Jump to contentJump to page navigation: previous page [access key p]/next page [access key n]
SUSE Linux Enterprise Server 15 SP3

Using KubeVirt on SUSE Linux Enterprise


KubeVirt is a virtual machine management add-on for Kubernetes. KubeVirt extends Kubernetes by adding additional virtualization resource types through Kubernetes' Custom Resource Definitions (CRD) API. Along with the Custom Resources, KubeVirt includes controllers and agents that provide virtual machine management capabilities on the cluster. By using this mechanism, the Kubernetes API can be used to manage virtual machine resources similar to other Kubernetes resources.

Disclaimer: Documents published as part of the SUSE Best Practices series have been contributed voluntarily by SUSE employees and third parties. They are meant to serve as examples of how particular actions can be performed. They have been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. SUSE cannot verify that actions described in these documents do what is claimed or whether actions described have unintended consequences. SUSE LLC, its affiliates, the authors, and the translators may not be held liable for possible errors or the consequences thereof.

Author: James Fehlig, Software Engineer, SUSE
Author: Vasily Ulyanov, Software Engineer, SUSE
Publication Date: October 12, 2021

1 KubeVirt components Edit source

KubeVirt consists of two RPM-based packages and six container images that provide the Kubernetes virtual machine management extension. The RPM packages include kubevirt-virtctl and kubevirt-manifests. The container images include virt-api, virt-controller, virt-handler, virt-launcher, and virt-operator, libguestfs-tools.

kubevirt-virtctl can be installed on any machine with administrator access to the cluster. It contains the virtctl tool, which provides syntactic sugar on top of the kubectl tool for virtual machine resources. Although the kubectl tool can be used to manage virtual machines, it is a bit awkward since, unlike standard Kubernetes resources, virtual machines maintain state. Migration is also unique to virtual machines. If a standard Kubernetes resource needs to be evacuated from a cluster node, it is destroyed and started again on an alternate node. Since virtual machines are stateful, they cannot be destroyed and must be live-migrated away if a node is under evacuation. The virtctl tool abstracts the complexity of managing virtual machines with kubectl. It can be used to stop, start, pause, unpause, and migrate virtual machines. virtclt also provides access to the virtual machine's serial console and graphics server.

kubevirt-manifests contains the manifests, or recipes, for installing KubeVirt. The most interesting files are /usr/share/kube-virt/manifests/release/kubevirt-cr.yaml and /usr/share/kube-virt/manifests/release/kubevirt-operator.yaml. kubevirt-cr.yaml contains the KubeVirt Custom Resource definition that represents the KubeVirt service. kubevirt-operator.yaml is the recipe for deploying the KubeVirt operator, which deploys the KubeVirt service to the cluster and manages its' lifecycle.

virt-api is a cluster component that provides the Kubernetes API extension for virtual machine resources. Like virt-api, virt-controller is a cluster component that watches for new objects created via virt-api, or updates to existing objects, and takes action to ensure the object state matches the requested state. virt-handler is a DaemonSet and a node component that has the job of keeping the cluster-level virtual machine object in sync with the libvirtd domain running in virt-launcher. virt-handler can also perform node-centric operations like configuring networking and/or storage on the node as per the virtual machine specification. virt-launcher is also a node component and has the job of running libvirt plus qemu to provide the virtual machine environment. virt-launcher is a lowly pod resource. libguestfs-tools is a component providing a set of utilities for accessing and modifying VM disk images.

virt-operator implements the Kubernetes operator pattern. Operators encode the human knowledge required to deploy, run, and maintain an application. Operators are a Kubernetes Deployment resource type and are often used to manage the custom resources and custom controllers that together provide a more complex Kubernetes application such as KubeVirt.

2 Installing KubeVirt on Kubernetes Edit source

KubeVirt can be installed on a Kubernetes cluster by installing the kubevirt-manifests package on an admin node, applying the virt-operator manifest, and creating the KubeVirt custom resource. For example, on a cluster admin node execute the following:

tux > sudo zypper install kubevirt-manifests
tux > kubectl apply -f /usr/share/kube-virt/manifests/release/kubevirt-operator.yaml
tux > kubectl apply -f /usr/share/kube-virt/manifests/release/kubevirt-cr.yaml

After creating the KubeVirt custom resource, virt-operator will deploy the remaining KubeVirt components. Progress can be monitored by viewing the status of the resources in the kubevirt namespace:

tux > kubectl get all -n kubevirt

The cluster is ready to deploy virtual machines once virt-api, virt-controller, and virt-handler are READY with STATUS 'Running'.

Alternatively it is possible to wait until KubeVirt custom resource becomes available:

tux > kubectl -n kubevirt wait kv kubevirt --for condition=Available

Some KubeVirt functionality is disabled by default and must be enabled via feature gates. For example live migration and the use of HostDisk for virtual machine disk images are disabled. Enabling KubeVirt feature gates can be done by altering an existing KubeVirt custom resource and specifying the list of features to enable. For example, you can enable live migration and the use of HostDisks:

tux > kubectl edit kubevirt kubevirt -n kubevirt
            - HostDisk
            - LiveMigration

The names of feature gates are case-sensitive.

3 Updating the KubeVirt deployment Edit source

Updating KubeVirt is similar to the initial installation. The updated operator manifest from the kubevirt-manifests package is applied to the cluster.

tux > sudo zypper update kubevirt-manifests
tux > kubectl apply -f /usr/share/kube-virt/manifests/release/kubevirt-operator.yaml

4 Deleting KubeVirt from a cluster Edit source

KubeVirt can be deleted from a cluster by deleting the custom resource and operator:

tux > kubectl delete -n kubevirt kubevirt kubevirt # or alternatively: kubectl delete -f /usr/share/kube-virt/manifests/release/kubevirt-cr.yaml
tux > kubectl delete -f /usr/share/kube-virt/manifests/release/kubevirt-operator.yaml

It is important to delete the custom resource first otherwise it will get stuck in the Terminating state. To fix that the resource finalizer needs to be manually deleted:

tux > kubectl -n kubevirt patch kv kubevirt --type=json -p '[{ "op": "remove", "path": "/metadata/finalizers" }]'

After deleting the resources from Kubernetes cluster the installed KubeVirt RPMs can be removed from the system:

tux > sudo zypper rm kubevirt-manifests kubevirt-virtctl

5 Containerized Data Importer Edit source

Containerized Data Importer (CDI) is an add-on for Kubernetes focused on persistent storage management. It is primarily used for building and importing Virtual Machine Disks for KubeVirt.

5.1 Installing CDI Edit source

CDI can be installed on a Kubernetes cluster in a way similar to KubeVirt by installing the RPMs and applying the operator and custom resource manifests using kubectl:

tux > sudo zypper in containerized-data-importer-manifests
tux > kubectl apply -f /usr/share/cdi/manifests/release/cdi-operator.yaml
tux > kubectl apply -f /usr/share/cdi/manifests/release/cdi-cr.yaml

5.2 Updating and deleting CDI: Edit source

To update CDI:

tux > sudo zypper update containerized-data-importer-manifests
tux > kubectl apply -f /usr/share/cdi/manifests/release/cdi-operator.yaml

To delete CDI:

tux > kubectl delete -f /usr/share/cdi/manifests/release/cdi-cr.yaml
tux > kubectl delete -f /usr/share/cdi/manifests/release/cdi-operator.yaml
tux > sudo zypper rm containerized-data-importer-manifests

6 Running virtual machines Edit source

Two of the most interesting custom resources provided by KubeVirt are VirtualMachine (VM) and VirtualMachineInstance (VMI). As the names imply, a VMI is a running instance of a VM. The lifecycle of a VMI can be managed independently from a VM, but long-lived, stateful virtual machines are managed as a VM. The VM is deployed to the cluster in a shutoff state, then activated by changing the desired state to running. Changing a VM resource state can be done with the standard Kubernetes client tool kubectl or with the client virtctl provided by KubeVirt.

The VM and VMI custom resources make up part of the KubeVirt API. To create a virtual machine, a VM or VMI manifest must be created that adheres to the API. The API supports setting a wide variety of the common virtual machine attributes, for example model of vCPU, number of vCPUs, amount of memory, disks, network ports, etc. Below is a simple example of a VMI manifest for a virtual machine with one Nehalem CPU, 2G of memory, one disk, and one network interface:

apiVersion: kubevirt.io/v1
kind: VirtualMachineInstance
    special: vmi-host-disk
  name: sles15sp2
      model: Nehalem-IBRS
      - disk:
          bus: virtio
        name: host-disk
        - name: green
          masquerade: {}
            - port: 80
      type: ""
        memory: 2048M
  terminationGracePeriodSeconds: 0
  - name: green
    pod: {}
  - hostDisk:
      path: /hostDisks/sles15sp2/disk.raw
      type: Disk
      shared: true
    name: host-disk
    status: {}

Applying this VMI manifest to the cluster will create a virt-launcher container running libvirt and qemu, providing the familiar KVM virtual machine environment.

tux > kubectl apply -f sles15sp2vmi.yaml
tux > kubectl get vmis

Similar to other Kubernetes resources, VMs and VMIs can be managed with the kubectl client tool. Any kubectl operation that works with resource types will work with the KubeVirt custom resources, for example describe, delete, get, log, patch, etc. VM resources are a bit more awkward to manage with kubectl. Since a VM resource can be in a shutoff state, turning it on requires patching the manifest to change the desired state to running. Find an example below:

tux > kubectl patch vm sles15sp2 --type merge -p '{"spec":{"running":true}}'

The virtctl tool included in the kubevirt-virtclt package provides syntactic sugar on top of kubectl for VM and VMI resources, allowing them to be stopped, started, paused, unpaused, and migrated. virtctl also provides access to the virtual machine's serial console and graphics server. Find an example below:

tux > virtctl start VM
tux > virtctl console VMI
tux > virtctl stop VM
tux > virtctl pause VM|VMI
tux > virtctl unpause VM|VMI
tux > virtctl vnc VMI
tux > virtctl migrate VM

7 Live migration Edit source

KubeVirt supports live migration of VMs. Though this functionality must first be activated by adding LiveMigration to the list of feature gates in the KubeVirt custom resource.

tux > kubectl edit kubevirt kubevirt -n kubevirt
        - LiveMigration

7.1 Prerequisites Edit source

  • All the Persistent Volume Claims (PVCs) used by a VM must have `ReadWriteMany` (RWX) access mode.

  • VM pod network binding must be of type masquerade:

            - name: green
              masquerade: {}

Whether live migration is possible or not can be checked via the VMI.status.conditions field of a running VM spec:

tux > kubectl describe vmi sles15sp2
    Status: True
    Type: LiveMigratable
  Migration Method: BlockMigration

7.2 Initiating live migration Edit source

Live migration of a VMI can be initiated by applying the following yaml file:

apiVersion: kubevirt.io/v1
kind: VirtualMachineInstanceMigration
  name: migration-job
  vmiName: sles15sp2
tux > kubectl apply -f migration-job.yaml

Alternatively it is possible to migrate a VM using virtctl tool:

tux > virtctl migrate VM

7.3 Cancelling live migration Edit source

Live migration can be canceled by deleting the existing migration object:

tux > kubectl delete VirtualMachineInstanceMigration migration-job

8 Volume hotplugging Edit source

KubeVirt allows hotplugging additional storage into a running VM. Both block and file system volume types are supported. The hotplug volumes feature can be activated via the HotplugVolumes feature gate:

tux > kubectl edit kubevirt kubevirt -n kubevirt
        - HotplugVolumes

Assuming that hp-volume is an existing DataVolume or PVC, virtctl can be used to operate with the volume on a runnig VM:

tux > virtctl addvolume sles15sp2 --volume-name=hp-volume
tux > virtctl removevolume sles15sp2 --volume-name=hp-volume

9 Running Windows VMs with VMDP ISO Edit source

The VMDP ISO is provided in the form of a container image which can be consumed by KubeVirt. To run a Windows VM with VMDP ISO attached, the corresponding containerDisk needs to be added to the VM definition:

        - name: vmdp
            bus: sata
  - containerDisk:
      image: registry.suse.com/suse/vmdp/vmdp:latest
    name: vmdp

The sequence in which the disks are defined affects the boot order. It is possible to specify the bootOrder explicitly or otherwise sort the disk items as needed.

10 Supported features Edit source

  • Guest Agent Information

  • Live migration

  • Hotplug volumes

  • VMI Dedicated CPU resource

10.1 VMI virtual hardware Edit source

  • machine type


  • cpu

  • clock

  • RNG

  • CPU/Memory limits and requirements

  • tablet input

  • hugepage

10.2 VMI disks and volumes Edit source

Disk types:

  • lun

  • disk

  • cdrom

Volume sources:

  • cloudInitNoCloud

  • cloudInitConfigDrive

  • persistentVolumeClaim

  • dataVolume

  • ephemeral

  • containerDisk

  • emptyDisk

  • hostDisk

  • configMap

  • secret

  • serviceAccount

  • downwardMetrics

High performance features:

  • IO threads

  • Virtio Block Multi-Queue

  • Disk cache

10.3 VMI interfaces and networks Edit source

Network (back-end) types:

  • pod

  • multus

Interface (front-end) types:

  • bridge

  • masquerade

11 Debugging Edit source

If issues are encountered the following debug resources are available to help identify the problem.

The status of all KubeVirt resources can be examined with the kubectl get command:

tux > kubectl get all -n kubevirt

Resources with failed status can be further queried by examining their definition and expanded status information.

tux > kubectl describe deployment virt-operator
tux > kubectl get deployment virt-operator -o yaml -n kubevirt
tux > kubectl describe pod virt-handler-xbjkg -n kubevirt
tux > kubectl get pod virt-handler-xbjkg -o yaml -n kubevirt

Logs from the problematic KubeVirt pod can contain a wealth of information since stderr and service logging from within the pod is generally available via the Kubernetes log service:

tux > kubectl logs virt-operator-558c57bc4-mg68w -n kubevirt
  tux > kubectl logs virt-handler-xbjkg -n kubevirt

If the underlying pod is running but there are problems with the service running in it, a shell can be accessed to inspect the pod environment and poke at its service:

tux > kubectl -n kubevirt exec -it virt-handler-xbjkg -- /bin/bash

12 Legal notice Edit source

Copyright ©2006-2022 SUSE LLC and contributors. All rights reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled GNU Free Documentation License.

SUSE, the SUSE logo and YaST are registered trademarks of SUSE LLC in the United States and other countries. For SUSE trademarks, see http://www.suse.com/company/legal/. Linux is a registered trademark of Linus Torvalds. All other names or trademarks mentioned in this document may be trademarks or registered trademarks of their respective owners.

Documents published as part of the SUSE Best Practices series have been contributed voluntarily by SUSE employees and third parties. They are meant to serve as examples of how particular actions can be performed. They have been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. SUSE cannot verify that actions described in these documents do what is claimed or whether actions described have unintended consequences. SUSE LLC, its affiliates, the authors, and the translators may not be held liable for possible errors or the consequences thereof.

Below we draw your attention to the license under which the articles are published.

13 GNU Free Documentation License Edit source

Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.

The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or non-commercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

  1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

  2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

  3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

  4. Preserve all the copyright notices of the Document.

  5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

  6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

  7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

  8. Include an unaltered copy of this License.

  9. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

  10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

  11. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

  12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

  13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

  14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

  15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

Copyright (c) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
 Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts". line with this:

with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

Print this page