Xen Overview

Modern computers are sufficiently powerful to use virtualization to present the illusion of many smaller virtual machines (VMs), each running a separate operating system instance. Successful partitioning of a machine to support the concurrent execution of multiple operating systems poses several challenges. Firstly, virtual machines must be isolated from one another: it is not acceptable for the execution of one to adversely affect the performance of another. This is particularly true when virtual machines are owned by mutually untrusting users. Secondly, it is necessary to support a variety of different operating systems to accommodate the heterogeneity of popular applications. Thirdly, the performance overhead introduced by virtualization should be small.

Xen is a virtual machine monitor for x86 that supports execution of multiple guest operating systems with unprecedented levels of performance and resource isolation. Xen is Open Source software, released under the terms of the GNU General Public License. We have a fully functional ports of Linux 2.6 running over Xen, and regularly use it for running demanding applications like MySQL, Apache and PostgreSQL. Any Linux distribution (RedHat, SuSE, Debian, Mandrake) should run unmodified over the ported OS.

In addition to Linux, members of Xen's user community have contributed or are working on ports to other operating systems such as NetBSD (Christian Limpach), FreeBSD (Kip Macy) and Plan 9 (Ron Minnich).

It is also possible to run some other, not ported, operating systems if your CPU has hardware virtualization support (VT or Pacifica).

Installation on etch

Upstream documentation can be found in the xen-docs-3.0 package (in /usr/share/doc/xen-docs-3.0/user.pdf.gz). It's also available [http://www.cl.cam.ac.uk/research/srg/netos/xen/readmes/user/user.html online].

Dom0 (host)

Debian 4.0 (etch) was released with the -2.6.18-4 packages.

You can get a list of all xen-linux-system packages with a command such as apt-cache -n search xen-linux-system, or by consulting xen-linux-system. The following packages are currently available:


etch (stable)



etch (stable)



etch (stable)



etch (stable)














If you need to apply some modifications to the kernel with the xen patch, then one way to do it is described ?DebianKernelCustomCompilation.

DomU (guests)

Installing Debian GNU/Linux from a Unix/Linux System ( [http://www.debian.org/releases/stable/i386/apds03.html] ) ; - and adding some tweaks which are necessary to get a Xen guest run properly - mainly adjusting inittab and installing libc6-xen, and probably the kernel modules needed by the kernel you want to run for the domU.

When not using xen-tools (which takes some decisions out of your hand, by giving you a in some ways very flexible, but in some others not easily changeable installation path), you have to decide some things:

Installation on sid/testing

Need to explain the procedure, since there ain't the same set of packages ATM with kernel 2.6.21

Installation on sarge (oldstable)

Most of the above packages seem to be present on http://backports.org/, so use them!

libc6-xen is not present. [http://saintaardvarkthecarpeted.com/blog/?p=182 Allegedly], creating the file /etc/ld.so.nohwcap will cause libraries in /lib/tls to be ignored, thus making it unnecessary to move the directory out of the way. Can anyone confirm this?

Using Debian-Installer

The page ["DebianInstaller/Xen"] contains instructions on how to install Xen Dom0 and DomU with ["DebianInstaller"].

Package maintenance

Debian's Xen packages are maintained by the [http://alioth.debian.org/projects/pkg-xen/ pkg-xen] project. ([http://lists.alioth.debian.org/mailman/listinfo/pkg-xen-devel developpers' mailing list])

The [http://qa.debian.org/developer.php?login=pkg-xen-devel@lists.alioth.debian.org Debian Developer's Package Overview] page lists source packages that are maintained by the team.

Common Errors

dom0 automatic reboots

error : CDROM boot failure

You get the error :

That's because Xen can't boot from a cdrom iso image at the moment. i.e you can't have tap:aio:/path/to/mycd.iso,hdc:cdrom,r or file:/path/to/mycd.iso,hdc:cdrom,r.

Workaround: use losetup to create a loopback device for the cdrom ISO image, then use it in Xen configuration file. for example :

Now you can use /dev/loop9 in xen configuration file (/etc/xen/foobar.cfg) :

then boot/install the guest OS.

note: yo should switch back to the tap:aio:/path/to/mycd.iso,hdc:cdrom,r syntax after installation, since loop back have to be recreated after you reboot the host system.