17.2. Changing between the KVM and Xen hypervisors

This section covers changing between the KVM and Xen hypervisors.

Fedora only supports one active hypervisor at a time.

Migrating virtualized guests between hypervisors

Presently, there is no application for switching Xen-based guests to KVM or KVM-based guests to Xen. Guests can only be used on the hypervisor type that they were created on.

17.2.1. Xen to KVM

The following procedure covers changing from the Xen hypervisor to the KVM hypervisor. This procedure assumes the kernel-xen package is installed and enabled.

Install the KVM package
Install the kvm package if you have not already done so.
```
# yum install kvm
```

Verify which kernel is in use

The kernel-xen package may be installed. Use the uname command to determine which kernel is running:

$ uname -r
2.6.23.14-107.fc8xen

The "2.6.23.14-107.fc8xen" kernel is running on the system. If the default kernel, "2.6.23.14-107.fc8", is running you can skip the substep.

Changing the Xen kernel to the default kernel

The grub.conf file determines which kernel is booted. To change the default kernel edit the /boot/grub/grub.conf file as shown below.

default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Fedora (2.6.23.14-107.fc8)
        root (hd0,0)
        kernel /vmlinuz-2.6.23.14-107.fc8 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
        initrd /initrd-2.6.23.14-107.fc8.img
title Fedora (2.6.23.14-107.fc8xen)
        root (hd0,0)
        kernel /xen.gz-2.6.23.14-107.fc8
        module /vmlinuz-2.6.23.14-107.fc8xen ro root=/dev/VolGroup00/LogVol00 rhgb quiet
        module /initrd-2.6.23.14-107.fc8xen.img

Notice the default=1 parameter. This is instructing the GRUB boot loader to boot the second entry, the Xen kernel. Change the default to 0 (or the number for the default kernel):

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Fedora (2.6.23.14-107.fc8)
        root (hd0,0)
        kernel /vmlinuz-2.6.23.14-107.fc8 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
        initrd /initrd-2.6.23.14-107.fc8.img
title Fedora (2.6.23.14-107.fc8xen)
        root (hd0,0)
        kernel /xen.gz-2.6.23.14-107.fc8
        module /vmlinuz-2.6.23.14-107.fc8xen ro root=/dev/VolGroup00/LogVol00 rhgb quiet
        module /initrd-2.6.23.14-107.fc8xen.img

Reboot to load the new kernel
Reboot the system. The computer will restart with the default kernel. The KVM module should be automatically loaded with the kernel. Verify KVM is running:
```
$ lsmod | grep kvm
kvm_intel              85992  1 
kvm                   222368  2 ksm,kvm_intel
```
The kvm module and either the kvm_intel module or the kvm_amd module are present if everything worked.