For the Ceph training at 42on I use VirtualBox to build Virtual Machines. This is because they work under MacOS, Windows, and Linux.

For the internal Git at 42on we use Gitlab and I wanted to use Gitlab’s CI to build my Virtual Machines automatically.

As we don’t have any physical hardware at 42on (everything runs in the cloud) I wanted to see if I could run VirtualBox Headless inside a VM with Nested KVM enabled.

Nested KVM

The first thing I checked was if my KVM Virtual Machine actually supported Nested KVM. This can be verified with the kvm-ok command under Ubuntu:

root@glrun01:~# kvm-ok 
INFO: /dev/kvm exists
KVM acceleration can be used
root@glrun01:~#

Now that’s verified I tried to install VirtualBox.

VirtualBox

Installing VirtualBox is straightforward. Just add the repository and install the packages. Don’t forget to reboot afterward to make sure all kernel modules are loaded and properly installed.

apt-get install virtualbox

VirtualBox Extension Pack

The trick to get everything working properly is to install Oracle’s VirtualBox Extension Pack. It took me a while to figure out that I need to install it manually. It wasn’t done by default after installation.

You need to download the pack and install it using the VBoxManage command.

wget http://download.virtualbox.org/virtualbox/5.0.24/Oracle_VM_VirtualBox_Extension_Pack-5.0.24.vbox-extpack
vboxmanage extpack install Oracle_VM_VirtualBox_Extension_Pack-5.0.24.vbox-extpack
vboxmanage list extpacks
vboxmanage setproperty vrdeextpack "Oracle VM VirtualBox Extension Pack"

With that installed and configured I rebooted the machine again just to be sure.

It works!

With that, it actually worked. The VirtualBox VMs can now be built inside a Nested KVM machine controlled by Gitlab’s CI 🙂