Chapter 2. Getting started with virtualization

Prerequisites

• Virtualization is enabled on your host system.
• You have a sufficient amount of system resources to allocate to your VMs, such as disk space, RAM, or CPUs. The recommended values may vary significantly depending on the intended tasks and workload of the VMs.

• An operating system (OS) installation source is available locally or on a network. This can be one of the following:

  • An ISO image of an installation medium

  • A disk image of an existing VM installation

    Warning

    Installing from a host CD-ROM or DVD-ROM device is not possible in RHEL 8. If you select a CD-ROM or DVD-ROM as the installation source when using any VM installation method available in RHEL 8, the installation will fail. For more information, see the Red Hat Knowledgebase.

    Also note that Red Hat provides support only for a limited set of guest operating systems.

• Optional: A Kickstart file can be provided for faster and easier configuration of the installation.

• --name: the name of the new machine
• --memory: the amount of allocated memory
• --vcpus: the number of allocated virtual CPUs
• --disk: the type and size of the allocated storage
• --cdrom or --location: the type and location of the OS installation source

• The following creates a VM named demo-guest1 that installs the Windows 10 OS from an ISO image locally stored in the /home/username/Downloads/Win10install.iso file. This VM is also allocated with 2048 MiB of RAM and 2 vCPUs, and an 80 GiB qcow2 virtual disk is automatically configured for the VM.

  # virt-install \
      --name demo-guest1 --memory 2048 \
      --vcpus 2 --disk size=80 --os-variant win10 \
      --cdrom /home/username/Downloads/Win10install.iso

• The following creates a VM named demo-guest2 that uses the /home/username/Downloads/rhel8.iso image to run a RHEL 8 OS from a live CD. No disk space is assigned to this VM, so changes made during the session will not be preserved. In addition, the VM is allocated with 4096 MiB of RAM and 4 vCPUs.

  # virt-install \
      --name demo-guest2 --memory 4096 --vcpus 4 \
      --disk none --livecd --os-variant rhel8.0 \
      --cdrom /home/username/Downloads/rhel8.iso

• The following creates a RHEL 8 VM named demo-guest3 that connects to an existing disk image, /home/username/backup/disk.qcow2. This is similar to physically moving a hard drive between machines, so the OS and data available to demo-guest3 are determined by how the image was handled previously. In addition, this VM is allocated with 2048 MiB of RAM and 2 vCPUs.

  # virt-install \
      --name demo-guest3 --memory 2048 --vcpus 2 \
      --os-variant rhel8.0 --import \
      --disk /home/username/backup/disk.qcow2

  Note that the --os-variant option is highly recommended when importing a disk image. If it is not provided, the performance of the created VM will be negatively affected.

• The following creates a VM named demo-guest4 that installs from the http://example.com/OS-install URL. For the installation to start successfully, the URL must contain a working OS installation tree. In addition, the OS is automatically configured using the /home/username/ks.cfg kickstart file. This VM is also allocated with 2048 MiB of RAM, 2 vCPUs, and a 160 GiB qcow2 virtual disk.

  # virt-install \
      --name demo-guest4 --memory 2048 --vcpus 2 --disk size=160 \
      --os-variant rhel8.0 --location http://example.com/OS-install \
      --initrd-inject /home/username/ks.cfg --extra-args="inst.ks=file:/ks.cfg console=tty0 console=ttyS0,115200n8"

• The following creates a VM named demo-guest5 that installs from a RHEL8.iso image file in text-only mode, without graphics. It connects the guest console to the serial console. The VM has 16384 MiB of memory, 16 vCPUs, and 280 GiB disk. This kind of installation is useful when connecting to a host over a slow network link.

  # virt-install \
      --name demo-guest5 --memory 16384 --vcpus 16 --disk size=280 \
      --os-variant rhel8.0 --location RHEL8.iso \
      --graphics none --extra-args='console=ttyS0'

• The following creates a VM named demo-guest6, which has the same configuration as demo-guest5, but resides on the 10.0.0.1 remote host.

  # virt-install \
      --connect qemu+ssh://root@10.0.0.1/system --name demo-guest6 --memory 16384 \
      --vcpus 16 --disk size=280 --os-variant rhel8.0 --location RHEL8.iso \
      --graphics none --extra-args='console=ttyS0'

Verification

• If the VM is created successfully, a virt-viewer window opens with a graphical console of the VM and starts the guest OS installation.

Troubleshooting

• If virt-install fails with a cannot find default network error:

  1. Ensure that the libvirt-daemon-config-network package is installed:

     # yum info libvirt-daemon-config-network
     Installed Packages
     Name         : libvirt-daemon-config-network
     [...]

  2. Verify that the libvirt default network is active and configured to start automatically:

     # virsh net-list --all
      Name      State    Autostart   Persistent
     --------------------------------------------
      default   active   yes         yes

  3. If it is not, activate the default network and set it to auto-start:

     # virsh net-autostart default
     Network default marked as autostarted
     
     # virsh net-start default
     Network default started

     1. If activating the default network fails with the following error, the libvirt-daemon-config-network package has not been installed correctly.

        error: failed to get network 'default'
        error: Network not found: no network with matching name 'default'

        To fix this, re-install libvirt-daemon-config-network.

        # yum reinstall libvirt-daemon-config-network

     2. If activating the default network fails with an error similar to the following, a conflict has occurred between the default network’s subnet and an existing interface on the host.

        error: Failed to start network default
        error: internal error: Network is already in use by interface ens2

        To fix this, use the virsh net-edit default command and change the 192.168.122.* values in the configuration to a subnet not already in use on the host.

Prerequisites

• The web console VM plug-in is installed on your system.
• Virtualization is enabled on your host system.
• You have a sufficient amount of system resources to allocate to your VMs, such as disk space, RAM, or CPUs. The recommended values may vary significantly depending on the intended tasks and workload of the VMs.

Prerequisites

• An inactive VM that is already defined.
• The name of the VM.

• For remote VMs:

  • The IP address of the host where the VM is located.
  • Root access privileges to the host.

Procedure

• For a local VM, use the virsh start utility.

  For example, the following command starts the demo-guest1 VM.

  # virsh start demo-guest1
  Domain 'demo-guest1' started

• For a VM located on a remote host, use the virsh start utility along with the QEMU+SSH connection to the host.

  For example, the following command starts the demo-guest1 VM on the 192.168.123.123 host.

  # virsh -c qemu+ssh://root@192.168.123.123/system start demo-guest1
  
  root@192.168.123.123's password:
  
  Domain 'demo-guest1' started

Prerequisites

• The web console VM plug-in is installed on your system.
• An inactive VM that is already defined.
• The name of the VM.

Prerequisites

• A created virtual machine

• To interact with the VM’s graphical interface in the web console, use the graphical console.
• To interact with the VM’s graphical interface in a remote viewer, use the graphical console in remote viewers.
• To interact with the VM’s CLI in the web console, use the serial console.

Prerequisites

• Your system, as well as the VM you are connecting to, must support graphical displays.
• If the target VM is located on a remote host, connection and root access privileges to the host are needed.
• Optional: If the target VM is located on a remote host, set up your libvirt and SSH for more convenient access to remote hosts.

Procedure

• To connect to a local VM, use the following command and replace guest-name with the name of the VM you want to connect to:

  # virt-viewer guest-name

• To connect to a remote VM, use the virt-viewer command with the SSH protocol. For example, the following command connects as root to a VM called guest-name, located on remote system 10.0.0.1. The connection also requires root authentication for 10.0.0.1.

  # virt-viewer --direct --connect qemu+ssh://root@10.0.0.1/system guest-name
  root@10.0.0.1's password:

Troubleshooting

• If clicking in the graphical console does not have any effect, expand the console to full screen. This is a known issue with the mouse cursor offset.

Prerequisites

• You have network connection and root access privileges to the target VM.
• If the target VM is located on a remote host, you also have connection and root access privileges to that host.

• Your VM network assigns IP addresses by dnsmasq generated by libvirt. This is the case for example in libvirt NAT networks.

  Notably, if your VM is using one of the following network configurations, you cannot connect to the VM using SSH:

  • hostdev interfaces
  • direct interfaces
  • bridge interaces

• The libvirt-nss component is installed and enabled on the VM’s host. If it is not, do the following:

  1. Install the libvirt-nss package:

     # yum install libvirt-nss

  2. Edit the /etc/nsswitch.conf file and add libvirt_guest to the hosts line:

     [...]
     passwd:      compat
     shadow:      compat
     group:       compat
     hosts:       files libvirt_guest dns
     [...]

Troubleshooting

• If you do not know the VM’s name, you can list all VMs available on the host using the virsh list --all command:

  # virsh list --all
  Id    Name                           State
  ----------------------------------------------------
  2     testguest1                    running
  -     testguest2                    shut off

Additional resources

• Upstream libvirt documentation

• Does not provide VNC or SPICE protocols, and thus does not offer video display for GUI tools.
• Does not have a network connection, and thus cannot be interacted with using SSH.

Prerequisites

• The VM must have a serial console device configured, such as console type='pty'. To verify, do the following:

  # virsh dumpxml vm-name | grep console
  
  <console type='pty' tty='/dev/pts/2'>
  </console>

• The VM must have the serial console configured in its kernel command line. To verify this, the cat /proc/cmdline command output on the VM should include console=ttyS0. For example:

  # cat /proc/cmdline
  BOOT_IMAGE=/vmlinuz-3.10.0-948.el7.x86_64 root=/dev/mapper/rhel-root ro console=tty0 console=ttyS0,9600n8 rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb

  If the serial console is not set up properly on a VM, using virsh console to connect to the VM connects you to an unresponsive guest console. However, you can still exit the unresponsive console by using the Ctrl+] shortcut.

  • To set up serial console on the VM, do the following:

    1. On the VM, enable the console=ttyS0 kernel option:

       # grubby --update-kernel=ALL --args="console=ttyS0"

    2. Clear the kernel options that might prevent your changes from taking effect.

       # grub2-editenv - unset kernelopts

    3. Reboot the VM.

Next steps

• If you want to use libvirt utilities exclusively on a single remote host, you can also set a specific connection as the default target for libvirt-based utilities. To do so, edit the /etc/libvirt/libvirt.conf file and set the value of the uri_default parameter to qemu-host-alias. For example, the following uses the t-rex host alias set up in the previous steps as a default libvirt target.

  # These can be used in cases when no URI is supplied by the application
  # (@uri_default also prevents probing of the hypervisor driver).
  #
  uri_default = "t-rex"

  As a result, all libvirt-based commands will automatically be performed on the specified remote host.

  $ virsh list
  root@10.0.0.1's password:
  
  Id   Name              State
  ---------------------------------
  1    velociraptor      running

  However, this is not recommended if you also want to manage VMs on your local host or on different remote hosts.

• When connecting to a remote host, you can avoid having to provide the root password to the remote system. To do so, use one or more of the following methods:

  • Set up key-based SSH access to the remote host
  • Use SSH connection multiplexing to connect to the remote system
  • Kerberos authentication in Identity Management
• The -c (or --connect) option can be used to run the virt-install, virt-viewer, virsh and virt-manager commands on a remote host.

• Use a shutdown command appropriate to the guest OS while connected to the guest.

• Use the virsh shutdown command on the host:

  • If the VM is on a local host:

    # virsh shutdown demo-guest1
    Domain 'demo-guest1' is being shutdown

  • If the VM is on a remote host, in this example 10.0.0.1:

    # virsh -c qemu+ssh://root@10.0.0.1/system shutdown demo-guest1
    
    root@10.0.0.1's password:
    Domain 'demo-guest1' is being shutdown

Prerequisites

• Back up important data from the VM.
• Shut down the VM.
• Make sure no other VMs use the same associated storage.

Procedure

• Use the virsh undefine utility.

  For example, the following command removes the guest1 VM, its associated storage volumes, and non-volatile RAM, if any.

  # virsh undefine guest1 --remove-all-storage --nvram
  Domain 'guest1' has been undefined
  Volume 'vda'(/home/images/guest1.qcow2) removed.

Prerequisites

• The web console VM plug-in is installed on your system.
• Back up important data from the VM.
• Make sure no other VM uses the same associated storage.
• Optional: Shut down the VM.