NAME¶

virt-sysprep - Reset or unconfigure 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 "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 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 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.

-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.

--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.

-q

--quiet

Don't print log messages.

 

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

--selinux-relabel

--no-selinux-relabel

--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.

-v

--verbose

Enable verbose messages for debugging.

-V

--version

Display version number and exit.

-x

Enable tracing of libguestfs API calls.

--hostname hostname (see "hostname" below)

Change the hostname. If not given, defaults to "localhost.localdomain".

--script script (see "script" below)

Run the named "script" (a shell script or program) against the guest. The script can be any program on the host. The script's current directory will be the guest's root directory.

 

Note: If the script is not on the $PATH, then you must give the full absolute path to the script.

--scriptdir scriptdir (see "script" below)

The mount point (an empty directory on the host) used when the "script" operation is enabled and one or more scripts are specified using --script parameter(s).

 

Note: "scriptdir" must be an absolute path.

 

If --scriptdir is not specified then a temporary mountpoint will be created.

OPERATIONS¶

If the --enable 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 option, sysprep operations are skipped for some guest types. 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..]

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 option is given.

bash-history *¶

Remove the bash history in the guest. Remove the bash history of user "root" and any other users who have a ".bash_history" file in their home directory.

blkid-tab *¶

Remove blkid tab in the guest.

ca-certificates¶

Remove CA certificates 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.

dovecot-data *¶

Remove Dovecot (mail server) data.

flag-reconfiguration¶

Flag the system for reconfiguration. Note that this may require user intervention when the guest is booted.

hostname *¶

Change the hostname of the guest. This operation changes the hostname of the guest to the value given in the --hostname parameter. If the --hostname parameter is not given, then the hostname is changed to "localhost.localdomain".

kerberos-data¶

Remove Kerberos data in the guest.

logfiles *¶

Remove many log files from the guest. On Linux the following files are removed:

 /root/anaconda-ks.cfg
 /root/install.log
 /root/install.log.syslog
 /var/account/pacct
 /var/cache/gdm/*
 /var/lib/AccountService/users/*
 /var/lib/fprint/*
 /var/lib/logrotate.status
 /var/log/*.log*
 /var/log/BackupPC/LOG
 /var/log/audit/*
 /var/log/btmp*
 /var/log/ceph/*.log
 /var/log/chrony/*.log
 /var/log/cron*
 /var/log/cups/*_log
 /var/log/dmesg*
 /var/log/glusterfs/*glusterd.vol.log
 /var/log/glusterfs/glusterfs.log
 /var/log/httpd/*log
 /var/log/jetty/jetty-console.log
 /var/log/lastlog*
 /var/log/libvirt/libvirtd.log
 /var/log/libvirt/lxc/*.log
 /var/log/libvirt/qemu/*.log
 /var/log/libvirt/uml/*.log
 /var/log/mail/*
 /var/log/maillog*
 /var/log/messages*
 /var/log/ppp/connect-errors
 /var/log/secure*
 /var/log/setroubleshoot/*.log
 /var/log/spooler*
 /var/log/squid/*.log
 /var/log/tallylog*
 /var/log/wtmp*
 /var/named/data/named.run

mail-spool *¶

Remove email from the local mail spool directory.

net-hwaddr *¶

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

package-manager-cache *¶

Remove package manager cache.

pam-data *¶

Remove the PAM data in the guest.

random-seed *¶

Generate random seed for guest. Write some random bytes from the host into the random seed file of the guest. See "RANDOM SEED" below.

rhn-systemid *¶

Remove the RHN system ID.

samba-db-log *¶

Remove the database and log files of Samba.

script *¶

Run arbitrary scripts against the guest. The "script" module lets you run arbitrary shell scripts or programs against the guest. Note this feature requires FUSE support. You may have to enable this in your host, for example by adding the current user to the "fuse" group, or by loading a kernel module. Use one or more --script parameters to specify scripts or programs that will be run against the guest. The script or program is run with its current directory being the guest's root directory, so relative paths should be used. For example: "rm etc/resolv.conf" in the script would remove a Linux guest's DNS configuration file, but "rm /etc/resolv.conf" would (try to) remove the host's file. Normally a temporary mount point for the guest is used, but you can choose a specific one by using the --scriptdir parameter.

smolt-uuid *¶

Remove the Smolt hardware UUID.

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!

ssh-userdir *¶

Remove ".ssh" directories in the guest. Remove the ".ssh" directory of user "root" and any other users who have a ".ssh" directory in their home directory.

sssd-db-log *¶

Remove the database and log files of sssd.

udev-persistent-net *¶

Remove udev persistent net rules. 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.

user-account¶

Remove the user accounts in the guest. Remove all the user accounts and their home directories. The "root" account is not removed.

utmp *¶

Remove the utmp file. This file 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.

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.

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:

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:

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
                              \---->
    

 

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: 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.

•

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

•

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.

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. 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 inodes.

RANDOM SEED¶

(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" operation:

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

SELINUX RELABELLING¶

(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 --selinux-relabel option. You can disable relabelling entirely by supplying the --no-selinux-relabel option.

SHELL QUOTING¶

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.

EXIT STATUS¶

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

SEE ALSO¶

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/>.

AUTHORS¶

Richard W.M. Jones <http://people.redhat.com/~rjones/> Wanlong Gao, Fujitsu Ltd.

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.