Installing a Debian unstable virtual machine


These are my notes about the installation of a virtual machine on my Debian GNU/Linux stable system (“AMD64” architecture). The installed virtual machine (the guest) is also a Debian system, but the unstable (also known as Sid) one.

Debian packages are available in unstable in more recent versions than in stable. I wanted a Debian unstable virtual machine to be able to test the new version of some packages.

Checking the virtualizations extensions presence on the CPU

If your hardware has virtualization support, then you should enable it in the BIOS.

To know whether your hardware has virtualization support, issue the following command. If it prints something, then your hardware has virtualization support:

grep "^flags\s*:" /proc/cpuinfo \
  | head -1 \
  | sed "s/^.\+:\s*//" \
  | sed "s/ \+/\n/g" \
  | grep "vmx\|svm"

Installing the libvirt family of tools

I install the libvirt family of tools as root with:

apt-get install virtinst libvirt-daemon-system libvirt-clients # As root.

The libvirt-clients package comes with the virsh program, to be used to manage the virtual machines and get useful information. Examples (as root):

virsh list --all     # List the virtual machines.
virsh net-list --all # List the virtual networks.

The osinfo and its querying tools are useful too:

apt-get install libosinfo-bin # As root.

Preparing storage locations

For the virtual machine images

The default location (“storage pool”) for the virtual machines is /var/lib/libvirt/images.

On some of my systems, the free space in /var is very limited. I want the virtual machines to be located in my home directory instead. So I create a directory with mkdir -p ~/vm/libvirt/images. And then, as root, I do:

chown root:root /home/my_user_name/vm/libvirt/images # Change directory
                                                     # ownership to root.

chmod 711 /home/my_user_name/vm/libvirt/images       # Change permissions (no
                                                     # read/write permission
                                                     # for non-root users).

You can see the list of the storage pools managed by libvirt with:

virsh pool-list # As root.

If this list is empty, then I define and start the default storage pool with:

virsh pool-define-as default dir \
  --target /home/my_user_name/vm/libvirt/images # As root.
virsh pool-autostart default                    # As root.
virsh pool-start default                        # As root.

If the default storage pool is already existing, then I check the path with virsh pool-dumpxml default (as root) and change it if needed with:

virsh pool-edit default # Edit the path and save.

After a reboot, virsh pool-dumpxml default (as root) shows the new path.

For the installer ISO image

Nothing complicated here, I just create a directory as an unprivileged user:

mkdir -p ~/vm/installer_iso/debian_testing

Searching operating systems in the osinfo database

When creating the virtual machine with virt-install, it is recommended to provide the –os-variant option. The possible values for that option are the short IDs provided by command osinfo-query os:

osinfo-query os|less
osinfo-query os|grep Debian

Getting a Debian testing installer image

Debian testing installer images are available for download and updated daily (for the small (“netinst”) images at least). See the Debian installer page of the Debian developers’ corner.

You can download the “netinst” Debian testing installer image for the “AMD64” architecture with:

cd ~/vm/installer_iso/debian_testing

You might want to verify the authenticity of the ISO image. It is the same process as for a Debian stable installer image.

Creating the Debian unstable virtual machine

Start the installation

I enable the default virtual network as root with:

virsh net-start default # As root.

You may want to set the default to start automatically:

virsh net-autostart default # As root.

I make sure the applications running as root can connect to the X server:

xhost +local: # As "normal" user.

Then I set and export the DISPLAY variable as root:

export DISPLAY=:0.0 # As root.

I create the virtual machine as root with the following command (my working directory was the one containing the Debian testing installer ISO image):

virt-install --name debian_unstable \
  --memory 1024 \
  --vcpus=1 \
  --cdrom debian-testing-amd64-netinst.iso \
  --disk pool=default,size=10 \
  --os-variant debiantesting \
  --graphics spice \
  --channel spicevmc & # As root.

Debian testing base installation

I proceed with the installation as I would for a “normal” Debian installation. I choose the most simple disk partition scheme (all in a single partition) and requires the installation of a SSH server.


Once the installation is complete, the virtual machine automatically restarts. I lauch virt-viewer (as root) to get a window to the virtual machine:

virt-viewer debian_unstable & # As root.

Upgrade to Debian unstable

The first step to upgrade to Debian unstable is to edit /etc/apt/sources.list (as root, on the guest):

  • Substitute the Debian testing distribution name (which was “bullseye”) with “unstable”.
  • Comment out any line containing

The second step is to execute:

apt-get update; apt-get dist-upgrade # As root, on the guest.

Install and Openbox

I then install and Openbox on the virtual machine:

apt-get install xorg openbox obmenu openbox-menu menu # As root, on the
                                                      # guest.

Enable copy’n’paste between host and guest

The package spice-vdagent enables copy’n’paste between host and guest:

apt-get install spice-vdagent # As root, on the guest.

Configure display resolution

By default, display resolution on the guest is 1024x768. I prefer 1920x1080 (which is the resolution of my monitor). So I create a specific configuration file (/etc/X11/xorg.conf, which does not exist by default).

The starting point is the file (/root/ that generates when this command is issued (exit first):

Xorg -configure # As root, in the guest.

In /root/, there is a Monitor section for a monitor with identifier Monitor0. I add “Modelines” in this section.

“Modelines” look like:

Modeline “1024x768_24” 65.00 1024 1048 1184 1344 768 771 777 806 -hsync -vsync
Modeline “1920x1080_24” 148.50 1920 2008 2052 2200 1080 1084 1089 1125 -hsync -vsync
Modeline “1600x900_24” 108.00 1600 1624 1704 1800 900 901 904 1000 +hsync +vsync

We can find the data that those “Modelines” are made of in a log file generated with (in this example, the file is called xlog.txt):

Xorg -verbose 6 > xlog.txt 2>&1 # As root, on the guest.

This gets you in Xorg with no way to exit. Use the “Send key” menu item of virt-viewer to send, say, “Ctrl-Alt-F3” and access a new console where you can log in as root, find the process ID of Xorg with ps -ef|grep Xorg and kill Xorg with a kill <process_id> command.

A more comfortable way of getting the log file is to automatically kill after a few seconds. We need the killall command for that, provided by the Debian package psmisc:

apt-get install psmisc # As root, on the guest.
Xorg -verbose 6 > xlog.txt 2>&1 & sleep 3 && killall Xorg # As root, on the
                                                          # guest.

In xlog.txt, we find lines like the following, which help building the “Modelines”:

(II) qxl(0): Modeline “1920x1080”x60.0 148.50 1920 2008 2052 2200 1080 1084 1089 1125 -hsync -vsync (67.5 kHz eP)
(II) qxl(0): Modeline “1600x900”x60.0 108.00 1600 1624 1704 1800 900 901 904 1000 +hsync +vsync (60.0 kHz e)
(II) qxl(0): Modeline “1024x768”x60.0 65.00 1024 1048 1184 1344 768 771 777 806 -hsync -vsync (48.4 kHz e)

Once I have added the “Modelines” in /root/, I edit the Screen section and add a Display subsection with a Modes line matching the resolution I want:

Section “Screen”
Identifier “Screen0”
Device “Card0”
Monitor “Monitor0”
SubSection “Display”
Modes “1920x1080”

You can check that your /root/ is a correct configuration file with a test of

Xorg -config /root/ -retro # As root, on the guest.


Xorg -config /root/ -retro & sleep 3 && killall Xorg # As root,
                                                                  # on the
                                                                  # guest.

The final step is to copy /root/ to /etc/X11/xorg.conf:

cp /etc/X11/xorg.conf # As root, on the guest.

You can download this xorg.conf file.


At this point, I reboot (or else the keyboard layout in may not be the expected one):

systemctl poweroff # As root, on the guest.

I then login as a normal user and starts and Openbox with:


Shutting down and restarting the virtual machine

To shut down the virtual machine, I just do as for a “real” machine. For example:

systemctl poweroff # As root, on the guest.

Alternatively, this virsh command run from the host should also shut down the virtual machine:

virsh shutdown debian_unstable # As root.

If it’s not enough:

virsh destroy debian_unstable # As root.

To restart the virtual machine I do:

virsh start debian_unstable # As root.
virt-viewer debian_unstable # As root.

or, if I want the viewer in full screen mode:

virt-viewer -f debian_unstable # As root.

Again, you need to make sure the applications running as root can connect to the X server, so you may have to do (prior to launching virt-viewer):

xhost +local: # As "normal" user.


export DISPLAY=:0.0 # As root.

Finding the IP address of the virtual machine

Having the IP address of the virtual machine is useful, for example to connect to it from the host via SSH.

On a Debian GNU/Linux system, you probably have the iproute2 package installed. In this case, the following command should show (among other information) the IP address:

ip addr # On the guest.

If you don’t have the ip command, you may have the ifconfig command (provided by package net-tools on a Debian GNU/Linux system) which does show (among other information) the IP address:

ifconfig # On the guest.

Alternatively, you should be able to get the IP address of a guest without login into the guest, using virsh:

virsh net-dhcp-leases default # As root, on the host.

Removing the virtual machine

Once shutdown, the virtual machine can be entirely removed with these commands:

virsh undefine debian_unstable # As root.
virsh vol-delete --pool default debian_unstable.qcow2 # As root.