Ubuntu Manpage: virt-builder - Build virtual machine images quickly

Provided by: libguestfs-tools_1.24.5-1ubuntu0.1_amd64

NAME

       virt-builder - Build virtual machine images quickly

SYNOPSIS

        virt-builder os-version
           [-o|--output DISKIMAGE] [--size SIZE] [--format raw|qcow2]
           [--attach ISOFILE]
           [--root-password SELECTOR]
           [--hostname HOSTNAME]
           [--install PKG,[PKG...]]
           [--upload FILE:DEST]
           [--edit FILE:EXPR]
           [--delete FILE] [--scrub FILE]
           [--run SCRIPT] [--run-command 'CMD ARGS ...']
           [--firstboot SCRIPT] [--firstboot-command 'CMD ARGS ...']
           [--firstboot-install PKG,[PKG...]]

        virt-builder -l|--list [--long]

        virt-builder --notes os-version

        virt-builder --print-cache

        virt-builder --cache-all-templates

        virt-builder --delete-cache

        virt-builder --get-kernel DISKIMAGE
           [--format raw|qcow2] [--output OUTPUTDIR]

DESCRIPTION

       Virt-builder is a tool for quickly building new virtual machines.  You can build a variety
       of VMs for local or cloud use, usually within a few minutes or less.  Virt-builder also
       has many ways to customize these VMs.  Everything is run from the command line and nothing
       requires root privileges, so automation and scripting is simple.

       Note that virt-builder does not install guests from scratch.  It takes cleanly prepared,
       digitally signed OS templates and customizes them.  This approach is used because it is
       much faster, but if you need to do fresh installs you may want to look at virt-install(1)
       and oz-install(1).

       The easiest way to get started is by looking at the examples in the next section.

EXAMPLES

List the virtual machines available
virt-builder --list

will list out the operating systems available to install. A selection of freely
redistributable OSes is available as standard. You can add your own too (see below).

After choosing a guest from the list, you may want to see if there are any installation
notes:

virt-builder --notes fedora-20

Build a virtual machine
virt-builder fedora-20

will build a Fedora 20 image. This will have all default configuration (minimal size, no
user accounts, random root password, only the bare minimum installed software, etc.).

You do not need to run this command as root.

The first time this runs it has to download the template over the network, but this gets
cached (see "CACHING").

The name of the output file is derived from the template name, so above it will be
"fedora-20.img". You can change the output filename using the -o option:

virt-builder fedora-20 -o mydisk.img

You can also use the -o option to write to existing devices or logical volumes.

virt-builder fedora-20 --format qcow2

As above, but write the output in qcow2 format to "fedora-20.qcow2".

virt-builder fedora-20 --size 20G

As above, but the output size will be 20 GB. The guest OS is resized as it is copied to
the output (automatically, using virt-resize(1)).

Setting the root password
virt-builder fedora-20 --root-password file:/tmp/rootpw

Create a Fedora 20 image. The root password is taken from the file "/tmp/rootpw".

Note if you don't set --root-password then the guest is given a random root password.

You can also create user accounts. See "USERS AND PASSWORDS" below.

Set the hostname
virt-builder fedora-20 --hostname virt.example.com

Set the hostname to "virt.example.com".

Installing software
To install packages from the ordinary (guest) software repository (eg. yum or apt):

virt-builder fedora-20 --install "inkscape,@Xfce Desktop"

(In Fedora, "@" is used to install groups of packages. On Debian you would install a
meta-package instead.)

Customizing the installation
There are many options that let you customize the installation. These include:
--run/--run-command, which run a shell script or command while the disk image is being
generated and lets you add or edit files that go into the disk image.
--firstboot/--firstboot-command, which let you add scripts/commands that are run the first
time the guest boots. --edit to edit files. --upload to upload files.

For example:

cat <<'EOF' > /tmp/yum-update.sh
yum -y update
EOF

virt-builder fedora-20 --firstboot /tmp/yum-update.sh

or simply:

virt-builder fedora-20 --firstboot-command 'yum -y update'

which makes the yum(8) "update" command run once the first time the guest boots.

Or:

virt-builder fedora-20 --edit '/etc/yum.conf: s/gpgcheck=1/gpgcheck=0/'

which edits "/etc/yum.conf" inside the disk image (during disk image creation, long before
boot).

You can combine these options, and have multiple options of all types.

OPTIONS

--help
Display help.

--attach ISOFILE
During the customization phase, the given disk is attached to the libguestfs
appliance. This is used to provide extra software repositories or other data for
customization.

You probably want to ensure the volume(s) or filesystems in the attached disks are
labelled (or use an ISO volume name) so that you can mount them by label in your run-
scripts:

mkdir /tmp/mount
mount LABEL=EXTRA /tmp/mount

You can have multiple --attach options, and the format can be any disk format (not
just an ISO).

See also: --run, "Installing packages at build time from a side repository",
genisoimage(1), virt-make-fs(1).

--attach-format FORMAT
Specify the disk format for the next --attach option. The "FORMAT" is usually "raw"
or "qcow2". Use "raw" for ISOs.

--cache DIR
--no-cache
--cache DIR sets the directory to use/check for cached template files. If not set,
defaults to either "$XDG_CACHE_HOME/virt-builder/" or "$HOME/.cache/virt-builder/".

--no-cache disables template caching.

--cache-all-templates
Download all templates to the cache and then exit. See "CACHING".

Note this doesn't cache everything. More templates might be uploaded. Also this
doesn't cache packages (the --install option).

--check-signature
--no-check-signature
Check/don't check the digital signature of the OS template. The default is to check
the signature and exit if it is not correct. Using --no-check-signature bypasses this
check.

REFERENCE

INSTALLING PACKAGES
There are several approaches to installing packages or applications in the guest which
have different trade-offs.

Installing packages at build time

If the guest OS you are installing is similar to the host OS (eg. both are Linux), and if
libguestfs supports network connections, then you can use --install to install packages
like this:

virt-builder fedora-20 --install inkscape

This uses the guest's package manager and the host's network connection.

Installing packages at first boot

Another option is to install the packages when the guest first boots:

virt-builder fedora-20 --firstboot-install inkscape

This uses the guest's package manager and the guest's network connection.

The downsides are that it will take the guest a lot longer to boot first time, and there's
nothing much you can do if package installation fails (eg. if a network problem means the
guest can't reach the package repositories).

Installing packages at build time from a side repository

If the software you want to install is not available in the main package repository of the
guest, then you can add a side repository. Usually this is presented as an ISO (CD disk
image) file containing extra packages.

You can create the disk image using either genisoimage(1) or virt-make-fs(1). For
genisoimage, use a command like this:

genisoimage -o extra-packages.iso -R -J -V EXTRA cdcontents/

Create a script that mounts the ISO and sets up the repository. For yum, create
/tmp/install.sh containing:

mkdir /tmp/mount
mount LABEL=EXTRA /tmp/mount

cat <<'EOF' > /etc/yum.repos.d/extra.repo
[extra]
name=extra
baseurl=file:///tmp/mount
enabled=1
EOF

yum -y install famousdatabase

For apt, create /tmp/install.sh containing:

mkdir /tmp/mount
mount LABEL=EXTRA /tmp/mount

apt-cdrom -d=/tmp/mount add
apt-get -y install famousdatabase

Use the --attach option to attach the CD / disk image and the --run option to run the
script:

virt-builder fedora-20 \
--attach extra-packages.iso \
--run /tmp/install.sh

USERS AND PASSWORDS
The --root-password option is used to change the root password (otherwise a random
password is used). This option takes a password "SELECTOR" in one of the following
formats:

--root-password file:FILENAME
Read the root password from "FILENAME". The whole first line of this file is the
replacement password. Any other lines are ignored. You should create the file with
mode 0600 to ensure no one else can read it.

--root-password password:PASSWORD
Set the root password to the literal string "PASSWORD".

Note: this is not secure since any user on the same machine can see the cleartext
password using ps(1).

Creating user accounts

To create user accounts, use the useradd(8) command with --firstboot-command like this:

virt-builder --firstboot-command \
'useradd -m -p "" rjones ; chage -d 0 rjones'

The above command will create an "rjones" account with no password, and force the user to
set a password when they first log in. There are other ways to manage passwords, see
useradd(8) for details.

LOG FILE
Scripts and package installation that runs at build time (--run, --run-command, --install,
but not firstboot) is logged in one of the following locations:

"/tmp/builder.log"
On Linux, BSD and other guests.

"C:\Temp\builder.log"
On Windows, DOS guests.

"/builder.log"
If "/tmp" or "C:\Temp" is missing.

If you don't want the log file to appear in the final image, then use the --no-logfile
command line option.

INSTALLATION PROCESS
When you invoke virt-builder, installation proceeds as follows:

• The template image is downloaded.

If the template image is present in the cache, the cached version is used instead.
(See "CACHING").

• The template signature is checked.

• The template is uncompressed to a tmp file.

• The template image is resized into the destination, using virt-resize(1).

• Extra disks are attached (--attach).

• A new random seed is generated for the guest.

• The hostname is set (--hostname).

• The root password is changed (--root-password).

• Packages are installed (--install).

• Files are uploaded (--upload).

• Files are edited (--edit).

• Files are deleted (--delete, --scrub).

• Firstboot scripts are installed (--firstboot, --firstboot-command,
--firstboot-install).

Note that although firstboot scripts are installed at this step, they do not run until
the guest is booted first time. Firstboot scripts will run in the order they appear
on the command line.

• Scripts are run (--run, --run-command).

Scripts run in the order they appear on the command line.

IMPORTING THE DISK IMAGE
Importing into libvirt

Import the disk image into libvirt using virt-install(1) --import option.

virt-install --import \
--name guest --ram 2048 --disk path=disk.img,format=raw

Notes:

1. You must specify the correct format. The format is "raw" unless you used virt-
builder's --format option.

2. You can run virt-install as root or non-root. Each works slightly differently because
libvirt manages a different set of virtual machines for each user. In particular
virt-manager normally shows the root-owned VMs, whereas Boxes shows the user-owned
VMs, and other tools probably work differently as well.

Importing into OpenStack

Import the image into Glance (the OpenStack image store) by doing:

glance image-create --name fedora-20-image --file fedora-20.img \
--disk-format raw --container-format bare \
--is-public True

The --file parameter is the virt-builder-generated disk image. It should match virt-
builder's --output option. The --disk-format parameter should match virt-builder's
--format option (or "raw" if you didn't use that option). The --container-format should
always be "bare" since virt-builder doesn't put images into containers.

You can use the "glance image-show fedora-20-image" command to display the properties of
the image.

To boot up an instance of your image on a Nova compute node, do:

nova boot fedora-20-server --image fedora-20-image \
--flavor m1.medium

Use "nova flavor-list" to list possible machine flavors. Use "nova list" to list running
instances.

DEBUGGING BUILDS
If virt-builder fails with an error, then enable debugging (-v) and report a bug (see
"BUGS" below).

If virt-builder is successful but the image doesn't work, here are some things to try:

Use virt-rescue
Run virt-rescue(1) on the disk image:

virt-rescue -a disk.img

This gives you a rescue shell. You can mount the filesystems from the disk image on
"/sysroot" and examine them using ordinary Linux commands. You can also chroot into
the guest to reinstall the bootloader. The virt-rescue man page has a lot more
information and examples.

Use guestfish
Run guestfish(1) on the disk image:

guestfish -a disk.img -i

Use guestfish commands like "ll /directory" and "cat /file" to examine directories and
files.

Use guestmount
Mount the disk image safely on the host using FUSE and guestmount(1):

mkdir /tmp/mp
guestmount -a disk.img -i /tmp/mp
cd /tmp/mp

To unmount the disk image do:

fusermount -u /tmp/mp

Add a serial console
If the guest hangs during boot, it can be helpful to add a serial console to the
guest, and direct kernel messages to the serial console. Adding the serial console
will involve looking at the documentation for your hypervisor. To direct kernel
messages to the serial console, add the following on the kernel command line:

console=tty0 console=ttyS0,115200

CREATING YOUR OWN TEMPLATES
For serious virt-builder use, you may want to create your own repository of templates.

Libguestfs.org repository

Out of the box, virt-builder downloads the file
http://libguestfs.org/download/builder/index.asc which is an index of available templates
plus some information about each one, wrapped up in a digital signature. The command
"virt-builder --list" lists out the information in this index file.

The templates hosted on libguestfs.org were created using shell scripts, kickstart files
and preseed files which can be found in the libguestfs source tree, in "builder/website".

Setting up the repository

You can set up your own site containing an index file and some templates, and then point
virt-builder at the site by using the --source option:

virt-builder --source https://example.com/builder/index.asc \
--fingerprint 'AAAA BBBB ...' \
--list

(Note setting the environment variables "VIRT_BUILDER_SOURCE" and
"VIRT_BUILDER_FINGERPRINT" may be easier to type!)

You can host this on any web or FTP server, or a local or network filesystem.

Setting up a GPG key

If you don't have a GnuPG key, you will need to set one up. (Strictly speaking this is
optional, but if your index and template files are not signed then virt-builder users will
have to use the --no-check-signature flag every time they use virt-builder.)

To create a key, see the GPG manual http://www.gnupg.org/gph/en/manual.html.

Export your GPG public key and add it to the keyring of all virt-builder users:

gpg --export -a "you@example.com" > pubkey

# For each virt-builder user:
gpg --import pubkey

Also find the fingerprint of your key:

gpg --list-keys --fingerprint

Create the templates

There are many ways to create the templates. For example you could clone existing guests
(see virt-sysprep(1)), or you could install a guest by hand (virt-install(1)). To see how
the templates were created for virt-builder, look at the scripts in "builder/website"

For best results when compressing the templates, use the following xz options (see
nbdkit-xz-plugin(1) for further explanation):

xz --best --block-size=16777216 disk

Creating and signing the index file

The index file has a simple text format (shown here without the digital signature):

[fedora-18]
name=Fedora® 18
osinfo=fedora18
file=fedora-18.xz
checksum[sha512]=...
format=raw
size=6442450944
compressed_size=148947524
expand=/dev/sda3

[fedora-19]
name=Fedora® 19
osinfo=fedora19
file=fedora-19.xz
checksum[sha512]=...
revision=3
format=raw
size=4294967296
compressed_size=172190964
expand=/dev/sda3

The part in square brackets is the "os-version", which is the same string that is used on
the virt-builder command line to build that OS.

After preparing the "index" file in the correct format, clearsign it using the following
command:

gpg --clearsign --armor index

This will create the final file called "index.asc" which can be uploaded to the server
(and is the --source URL). As noted above, signing the index file is optional, but
recommended.

The following fields can appear:

"name=NAME"
The user-friendly name of this template. This is displayed in the --list output but
is otherwise not significant.

"osinfo=ID"
This optional field maps the operating system to the associated libosinfo ID. Virt-
builder does not use it (yet).

"file=PATH"
The path (relative to the index) of the xz-compressed template.

Note that absolute paths or URIs are not permitted here. This is because virt-builder
has a "same origin" policy for templates so they cannot come from other servers.

"sig=PATH"
This option is deprecated. Use the checksum field instead.

The path (relative to the index) of the GPG detached signature of the xz file.

Note that absolute paths or URIs are not permitted here. This is because virt-builder
has a "same origin" policy for templates so they cannot come from other servers.

The file can be created as follows:

gpg --detach-sign --armor -o disk.xz.sig disk.xz

"checksum[sha512]=7b882fe9b82eb0fef..."
The SHA-512 checksum of the compressed file is checked after it is downloaded. To
work out the signature, do:

sha512sum disk.xz

Note if you use this, you don't need to sign the file, ie. don't use "sig". This
option overrides "sig".

"checksum=7b882fe9b82eb0fef..."
"checksum" is an alias for "checksum[sha512]".

If you need to interoperate with virt-builder = 1.24.0 then you have to use "checksum"
because that version would give a parse error with square brackets and numbers in the
key of a field. This is fixed in virt-builder ≥ 1.24.1.

"revision=N"
The revision is an integer which is used to control the template cache. Increasing
the revision number causes clients to download the template again even if they have a
copy in the cache.

The revision number is optional. If omitted it defaults to 1.

"format=raw"
"format=qcow2"
Specify the format of the disk image (before it was compressed). If not given, the
format is autodetected, but generally it is better to be explicit about the intended
format.

Note this is the source format, which is different from the --format option (requested
output format). Virt-builder does on-the-fly conversion from the source format to the
requested output format.

"size=NNN"
The virtual size of the image in bytes. This is the size of the image when
uncompressed. If using a non-raw format such as qcow2 then it means the virtual disk
size, not the size of the qcow2 file.

This field is required.

Virt-builder also uses this as the minimum size that users can request via the --size
option, or as the default size if there is no --size option.

"compressed_size=NNN"
The compressed size of the disk image in bytes. This is just used for information
(when using --list --long).

"expand=/dev/sdaX"
When expanding the image to its final size, instruct virt-resize(1) to expand the
named partition in the guest image to fill up all available space. This works like
the virt-resize --expand option.

You should usually put the device name of the guest's root filesystem here.

It's a good idea to use this, but not required. If the field is omitted then virt-
resize will create an extra partition at the end of the disk to cover the free space,
which is much less user-friendly.

"lvexpand=/dev/VolGroup/LogVol"
When expanding the image to its final size, instruct virt-resize(1) to expand the
named logical volume in the guest image to fill up all available space. This works
like the virt-resize --lv-expand option.

If the guest uses LVM2 you should usually put the LV of the guest's root filesystem
here. If the guest does not use LVM2 or its root filesystem is not on an LV, don't
use this option.

"notes=NOTES"
Any notes that go with this image, especially notes describing what packages are in
the image, how the image was prepared, and licensing information.

This information is shown in the --notes and --list --long modes.

You can use multi-line notes here by indenting each new line with at least one
character of whitespace (even on blank lines):

notes=This image was prepared using
the following kickstart script:
<-- one space at beginning of line
part /boot --fstype ext3
...

"hidden=true"
Using the hidden flag prevents the template from being listed by the --list option
(but it is still installable). This is used for test images.

Running virt-builder against the alternate repository

Ensure each virt-builder user has imported your public key into their gpg keyring (see
above).

Each virt-builder user should export these environment variables:

• "VIRT_BUILDER_SOURCE" to point to the URL of the "index.asc" file.

• "VIRT_BUILDER_FINGERPRINT" to contain the fingerprint (long hex string) of the user
who signed the index file and the templates.

Now run virt-builder commands as normal, eg:

virt-builder --list --long

virt-builder os-version

To debug problems, add the "-v" option to these commands.

Licensing of templates

You should be aware of the licensing of images that you distribute. For open source
guests, provide a link to the source code in the "notes" field and comply with other
requirements (eg. around trademarks).

CACHING
Since the templates are usually very large, downloaded templates are cached in the user's
home directory.

The location of the cache is "$XDG_CACHE_HOME/virt-builder/" or
"$HOME/.cache/virt-builder".

You can print out information about the cache directory, including which guests are
currently cached, by doing:

virt-builder --print-cache

The cache can be deleted if you want to save space by doing:

virt-builder --delete-cache

You can download all (current) templates to the local cache by doing:

virt-builder --cache-all-templates

To disable the template cache, use --no-cache.

Only templates are cached. The index and detached digital signatures are not cached.

Virt-builder uses curl(1) to download files and it also uses the current "http_proxy"
(etc) settings when installing packages (--install). You may therefore want to set those
environment variables in order to maximize the amount of local caching that happens. See
"ENVIRONMENT VARIABLES" and curl(1).

DIGITAL SIGNATURES
Virt-builder uses GNU Privacy Guard (GnuPG or gpg) to verify that the index and templates
have not been tampered with.

The source points to an index file, which is optionally signed.

Virt-builder downloads the index and checks that the signature is valid and the signer's
fingerprint matches the specified fingerprint (ie. --fingerprint,
"VIRT_BUILDER_FINGERPRINT", or a built-in fingerprint, in that order).

For checking against the built-in public key/fingerprint, this requires importing the
public key into the user's local gpg keyring (that's just the way that gpg works).

When a template is downloaded, its signature is checked in the same way.

Although the signatures are optional, if you don't have them then virt-builder users will
have to use --no-check-signature on the command line. This prevents an attacker from
replacing the signed index file with an unsigned index file and having virt-builder
silently work without checking the signature. In any case it is highly recommended that
you always create signed index and templates.

ARCHITECTURE
Virt-builder can build a guest for any architecture no matter what the host architecture
is. For example an x86-64 guest on an ARM host.

However certain options may not work correctly, specifically options that require running
commands in the guest during the build process: --install, --run, --run-command. You may
need to replace these with their firstboot-equivalents.

An x86-64 host building 32 bit i686 guests should work without any special steps.

SECURITY
Virt-builder does not need to run as root (in fact, should not be run as root), and
doesn't use setuid, "sudo" or any similar mechanism.

--install, --run and --run-command are implemented using an appliance (a small virtual
machine) so these commands do not run on the host. If you are using the libguestfs
libvirt backend and have SELinux enabled then the virtual machine is additionally
encapsulated in an SELinux container (sVirt).

However these options will have access to the host's network and since the template may
contain untrusted code, the code might try to access host network resources which it
should not. You can use --no-network to prevent this.

Firstboot commands run in the context of the guest when it is booted, and so the security
of your hypervisor / cloud should be considered.

Virt-builder injects a random seed into every guest which it builds. This helps to ensure
that TCP sequence numbers, UUIDs, ssh host keys etc are truly random when the guest boots.

You should check digital signatures and not ignore any signing errors.

USER MODE LINUX
You can use virt-builder with the User-Mode Linux (UML) backend. This may be faster when
running virt-builder inside a virtual machine (eg. in the cloud).

To enable the UML backend, read the instructions in "USER-MODE LINUX BACKEND" in
guestfs(3).

Currently you have to use the --no-network option. This should be fixed in a future
version.

The qcow2 output format is not supported by UML. You can only create raw-format guests.

SELINUX
Guests which use SELinux (such as Fedora and Red Hat Enterprise Linux) require that each
file has a correct SELinux label.

Since virt-builder does not know how to give new files a correct label, it touches
"/.autorelabel" in the guest and relies on the guest to relabel itself at first boot.

This usually means that these guests will reboot themselves once the first time you use
them. This is normal, and harmless.

ENVIRONMENT VARIABLES

       For other environment variables which affect all libguestfs programs, see "ENVIRONMENT
       VARIABLES" in guestfs(3).

       "http_proxy"
       "https_proxy"
       "no_proxy"
           Set the proxy for downloads.  These environment variables (and more) are actually
           interpreted by curl(1), not virt-builder.

       "HOME"
           Used to determine the location of the template cache.  See "CACHING".

       "LIBGUESTFS_MEMSIZE"
           The size (in megabytes) of the appliance.  The default can be found using the command
           "guestfish get-memsize".  Increase this if you find that --run scripts are running out
           of memory.

       "VIRT_BUILDER_FINGERPRINT"
           Set the default value for the GPG signature fingerprint (see --fingerprint option).

       "VIRT_BUILDER_SOURCE"
           Set the default value for the source URL for the template repository (see --source
           option).

       "XDG_CACHE_HOME"
           Used to determine the location of the template cache.  See "CACHING".

EXIT STATUS

       This program returns 0 if successful, or non-zero if there was an error.

AUTHOR

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

COPYRIGHT

       Copyright (C) 2013 Red Hat Inc.

LICENSE

       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.

BUGS

       To get a list of bugs against libguestfs, use this link:
       https://bugzilla.redhat.com/buglist.cgi?component=libguestfs&product=Virtualization+Tools

       To report a new bug against libguestfs, use this link:
       https://bugzilla.redhat.com/enter_bug.cgi?component=libguestfs&product=Virtualization+Tools

       When reporting a bug, please supply:

       •   The version of libguestfs.

       •   Where you got libguestfs (eg. which Linux distro, compiled from source, etc)

       •   Describe the bug accurately and give a way to reproduce it.

       •   Run libguestfs-test-tool(1) and paste the complete, unedited output into the bug
           report.

NAME

SYNOPSIS

DESCRIPTION

EXAMPLES

OPTIONS

REFERENCE

ENVIRONMENT VARIABLES

EXIT STATUS

SEE ALSO

AUTHOR

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