Provided by: libguestfs-tools_1.14.8-1_i386
virt-sysprep - Reset or unconfigure a virtual machine so clones can be
virt-sysprep [--options] -d domname
virt-sysprep [--options] -a disk.img [-a disk.img ...]
Virt-sysprep "resets" or "unconfigures" a virtual machine so that
clones can be made from it. Steps in this process include removing SSH
host keys, removing persistent network MAC configuration, and removing
user accounts. Each step can be enabled or disabled as required.
Virt-sysprep is a simple shell script, allowing easy inspection or
customization by the system administrator.
Virt-sysprep modifies the guest or disk image in place. The guest must
be shut down. If you want to preserve the existing contents of the
guest, you must copy or clone the disk first. See "COPYING AND
You do not need to run virt-sysprep as root. In fact we'd generally
recommend that you don't. The time you might want to run it as root is
when you need root in order to access the disk image, but even in this
case it would be better to change the permissions on the disk image to
be writable as the non-root user running virt-sysprep.
"Sysprep" stands for "system preparation" tool. The name comes from
the Microsoft program "sysprep.exe" which is used to unconfigure
Windows machines in preparation for cloning them. Having said that,
virt-sysprep does not currently work on Microsoft Windows guests. We
plan to support Windows sysprepping in a future version, and we already
have code to do it.
Display brief help.
Add file which should be a disk image from a virtual machine.
The format of the disk image is auto-detected. To override this
and force a particular format use the --format=.. option.
If using libvirt, connect to the given URI. If omitted, then we
connect to the default libvirt hypervisor.
If you specify guest block devices directly (-a), then libvirt is
not used at all.
Add all the disks from the named libvirt guest. Domain UUIDs can
be used instead of names.
Choose which sysprep operations to perform. Give a comma-separated
list of operations, for example:
would enable ONLY "ssh-hostkeys" and "udev-persistent-net"
If the --enable option is not given, then we default to trying all
possible sysprep operations. But some sysprep operations are
skipped for some guest types.
Use --list-operations to list operations supported by a particular
version of virt-sysprep.
See "OPERATIONS" below for a list and an explanation of each
The default for the -a option is to auto-detect the format of the
disk image. Using this forces the disk format for -a options which
follow on the command line. Using --format with no argument
switches back to auto-detection for subsequent -a options.
virt-sysprep --format=raw -a disk.img
forces raw format (no auto-detection) for "disk.img".
virt-sysprep --format=raw -a disk.img --format -a another.img
forces raw format (no auto-detection) for "disk.img" and reverts to
auto-detection for "another.img".
If you have untrusted raw-format guest disk images, you should use
this option to specify the disk format. This avoids a possible
security problem with malicious guests (CVE-2010-3851).
Change the hostname. See the "hostname" operation below. If not
given, defaults to "localhost.localdomain".
List the operations supported by the virt-sysprep program.
--selinux-relabel forces SELinux relabelling next time the guest
boots. --no-selinux-relabel disables relabelling.
The default is to try to detect if SELinux relabelling is required.
See "SELINUX RELABELLING" below for more details.
Enable verbose messages for debugging.
Display version number and exit.
-x Enable tracing of libguestfs API calls.
If the --enable option is not given, then all sysprep operations are
enabled, although some are skipped depending on the type of guest.
Operations can be individually enabled using the --enable option. Use
a comma-separated list, for example:
virt-sysprep --enable=ssh-hostkeys,udev-persistent-net [etc..]
To list the operations supported by the current version of virt-
sysprep, use --list-operations.
Future versions of virt-sysprep may add more operations. If you are
using virt-sysprep and want predictable behaviour, specify only the
operations that you want to have enabled.
Remove user at-jobs and cron-jobs.
Remove DHCP client leases.
Remove DHCP server leases.
Changes the hostname of the guest to the value given in the --hostname
If the --hostname parameter is not given, then the hostname is changed
Remove many log files.
Remove email from the local mail spool directory.
Remove HWADDR (hard-coded MAC address) configuration. For Fedora and
Red Hat Enterprise Linux, this is removed from "ifcfg-*" files.
Write some random bytes from the host into the random seed file of the
See "RANDOM SEED" below.
Remove the RHN system ID.
Remove the Smolt hardware UUID.
Remove the SSH host keys in the guest.
The SSH host keys are regenerated (differently) next time the guest is
If, after cloning, the guest gets the same IP address, ssh will give
you a stark warning about the host key changing:
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Remove udev persistent net rules which map the guest's existing MAC
address to a fixed ethernet device (eg. eth0).
After a guest is cloned, the MAC address usually changes. Since the
old MAC address occupies the old name (eg. eth0), this means the fresh
MAC address is assigned to a new name (eg. eth1) and this is usually
undesirable. Erasing the udev persistent net rules avoids this.
Remove the utmp file.
This records who is currently logged in on a machine. In modern Linux
distros it is stored in a ramdisk and hence not part of the virtual
machine's disk, but it was stored on disk in older distros.
Remove the yum UUID.
Yum creates a fresh UUID the next time it runs when it notices that the
original UUID has been erased.
COPYING AND CLONING
Virt-sysprep can be used as part of a process of cloning guests, or to
prepare a template from which guests can be cloned. There are many
different ways to achieve this using the virt tools, and this section
is just an introduction.
A virtual machine (when switched off) consists of two parts:
The configuration or description of the guest. eg. The libvirt XML
(see "virsh dumpxml"), the running configuration of the guest, or
another external format like OVF.
Some configuration items that might need to be changed:
o path to block device(s)
o network card MAC address
One or more hard disk images, themselves containing files,
directories, applications, kernels, configuration, etc.
Some things inside the block devices that might need to be changed:
o hostname and other net configuration
o SSH host keys
o Windows unique security ID (SID)
o Puppet registration
COPYING THE BLOCK DEVICE
Starting with an original guest, you probably wish to copy the guest
block device and its configuration to make a template. Then once you
are happy with the template, you will want to make many clones from it.
original guest --------> template ---------->
You can, of course, just copy the block device on the host using cp(1)
original guest --------> template ---------->
There are some smarter (and faster) ways too:
Use the block device as a backing file and create a snapshot on top
for each guest. The advantage is that you don't need to copy the
block device (very fast) and only changes are stored (less storage
Note that writing to the backing file once you have created guests
on top of it is not possible: you will corrupt the guests.
Tools that can do this include: qemu-img(1) (with the create -f
qcow2 -o backing_file option), lvcreate(8) (--snapshot option).
Some filesystems (such as btrfs) and most Network Attached Storage
devices can also create cheap snapshots from files or LUNs.
o Get your NAS to snapshot and/or duplicate the LUN.
o Prepare your template using virt-sparsify(1). See below.
A separate tool, virt-clone(1), can be used to duplicate the block
device and/or modify the external libvirt configuration of a guest. It
will reset the name, UUID and MAC address of the guest in the libvirt
virt-clone(1) does not use libguestfs and cannot look inside the disk
image. This was the original motivation to write virt-sysprep.
original guest --------> template
virt-sparsify(1) can be used to make the cloning template smaller,
making it easier to compress and/or faster to copy.
Notice that since virt-sparsify also copies the image, you can use it
to make the initial copy (instead of "dd").
If you want to give people cloned guests, but let them pick the size of
the guest themselves (eg. depending on how much they are prepared to
pay for disk space), then instead of copying the template, you can run
virt-resize(1). Virt-resize performs a copy and resize, and thus is
ideal for cloning guests from a template.
Although virt-sysprep removes some sensitive information from the
guest, it does not pretend to remove all of it. You should examine the
"OPERATIONS" above, and the implementation of the operations in the
shell script. You should also examine the guest afterwards.
Sensitive files are simply removed. The data they contained may still
exist on the disk, easily recovered with a hex editor or undelete tool.
Use virt-sparsify(1) as one way to remove this content. See also the
scrub(1) command to get rid of deleted content in directory entries and
(This section applies to Linux guests only)
The virt-sysprep "random-seed" operation writes a few bytes of
randomness from the host into the guest's random seed file.
If this is just done once and the guest is cloned from the same
template, then each guest will start with the same entropy, and things
like SSH host keys and TCP sequence numbers may be predictable.
Therefore you should arrange to add more randomness after cloning from
a template too, which can be done by just enabling the "random-seed"
cp template.img newguest.img
virt-sysprep --enable=random-seed -a newguest.img
(This section applies to Linux guests using SELinux only)
If any new files are created by virt-sysprep, then virt-sysprep touches
"/.autorelabel" so that these will be correctly labelled by SELinux the
next time the guest is booted. This process interrupts boot and can
take some time.
You can force relabelling for all guests by supplying the
You can disable relabelling entirely by supplying the
Libvirt guest names can contain arbitrary characters, some of which
have meaning to the shell such as "#" and space. You may need to quote
or escape these characters on the command line. See the shell manual
page sh(1) for details.
This program returns 0 on success, or 1 if there was an error.
guestfs(3), guestfish(1), virt-clone(1), virt-rescue(1),
virt-resize(1), virt-sparsify(1), virsh(1), lvcreate(8), qemu-img(1),
scrub(1), <http://libguestfs.org/>, <http://libvirt.org/>.
Richard W.M. Jones <http://people.redhat.com/~rjones/>
Copyright (C) 2011 Red Hat Inc.
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.