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''HenningSprang wrote:''

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/sid

Upstream documentation can be found in the xen-docs-3.0 package.

Dom0 (host)

  • Choose and install a xen-linux-system-KERNELVERSION package. This installs the kernel, a hypervisor and matching utilities.

  • On i386, install libc6-xen. This means that you don't have to delete /lib/tls or move it out of the way, as suggested by most Xen guides.

  • Use Grub as bootloader (since Lilo and Xen don't play well with one another)
  • You probably want to cponfigure /etc/xen/xend-config.sxp (especially the network-script scheme).
  • You may find the xen-tools package helpful. It is a set of scripts to manage guest Xen domains that run Debian/Ubuntu/CentOS. More information and examples at http://xen-tools.org/software/xen-tools/.

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 [http://packages.debian.org/cgi-bin/search_packages.pl?keywords=xen-linux-system&searchon=names&subword=1&version=all&release=all packages.debian.org]. The following packages are currently available:

xen-linux-system-2.6.18-4-xen-686

etch (stable)

i386

xen-linux-system-2.6.18-4-xen-vserver-686

etch (stable)

i386

xen-linux-system-2.6.18-4-xen-amd64

etch (stable)

amd64

xen-linux-system-2.6.18-4-xen-vserver-amd64

etch (stable)

amd64

xen-linux-system-2.6.18-5-xen-686

testing/unstable

i386

xen-linux-system-2.6.18-5-xen-vserver-686

testing/unstable

i386

xen-linux-system-2.6.18-5-xen-amd64

testing/unstable

amd64

xen-linux-system-2.6.18-5-xen-vserver-amd64

testing/unstable

amd64

DomU (guests)

  • The easiest way to get this done is to use xen-tools (and, if this doesn' do what you need, Steve Kemp is keen and fast in impementing useful suggestions).
  • The next well tested and working way is to create a domU filesystem from a dom0 by following

["Installing Debian GNU/Linux from a Unix/Linux System"]; http://www.debian.org/releases/stable/i386/apcs04.html.en ; - and adding some tweaks which are necessary to get a Xen guest run properly - mainly adjusting inittab and installing libc6-xen, and maybe 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:

  • If you want to use pygrub (a grub clone written in python and running on the Dom0): install a Xen kernel. Get a list with apt-cache -n search linux-image-xen.

  • If you want to use a kernel image in the Dom0: install the matching modules. Get a list with apt-cache -n search linux-modules.

  • On i386, install libc6-xen.

  • If you want a not ported operating system (Windows..), you go for the so-called HVM mode, and you will have to install xen-ioemu-3.0.3-1

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 unecessary to move the directory out of the way. Can anyone confirm this?

  • {i} This is a Debian-specific feature. Other guest operating systems will still require /lib/tls to be removed/renamed.

Package maintenance

Debian's Xen packages are maintained by the [http://alioth.debian.org/projects/pkg-xen/ pkg-xen] project.

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.

Old stuff

HenningSprang wrote:

I am just about to get started installing xen with Debian as dom0 and Debian, Ubuntu, Redhat as domU. There are multiple Howto's about that, unfortunately I don't see which of them is really useful, still undecided which one I will use. If someone can say something clear about which of these describes a really working, easy, and good way to go, comments would be cool:

These are only half of those I found, there are also numerous describing all that for Ubuntu Linux - very confusing. The people at cosi.clarkson.edu seem to do some stuff, also, but their stuff is also very badly documented. Anybody having any insights on that is really welcome to comment here!