Introduction

The Xen virtual machine monitor allows multiple operating systems to be run on shared hardware. (For slightly more helpful information, see their web page.)

To set up a working copy of Xen, four things are needed: the Xen kernel itself, various tools, a XenLinux kernel to run as the "domain 0" operating system, and usually at least one unprivileged kernel to run the virtual machines.

Xen and tools

It may first be necessary to unmask a couple of packages before emerge will install them: add the following lines to /etc/portage/package.keywords:

  sys-apps/xen ~x86
  sys-kernel/xen-sources ~x86
  dev-python/twisted ~x86

Then simply run

  USE="doc" emerge xen

(omitting USE="doc" if you don't care about the documentation).

XenLinux

To download the 2.6.9 kernel source with Xen patches, run:

  emerge xen-sources

If you want to use these sources to compile an unprivileged kernel (which you probably do, unless you're planning to use Xen Linux/BSD kernels from elsewhere), it's best to make a copy of the kernel source:

  cp -R /usr/src/linux-2.6.9-xen0 /usr/src/linux-2.6.9-xenU
  cd /usr/src/linux-2.6.9-xenU
  sed -i s/-xen0/-xenU/ Makefile
  cp arch/xen/configs/xenU_defconfig arch/xen/defconfig

When this has finished, configure and compile the kernel as normal (see the Gentoo Handbook):

  cd /usr/src/linux-2.6.9-xen0
  make xconfig
  make && make modules_install

  mount /boot
  cp vmlinux /boot/vmlinux-syms-2.6.9-xen0
  cp vmlinuz /boot/vmlinuz-2.6.9-xen0
  cp System.map /boot/System.map-2.6.9-xen0
  cp .config /boot/config-2.6.9-xen0

and update your GRUB config file (/boot/grub/grub.conf) to add something like

  title Xen 2.0 / XenLinux 2.6.9
  root (hd0,0)
  kernel (hd0,0)/boot/xen.gz dom0_mem=131072
  module (hd0,0)/boot/vmlinuz-2.6.9-xen0 root=/dev/sda4 ro console=tty0

(Make sure you give yourself the option to boot into your normal kernel, in case Xen fails to boot.)

It should then be possible to reboot into XenLinux and use the system as normal. Follow the procedures in the standard Xen documentation to play with virtual machines, using kernel = "/usr/src/linux-2.6.9-xenU/vmlinuz" in the config file if you compiled the xenU kernel earlier.