Chapter 5. Connecting to virtual machines

• 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.

• 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:

     # dnf 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 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, edit the /etc/default/grub file and add console=ttyS0 to the line that starts with GRUB_CMDLINE_LINUX.

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

       # grub2-editenv - unset kernelopts

    3. Reload the Grub configuration:

       # grub2-mkconfig -o /boot/grub2/grub.cfg
       Generating grub configuration file ...
       Found linux image: /boot/vmlinuz-3.10.0-948.el7.x86_64
       Found initrd image: /boot/initramfs-3.10.0-948.el7.x86_64.img
       [...]
       done

    4. 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, and virsh commands on a remote host.