Chapter 7. Connecting to virtual machines

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

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• 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 192.0.2.1. The connection also requires root authentication for 192.0.2.1.

  # virt-viewer --direct --connect qemu+ssh://root@192.0.2.1/system guest-name
  root@192.0.2.1's password:

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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 by 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:

     # dnf install libvirt-nss

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  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
     ...

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Troubleshooting

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

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

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• Does not have a network connection, and thus cannot be interacted with using SSH.

Prerequisites

• The GRUB boot loader on your host must be configured to use serial console. To verify, check that the /etc/default/grub file on your host contains the GRUB_TERMINAL=serial parameter.

  $ sudo grep GRUB_TERMINAL /etc/default/grub
  GRUB_TERMINAL=serial

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• 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>

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• 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=<console-name>, where <console-name> is architecture-specific:

  • For AMD64 and Intel 64: ttyS0

    Note

    The following commands in this procedure use ttyS0.

    # cat /proc/cmdline
    BOOT_IMAGE=/vmlinuz-6.12.0-0.el10_0.x86_64 root=/dev/mapper/rhel-root ro console=tty0 console=ttyS0,9600n8 rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb

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    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"

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

       # grub2-editenv - unset kernelopts

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    3. Reboot the VM.

• The serial-getty@<console-name> service must be enabled. For example, on AMD64 and Intel 64:

  # systemctl status serial-getty@ttyS0.service
  
  ○ serial-getty@ttyS0.service - Serial Getty on ttyS0
       Loaded: loaded (/usr/lib/systemd/system/serial-getty@.service; enabled; preset: enabled)

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• You can edit the /etc/libvirt/libvirt.conf file and set the value of the uri_default parameter to example-qemu-host-alias 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 = "example-qemu-host-alias"

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

  $ virsh list
  root@192.0.2.1's password:
  
  Id   Name              State
  ---------------------------------
  1   example-remote-guest      running

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• When connecting to a remote host, you can avoid providing 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.

Prerequisites

• You have an existing VM that is configured to use the SPICE remote display protocol and is already shut-down.

Procedure

• On the host, run the following command, and replace `<vm-name>` with the name of the VM that you want to convert to VNC.

  # virt-xml <vm-name> --edit --convert-to-vnc
  
  Domain 'vm-name' defined successfully

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Verification

• Inspect the configuration of the VM you converted, and make sure the graphics type is listed as vnc.

  # virsh dumpxml -xml <vm-name> | grep "graphics"
  
  <graphics type='vnc' port='5900' autoport='yes' listen='127.0.0.1'>

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