path: root/sysprep/virt-sysprep.pod

=encoding utf8

=head1 NAME

virt-sysprep - Reset or unconfigure a virtual machine so clones can be made

=head1 SYNOPSIS

 virt-sysprep [--options] -d domname

 virt-sysprep [--options] -a disk.img [-a disk.img ...]

=head1 DESCRIPTION

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 modifies the guest or disk image I<in place>.  The guest
must be shut down.  If you want to preserve the existing contents of
the guest, you I<must snapshot, copy or clone the disk first>.
See L</COPYING AND CLONING> below.

You do I<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 C<sysprep.exe> which is used to unconfigure
Windows machines in preparation for cloning them.  Having said that,
virt-sysprep does I<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.

=head1 OPTIONS

=over 4

=item B<--help>

Display brief help.

=item B<-a> file

=item B<--add> file

Add I<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 I<--format> option.

=item B<-c> URI

=item B<--connect> URI

If using libvirt, connect to the given I<URI>.  If omitted, then we
connect to the default libvirt hypervisor.

If you specify guest block devices directly (I<-a>), then libvirt is
not used at all.

=item B<-d> guest

=item B<--domain> guest

Add all the disks from the named libvirt guest.  Domain UUIDs can be
used instead of names.

=item B<-n>

=item B<--dry-run>

Perform a read-only "dry run" on the guest.  This runs the sysprep
operation, but throws away any changes to the disk at the end.

=item B<--enable> operations

Choose which sysprep operations to perform.  Give a comma-separated
list of operations, for example:

 --enable ssh-hostkeys,udev-persistent-net

would enable ONLY C<ssh-hostkeys> and C<udev-persistent-net> operations.

If the I<--enable> option is not given, then we default to trying most
sysprep operations (see I<--list-operations> to show which are
enabled).

Regardless of the I<--enable> option, sysprep operations are skipped
for some guest types.

Use I<--list-operations> to list operations supported by a particular
version of virt-sysprep.

See L</OPERATIONS> below for a list and an explanation of each
operation.

=item B<--format> raw|qcow2|..

=item B<--format> auto

The default for the I<-a> option is to auto-detect the format of the
disk image.  Using this forces the disk format for I<-a> options which
follow on the command line.  Using I<--format auto> switches back to
auto-detection for subsequent I<-a> options.

For example:

 virt-sysprep --format raw -a disk.img

forces raw format (no auto-detection) for C<disk.img>.

 virt-sysprep --format raw -a disk.img --format auto -a another.img

forces raw format (no auto-detection) for C<disk.img> and reverts to
auto-detection for C<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).

=item B<--list-operations>

List the operations supported by the virt-sysprep program.

These are listed one per line, with one or more single-space-separated
fields, eg:

 $ virt-sysprep --list-operations
 bash-history * Remove the bash history in the guest
 cron-spool * Remove user at-jobs and cron-jobs
 dhcp-client-state * Remove DHCP client leases
 dhcp-server-state * Remove DHCP server leases
 [etc]

The first field is the operation name, which can be supplied
to I<--enable>.  The second field is a C<*> character if the
operation is enabled by default or blank if not.  Subsequent
fields on the same line are the description of the operation.

Before libguestfs 1.17.33 only the first (operation name) field was
shown and all operations were enabled by default.

=item B<-q>

=item B<--quiet>

Don't print log messages.

To enable detailed logging of individual file operations, use I<-x>.

=item B<--selinux-relabel>

=item B<--no-selinux-relabel>

I<--selinux-relabel> forces SELinux relabelling next time the guest
boots.  I<--no-selinux-relabel> disables relabelling.

The default is to try to detect if SELinux relabelling is required.
See L</SELINUX RELABELLING> below for more details.

=item B<-v>

=item B<--verbose>

Enable verbose messages for debugging.

=item B<-V>

=item B<--version>

Display version number and exit.

=item B<-x>

Enable tracing of libguestfs API calls.

@EXTRA_OPTIONS@

=back

=head1 OPERATIONS

If the I<--enable> option is I<not> given, then most sysprep
operations are enabled.

Use C<virt-sysprep --list-operations> to list all operations for your
virt-sysprep binary.  The ones which are enabled by default are marked
with a C<*> character.  Regardless of the I<--enable> option, sysprep
operations are skipped for some guest types.

Operations can be individually enabled using the I<--enable> option.
Use a comma-separated list, for example:

 virt-sysprep --enable=ssh-hostkeys,udev-persistent-net [etc..]

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.

C<*> = enabled by default when no I<--enable> option is given.

@OPERATIONS@

=head1 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:

=over 4

=item I<configuration>

The configuration or description of the guest.  eg. The libvirt
XML (see C<virsh dumpxml>), the running configuration of the guest,
or another external format like OVF.

Some configuration items that might need to be changed:

=over 4

=item *

name

=item *

UUID

=item *

path to block device(s)

=item *

network card MAC address

=back

=item I<block device(s)>

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:

=over 4

=item *

hostname and other net configuration

=item *

UUID

=item *

SSH host keys

=item *

Windows unique security ID (SID)

=item *

Puppet registration

=back

=back

=head2 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.

                        virt-sysprep
                             |
                             v
 original guest --------> template ---------->
                                      \------> cloned
                                       \-----> guests
                                        \---->

You can, of course, just copy the block device on the host using
L<cp(1)> or L<dd(1)>.

                   dd                 dd
 original guest --------> template ---------->
                                      \------> cloned
                                       \-----> guests
                                        \---->

There are some smarter (and faster) ways too:

                          snapshot
                template ---------->
                            \------> cloned
                             \-----> guests
                              \---->

=over 4

=item *

Create a snapshot using qemu-img:

 qemu-img create -f qcow2 -o backing_file=original snapshot.qcow

The advantage is that you don't need to copy the original (very fast)
and only changes are stored (less storage required).

Note that writing to the backing file once you have created guests on
top of it is not possible: you will corrupt the guests.

=item *

Create a snapshot using C<lvcreate --snapshot>.

=item *

Other ways to create snapshots include using filesystems-level tools
(for filesystems such as btrfs).

Most Network Attached Storage (NAS) devices can also create cheap
snapshots from files or LUNs.

=item *

Get your NAS to duplicate the LUN.  Most NAS devices can also
duplicate LUNs very cheaply (they copy them on-demand in the
background).

=item *

Prepare your template using L<virt-sparsify(1)>.  See below.

=back

=head2 VIRT-CLONE

A separate tool, L<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 XML.

L<virt-clone(1)> does not use libguestfs and cannot look inside the
disk image.  This was the original motivation to write virt-sysprep.

=head2 SPARSIFY

              virt-sparsify
 original guest --------> template

L<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 C<dd>).

=head2 RESIZE

                         virt-resize
                template ---------->
                            \------> cloned
                             \-----> guests
                              \---->

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 L<virt-resize(1)>.  Virt-resize performs a copy and resize, and
thus is ideal for cloning guests from a template.

=head1 SECURITY

Although virt-sysprep removes some sensitive information from the
guest, it does not pretend to remove all of it.  You should examine
the L</OPERATIONS> above and 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 L<virt-sparsify(1)> as one way to remove this content.  See
also the L<scrub(1)> command to get rid of deleted content in
directory entries and inodes.

=head2 RANDOM SEED

I<(This section applies to Linux guests only)>

The virt-sysprep C<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 I<after> cloning
from a template too, which can be done by just enabling the
C<random-seed> operation:

 cp template.img newguest.img
 virt-sysprep --enable random-seed -a newguest.img

=head2 SELINUX RELABELLING

I<(This section applies to Linux guests using SELinux only)>

If any new files are created by virt-sysprep, then virt-sysprep
touches C</.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
I<--selinux-relabel> option.

You can disable relabelling entirely by supplying the
I<--no-selinux-relabel> option.

=head1 SHELL QUOTING

Libvirt guest names can contain arbitrary characters, some of which
have meaning to the shell such as C<#> and space.  You may need to
quote or escape these characters on the command line.  See the shell
manual page L<sh(1)> for details.

=head1 EXIT STATUS

This program returns 0 on success, or 1 if there was an error.

=head1 SEE ALSO

L<guestfs(3)>,
L<guestfish(1)>,
L<virt-clone(1)>,
L<virt-rescue(1)>,
L<virt-resize(1)>,
L<virt-sparsify(1)>,
L<virsh(1)>,
L<lvcreate(8)>,
L<qemu-img(1)>,
L<scrub(1)>,
L<http://libguestfs.org/>,
L<http://libvirt.org/>.

=head1 AUTHORS

Richard W.M. Jones L<http://people.redhat.com/~rjones/>

Wanlong Gao, Fujitsu Ltd.

=head1 COPYRIGHT

Copyright (C) 2011-2012 Red Hat Inc.

Copyright (C) 2012 Fujitsu Ltd.

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.