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Xen (pronounced ) is a type-1
hypervisor A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called ...
, providing services that allow multiple computer
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
s to execute on the same
computer hardware Computer hardware includes the physical parts of a computer, such as the case, central processing unit (CPU), random access memory (RAM), monitor, mouse, keyboard, computer data storage, graphics card, sound card, speakers and motherboard. ...
concurrently. It was originally developed by the
University of Cambridge Computer Laboratory The Department of Computer Science and Technology, formerly the Computer Laboratory, is the computer science department of the University of Cambridge. it employed 35 academic staff, 25 support staff, 35 affiliated research staff, and about 15 ...
and is now being developed by the
Linux Foundation The Linux Foundation (LF) is a non-profit technology consortium founded in 2000 as a merger between Open Source Development Labs and the Free Standards Group to standardize Linux, support its growth, and promote its commercial adoption. Addi ...
with support from
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...
,
Citrix Citrix Systems, Inc. is an American multinational cloud computing and virtualization technology company that provides server, application and desktop virtualization, networking, software as a service (SaaS), and cloud computing technologi ...
,
Arm Ltd Arm is a British semiconductor and software design company based in Cambridge, England. Its primary business is in the design of ARM processors (CPUs). It also designs other chips, provides software development tools under the DS-5, RealVi ...
,
Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various sma ...
,
AWS Amazon Web Services, Inc. (AWS) is a subsidiary of Amazon that provides on-demand cloud computing platforms and APIs to individuals, companies, and governments, on a metered pay-as-you-go basis. These cloud computing web services provide di ...
,
Alibaba Cloud Alibaba Cloud, also known as Aliyun (), is a cloud computing company, a subsidiary of Alibaba Group. Alibaba Cloud provides cloud computing services to online businesses and Alibaba's own e-commerce ecosystem. Its international operations are re ...
, AMD,
Bitdefender Bitdefender is a Romanian cybersecurity technology company headquartered in Bucharest, Romania, with offices in the United States, Europe, Australia and the Middle East. The company was founded in 2001 by the current CEO and main shareholder, ...
and
epam EPAM Systems, Inc. ("Effective Programming for America") is an American company that specializes in service development, digital platform engineering, and digital product design, operating out of Newtown, Pennsylvania. History Early years I ...
. The Xen Project community develops and maintains Xen Project as
free and open-source software Free and open-source software (FOSS) is a term used to refer to groups of software consisting of both free software and open-source software where anyone is freely licensed to use, copy, study, and change the software in any way, and the source ...
, subject to the requirements of the
GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...
(GPL), version 2. Xen Project is currently available for the
IA-32 IA-32 (short for "Intel Architecture, 32-bit", commonly called i386) is the 32-bit version of the x86 instruction set architecture, designed by Intel and first implemented in the 80386 microprocessor in 1985. IA-32 is the first incarnatio ...
,
x86-64 x86-64 (also known as x64, x86_64, AMD64, and Intel 64) is a 64-bit version of the x86 instruction set, first released in 1999. It introduced two new modes of operation, 64-bit mode and compatibility mode, along with a new 4-level paging ...
and
ARM In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...
instruction set In computer science, an instruction set architecture (ISA), also called computer architecture, is an abstract model of a computer. A device that executes instructions described by that ISA, such as a central processing unit (CPU), is called an ...
s.


Software architecture

Xen Project runs in a more privileged CPU state than any other software on the machine, except for
Firmware In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide h ...
. Responsibilities of the hypervisor include memory management and CPU scheduling of all virtual machines ("domains"), and for launching the most privileged domain ("dom0") - the only virtual machine which by default has direct access to hardware. From the dom0 the hypervisor can be managed and unprivileged domains ("domU") can be launched. The dom0 domain is typically a version of
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
or BSD. User domains may either be traditional operating systems, such as
Microsoft Windows Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ...
under which privileged instructions are provided by hardware virtualization instructions (if the host processor supports
x86 virtualization x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-a ...
, e.g.,
Intel VT-x x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-a ...
and
AMD-V x86 virtualization is the use of hardware-assisted virtualization capabilities on an x86/x86-64 CPU. In the late 1990s x86 virtualization was achieved by complex software techniques, necessary to compensate for the processor's lack of hardware-as ...
), or paravirtualized operating systems whereby the operating system is aware that it is running inside a virtual machine, and so makes hypercalls directly, rather than issuing privileged instructions. Xen Project boots from a
bootloader A bootloader, also spelled as boot loader or called boot manager and bootstrap loader, is a computer program that is responsible for booting a computer. When a computer is turned off, its softwareincluding operating systems, application code, an ...
such as
GNU GRUB GNU GRUB (short for GNU GRand Unified Bootloader, commonly referred to as GRUB) is a boot loader package from the GNU Project. GRUB is the reference implementation of the Free Software Foundation's Multiboot Specification, which provides a u ...
, and then usually loads a paravirtualized host operating system into the host domain (dom0).


History

Xen originated as a research project at the
University of Cambridge , mottoeng = Literal: From here, light and sacred draughts. Non literal: From this place, we gain enlightenment and precious knowledge. , established = , other_name = The Chancellor, Masters and Schola ...
led by Ian Pratt, a
senior lecturer Senior lecturer is an academic rank. In the United Kingdom, Ireland, New Zealand, Australia, Switzerland, and Israel senior lecturer is a faculty position at a university or similar institution. The position is tenured (in systems with this conce ...
in the Computer Laboratory, and his PhD student Keir Fraser. The first public release of Xen was made in 2003, with v1.0 following in 2004. Soon after, Pratt and Fraser along with other Cambridge alumni including
Simon Crosby Simon Crosby is Co-founder and CTO of security software vendor Bromium Inc. and was a faculty member at the University of Cambridge, UK. Career Simon Crosby, Ph.D., is CTO at SWIM.AI, a continuous intelligence software vendor that focuses on ...
and founding CEO Nick Gault created XenSource Inc. to turn Xen into a competitive enterprise product. To support embedded systems such as smartphone/ IoT with relatively scarce hardware computing resources, the Secure Xen ARM architecture on an ARM CPU was exhibited at Xen Summit on April 17, 2007, held in IBM TJ Watson. The first public release of Secure Xen ARM source code was made at Xen Summit on June 24, 2008 by Sang-bum Suh, a Cambridge alumnus, in Samsung Electronics. On October 22, 2007,
Citrix Systems Citrix Systems, Inc. is an American multinational corporation, multinational cloud computing and virtualization technology company that provides server, application and desktop virtualization, networking, software as a service (SaaS), and cloud ...
completed its acquisition of XenSource, and the Xen Project moved to the xen.org domain. This move had started some time previously, and made public the existence of the Xen Project Advisory Board (Xen AB), which had members from
Citrix Citrix Systems, Inc. is an American multinational cloud computing and virtualization technology company that provides server, application and desktop virtualization, networking, software as a service (SaaS), and cloud computing technologi ...
, IBM,
Intel Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the developers of the x86 ser ...
,
Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
,
Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi- platform network operating system known as Novell NetWare. Under the le ...
,
Red Hat Red Hat, Inc. is an American software company that provides open source software products to enterprises. Founded in 1993, Red Hat has its corporate headquarters in Raleigh, North Carolina, with other offices worldwide. Red Hat has become a ...
,
Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, t ...
and
Oracle An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ...
. The Xen Advisory Board advises the Xen Project leader and is responsible for the Xen trademark, which Citrix has freely licensed to all vendors and projects that implement the Xen
hypervisor A hypervisor (also known as a virtual machine monitor, VMM, or virtualizer) is a type of computer software, firmware or hardware that creates and runs virtual machines. A computer on which a hypervisor runs one or more virtual machines is called ...
. Citrix also used the Xen brand itself for some proprietary products unrelated to Xen, including
XenApp Citrix Virtual Apps (formerly WinFrame, MetaFrame, Presentation Server and XenApp) is an application virtualization software produced by Citrix Systems that allows Windows applications to be accessed via individual devices from a shared server o ...
and
XenDesktop Citrix Virtual Desktops (formerly XenDesktop) is a desktop virtualization product. History The virtualization technology that led to XenDesktop was first developed in 2000 through an open-source hypervisor research project led by Ian Pratt at the ...
. On April 15, 2013, it was announced that the Xen Project was moved under the auspices of the
Linux Foundation The Linux Foundation (LF) is a non-profit technology consortium founded in 2000 as a merger between Open Source Development Labs and the Free Standards Group to standardize Linux, support its growth, and promote its commercial adoption. Addi ...
as a Collaborative Project. The Linux Foundation launched a new trademark for "Xen Project" to differentiate the project from any commercial use of the older "Xen" trademark. A new community website was launched at xenproject.org as part of the transfer. Project members at the time of the announcement included: Amazon, AMD, Bromium, CA Technologies, Calxeda, Cisco, Citrix, Google, Intel, Oracle, Samsung, and Verizon. The Xen project itself is self-governing. Since version 3.0 of the
Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ...
, Xen support for dom0 and domU exists in the mainline kernel.


Release history


Uses

Internet hosting service An Internet hosting service is a service that runs servers connected to the Internet, allowing organizations and individuals to serve content or host services connected to the Internet. A common kind of hosting is web hosting. Most hosting provi ...
companies use hypervisors to provide
virtual private server A virtual private server (VPS) is a virtual machine sold as a service by an Internet hosting service. The virtual dedicated server (VDS) also has a similar meaning. A virtual private server runs its own copy of an operating system (OS), and cus ...
s.
Amazon EC2 Amazon Elastic Compute Cloud (EC2) is a part of Amazon.com's cloud-computing platform, Amazon Web Services (AWS), that allows users to rent virtual computers on which to run their own computer applications. EC2 encourages scalable deployment of ...
(since August 2006), IBM
SoftLayer IBM Cloud, (formerly known as Bluemix) is a set of cloud computing services for business offered by the information technology company IBM. Services As of 2021, IBM Cloud contains more than 170 services including compute, storage, networ ...
, Liquid Web,
Fujitsu Global Cloud Platform FUJITSU Cloud IaaS Trusted Public S5 is a Fujitsu cloud computing platform that aims to deliver standardized enterprise-class Cloud computing#Public cloud, public cloud services globally. It offers Infrastructure-as-a-Service (IaaS) from Fujitsu ...
,
Linode Linode, LLC () is an American cloud hosting provider that focuses on providing Linux powered virtual machines to support a wide range of applications. It was acquired by Akamai Technologies on March 21, 2022. Back in 2003, at the time of its la ...
, OrionVM and
Rackspace Cloud The Rackspace Cloud is a set of cloud computing products and services billed on a utility computing basis from the US-based company Rackspace. Offerings include Cloud Storage ("''Cloud Files''"), virtual private server ("''Cloud Servers''") ...
use Xen as the primary VM hypervisor for their product offerings. Virtual machine monitors (also known as hypervisors) also often operate on
mainframes A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...
and large servers running IBM, HP, and other systems. Server virtualization can provide benefits such as: * Consolidation leading to increased utilization * Rapid provisioning * Dynamic
fault tolerance Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
against software failures (through rapid bootstrapping or rebooting) * Hardware fault tolerance (through migration of a virtual machine to different hardware) * Secure separations of virtual operating systems * Support for legacy software as well as new OS instances on the same computer Xen's support for virtual machine live migration from one host to another allows load balancing and the avoidance of downtime. Virtualization also has benefits when working on development (including the development of operating systems): running the new system as a guest avoids the need to reboot the physical computer whenever a bug occurs. Sandboxed guest systems can also help in computer-security research, allowing study of the effects of some
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...
or
worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...
without the possibility of compromising the host system. Finally, hardware appliance vendors may decide to ship their appliance running several guest systems, so as to be able to execute various pieces of software that require different operating systems.


Types of virtualization

Xen offers five approaches to running the guest operating system: * HVM (hardware virtual machine) * HVM with PV drivers * PVHVM (paravirtualization with full hardware virtualization, i.e. HVM with PVHVM drivers) * PVH (PV in an HVM container) * PV (paravirtualization). Xen provides a form of virtualization known as paravirtualization, in which guests run a modified operating system. The guests are modified to use a special hypercall ABI, instead of certain architectural features. Through paravirtualization, Xen can achieve high performance even on its host architecture (x86) which has a reputation for non-cooperation with traditional virtualization techniques.Robin and Irvine
"Analysis of the Intel Pentium's Ability to Support a Secure Virtual Machine Monitor"
9th Usenix Security Symposium, 2000
Gil Neiger, Amy Santoni, Felix Leung, Dion Rodgers, Rich Uhlig

''Intel Technology Journal'', Volume 10 Issue 03, August 2006.
Xen can run paravirtualized guests ("PV guests" in Xen terminology) even on CPUs without any explicit support for virtualization. Paravirtualization avoids the need to emulate a full set of hardware and firmware services, which makes a PV system simpler to manage and reduces the attack surface exposed to potentially malicious guests. On 32-bit x86, the Xen host kernel code runs in Ring 0, while the hosted domains run in ''Ring 1'' (kernel) and ''Ring 3'' (applications). CPUs that support virtualization make it possible to run unmodified guests, including proprietary operating systems (such as Microsoft Windows). This is known as
hardware-assisted virtualization In computing, hardware-assisted virtualization is a platform virtualization approach that enables efficient full virtualization using help from hardware capabilities, primarily from the host processors. A full virtualization is used to emulate a ...
, however, in Xen this is known as hardware virtual machine (HVM). HVM extensions provide additional execution modes, with an explicit distinction between the most-privileged modes used by the hypervisor with access to the real hardware (called "root mode" in x86) and the less-privileged modes used by guest kernels and applications with "hardware" accesses under complete control of the hypervisor (in x86, known as "non-root mode"; both root and non-root mode have Rings 0–3). Both Intel and AMD have contributed modifications to Xen to exploit their respective Intel VT-x and AMD-V architecture extensions.Extending Xen with Intel Virtualization Technology
''intel.com''
Use of
ARM In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between th ...
v7A and v8A virtualization extensions came with Xen 4.3. HVM extensions also often offer new instructions to allow direct calls by a paravirtualized guest/driver into the hypervisor, typically used for I/O or other operations needing high performance. These allow HVM guests with suitable minor modifications to gain many of the performance benefits of paravirtualized I/O. In current versions of Xen (up to 4.2) only fully virtualized HVM guests can make use of hardware facilities for multiple independent levels of memory protection and paging. As a result, for some workloads, HVM guests with PV drivers (also known as PV-on-HVM, or PVH) provide better performance than pure PV guests. Xen HVM has device emulation based on the
QEMU QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine's central processing unit, processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it t ...
project to provide I/O virtualization to the virtual machines. The system emulates hardware via a patched QEMU "device manager" (qemu-dm) daemon running as a backend in dom0. This means that the virtualized machines see an emulated version of a fairly basic PC. In a performance-critical environment, PV-on-HVM disk and network drivers are used during the normal guest operation, so that the emulated PC hardware is mostly used for booting.


Features

Administrators can "live migrate" Xen virtual machines between physical hosts across a LAN without loss of availability. During this procedure, the LAN iteratively copies the memory of the virtual machine to the destination without stopping its execution. The process requires a stoppage of around 60–300 ms to perform final synchronization before the virtual machine begins executing at its final destination, providing an illusion of seamless migration. Similar technology can serve to suspend running virtual machines to disk, "freezing" their running state for resumption at a later date. Xen can scale to 4095 physical CPUs, 256 VCPUs per HVM guest, 512 VCPUs per PV guest, 16 TB of RAM per host, and up to 1 TB of RAM per HVM guest or 512 GB of RAM per PV guest.


Availability

The Xen hypervisor has been ported to a number of processor families: * Intel: IA-32, IA-64 (before version 4.2), x86-64 * PowerPC: previously supported under the XenPPC project, no longer active after Xen 3.2 * ARM: previously supported under the XenARM project for older versions of ARM without virtualization extensions, such as the Cortex-A9. Currently supported since Xen 4.3 for newer versions of the ARM with virtualization extensions, such as the Cortex-A15. * MIPS: XLP832 experimental port


Hosts

Xen can be shipped in a dedicated virtualization platform, such as XCP-ng or Citrix Hypervisor (formerly Citrix XenServer, and before that XenSource's XenEnterprise). Alternatively, Xen is distributed as an optional configuration of many standard operating systems. Xen is available for and distributed with: *
Alpine Linux Alpine Linux is a Linux distribution designed to be small, simple and secure. Alpine Linux uses musl, BusyBox and OpenRC instead of the more commonly used glibc, GNU Core Utilities and systemd respectively.
offers a minimal dom0 system (
Busybox BusyBox is a software suite that provides several Unix utilities in a single executable file. It runs in a variety of POSIX environments such as Linux, Android, and FreeBSD, although many of the tools it provides are designed to work with inte ...
,
UClibc __NOTOC__ In computing, uClibc (sometimes written µClibc) is a small C standard library intended for Linux kernel-based operating systems for embedded systems and mobile devices. uClibc was written to support μClinux, a version of Linux n ...
) that can be run from removable media, like USB sticks. *
Arch Linux Arch Linux () is an independently developed, x86-64 general-purpose Linux distribution that strives to provide the latest stable versions of most software by following a rolling-release model. The default installation is a minimal base system, ...
provides the necessary packages with detailed setup instructions on their Wiki. *
Debian Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of De ...
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
(since version 4.0 "etch") and many of its derivatives; *
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
11 includes experimental host support. * Gentoo has the necessary packages available to support Xen, along with instructions on their Wiki. *
Mageia Mageia is a Linux-based operating system, distributed as free and open source software. It was forked from the Mandriva Linux distribution. The Greek term () means enchantment, fascination, glamour, wizardry. The first release of the soft ...
(since version 4); *
NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...
can function as domU and dom0. *
OpenSolaris OpenSolaris () is a discontinued open-source computer operating system based on Solaris and created by Sun Microsystems. It was also, perhaps confusingly, the name of a project initiated by Sun to build a developer and user community around t ...
-based distributions can function as dom0 and domU from Nevada build 75 onwards. *
openSUSE openSUSE () is a free and open source RPM-based Linux distribution developed by the openSUSE project. The initial release of the community project was a beta version of SUSE Linux 10.0. Additionally the project creates a variety of tools, s ...
10.x to 12.x: only 64-bit hosts are supported since 12.1; *
Qubes OS Qubes OS is a security-focused desktop Linux distribution that aims to provide security through isolation. Virtualization is performed by Xen, and user environments can be based on (with official support) Fedora or Debian, or (with communit ...
uses Xen to isolate applications for a more secure desktop. *
SUSE Linux Enterprise Server SUSE Linux Enterprise (often abbreviated to SLE) is a Linux-based operating system developed by SUSE. It is available in two editions, suffixed with Server (SLES) for servers and mainframes, and Desktop (SLED) for workstations and desktop com ...
(since version 10); * Solaris (since 2013 with
Oracle VM Server for x86 An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ''o ...
, before with
Sun xVM Sun xVM was a product line from Sun Microsystems that addressed virtualization technology on x86 platforms. One component was discontinued before the Oracle acquisition of Sun; the remaining two continue under Oracle branding. History Sun orig ...
); *
Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...
(since 12.04 "Precise Pangolin"; also 8.04 "Hardy Heron", but no dom0-capable kernel in 8.10 "Intrepid Ibex" until 12.04.)


Guests

Guest systems can run fully virtualized (which requires hardware support), paravirtualized (which requires a modified guest operating system), or fully virtualized with paravirtualized drivers (PVHVM). Most operating systems which can run on PCs can run as a Xen HVM guest. The following systems can operate as paravirtualized Xen guests: *
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whi ...
*
FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...
in 32-bit, or 64-bit through PVHVM; *
OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project e ...
, through PVHVM; *
NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...
* MINIX *
GNU Hurd GNU Hurd is a collection of microkernel servers written as part of GNU, for the GNU Mach microkernel. It has been under development since 1990 by the GNU Project of the Free Software Foundation, designed as a replacement for the Unix kernel, and ...
(gnumach-1-branch-Xen-branch) *
Plan 9 from Bell Labs Plan 9 from Bell Labs is a distributed operating system which originated from the Computing Science Research Center (CSRC) at Bell Labs in the mid-1980s and built on UNIX concepts first developed there in the late 1960s. Since 2000, Plan 9 has be ...
Xen version 3.0 introduced the capability to run Microsoft Windows as a guest operating system unmodified if the host machine's processor supports
hardware virtualization Hardware virtualization is the virtualization of computers as complete hardware platforms, certain logical abstractions of their componentry, or only the functionality required to run various operating systems. Virtualization hides the physica ...
provided by Intel VT-x (formerly codenamed Vanderpool) or AMD-V (formerly codenamed Pacifica). During the development of Xen 1.x,
Microsoft Research Microsoft Research (MSR) is the research subsidiary of Microsoft. It was created in 1991 by Richard Rashid, Bill Gates and Nathan Myhrvold with the intent to advance state-of-the-art computing and solve difficult world problems through technolog ...
, along with the University of Cambridge Operating System group, developed a port of
Windows XP Windows XP is a major release of Microsoft's Windows NT operating system. It was release to manufacturing, released to manufacturing on August 24, 2001, and later to retail on October 25, 2001. It is a direct upgrade to its predecessors, Wind ...
to Xen — made possible by
Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...
's Academic Licensing Program. The terms of this license do not allow the publication of this port, although documentation of the experience appears in the original Xen SOSP paper. James Harper and the Xen open-source community have started developing free software paravirtualization drivers for Windows. These provide front-end drivers for the Xen block and network devices and allow much higher disk and network performance for Windows systems running in HVM mode. Without these drivers all disk and network traffic has to be processed through QEMU-DM. Subsequently, Citrix has released under a BSD license (and continues to maintain) PV drivers for Windows.


Management

Third-party developers have built a number of tools (known as Xen Management Consoles) to facilitate the common tasks of administering a Xen host, such as configuring, starting, monitoring and stopping of Xen guests. Examples include: * The
OpenNebula OpenNebula is a cloud computing platform for managing heterogeneous distributed data center infrastructures. The OpenNebula platform manages a data center's virtual infrastructure to build private, public and hybrid implementations of Infrastru ...
cloud management toolkit * On openSUSE
YaST YaST (Yet another Setup Tool) is a Linux operating system setup and configuration tool. YaST is featured in the openSUSE Linux distribution, as well as in SUSE's derived commercial distributions. It is also part of the defunct United Linux. YaS ...
and virt-man offer graphical VM management *
OpenStack OpenStack is a free, open standard cloud computing platform. It is mostly deployed as infrastructure-as-a-service (IaaS) in both public and private clouds where virtual servers and other resources are made available to users. The software pl ...
natively supports Xen as a Hypervisor/Compute target *
Apache CloudStack CloudStack is open-source cloud computing software for creating, managing, and deploying infrastructure cloud services. It uses existing hypervisor platforms for virtualization, such as KVM, VMware vSphere, including ESXi and vCenter, and X ...
also supports Xen as a Hypervisor * Novell's PlateSpin Orchestrate also manages Xen virtual machines for Xen shipping in SUSE Linux Enterprise Server.
Xen Orchestra
for both XCP-ng and Citrix Hypervisor platforms


Commercial versions

* XCP-ng (Open Source, within the Linux Foundation and Xen Project, originally a fork of XenServer) * Citrix Hypervisor (formerly XenServer until 2019) *
Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various sma ...
FusionSphereHuawei to virtual world: Give us your desktops and no-one gets hurt
/ref> *
Oracle VM Server for x86 An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination. Description The word ''o ...
* Thinsy Corporation * Virtual Iron (discontinued by Oracle) *
Crucible (hypervisor) A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. Although crucibles have historically tended to be made out of clay, they can be made from any material that wit ...
by Star Lab Corp.Crucible - Secure Embedded Virtualization
/ref> The Xen hypervisor is covered by the GNU General Public Licence, so all of these versions contain a core of free software with source code. However, many of them contain proprietary additions.


See also

*
CloudStack CloudStack is open-source cloud computing software for creating, managing, and deploying infrastructure cloud services. It uses existing hypervisor platforms for virtualization, such as KVM, VMware vSphere, including ESXi and vCenter, and X ...
*
Kernel-based Virtual Machine Kernel-based Virtual Machine (KVM) is a virtualization module in the Linux kernel that allows the kernel to function as a hypervisor. It was merged into the mainline Linux kernel in version 2.6.20, which was released on February 5, 2007. KV ...
(KVM) *
OpenStack OpenStack is a free, open standard cloud computing platform. It is mostly deployed as infrastructure-as-a-service (IaaS) in both public and private clouds where virtual servers and other resources are made available to users. The software pl ...
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Virtual disk image A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image is usua ...
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tboot Intel Trusted Execution Technology (Intel TXT, formerly known as LaGrande Technology) is a computer hardware technology whose primary goals are: * Attestation of the authenticity of a platform and its operating system. * Assuring that an authent ...
, a TXT-based integrity system for the Linux kernel and Xen hypervisor *
VMware ESX VMware ESXi (formerly ESX) is an enterprise-class, type-1 hypervisor developed by VMware for deploying and serving virtual computers. As a type-1 hypervisor, ESXi is not a software application that is installed on an operating system (OS ...
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Qubes OS Qubes OS is a security-focused desktop Linux distribution that aims to provide security through isolation. Virtualization is performed by Xen, and user environments can be based on (with official support) Fedora or Debian, or (with communit ...


References


Further reading

* Paul Venezia (April 13, 2011
Virtualization shoot-out: Citrix, Microsoft, Red Hat, and VMware. The leading server virtualization contenders tackle InfoWorld's ultimate virtualization challenge
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InfoWorld ''InfoWorld'' (abbreviated IW) is an information technology media business. Founded in 1978, it began as a monthly magazine. In 2007, it transitioned to a web-only publication. Its parent company today is International Data Group, and its siste ...
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External links

* {{Citrix Systems 2003 software Citrix Systems Cross-platform free software Free virtualization software Linux Foundation projects University of Cambridge Computer Laboratory Virtualization software for Linux