libguestfs/clone/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 is a simple shell script, allowing easy inspection or
customization by the system administrator.

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 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<--enable=...>

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 all
possible sysprep operations.  But some 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>

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> with no argument
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 -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<--hostname> newhostname

Change the hostname.  See the L</hostname> operation below.
If not given, defaults to C<localhost.localdomain>.

=item B<--list-operations>

List the operations supported by the virt-sysprep program.

=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.

=back

=head1 OPERATIONS

If the I<--enable> option is I<not> given, then
I<all sysprep operations are enabled>, although some are skipped
depending on the type of guest.

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..]

To list the operations supported by the current version of
virt-sysprep, use I<--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.

=head2 cron-spool

Remove user at-jobs and cron-jobs.

=head2 dhcp-client-state

Remove DHCP client leases.

=head2 dhcp-server-state

Remove DHCP server leases.

=head2 hostname

Changes the hostname of the guest to the value given in the
I<--hostname> parameter.

If the I<--hostname> parameter is not given, then the hostname is
changed to C<localhost.localdomain>.

=head2 logfiles

Remove many log files.

=head2 mail-spool

Remove email from the local mail spool directory.

=head2 net-hwaddr

Remove HWADDR (hard-coded MAC address) configuration.  For Fedora and
Red Hat Enterprise Linux, this is removed from C<ifcfg-*> files.

=head2 random-seed

Write some random bytes from the host into the random seed file of
the guest.

See C</RANDOM SEED> below.

=head2 rhn-systemid

Remove the RHN system ID.

=head2 smolt-uuid

Remove the Smolt hardware UUID.

=head2 ssh-hostkeys

Remove the SSH host keys in the guest.

The SSH host keys are regenerated (differently) next time the guest is
booted.

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!

=head2 udev-persistent-net

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.

=head2 utmp

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.

=head2 yum-uuid

Remove the yum UUID.

Yum creates a fresh UUID the next time it runs when it notices that
the original UUID has been erased.

=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:

=over 4

=item *

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

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
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.

Tools that can do this include:
L<qemu-img(1)> (with the I<create -f qcow2 -o backing_file> option),
L<lvcreate(8)> (I<--snapshot> option).  Some filesystems (such as
btrfs) and most Network Attached Storage devices can also create cheap
snapshots from files or LUNs.

=item *

Get your NAS to snapshot and/or duplicate the LUN.

=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 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 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 AUTHOR

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

=head1 COPYRIGHT

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., 675 Mass Ave, Cambridge, MA 02139, USA.