Xen to KVM Migration Guide #
SUSE Linux Enterprise Server 12 SP5
As the KVM virtualization solution is becoming more and more popular among server administrators, many of them need a path to migrate their existing Xen based environments to KVM. As of now, there are no mature tools to automatically convert Xen VMs to KVM. There is, however, a technical solution that helps convert Xen virtual machines to KVM. The following information and procedures help you to perform such a migration.
The migration procedure described in this document is not fully supported by SUSE. We provide it as a guidance only.
1 Migration to KVM Using virt-v2v
#
This section contains information to help you import virtual machines
from foreign hypervisors (such as Xen) to KVM managed by
libvirt
.
This section is focused on converting Linux guests. Converting Microsoft
Windows guests using virt-v2v
is the same as
converting Linux guests, except in regards to handling the Virtual
Machine Driver Pack (VMDP). Additional details on converting Windows
guests with the VMDP can be found in the separate Virtual Machine Driver
Pack documentation at https://documentation.suse.com/sle-vmdp/.
1.1 Introduction to virt-v2v
#
virt-v2v
is a command line tool to convert
VM Guests from a foreign hypervisor to run on KVM managed by
libvirt
. It enables paravirtualized virtio drivers in the converted
virtual machine if possible. A list of supported operating systems and
hypervisors follows:
SUSE Linux Enterprise Server
openSUSE
Red Hat Enterprise Linux
Fedora
Microsoft Windows Server 2003 and 2008
Xen
KVM (managed by
libvirt
)
1.2 Installing virt-v2v
#
The installation of virt-v2v
is simple:
sudo zypper install virt-v2v
Remember that virt-v2v
requires root
privileges, so you need to run it either as root
, or via
sudo
.
1.3 Preparing the Virtual Machine #
If running virt-v2v
on SLES 12 SP1 or before,
this step can be safely skipped. This step can also be ignored if the
virtual machine is fully virtualized or if it runs on SLES 12 SP2
or later.
The Xen virtual machine must have default kernel installed. To
ensure this, run zypper in kernel-default
on the virtual machine.
1.4 Converting Virtual Machines to Run under KVM Managed by
libvirt
#
virt-v2v
converts virtual machines from the Xen
hypervisor to run under KVM managed by libvirt
. To learn more
about libvirt
and virsh
, see Part II, “Managing Virtual Machines with libvirt
”. Additionally, all
virt-v2v
command line options are explained in
the virt-v2v
manual page (man 1
virt-v2v
).
Before converting a virtual machine, make sure to complete the following steps:
Create a new local storage pool.
virt-v2v
copies the storage of the source virtual machine to a local storage pool managed bylibvirt
(the original disk image remains unchanged). You can create the pool either with Virtual Machine Manager, orvirsh
. For more information, see Section 12.1, “Managing Storage with Virtual Machine Manager” and Section 12.2, “Managing Storage withvirsh
”.Prepare the local network interface.
Check that the converted virtual machine can use a local network interface on the VM Host Server. It is usually a network bridge. If it is not defined yet, create it with
› › › › .Note: Mappings of Network DevicesNetwork devices on the source Xen host can be mapped during the conversion process to corresponding network devices on the KVM target host. For example, the Xen bridge
br0
can be mapped to the KVM network default. Sample mappings can be found in/etc/virt-v2v.conf
. To enable these mappings, modify the XML rule as necessary and ensure the section is not commented out with<!--
and-->
markers. For example:<network type='bridge' name='br0'> <network type='network' name='default'/> </network>
Tip: No Network BridgeIf there is no network bridge available, Virtual Machine Manager can optionally create it.
virt-v2v
has the following basic command syntax:
virt-v2v -i INPUT_METHOD -os STORAGE_POOL SOURCE_VM
- input_method
There are two input methods:
libvirt
orlibvirtxml
. See the SOURCE_VM parameter for more information.- storage_pool
The storage pool you already prepared for the target virtual machine.
- source_vm
The source virtual machine to convert. It depends on the INPUT_METHOD parameter: For
libvirt
, specify the name of a libvirt domain. Forlibvirtxml
, specify the path to an XML file containing a libvirt domain specification.
Conversion of a virtual machine takes a lot of system resources, mainly for copying the whole disk image for a virtual machine. Converting a single virtual machine typically takes up to 10 minutes, although virtual machines using very large disk images can take much longer.
1.4.1 Conversion Based on the libvirt
XML Description File #
This section describes how to convert a local Xen virtual machine
using the libvirt
XML configuration file. This method is suitable
if the host is already running the KVM hypervisor. Make sure that the
libvirt
XML file of the source virtual machine, and the libvirt
storage pool referenced from it are available on the
local host.
Obtain the
libvirt
XML description of the source virtual machine.Tip: Obtaining the XML FilesTo obtain the
libvirt
XML files of the source virtual machine, you must run the host OS under the Xen kernel. If you already rebooted the host to the KVM-enabled environment, reboot back to the Xen kernel, dump thelibvirt
XML file, and then reboot back to the KVM environment.First identify the source virtual machine under virsh:
root #
virsh list Id Name State ---------------------------------------------------- [...] 2 sles12_xen running [...]sles12_xen
is the source virtual machine to convert. Now export its XML and save it tosles12_xen.xml
:root #
virsh dumpxml sles12_xen > sles12_xen.xmlVerify all disk image paths are correct from the KVM host's perspective. This is not a problem when converting on one machine, but may require manual changes when converting using an XML dump from another host.
<source file='/var/lib/libvirt/images/XenPool/SLES.qcow2'/>
Tip: Copying ImagesTo avoid copying an image twice, manually copy the disk image(s) directly to the
libvirt
storage pool. Update the source file entries in the XML description file. Thevirt-v2v
process will detect the existing disks and convert them in place.Run
virt-v2v
to convert to KVM virtual machine:root #
virt-v2v sles12_xen.xml1 \ -i LIBVIRTXML2 \ -os remote_host.example.com:/exported_dir3 \ --bridge br04 \ -on sles12_kvm5The XML description of the source Xen-based virtual machine.
virt-v2v
will read the information about the source virtual machine form alibvirt
XML file.Storage pool where the target virtual machine disk image will be placed. In this example, the image will be placed on an NFS share
/exported_dir
on theremote_host.example.com
server.The target KVM-based virtual machine will use the network bridge
br0
on the host.The target virtual machine will be renamed to
sles12_kvm
to prevent name collision with the existing virtual machine of the same name.
1.4.2 Conversion Based on the libvirt
Domain Name #
This method is useful if you are still running libvirt
under
Xen, and plan to reboot to the KVM hypervisor later.
Find the
libvirt
domain name of the virtual machine you want to convert.root #
virsh list Id Name State ---------------------------------------------------- [...] 2 sles12_xen running [...]sles12_xen
is the source virtual machine to convert.Run
virt-v2v
to convert to KVM virtual machine:root #
virt-v2v sles12_xen1 \ -i libvirt2 \ -os storage_pool3 \ --network eth04 \ -of qcow25 \ -oa sparce6 \ -on sles12_kvmThe domain name of the Xen-based virtual machine.
virt-v2v
will read the information about the source virtual machine directly from the activelibvirt
connection.The target disk image will be placed in a local
libvirt
storage pool.All guest bridges (or networks) will be connected to a locally managed network.
Format for the disk image of the target virtual machine. Supported options are
raw
orqcow2
.If the converted guest disk space will be
sparse
orpreallocated
.
1.4.3 Converting a Remote Xen Virtual Machine #
This method is useful if you need to convert a Xen virtual machine
running on a remote host. As virt-v2v
connects to
the remote host via ssh
, ensure that SSH service is
running on the host.
Starting with SLES 12 SP2, virt-v2v
requires a
passwordless SSH connection to the remote host. This means a connection
using an SSH key added to the ssh-agent. See man
ssh-keygen
and man ssh-add
for more details
on this.
To connect to a remote libvirt
connection, construct a
valid connection URI relevant for your remote host. In the following
example, the remote host name is
remote_host.example.com
, and the user name for the
connection is root
. The connection URI then looks as follows:
xen+ssh://root@remote_host.example.com/
For more information on libvirt
connection URIs, see
https://libvirt.org/uri.html.
Find the
libvirt
domain name of the remote virtual machine you want to convert.root #
virsh -c xen+ssh://root@remote_host.example.com/ list Id Name State ---------------------------------------------------- 1 sles12_xen running [...]sles12_xen
is the source virtual machine to convert.The
virt-v2v
command for the remote connection looks like this:root #
virt-v2v sles12_xen \ -i libvirt \ -ic xen+ssh://root@remote_host.example.com/ \ -os local_storage_pool \ --bridge br0
1.5 Running Converted Virtual Machines #
After virt-v2v
completes successfully, a new
libvirt
domain will be created with the name specified with the
-on
option. If you did not specify
-on
, the same name as the source virtual machine will
be used. The new guest can be managed with standard
libvirt
tools, such as virsh
or Virtual Machine Manager.
If you completed the conversion under Xen as described in Section 1.4.2, “Conversion Based on the libvirt
Domain Name”, you may need to reboot the host machine
and boot with the non-Xen kernel.
2 Xen to KVM Manual Migration #
2.1 General Outline #
The preferred solution to manage virtual machines is based on
libvirt
; for more information, see https://libvirt.org/. It has several advantages over
the manual way of defining and running virtual
machines—libvirt
is cross-platform, supports many
hypervisors, has secure remote management, has virtual networking, and, most
of all, provides a unified abstract layer to manage virtual
machines. Therefore the main focus of this article is on the
libvirt
solution.
Generally, the Xen to KVM migration runs in the following basic steps:
Make a backup copy of the original Xen VM Guest.
OPTIONAL: Apply changes specific to paravirtualized guests.
Obtain information about the original Xen VM Guest and update it to KVM equivalents.
Shut down the guest on the Xen host, and run the new one under the KVM hypervisor.
The Xen to KVM migration cannot be done live while the source VM Guest is running. Before running the new KVM-ready VM Guest, you are advised to shut down the original Xen VM Guest.
2.2 Back Up the Xen VM Guest #
To back up your Xen VM Guest, follow these steps:
Identify the relevant Xen guest you want to migrate, and remember its ID/name.
# virsh list --all Id Name State ---------------------------------- 0 Domain-0 running 1 SLES11SP3 running [...]
Shut down the guest. You can do this either by shutting down the guest OS, or with
virsh
:# virsh shutdown SLES11SP3
Backup its configuration to an XML file.
# virsh dumpxml SLES11SP3 > sles11sp3.xml
Backup its disk image file. Use the
cp
orrsync
commands to create the backup copy. Remember that it is always a good idea to check the copy with themd5sum
command.After the image file is backed up, you can start the guest again with
# virsh start SLES11SP3
2.3 Changes Specific to Paravirtualized Guests #
Apply the following changes if you are migrating a paravirtualized
Xen guest. You can do it either on the running guest, or on the
stopped guest using guestfs-tools
.
After applying the changes described in this section, the image file related to the migrated VM Guest will not be usable under Xen anymore.
2.3.1 Install the Default Kernel #
After you installed the default kernel, do not try to boot the Xen guest with it, the system will not boot.
Before cloning the Xen guest disk image for use under the KVM hypervisor, make sure it is bootable without the Xen hypervisor. This is very important for paravirtualized Xen guests as they usually contain a special Xen kernel, and often do not have a complete GRUB 2 boot loader installed.
For SLES 11 update the
/etc/sysconfig/kernel
file. Change theINITRD_MODULES
parameter by removing all Xen drivers and replacing the with virtio drivers. ReplaceINITRD_MODULES="xenblk xennet"
with
INITRD_MODULES="virtio_blk virtio_pci virtio_net virtio_balloon"
For SLES 12 search for
xenblk xennet
in/etc/dracut.conf.d/*.conf
and replace them withvirtio_blk virtio_pci virtio_net virtio_balloon
Paravirtualized Xen guests are running a specific Xen kernel. To run the guest under KVM, you need to install the default kernel.
Note: Default Kernel Is Already InstalledYou do not need to install the default kernel for a fully virtualized guests as it is already installed.
Enter
rpm -q kernel-default
on the Xen guest to find out if the default kernel is installed. If not, install it withzypper in kernel-default
.The kernel we are going to use to boot the guest under KVM must have virtio (paravirtualized) drivers available. Run the following command to find out. Do not forget to replace
4.12.14-94.37
with your kernel version:# find /lib/modules/4.12.14-94.37-default/kernel/drivers/ -name virtio* /lib/modules/4.12.14-94.37-default/kernel/drivers/net/virtio_net.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/scsi/virtio_scsi.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/block/virtio_blk.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/char/virtio_console.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/char/hw_random/virtio-rng.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio/virtio.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio/virtio_pci.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio/virtio_balloon.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio/virtio_ring.ko /lib/modules/4.12.14-94.37-default/kernel/drivers/virtio/virtio_mmio.ko
Update
/etc/fstab
. Change any storage devices fromxvda
tovda
.Update the boot loader configuration. Enter
rpm -q grub2
on the Xen guest to find out if GRUB 2 is already installed. If not, install it withzypper in grub2
.Now make the newly installed default kernel the default for booting the OS. Also remove/update the kernel command line options that may refer to Xen-specific devices. You can do it either with YaST (
› ), or manually:Find the preferred Linux boot menu entry by listing them all:
cat /boot/grub2/grub.cfg | grep 'menuentry '
Remember the order number (counted from zero) of the one you newly installed.
Set it the default boot menu entry:
grub2-set-default N
Replace N with the number of the boot menu entry you previously discovered.
Open
/etc/default/grub
for editing, and look forGRUB_CMDLINE_LINUX_DEFAULT
andGRUB_CMDLINE_LINUX_RECOVERY
options. Remove/update any reference to Xen-specific devices. In the following example, you can replaceroot=/dev/xvda1 disk=/dev/xvda console=xvc
with
root=/dev/vda1 disk=/dev/vda
Note that you need to remove all references to
xvc
-type consoles (such asxvc0
).
Update
device.map
in one of/boot/grub2
or/boot/grub2-efi
directories. Change any storage device fromxvda
tovda
.To import new default settings, run
grub2-mkconfig -o /boot/grub2/grub.cfg
2.3.2 Update the Guest for Boot under KVM #
Update the system to use default serial console. List the configured consoles, and remove symbolic links to
xvc?
ones.# ls -l /etc/systemd/system/getty.target.wants/ getty@tty1.service -> /usr/lib/systemd/system/getty@.service getty@xvc0.service -> /usr/lib/systemd/system/getty@xvc0.service getty@xvc1.service -> /usr/lib/systemd/system/getty@xvc1.service # rm /etc/systemd/system/getty.target.wants/getty@xvc?.service
Update the
/etc/securetty
file. Replacexvc0
withttyS0
.
2.4 Update the Xen VM Guest Configuration #
This section describes how to export the configuration of the original
Xen VM Guest, and what particular changes to apply to it so it can be
imported as a KVM guest into libvirt
.
2.4.1 Export the Xen VM Guest Configuration #
First export the configuration of the guest and save it to a file. A typical one may look like this:
# virsh dumpxml SLES11SP3 <domain type='xen'> <name>SLES11SP3</name> <uuid>fa9ea4d7-8f95-30c0-bce9-9e58ffcabeb2</uuid> <memory>524288</memory> <currentMemory>524288</currentMemory> <vcpu>1</vcpu> <bootloader>/usr/bin/pygrub</bootloader> <os> <type>linux</type> </os> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <emulator>/usr/lib/xen/bin/qemu-dm</emulator> <disk type='file' device='disk'> <driver name='file'/> <source file='/var/lib/libvirt/images/SLES_11_SP2_JeOS.x86_64-0.0.2_para.raw'/> <target dev='xvda' bus='xen'/> </disk> <interface type='bridge'> <mac address='00:16:3e:2d:91:c3'/> <source bridge='br0'/> <script path='vif-bridge'/> </interface> <console type='pty'> <target type='xen' port='0'/> </console> <input type='mouse' bus='xen'/> <graphics type='vnc' port='-1' autoport='yes' keymap='en-us'/> </devices> </domain>
You can find detailed information on the libvirt XML format for VM Guest description at https://libvirt.org/formatdomain.html.
2.4.2 General Changes to the Guest Configuration #
You need to make a few general changes to the exported Xen guest XML configuration to run it under the KVM hypervisor. The following applies to both fully virtualized and paravirtualized guests. Note that not all of the following XML elements need to be in your specific configuration.
To refer to a node in the XML configuration file, an XPath syntax will
be used throughout this document. For example, to refer to a
<name>
inside the
<domain>
tag
<domain> <name>sles11sp3</name> </domain>
an XPath equivalent /domain/name
will be used.
Change the
type
attribute of the/domain
element fromxen
tokvm
.Remove the
/domain/bootloader
element section.Remove the
/domain/bootloader_args
element section.Change the
/domain/os/type
element value fromlinux
tohvm
.Add
<boot dev="hd"/>
under the/domain/os
element.Add the
arch
attribute to the/domain/os/type
element. Acceptable values arearch=”x86_64”
orarch=”i686”
Change the
/domain/devices/emulator
element from/usr/lib/xen/bin/qemu-dm'
to/usr/bin/qemu-kvm
.For each disk associated with the paravirtualized (PV) guest, change the following:
Change the
name
attribute of the/domain/devices/disk/driver
element fromfile
toqemu
, and add atype
attribute for the disk type. For example, valid options includeraw
orqcow2
.Change the
dev
attribute of the/domain/devices/disk/target
element fromxvda
tovda
.Change the
bus
attribute of the/domain/devices/disk/target
element fromxen
tovirtio
.
For each network interface card, do the following changes:
If there is
model
defined in/domain/devices/interface
, change itstype
attribute value tovirtio
<model type=”virtio”>
Delete all
/domain/devices/interface/script
sections.Delete all
/domain/devices/interface/target
elements if thedev
attribute starts withvif
orvnet
orveth
. If using a custom network then change thedev
value to that target.
Remove the
/domain/devices/console
element section if it exists.Remove the
/domain/devices/serial
element section if it exists.Change the
bus
attribute on the/domain/devices/input
element fromxen
tops2
.Add the following element for memory ballooning features under the
/domain/devices
element.<memballoon model="virtio"/>
<target dev='hda' bus='ide'/>
controls
the device under which the disk is exposed to the guest OS. The
dev
attribute indicates the "logical" device name.
The actual device name specified is not guaranteed to map to the
device name in the guest OS. Therefore you may need to change the disk
mapping on the boot loader command line. For example, if the boot
loader expects a root disk to be hda2
but KVM
still sees it as sda2
, change the boot loader
command line from
[...] root=/dev/hda2 resume=/dev/hda1 [...]
to
[...] root=/dev/sda2 resume=/dev/sda1 [...]
In the case of paravirtualized xvda
devices, change it
to
[...] root=/dev/vda2 resume=/dev/vda1 [...]
Otherwise the VM Guest will refuse to boot in the KVM environment.
2.4.3 The Target KVM Guest Configuration #
After having applied all the modifications mentioned above, you end up with the following configuration for your KVM guest:
<domain type='kvm'> <name>SLES11SP3</name> <uuid>fa9ea4d7-8f95-30c0-bce9-9e58ffcabeb2</uuid> <memory>524288</memory> <currentMemory>524288</currentMemory> <vcpu cpuset='0-3'>1</vcpu> <os> <type arch=”x86_64”>hvm</type> <boot dev="hd"/> </os> <clock offset='utc'/> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <emulator>/usr/bin/qemu-kvm</emulator> <disk type='file' device='disk'> <driver name='qemu' type="raw"/> <source file='/var/lib/libvirt/images/SLES_11_SP2_JeOS.x86_64-0.0.2_para.raw'/> <target dev='vda' bus='virtio'/> </disk> <interface type='bridge'> <mac address='00:16:3e:2d:91:c3'/> <source bridge='br0'/> </interface> <input type='mouse' bus='usb'/> <graphics type='vnc' port='5900' autoport='yes' keymap='en-us'/> <memballoon model="virtio"/> </devices> </domain>
Save the configuration to a file in your home directory. After you
later import it, it will be copied to the default
/etc/libvirt/qemu
. Suppose you save the file as
SLES11SP3.xml
.
2.5 Migrate the VM Guest #
After you updated the VM Guest configuration, and applied necessary changes to the guest OS, shut down the original Xen guest, and run its clone under the KVM hypervisor.
Shut down the guest on the Xen host by running
shutdown -h now
asroot
from the console.Copy the disk files associated with the VM Guest if needed. A default configuration will require the Xen disk files to be copied from
/var/lib/xen/images
to/var/lib/kvm/images
. The/var/lib/kvm/images
directory may need to be created (asroot
) if you have not previously created a VM Guest.Create the new domain, and register it with
libvirt
:# virsh define SLES11SP3.xml Domain SLES11SP3 defined from SLES11SP3.xml
Verify that the new guest is seen in the KVM configuration:
virsh list –all
After the domain is created, you can start it:
# virsh start SLES11SP3 Domain SLES11SP3 started
3 For More Information #
For more information on libvirt, see https://libvirt.org.
You can find more details on libvirt
XML format at
https://libvirt.org/formatdomain.html.
For more information on virtualization with Xen and KVM, see the SUSE Linux Enterprise Server documentation at http://www.suse.com/doc/.
4 Documentation Updates #
This section lists content changes for this document.
4.1 October 2016 (Release of SUSE Linux Enterprise Server 12 SP2) #
- Section 1, “Migration to KVM Using
virt-v2v
” New section (FATE #316274).
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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.
2. VERBATIM COPYING #
You may copy and distribute the Document in any medium, either commercially or non-commercially, 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.
3. COPYING IN QUANTITY #
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.
4. MODIFICATIONS #
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:
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.
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.
State on the Title page the name of the publisher of the Modified Version, as the publisher.
Preserve all the copyright notices of the Document.
Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
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.
Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
Include an unaltered copy of this License.
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.
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.
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.
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.
Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.
Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.
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.
5. COMBINING DOCUMENTS #
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".
6. COLLECTIONS OF DOCUMENTS #
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.
7. AGGREGATION WITH INDEPENDENT WORKS #
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.
8. TRANSLATION #
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.
9. TERMINATION #
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.
10. FUTURE REVISIONS OF THIS LICENSE #
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 https://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.
ADDENDUM: How to use this License for your documents #
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.