====== Migrate_Xen_based_VM_(domU)_to_KVM_based_VM ======

Xen VMs do not have bootable disks. I.E. there is typically no grub config to worry about as a Xen kernel is used to boot DomU's. KVM however "typically" allows guest VMs to run unmodified kernels and as a result typically have disks and partitions including a /boot and grub mbr.

====== Method 1 ======
KVM however can boot a Xen (disk based or LVM) VM using a kernel and initrd config.

 OrigXen: lvcreate -L1G -s -n vmdisksnap /dev/vg0/vm01-disk              <nowiki>//</nowiki>Create a LVM Snapshot
 NewKVM : lvcreate -n deb05-disk --size 3g vg0                           <nowiki>//</nowiki>Create a new LV with same size
 NewKVM : lvcreate -n deb05-swap --size 512M vg0                         <nowiki>//</nowiki>Create swap LV as was done on the Xen host originally
 NewKVM : nc -l -p 7000 | dd of=/dev/vg0/deb05-disk bs=2M                   <nowiki>//</nowiki>use net cat and dd with bs=2M to speed things up.
 OrigXen: dd if=/dev/vg0/vmdisksnap bs=2M | nc x.x.x.x 7000 -q 10        <nowiki>//</nowiki>using port 7000 for nc
 scp initrd.img-2.6.26-2-686-bigmem to new host                          <nowiki>//</nowiki>scp across original kernel and initrd image.
 scp vmlinuz-2.6.26-2-686-bigmem to new host
 cp /etc/libvirt/qemu/deb04.xml /etc/libvirt/qemu/deb05.xml              <nowiki>//</nowiki>copy an existing libvirt xml domain. We are going to edit it by hand instead of going virt-install

 vi /etc/libvirt/qemu/deb05.xml
 <nowiki>//</nowiki>delete the uuid line.
 <nowiki>//</nowiki>change the name. Delete the mac address line.
 <nowiki>//</nowiki>add the jernel and initrd options.
 <nowiki>//</nowiki>add a cmdline root=/dev/vda and an optional console=ttyS0 allowing you to go virsh console deb05
 
 <domain type='kvm'>
  <name>deb05</name>
  <memory>196608</memory>
  <currentMemory>196608</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch='i686' machine='pc'>hvm</type>
    **<kernel>/root/vmlinuz-2.6.26-2-686-bigmem</kernel>**
    **<initrd>/root/initrd.img-2.6.26-2-686-bigmem</initrd>**
    **<cmdline>root=/dev/vda console=ttyS0</cmdline>**
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='block' device='disk'>
      <source dev='/dev/vg0/deb05-disk'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <disk type='block' device='disk'>
      <source dev='/dev/vg0/deb05-swap'/>
      <target dev='vdb' bus='virtio'/>
    </disk>
    <interface type='bridge'>
      <source bridge='br0'/>
      <model type='virtio'/>
    </interface>
    <serial type='pty'>
      <source path='/dev/pts/8'/>
      <target port='0'/>
    </serial>
    <console type='pty' tty='/dev/pts/8'>
      <source path='/dev/pts/8'/>
      <target port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes' keymap='en-us'/>
  </devices>
 </domain>
===== Notes =====
Make sure that the kernel specified is contained on the VM disk under /lib/modules/2.6.... otherwise iptables etc. won't work.

The above config uses a separate network br0 bridge. See: [[KVM_Setup_on_Debian_Lenny]]

For faster dd's see: http://serverfault.com/questions/147935/how-to-determine-the-best-byte-size-for-the-dd-command 

For LVM snapshots, see: http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html  http://arstechnica.com/open-source/news/2004/10/linux-20041013.ars     http://sysadminsjourney.com/content/2008/11/29/backup-lamp-stacks-lvm-snapshots

On the original Xen host, you can go:
 lvremove /dev/vg0/vmdisksnap
 lvscan  <nowiki>//</nowiki>shows all LVs

Other tidying up to be done is to: vi /etc/fstab and replace in vda and vdb for swap. Update the IP and gateway in /etc/network/interface