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NAME

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

SYNOPSIS

virt-sysprep [--options] -d domname

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

DESCRIPTION

Virt-sysprep can reset or unconfigure 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. Virt-sysprep can also customize a virtual machine, for instance by adding SSH keys, users or logos. Each step can be enabled or disabled as required.

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 snapshot, copy or clone the disk first. See "COPYING AND CLONING" below.

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.

OPTIONS

--help

Display brief help.

-a file
--add file

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.

-a URI
--add URI

Add a remote disk. The URI format is compatible with guestfish. See "ADDING REMOTE STORAGE" in guestfish(1).

-c URI
--connect URI

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.

-d guest
--domain guest

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

-n
--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.

--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 ssh-hostkeys and udev-persistent-net operations.

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

Regardless of the --enable option, 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 operation.

--operation operations
--operations operations

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

--operations ssh-hostkeys,udev-persistent-net

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

--operations allows you to enable and disable any operation, including the default ones (which would be tried when specifying neither --operations nor --enable) and all the available ones; prepending a - in front of an operation name removes it from the list of enabled operations, while the meta-names defaults and all represent respectively the operations enabled by default and all the available ones. For example:

--operations firewall-rules,defaults,-tmp-files

would enable the firewall-rules operation (regardless whether it is enabled by default), all the default ones, and disable the tmp-files operation.

--operations can be specified multiple times; the first time the set of enabled operations is empty, while any further --operations affects the operations enabled so far.

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

Regardless of the --operations option, 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 operation.

--format raw|qcow2|..
--format auto

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 auto switches back to auto-detection for subsequent -a options.

For example:

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

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

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

--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 --enable. The second field is a * 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.

--mount-options mp:opts[;mp:opts;...]

Set the mount options used when libguestfs opens the disk image. Note this has no effect on the guest. It is used when opening certain guests such as ones using the UFS (BSD) filesystem.

Use a semicolon-separated list of mountpoint:options pairs. You may need to quote this list to protect it from the shell.

For example:

--mount-options "/:noatime"

will mount the root directory with notime. This example:

--mount-options "/:noatime;/var:rw,nodiratime"

will do the same, plus mount /var with rw,nodiratime.

-q
--quiet

Don't print log messages.

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

-v
--verbose

Enable verbose messages for debugging.

-V
--version

Display version number and exit.

-x

Enable tracing of libguestfs API calls.

__EXTRA_OPTIONS__

OPERATIONS

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

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

Operations can be individually enabled using the --enable/--operations options. Use a comma-separated list, for example:

virt-sysprep --operations 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.

* = enabled by default when no --enable/--operations option is given.

__OPERATIONS__

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:

configuration

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:

  • name

  • UUID

  • path to block device(s)

  • network card MAC address

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:

  • hostname and other net configuration

  • UUID

  • SSH host keys

  • Windows unique security ID (SID)

  • 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.

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

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

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

There are some smarter (and faster) ways too:

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

You may want to run virt-sysprep twice, once to reset the guest (to make a template) and a second time to customize the guest for a specific user:

virt-sysprep        virt-sysprep
  (reset)      (add user, keys, logos)
     |                   |
                 dd      v          dd       v
 original guest ----> template ---------> copied ------> custom
                      template       guest

  • 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.

  • Create a snapshot using lvcreate --snapshot.

  • 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.

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

  • Prepare your template using virt-sparsify(1). See below.

VIRT-CLONE

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 XML.

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

SPARSIFY

virt-sparsify
 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).

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

FIRSTBOOT VS SCRIPT

The two options --firstboot and --script both supply shell scripts that are run against the guest. However these two options are significantly different.

--firstboot script uploads the file script into the guest and arranges that it will run, in the guest, when the guest is next booted. (The script will only run once, at the "first boot").

--script script runs the shell script on the host, with its current directory inside the guest filesystem.

If you needed, for example, to yum install new packages, then you must not use --script for this, since that would (a) run the yum command on the host and (b) wouldn't have access to the same resources (repositories, keys, etc.) as the guest. Any command that needs to run on the guest must be run via --firstboot.

On the other hand if you need to make adjustments to the guest filesystem (eg. copying in files), then --script is ideal since (a) it has access to the host filesystem and (b) you will get immediate feedback on errors.

Either or both options can be used multiple times on the command line.

SECURITY

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 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. The --scrub option can be used to scrub files instead of just deleting them. virt-sparsify(1) is another way to remove this content. See also the scrub(1) command to get rid of deleted content in directory entries and inodes.

RANDOM SEED

(This section applies to Linux guests only)

For supported guests, virt-sysprep 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 enabling just the customize module:

cp template.img newguest.img
virt-sysprep --enable customize -a newguest.img

WINDOWS 8

Windows 8 "fast startup" can prevent virt-sysprep from working. See "WINDOWS HIBERNATION AND WINDOWS 8 FAST STARTUP" in guestfs(3).

EXIT STATUS

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

ENVIRONMENT VARIABLES

VIRT_TOOLS_DATA_DIR

This can point to the directory containing data files used for Windows firstboot installation.

Normally you do not need to set this. If not set, a compiled-in default will be used (something like /usr/share/virt-tools).

This directory may contain the following files:

rhsrvany.exe

This is the RHSrvAny Windows binary, used to install a "firstboot" script in Windows guests. It is required if you intend to use the --firstboot or --firstboot-command options with Windows guests.

See also: https://github.com/rwmjones/rhsrvany

For other environment variables, see "ENVIRONMENT VARIABLES" in guestfs(3).

SEE ALSO

guestfs(3), guestfish(1), virt-builder(1), virt-clone(1), virt-customize(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/.

AUTHORS

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

Wanlong Gao, Fujitsu Ltd.

COPYRIGHT

Copyright (C) 2011-2014 Red Hat Inc.

Copyright (C) 2012 Fujitsu Ltd.