <icmp connlimit-above='1'/>
  </rule>
  <rule action='accept' direction='out' priority='500'>
    <icmp/>
  </rule>
  <rule action='accept' direction='out' priority='500'>
    <udp dstportstart='53'/>
  </rule>
  <rule action='drop' direction='inout' priority='1000'>
    <all/>
  </rule>
  [...]

Note

Limitation rules must be listed in the XML prior to the rules for accepting traffic. According to the XML file in Example 19.10, “XML sample file that sets limits to connections”, an additional rule for allowing DNS traffic sent to port 22 go out the guest virtual machine, has been added to avoid ssh sessions not getting established for reasons related to DNS lookup failures by the ssh daemon. Leaving this rule out may result in the ssh client hanging unexpectedly as it tries to connect. Additional caution should be used in regards to handling timeouts related to tracking of traffic. An ICMP ping that the user may have terminated inside the guest virtual machine may have a long timeout in the host physical machine's connection tracking system and will therefore not allow another ICMP ping to go through.
The best solution is to tune the timeout in the host physical machine's sysfs with the following command:# echo 3 > /proc/sys/net/netfilter/nf_conntrack_icmp_timeout. This command sets the ICMP connection tracking timeout to 3 seconds. The effect of this is that once one ping is terminated, another one can start after 3 seconds.
If for any reason the guest virtual machine has not properly closed its TCP connection, the connection to be held open for a longer period of time, especially if the TCP timeout value was set for a large amount of time on the host physical machine. In addition, any idle connection may result in a time out in the connection tracking system which can be re-activated once packets are exchanged.
However, if the limit is set too low, newly initiated connections may force an idle connection into TCP backoff. Therefore, the limit of connections should be set rather high so that fluctuations in new TCP connections don't cause odd traffic behavior in relation to idle connections.

19.12.11.3. Command line tools

virsh has been extended with life-cycle support for network filters. All commands related to the network filtering subsystem start with the prefix nwfilter. The following commands are available:
  • nwfilter-list : lists UUIDs and names of all network filters
  • nwfilter-define : defines a new network filter or updates an existing one (must supply a name)
  • nwfilter-undefine : deletes a specified network filter (must supply a name). Do not delete a network filter currently in use.
  • nwfilter-dumpxml : displays a specified network filter (must supply a name)
  • nwfilter-edit : edits a specified network filter (must supply a name)

19.12.11.4. Pre-existing network filters

The following is a list of example network filters that are automatically installed with libvirt:

Table 19.15. ICMPv6 protocol types

Command NameDescription
no-arp-spoofingPrevents a guest virtual machine from spoofing ARP traffic; this filter only allows ARP request and reply messages and enforces that those packets contain the MAC and IP addresses of the guest virtual machine.
allow-dhcpAllows a guest virtual machine to request an IP address via DHCP (from any DHCP server)
allow-dhcp-serverAllows a guest virtual machine to request an IP address from a specified DHCP server. The dotted decimal IP address of the DHCP server must be provided in a reference to this filter. The name of the variable must be DHCPSERVER.
no-ip-spoofingPrevents a guest virtual machine from sending IP packets with a source IP address different from the one inside the packet.
no-ip-multicastPrevents a guest virtual machine from sending IP multicast packets.
clean-trafficPrevents MAC, IP and ARP spoofing. This filter references several other filters as building blocks.
These filters are only building blocks and require a combination with other filters to provide useful network traffic filtering. The most used one in the above list is the clean-traffic filter. This filter itself can for example be combined with the no-ip-multicast filter to prevent virtual machines from sending IP multicast traffic on top of the prevention of packet spoofing.

19.12.11.5. Writing your own filters

Since libvirt only provides a couple of example networking filters, you may consider writing your own. When planning on doing so there are a couple of things you may need to know regarding the network filtering subsystem and how it works internally. Certainly you also have to know and understand the protocols very well that you want to be filtering on so that no further traffic than what you want can pass and that in fact the traffic you want to allow does pass.
The network filtering subsystem is currently only available on Linux host physical machines and only works for Qemu and KVM type of virtual machines. On Linux, it builds upon the support for ebtables, iptables and ip6tables and makes use of their features. Considering the list found in Section 19.12.10, “Supported protocols” the following protocols can be implemented using ebtables:
  • mac
  • stp (spanning tree protocol)
  • vlan (802.1Q)
  • arp, rarp
  • ipv4
  • ipv6
Any protocol that runs over IPv4 is supported using iptables, those over IPv6 are implemented using ip6tables.
Using a Linux host physical machine, all traffic filtering rules created by libvirt's network filtering subsystem first passes through the filtering support implemented by ebtables and only afterwards through iptables or ip6tables filters. If a filter tree has rules with the protocols including: mac, stp, vlan arp, rarp, ipv4, or ipv6; the ebtable rules and values listed will automatically be used first.
Multiple chains for the same protocol can be created. The name of the chain must have a prefix of one of the previously enumerated protocols. To create an additional chain for handling of ARP traffic, a chain with name arp-test, can for example be specified.
As an example, it is possible to filter on UDP traffic by source and destination ports using the IP protocol filter and specifying attributes for the protocol, source and destination IP addresses and ports of UDP packets that are to be accepted. This allows early filtering of UDP traffic with ebtables. However, once an IP or IPv6 packet, such as a UDP packet, has passed the ebtables layer and there is at least one rule in a filter tree that instantiates iptables or ip6tables rules, a rule to let the UDP packet pass will also be necessary to be provided for those filtering layers. This can be achieved with a rule containing an appropriate udp or udp-ipv6 traffic filtering node.

Example 19.11. Creating a custom filter

Suppose a filter is needed to fulfill the following list of requirements:
  • prevents a VM's interface from MAC, IP and ARP spoofing
  • opens only TCP ports 22 and 80 of a VM's interface
  • allows the VM to send ping traffic from an interface but not let the VM be pinged on the interface
  • allows the VM to do DNS lookups (UDP towards port 53)
The requirement to prevent spoofing is fulfilled by the existing clean-traffic network filter, thus the way to do this is to reference it from a custom filter.
To enable traffic for TCP ports 22 and 80, two rules are added to enable this type of traffic. To allow the guest virtual machine to send ping traffic a rule is added for ICMP traffic. For simplicity reasons, general ICMP traffic will be allowed to be initiated from the guest virtual machine, and will not be specified to ICMP echo request and response messages. All other traffic will be prevented to reach or be initiated by the guest virtual machine. To do this a rule will be added that drops all other traffic. Assuming the guest virtual machine is called test and the interface to associate our filter with is called eth0, a filter is created named test-eth0.
The result of these considerations is the following network filter XML:
<filter name='test-eth0'>
  <!- - This rule references the clean traffic filter to prevent MAC, IP and ARP spoofing. By not providing an IP address parameter, libvirt will detect the IP address the guest virtual machine is using. - ->
  <filterref filter='clean-traffic'/>

  <!- - This rule enables TCP ports 22 (ssh) and 80 (http) to be reachable - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='22'/>
  </rule>

  <rule action='accept' direction='in'>
    <tcp dstportstart='80'/>
  </rule>

  <!- - This rule enables general ICMP traffic to be initiated by the guest virtual machine including ping traffic - ->
  <rule action='accept' direction='out'>
    <icmp/>
  </rule>>

  <!- - This rule enables outgoing DNS lookups using UDP - ->
  <rule action='accept' direction='out'>
    <udp dstportstart='53'/>
  </rule>

  <!- - This rule drops all other traffic - ->
  <rule action='drop' direction='inout'>
    <all/>
  </rule>

</filter>

19.12.11.6. Sample custom filter

Although one of the rules in the above XML contains the IP address of the guest virtual machine as either a source or a destination address, the filtering of the traffic works correctly. The reason is that whereas the rule's evaluation occurs internally on a per-interface basis, the rules are additionally evaluated based on which (tap) interface has sent or will receive the packet, rather than what their source or destination IP address may be.

Example 19.12. Sample XML for network interface descriptions

An XML fragment for a possible network interface description inside the domain XML of the test guest virtual machine could then look like this:
   [...]
    <interface type='bridge'>
      <source bridge='mybridge'/>
      <filterref filter='test-eth0'/>
    </interface>
   [...]
To more strictly control the ICMP traffic and enforce that only ICMP echo requests can be sent from the guest virtual machine and only ICMP echo responses be received by the guest virtual machine, the above ICMP rule can be replaced with the following two rules:
  <!- - enable outgoing ICMP echo requests- ->
  <rule action='accept' direction='out'>
    <icmp type='8'/>
  </rule>
  <!- - enable incoming ICMP echo replies- ->
  <rule action='accept' direction='in'>
    <icmp type='0'/>
  </rule>

Example 19.13. Second example custom filter

This example demonstrates how to build a similar filter as in the example above, but extends the list of requirements with an ftp server located inside the guest virtual machine. The requirements for this filter are:
  • prevents a guest virtual machine's interface from MAC, IP, and ARP spoofing
  • opens only TCP ports 22 and 80 in a guest virtual machine's interface
  • allows the guest virtual machine to send ping traffic from an interface but does not allow the guest virtual machine to be pinged on the interface
  • allows the guest virtual machine to do DNS lookups (UDP towards port 53)
  • enables the ftp server (in active mode) so it can run inside the guest virtual machine
The additional requirement of allowing an FTP server to be run inside the guest virtual machine maps into the requirement of allowing port 21 to be reachable for FTP control traffic as well as enabling the guest virtual machine to establish an outgoing TCP connection originating from the guest virtual machine's TCP port 20 back to the FTP client (FTP active mode). There are several ways of how this filter can be written and two possible solutions are included in this example.
The first solution makes use of the state attribute of the TCP protocol that provides a hook into the connection tracking framework of the Linux host physical machine. For the guest virtual machine-initiated FTP data connection (FTP active mode) the RELATED state is used to enable detection that the guest virtual machine-initiated FTP data connection is a consequence of ( or 'has a relationship with' ) an existing FTP control connection, thereby allowing it to pass packets through the firewall. The RELATED state, however, is only valid for the very first packet of the outgoing TCP connection for the FTP data path. Afterwards, the state is ESTABLISHED, which then applies equally to the incoming and outgoing direction. All this is related to the FTP data traffic originating from TCP port 20 of the guest virtual machine. This then leads to the following solution:
<filter name='test-eth0'>
  <!- - This filter (eth0) references the clean traffic filter to prevent MAC, IP, and ARP spoofing. By not providing an IP address parameter, libvirt will detect the IP address the guest virtual machine is using. - ->
  <filterref filter='clean-traffic'/>

  <!- - This rule enables TCP port 21 (FTP-control) to be reachable - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='21'/>
  </rule>

  <!- - This rule enables TCP port 20 for guest virtual machine-initiated FTP data connection related to an existing FTP control connection - ->
  <rule action='accept' direction='out'>
    <tcp srcportstart='20' state='RELATED,ESTABLISHED'/>
  </rule>

  <!- - This rule accepts all packets from a client on the FTP data connection - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='20' state='ESTABLISHED'/>
  </rule>

  <!- - This rule enables TCP port 22 (SSH) to be reachable - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='22'/>
  </rule>

  <!- -This rule enables TCP port 80 (HTTP) to be reachable - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='80'/>
  </rule>

  <!- - This rule enables general ICMP traffic to be initiated by the guest virtual machine, including ping traffic - ->
  <rule action='accept' direction='out'>
    <icmp/>
  </rule>

  <!- - This rule enables outgoing DNS lookups using UDP - ->
  <rule action='accept' direction='out'>
    <udp dstportstart='53'/>
  </rule>

  <!- - This rule drops all other traffic - ->
  <rule action='drop' direction='inout'>
    <all/>
  </rule>

</filter>
Before trying out a filter using the RELATED state, you have to make sure that the appropriate connection tracking module has been loaded into the host physical machine's kernel. Depending on the version of the kernel, you must run either one of the following two commands before the FTP connection with the guest virtual machine is established:
  • #modprobe nf_conntrack_ftp - where available OR
  • #modprobe ip_conntrack_ftp if above is not available
If protocols other than FTP are used in conjunction with the RELATED state, their corresponding module must be loaded. Modules are available for the protocols: ftp, tftp, irc, sip, sctp, and amanda.
The second solution makes use of the state flags of connections more than the previous solution did. This solution takes advantage of the fact that the NEW state of a connection is valid when the very first packet of a traffic flow is detected. Subsequently, if the very first packet of a flow is accepted, the flow becomes a connection and thus enters into the ESTABLISHED state. Therefore a general rule can be written for allowing packets of ESTABLISHED connections to reach the guest virtual machine or be sent by the guest virtual machine. This is done writing specific rules for the very first packets identified by the NEW state and dictates the ports that the data is acceptable. All packets meant for ports that are not explicitly accepted are dropped, thus not reaching an ESTABLISHED state. Any subsequent packets sent from that port are dropped as well.
<filter name='test-eth0'>
  <!- - This filter references the clean traffic filter to prevent MAC, IP and ARP spoofing. By not providing and IP address parameter, libvirt will detect the IP address the VM is using. - ->
  <filterref filter='clean-traffic'/>

  <!- - This rule allows the packets of all previously accepted connections to reach the guest virtual machine - ->
  <rule action='accept' direction='in'>
    <all state='ESTABLISHED'/>
  </rule>

  <!- - This rule allows the packets of all previously accepted and related connections be sent from the guest virtual machine - ->
  <rule action='accept' direction='out'>
    <all state='ESTABLISHED,RELATED'/>
  </rule>

  <!- - This rule enables traffic towards port 21 (FTP) and port 22 (SSH)- ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='21' dstportend='22' state='NEW'/>
  </rule>

  <!- - This rule enables traffic towards port 80 (HTTP) - ->
  <rule action='accept' direction='in'>
    <tcp dstportstart='80' state='NEW'/>
  </rule>

  <!- - This rule enables general ICMP traffic to be initiated by the guest virtual machine, including ping traffic - ->
  <rule action='accept' direction='out'>
    <icmp state='NEW'/>
  </rule>

  <!- - This rule enables outgoing DNS lookups using UDP - ->
  <rule action='accept' direction='out'>
    <udp dstportstart='53' state='NEW'/>
  </rule>

  <!- - This rule drops all other traffic - ->
  <rule action='drop' direction='inout'>
    <all/>
  </rule>

</filter>

19.12.12. Limitations

The following is a list of the currently known limitations of the network filtering subsystem.
  • VM migration is only supported if the whole filter tree that is referenced by a guest virtual machine's top level filter is also available on the target host physical machine. The network filter clean-traffic for example should be available on all libvirt instal