I've learned that CirrusCI offers nested virtualization in their free package for public repos and I am trying to make use of it for testing my Ansible playbooks.

Unfortunately, libvirt is insisting that CI environment has no support for full virtualization. All checks (known to me) testify of the opposite, and qemu-kvm works fine when called directly. I'm almost certain the problem is with my host OS configuration, and not with the CI engine. I've seen other people use full virtualization on CirrusCI for their purposes (Android emulation, redox testing).

I use Debian 10 for host system, slim image from DockerHub with the following extra packages installed (--no-install-recommends):

bridge-utils  libguestfs-tools       python3-dev
coreutils     libosinfo-bin          python3-venv
cpu-checker   libssl-dev             qemu-kvm
curl          libvirt-clients        qemu-kvm
gcc           libvirt-daemon         qemu-utils
gpg           libvirt-daemon-system  systemd
gpg-agent     linux-image-amd64      vagrant
iproute2      make                   vagrant-libvirt
kmod          procps                 virt-goodies
libc-dev      python3                virtinst

Base image, CirrusCI configuration

What may I be missing? Why would libvirt tell that there is no KVM when qemu-kvm works perfectly?

libvirt error

Error while creating domain: Error saving the server: Call to virDomainDefineXML failed: invalid argument: could not find capabilities for domaintype=kvm

virsh capabilities contains only <domain type='qemu'/> entries.

Demo of inconsistent behavior

Any tool based on libvirt fails to invoke KVM:

$ virt-install --import --virt-type kvm --name debian10-vm --memory 512 --disk path=/debian.qcow2,format=qcow2 --os-variant debian10 --noautoconsole || echo "Exit code: $?"
ERROR    Host does not support domain type kvm for virtualization type 'hvm' arch 'x86_64'
Exit code: 1

But qemu-kvm works when executed directly:

$ kvm -nographic /debian.qcow2
cSeaBIOS (version 1.12.0-1)
iPXE (http://ipxe.org) 00:03.0 C980 PCI2.10 PnP PMM+07F900F0+07ED00F0 C980
Press Ctrl-B to configure iPXE (PCI 00:03.0)...

Booting from Hard Disk...
GNU GRUB  version 2.02+dfsg1-20

Full CI logs


  • lsmod shows that kvm and kvm_intel are loaded
  • cat /proc/cpuinfo - contains vmx flag
  • lscpu - Virtualization type: full
  • kvm-ok - OK
  • ls -l /dev/kvm - exists, owned by root:rdma
  • ls -l /var/run/libvirt - sockets exist, owned by root:root
  • whoami - root
  • groups $(whoami) - root
  • systemctl status - systemd is not started, libvirtd was launched via CI rules
  • virt-host-validate - all checks pass, except IOMMU - should not be important for my use case

Full listings are available in the CI log, section "kvm_before".

4 Answers 4


Most distro libvirt packages will be configured to run qemu as qemu:qemu user. See the UID+GID reported by virsh --connect qemu:///system capabilities | grep baselabel. If that's the case for your distro, then qemu doesn't have permissions to access /dev/kvm, so libvirt is not advertising kvm support. chmod 666 /dev/kvm should fix it. This is the default in Fedora FWIW

  • 3
    Yes, that was it. Thank you! I've added explicit user = "root" to /etc/libvirt/qemu.conf instead of changing owners of /dev/kvm. It was unexpected because that file contains comments that say "root" is used by default. Guess the comments got outdated.
    – SIO
    Commented Feb 7, 2020 at 14:04

for ubuntu i had that same thing.

I ran this to make sure nothing had gotten removed

sudo apt-get install qemu uml-utilities virt-manager git wget libguestfs-tools p7zip-full uml-utilities virt-viewer qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils -y

Was all installed which was weird.

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Note, selecting 'qemu-system-x86' instead of 'qemu-kvm'
bridge-utils is already the newest version (1.7-1ubuntu2).
git is already the newest version (1:2.32.0-1ubuntu1).
wget is already the newest version (1.21-1ubuntu3).
libguestfs-tools is already the newest version (1:1.44.1-1ubuntu6).
p7zip-full is already the newest version (16.02+dfsg-8).
uml-utilities is already the newest version (20070815.4-1).
virt-manager is already the newest version (1:3.2.0-3).
virt-viewer is already the newest version (7.0-2build1).
qemu-system-x86 is already the newest version (1:6.0+dfsg-2expubuntu1.2).
qemu is already the newest version (1:6.0+dfsg-2expubuntu1.2).
libvirt-clients is already the newest version (7.6.0-0ubuntu1.1).
libvirt-daemon-system is already the newest version (7.6.0-0ubuntu1.1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

I than reran the commands for the user groups and bam started working again. Super odd but maybe helpful to others

sudo usermod -aG libvirt $USER
sudo usermod -aG kvm $USER

This is extending Cole Robinson's answer a bit, which was very helpful for me to figure out a similar problem on Ubuntu.

I think Debian does it the same way as Ubuntu, where you need to install qemu-system-x86 and /dev/kvm magically becomes group-writable and owned by the kvm group (instead of 0600 root:root).

libvirtd on Debian/Ubuntu uses the libvirt-qemu user by default, and that user's primary group is kvm.


I had exactly the same issue - the kvm command worked but virt-install ended with the same error.

The culprit was that there was a running Virtualbox VM.

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