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Xen logo
Xen screenshot.png
Basic data

developer Linux Foundation
Current  version 4.13
(December 18, 2019)
operating system cross-platform
programming language C.
category Virtualization
License GPL ( Free Software )
German speaking No

Xen (pronounced / ˈzɛn /) (also Xen Project , in contrast to commercial products based on it) is a hypervisor , i.e. software that allows the operation of several virtual machines on one physical computer. It originated at the British University of Cambridge and is now being developed by the US company Citrix Systems . The name is derived from the prefix xeno ( Greek  ξένος , xénos : stranger).

Technical details

Xen is a type 1 hypervisor (also called Virtual Machine Monitor (VMM)) that runs directly on hardware . Xen can start several operating systems in virtual machines, the so-called domains . Neither the hypervisor nor other domains are "visible" to these operating systems. In principle, the procedure is comparable to virtual memory and processes : With virtual memory, every process (here: the virtual system) can use the memory as if it were the only process that is being executed by the operating system. To be more precise: the hypervisor assigns parts of the entire main memory to the virtual system. These appear to the virtual system as a contiguous address space, just as physical memory appears to a non-virtual system. It can be used accordingly and exclusively by the virtual system.

The first domain started by Xen has a special meaning: This domain is privileged and is used for interaction with the actual hypervisor. The privileged domain, called Dom0 , can start, stop, and manage other domains. For this purpose, this administration functionality must be integrated into the operating system that runs in the Dom0.

In order to be completely transparent for the unprivileged domains, often called DomU , Xen requires a main processor with the instruction set extension Secure Virtual Machine , such as Intel VT or AMD-V . With this hardware, the operating systems running in the domains do not have to be adjusted - they do not “notice” that they are actually sharing the hardware with other systems. This operating mode is known as full virtualization or hardware virtual machine (HVM). If virtualization is carried out on other hardware, the respective kernels have full hardware access and could access external resources (e.g. main memory) due to faulty or malicious code, which is undesirable for reasons of stability and security.

The efficiency of virtualized systems can be increased by integrating support for operation as a DomU into the operating system. This approach is called paravirtualization and requires a modification of the system that is to run in a DomU.

Supported Operating Systems

The Linux kernel is version 2.6.21 the conditions for the operation under any hypervisor in the form of so-called paravirt ops ready. From version 2.6.23, limited support for operation under Xen is integrated. However, this basic support did not support numerous possibilities of Xen, for example the (dynamic) pass-through of PCI devices or dynamic memory expansion. As of version 3.0 of the kernel, it fully supports Xen.

Xen version 9.3 or higher is integrated in the Linux distributions openSUSE and version 4 or higher in Fedora . Xen is also included in Novell / SUSE Linux Enterprise Server (SLES) from version 10 and in Red Hat Enterprise Linux  5 (RHEL5). Debian contains a Xen kernel from version 4 ( Etch ) and Ubuntu from version 12.04 ( Precise Pangolin ). Gentoo Linux and Arch Linux both offer packages for full Xen support.

With versions up to Xen 3.x, only the "official" Linux kernel source code from Xen can be used for operation as Dom0 or as a full native DomU, which is only available in version Due to the active development on the Linux kernel, the patch for this version cannot be applied to a current kernel without considerable effort. The time-consuming practice of adapting Xen patches to more recent versions, for example by Debian, was discontinued.

Since Xen 4.0, Xen also supports the standard kernel option PVOps by default for its dom0 kernel in kernel version 2.6.31.x. A long-term support version (LTS) is also available under pvops and the Linux kernel 2.6.32.x for the dom0 kernel. In spite of this, the compatibility with the previous 2.6.18 kernel will still be maintained and further Xen patches are planned for this version as well as for some kernels with forward patches (such as the kernel from RHEL 5.x).

NetBSD  2.0 supports Xen 1.2 as host and guest and Xen 2.0 only as guest, version NetBSD 3.1 supports Xen 2.0 completely, i.e. as host and guest, and Xen 3.0 as guest. Xen 3.0 has been fully supported since NetBSD 4.0.

At the beginning of October 2007, Sun fully integrated Xen into OpenSolaris with Nevada build 75 under the name xVM ; test versions existed before that.

At the Novell BrainShare Conference in 2005 , Novell presented a port from Netware to Xen.

We have been working on porting ReactOS to Xen since 2005.

Supporters and collaboration

The supporters of Xen include globally operating IT companies - even companies that are strongly competing with one another are united under this roof, including: Microsoft , Oracle , Intel , AMD , IBM , HP , Red Hat and SUSE .

The open source software Xen was originally developed at Cambridge University. With XenSource, the developers have founded a company that aims to make Xen the industry standard . XenSource was taken over by Citrix Systems in August 2007 for US $ 500 million .

At the beginning of 2013, Xapi, together with Xen.org, was transferred back to the Xen Project, which works under the umbrella of the Linux Foundation. Xapi is therefore now a sub-project of the Xen Project.

Commercial products

The Citrix products XenServer and XenClient are based on Xen.


version publication Remarks
1.0 September 9, 2003
2.0 November 5, 2004
3.0 December 5, 2005
  • Intel VT support for HVM guests.
  • Support of the IA-64 architecture.

The following features were also added up to version 3.0.4:

3.1 May 18, 2007
3.2 January 17, 2008 PCI passthrough and ACPI-S3 standby mode for the host system.
3.3 August 24, 2008 Improvements to PCI passthrough and power management.
3.4 May 18, 2009 Contains a first version of the "Xen Client Initiative", XCI for short.
4.0 April 7, 2010 Creates the conditions to be able to use a dom0 kernel implemented using PVOps. A kernel in version 2.6.31 was specially adapted for this purpose, since the functions of the official kernel based on PVOps do not yet support operation as dom0 (as of July 2010).
4.1 March 25, 2011 Among other things: support for more than 255 processors, stability improvement.
4.2 17th September 2012 Among other things, a new standard management tool (XL instead of xend), support for larger systems (up to 4095 processors), further developments of the security subsystem and efforts to improve documentation.
4.3 July 9, 2013 Experimental support for ARM virtualization, NUMA-aware scheduling, support for openvswitch as bridging mechanism, improved security, PCI passthrough.
4.4 March 10, 2014 Product-ready ARM support, stable “libvirt” support for “libxl”, scalable event channel interface, nested virtualization on Intel hardware.
4.5 January 14, 2015 Lean code, new PVH extension, xf or libxf instead of xen
4.6 October 13, 2015
4.7 20th June 2016
4.8 5th December 2016
4.9 June 28, 2017
4.10 December 12, 2017
4.11 July 10, 2018

See also


  • Andrej Radonic, Frank Meyer, Thomas Halinka: Xen 3.2 . Franzis' Verlag, Poing 2008, ISBN 978-3-7723-7247-6 .
  • Timo Benk, Henning Sprang, Jaroslaw Zdrzalek, Ralph Dehner: Xen - virtualization under Linux . Open Source Press, Munich 2007, ISBN 978-3-937514-29-1 .
  • Hans-Joachim Picht: Xen cookbook . O'Reilly Verlag, Cologne 2009, ISBN 978-3-89721-729-4 .
  • Marcus Fischer: Xen - The comprehensive manual . Galileo Press, Bonn 2009, ISBN 978-3-8362-1118-5 .
  • David Chisnall: The Definitive Guide to the Xen Hypervisor . Prentice Hall Press, Upper Saddle River, NJ, USA 2007, ISBN 978-0-13-234971-0 .

Web links

Graphic administrations

Administrations for console

  • XEN-SHELL2 - lightweight, console-based multi-user Xen VM management

Individual evidence

  1. https://xenproject.org/2019/12/18/whats-new-in-xen-4-13/
  2. ^ New Linux Does Inclusive Virtualization , April 27, 2007
  3. Peter Siering: Xen / c't Debian Server (box "Xen and the Linux Kernel"), c't 19/2008, p. 222 or online ( Memento from September 2, 2008 in the Internet Archive )
  4. http://www.netbsd.org/ports/xen/howto.html
  5. OpenSolaris Community: Xen ( Memento from September 29, 2009 in the Internet Archive )
  6. Article Xen port ( memo of November 22, 2008 in the Internet Archive ) in the ReactOS Wiki
  7. http://sourceforge.net/mailarchive/forum.php?forum_name=xen-announce&max_rows=50&style=nested&viewmonth=200309
  8. http://lwn.net/Articles/109789/
  9. https://www.heise.de/newsticker/meldung/Virtualisierungssoftware-Xen-3-0-freigierter-155099.html
  10. http://www.linux-community.de/Internal/Nachrichten/Virtualisierung-neu-auflege-Xen-3.0
  11. Press Releases. XenSource, Inc., December 5, 2005, archived from the original on December 10, 2005 ; accessed on January 10, 2015 .
  12. xen-users ( Memento from October 1, 2011 in the Internet Archive )
  13. http://lists.xensource.com/archives/html/xen-devel/2006-10/msg00733.html
  14. http://lists.xensource.com/archives/html/xen-devel/2006-12/msg00889.html
  15. http://lists.xensource.com/archives/html/xen-announce/2007-05/msg00002.html
  16. http://www.linux-magazin.de/NEWS/Xen-3.2-freigierter
  17. https://www.heise.de/newsticker/meldung/Hypervisor-Xen-3-3-0-haben-zum-Download-ready-199040.html
  18. http://community.citrix.com/display/ocb/2009/05/18/Xen.org+Announces+Release+of+Xen+3.4+Hypervisor
  19. http://www.pro-linux.de/news/1/14211/xen-34-veroeffentlicht.html
  20. https://www.heise.de/newsticker/meldung/Virtualisierung-Xen-sucht-mit-Version-4-Anschluss-974343.html
  21. http://www.xen.org/files/Xen_4_0_Datasheet.pdf
  22. http://blog.xen.org/index.php/2011/03/25/xen-4-1-releases/
  23. http://blog.xen.org/index.php/2012/09/17/xen-4-2-0-released/
  24. http://blog.xen.org/index.php/2013/07/09/xen-4-3-0-released/
  25. http://wiki.xenproject.org/wiki/Xen_4.3_Feature_List
  26. https://www.heise.de/newsticker/meldung/Virtualisierer-Xen-4-3-jetzt-auch-fuer-ARM-1914140.html
  27. http://blog.xen.org/index.php/2014/03/10/xen-4-4-released/
  28. http://wiki.xenproject.org/wiki/Xen_4.4_Feature_List
  29. https://www.heise.de/newsticker/meldung/Xen-4-4-virtuelle-Maschinen-fuer-ARM-2139439.html
  30. http://xenproject.org/about/in-the-news/183-xen-project-announces-4-5-release.html
  31. https://blog.xenproject.org/2015/10/13/xen-4-6/
  32. a b Xen Project 4.7 and 4.6.3 Release | Xen Project Blog. Retrieved April 6, 2017 (American English).
  33. What's New in the Xen Project Hypervisor 4.9? | Xen Project Blog. Retrieved January 19, 2018 (American English).
  34. ^ What's New in the Xen Project Hypervisor 4.10 | Xen Project Blog. Retrieved January 19, 2018 (American English).