Chapter 7. Connecting to virtual machines

Prerequisites

• Your system and the VM that you are connecting to must support graphical displays.
• If the target VM is located on a remote host, you must have connection and root access privileges to the host.
• Optional: If the target VM is located on a remote host, it is helpful to set up libvirt and SSH for more convenient access to remote hosts. For instructions, see Setting up easier access to remote virtualization hosts.
• The VMs that you want to interact with are installed and started. For instructions, see Creating virtual machines and Starting virtual machines.

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 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

  Successful output:

  root@192.0.2.1'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 by using SSH:

  • hostdev interfaces
  • Direct interfaces
  • Bridge interfaces

• 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
     ...

• The VMs that you want to interact with are installed and started. For instructions, see Creating virtual machines and Starting virtual machines.

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

  Example output:

  Id    Name                           State
  ----------------------------------------------------
  2     testguest1                    running
  -     testguest2                    shut off

• The VM does not provide VNC protocols, so it does not offer video display for GUI tools.
• The VM does not have a network connection, so it cannot be interacted with by 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

• 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=<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

    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.

• 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)

• The VMs that you want to interact with are installed and started. For instructions, see Creating virtual machines and Starting virtual machines.

Prerequisites

• You have an existing VM that is configured to use the SPICE remote display protocol and is already shut-down.
• The VMs that you want to interact with are installed and started. For instructions, see Creating virtual machines and Starting virtual machines.

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

  Successful output:

  Domain 'vm-name' defined successfully

  Important

  This also removes certain SPICE devices from the VM, such as audio and USB passthrough, because they do not have a suitable replacement in the VNC protocol. For more information, see Considerations in adopting RHEL 9.

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"

  Successful output:

  <graphics type='*vnc*' port='5900' autoport='yes' listen='127.0.0.1'>