This post outlines the procedure to convert a (Linux) vm from VirtualBox to KVM. Preferably VMs would be built on KVM directly, but this is the process used to migrate a VM built prior to standing up KVM infrastructure into KVM. Much was learned during this process which I wanted to capture before it fades from memory.

UPDATE 31/7/2021: These instructions were accurate at the time of writing in 2015, but I haven't had need of this process recently and can't vouch for their accuracy in 2021.

On the Virtualbox host:

• Delete all snapshots of the VM so that there is a single, canonical disk image file that can be converted.
• Shutdown the VM cleanly
• Run mkdir ~/tmp && cd ~/tmp to create a temporary folder to work in.
• If you've converted the disk image previously use the "Virtual Media Manager" in Virtualbox, and find and delete the .raw file.
• Run VBoxManage clonehd ../VirtualBox\ VMs/VMNameHere/VMNameHere-disk1_2.vmdk ./VMNameHere.raw --format raw to export the virtualbox to a raw disk image. Make sure the source file name is correct and confirm that it has a current date.
• Run qemu-img convert -f raw VMNameHere.raw -O qcow2 VMNameHere.qcow to convert the raw image to the QCOW2 format KVM/QEMU uses.
• SCP the .qcow2 file to the KVM server. I dropped it into my home directory.

On the KVM server:

• Log in via ssh and su to root.
• Change to the KVM images folder: cd /var/lib/libvirt/images
• Move the QCOW2 file into the KVM images folder and set it's permissions: mv /home/jim/VMNameHere.qcow2 . && chown qemu:qemu VMNameHere.qcow2 && chmod 644 VMNameHere.qcow2
• Using virt-manager from your workstation:
• Create a new vm with the following settings:
  • Import Existing Disk Image
  • Browse and find your QCOW2 file
  • Select the appropriate OS (CentOS 7 is available under "Show Other Linux Versions")
  • Set memory and CPU to be the same as the VirtualBox vm
  • Name the VM appropriately (internal host name of the vm is the convention I use)
  • Tick "Customise configuration before install"
  • Expand "Advanced Options" and select the correct network type, and give the interface the same MAC address as the virtualbox VM.
• When customising hardware, add a Storage device
  • Type CDROM
  • Download a CentOS 7 ISO and place it in the images folder, or use a different ISO if the machine you're converting isn't Centos 7.
• Set the CROM to be the first boot device
• Boot the VM and select "Rescue an Installed Centos System" from the boot menu
• Once the VM has booted to the rescue mode shell run the following commands via the VM's console:
  • chroot /mnt/sysimage
  • vi /boot/grub2/device.map
  • Change any /dev/sda references to /dev/vda
  • grub2-mkconfig -o /etc/grub2.cfg
  • vi /etc/dracut.conf
  • Look for the #add_devices+="" line and change it to add_devices+="virtio_blk"
  • Run ls /lib/modules and find the latest kernel version that's installed. The kernel version on the CD ISO may not match the latest in the vm, so we'll rebuild Dracut for a specific version instead.
  • Run dracut kver <version found above> force
  • Run ls -al /boot and check that there's an initramfs-*.img file with a current time stamp (i.e. Dracut has rebuilt initramfs correctly).
  • exit
  • exit
• The vm should reboot. Press a key on the grub menu to hold the machine there and stop it from booting.
• Force Power off the VM.
• Change the boot order so that the "VirtIO Disk" is the first and only boot option, and set the VM to start automatically on host boot up.
• Start the VM, and ensure that the kernel version used previously is selected on the grub menu.
• The VM may reboot once during the initial boot up process, but should be good to go after that.

And you're done!