Paravirtualize an Ubuntu VM using XenServer

1. Create and install the VM in HVM mode

1. create the VM from the "Other install media" template. The VM name shouldn’t contain whitespace.
2. attach the Ubuntu 11.10 ISO image to the VM DVD drive
3. boot the VM
4. while partitioning the hard drive, choose Ext3 rather than Ext4, because ’pygrub’, the XenServer bootloader for the PV mode, can’t read Ext4. If you wish to benefit from Ext4 advantages anyway, then you’ll have to create a /boot partition in Ext3 and the / partition in Ext4
5. finish install and reboot VM

2. Preparing VM conversion

1. connect to VM console through XenCenter and install an SSH server
   sudo apt-get install openssh-server
2. create a new console for Xen and replace all ’tty1’ occurences by ’hvc0’
   sudo cp /etc/init/tty1.conf /etc/init/hvc0.conf
sudo vi /etc/init/hvc0.conf
3. identify grub2 default entry and copy it
   cat /boot/grub/grub.cfg
[...]
menuentry 'Ubuntu, avec Linux 3.0.0-12-generic' --class ubuntu --class gnu-linux --class gnu --class os {
        recordfail
        set gfxpayload=$linux_gfx_mode
        insmod gzio
        insmod part_msdos
        insmod ext2
        set root='(hd0,msdos1)'
        search --no-floppy --fs-uuid --set=root 51a2ba97-2521-44d7-9b08-316b7059db89
        linux        /boot/vmlinuz-3.0.0-12-generic root=UUID=51a2ba97-2521-44d7-9b08-316b7059db89 ro   quiet splash vt.handoff=7
        initrd        /boot/initrd.img-3.0.0-12-generic
}
[...]
4. because of a regression since Ubuntu Natty release, the xen module doesn’t seem to be loaded anymore into the initramfs. That can be corrected like this:
   sudo echo "xen-blkfront" >> /etc/initramfs-tools/modules
sudo update-initramfs -u
5. shutdown the VM
6. create a snapshot so that you can fallback to a stable version in case of trouble later on

3. Conversion using makepv.sh

1. ssh on the XenServer host and identify the name of the VM you wish to convert to PV mode
   ssh root@<XenServer>
xe vm-list
2. download the makepv.sh. It will:
   • change the bootloader from HVM to PV mode
   • prompt for kernel path (/boot/vmlinuz-3.0.0-12-generic),
   • prompt for kernel parameters (root=UUID=51a2ba97-2521-44d7-9b08-316b7059db89 ro   quiet splash vt.handoff=7)
   • prompt for initrd path (/boot/initrd.img-3.0.0-12-generic)
   • convert VM hard drive
     chmod +x makepv.sh
./makepv.sh <vm name> # sans espace

4. Install XenServer tools

1. empty the DVD drive in order to avoid an error related to two bootable drives detected, then boot the VM
2. from XenCenter, attach xs-tools.iso to the DVD drive
3. mount the image and install guest tools
   ssh <vm ip address>
sudo mount /dev/cdrom1 /media/cdrom
cd /media/cdrom/Linux
sudo dpkg -i xe-guest-utilities_6.0.0-743_amd64.deb
4. unmount the volume and reboot
   sudo umount /media/cdrom
sudo init 6
5. ssh on the VM and define runlevels of the services
   ssh <vm ip address>
sudo update-rc.d -f xe-linux-distribution remove
sudo update-rc.d xe-linux-distribution defaults
6. reboot for the last time. You can now enjoy your Ubuntu Oneiric Ocelot 11.10 paravirtualized virtual machine. The console in XenCenter is available again. However, the X server will complain that it doesn’t find a driver and Xorg will fail launching. This is the dark side of paravirtualization. If you ever happen to figure out how to run Xorg in PV mode, I’ll be happy to update this article.

References

• http://blog.403labs.com/post/1546501840/paravirtulization-with-citrix-xenserver-5-5-and-ubuntu
• http://www.jansipke.nl/installing-xenserver-tools-on-ubuntu-10-04
• https://bugs.launchpad.net/ubuntu/+source/xen-tools/+bug/839492