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Using kvm, qemu, and virsh for a virtual Ubuntu install

  • Jul 28, 2021

This is a concise description of how to get a virtual machine up and running that focuses on command line and console use. The instructions are written for Gentoo and assume a reasonable understanding of linux. They likely can be easily adapted for other distributions.

Install

Install libvirt

raptor ~ # sudo emerge -av libvirt

The above will install dependencies (including qemu) may require adding some keywords. Ensure you have appropriate qemu targets in your /etc/portage/make.conf file. A typical target is x86_64.

QEMU_SOFTMMU_TARGETS="x86_64"
QEMU_USER_TARGETS="x86_64"

Set permissions for libvirt

See this link about permissions and libvirt: https://wiki.gentoo.org/wiki/QEMU#Permissions

Note from those instructions that the following needed to be uncommented in the /etc/libvirt/libvirtd.conf file:

auth_unix_ro = "none"
auth_unix_rw = "none"
unix_sock_group = "libvirt"
unix_sock_ro_perms = "0777"
unix_sock_rw_perms = "0770"

You should add your non-privileged user to the libvirt group (if it exists… depends on policykit use flag) and the kvm group.

Also make sure you configure/compile appropriate kernel modules as described: https://wiki.gentoo.org/wiki/QEMU#Kernel

raptor ~ # usermod -a -G libvirt exampleusername
raptor ~ # usermod -a -G kvm exampleusername

Adding yourself to a group typically requires you to re-login.

Start the libvirt daemon

raptor ~ # /etc/init.d/libvirtd restart

Create a virtual hard drive image

foo@bar:~$ qemu-img create -f qcow2 Ubuntu-Focal-Fossa.qcow 20G

Download Ubuntu

foo@bar:~$ wget https://releases.ubuntu.com/20.04/ubuntu-20.04.3-live-server-amd64.iso

Install the image

foo@bar:~$ virt-install --location ubuntu-20.04.3-live-server-amd64.iso --memory 4096 --vcpus 4 \
                        --disk Ubuntu-Focal-Fossa.qcow --nographics --extra-args='console=ttyS0'

Complete the installation then shutdown the machine. I found that I had to force the shutdown:

foo@bar:~$ virsh destroy ubuntu20.04 ## Force shutdown of running virtual machine

Use the virtual machine

Start the machine and connect to its console

Once installed, start and connect to the virtual machine console

foo@bar:~$ virsh start ubuntu20.04 ## Start the virtual machine in the background
foo@bar:~$ virsh console ubuntu20.04 ## Connect to the virtual machine in a console mode

Note it reads the console is real time. Hence, you may have to press return to get a login prompt (or similar).

List virtual machines and their state

foo@bar:~$ virsh list --all

Force shutdown

To force a shutdown the machine (potentially with data loss if files have not yet been written)

foo@bar:~$ virsh destroy ubuntu20.04 ## Force shutdown of running virtual machine

Delete the virtual machine

The following command deletes the machine from virsh but doesn’t delete the disk image

foo@bar:~$ virsh undefine ubuntu20.04 ## Delete the virtual machine from virsh (doesn't delete the disk image)

Rename a machine

foo@bar:~$ virsh domrename {domain} {new-name}

Edit the configuration to add graphics

The goal of the above was a primarily console based system. To get a video display via spice, you must edit the xml. Source

foo@bar:~$ virsh edit ubuntu20.04

Then you can add a grahics video device (qml) and graphics protocol (spice). These must live within the <device></device>.

    <graphics type='spice' autoport='yes'>
      <listen type='address'/>
      <image compression='off'/>
    </graphics>
    <video>
      <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>
      <address type='pci' domain='0x0000' bus='0x08' slot='0x01' function='0x0'/>
    </video>

Restart the machine. Then list the available virtual displays:

foo@bar:~$ virsh domdisplay ubuntu20.04
spice://127.0.0.1:5900

Open a display:

foo@bar:~$ virt-viewer ubuntu20.04

The above, with no arguments, will open the running domain (if there is only one).

Start the graphical environment:

From here:

foo@bar:~$ sudo systemctl isolate graphical

Snapshots

Take a snapshot

foo@bar:~$ virsh snapshot-create-as --domain ubuntu20.04 --name "2021-08-03" --description "Prior to install of ubuntu-desktop"

Note the above can include a –live flag if the snapshot is running

Delete a snapshot

foo@bar:~$ virsh snapshot-delete --domain ubuntu20.04 --snapshotname "2021-08-03"
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