virt-dib - Online in the Cloud

PROGRAM:

NAME

virt-dib - Run diskimage-builder elements

SYNOPSIS

virt-dib -B DIB-LIB [options] elements...

DESCRIPTION

Virt-dib is a tool for using the elements of "diskimage-builder" to build a new disk
image, generate new ramdisks, etc.

Virt-dib is intended as safe replacement for "diskimage-builder" and its
"ramdisk-image-create" mode, see "COMPARISON WITH DISKIMAGE-BUILDER" for a quick
comparison with usage of "diskimage-builder".

"diskimage-builder" is part of the TripleO OpenStack project:
https://wiki.openstack.org/wiki/TripleO.

EXAMPLES

Build simple images of distributions
virt-dib \
-B /path/to/diskimage-builder/lib \
-p /path/to/diskimage-builder/elements \
--envvar DIB_RELEASE=jessie \
--name debian-jessie \
debian vm

This builds a Debian Jessie (8.x) disk image, suitable for running as virtual machine,
saved as debian-jessie.qcow2.

Build ramdisks
virt-dib \
-B /path/to/diskimage-builder/lib \
-p /path/to/diskimage-builder/elements \
--ramdisk \
--name ramdisk \
ubuntu deploy-ironic

This builds a ramdisk for the Ironic OpenStack component based on the Ubuntu distribution.

OPTIONS

--help
Display help.

-B PATH
Set the path to the library directory of "diskimage-builder". This is usually the lib
subdirectory in the sources and when installed, and /usr/share/diskimage-builder/lib
when installed in /usr.

This parameter is mandatory, as virt-dib needs to provide it for the elements (as some
of them might use scripts in it). Virt-dib itself does not make use of the library
directory.

--arch ARCHITECTURE
Use the specified architecture for the output image. The default value is the same as
the host running virt-dib.

Right now this option does nothing more than setting the "ARCH" environment variable
for the elements, and it's up to them to produce an image for the requested
architecture.

--debug LEVEL
Set the debug level to "LEVEL", which is a non-negative integer number. The default
is 0.

This debug level is different than what -x and -v set, and it increases the debugging
information printed out. Specifically, this sets the "DIB_DEBUG_TRACE", and any value
> 0 enables tracing in the scripts executed.

--drive DISK
Add the specified disk to be used as helper drive where to cache files of the
elements, like disk images, distribution packages, etc.

See "HELPER DRIVE".

-p PATH
--element-path PATH
Add a new path with elements. Paths are used in the same order as the -p parameters
appear, so a path specified first is looked first, and so on.

Obviously, it is recommended to add the path to the own elements of
"diskimage-builder", as most of the other elements will rely on them.

--extra-packages PACKAGE,...
Install additional packages in the image being built.

This relies on the "install-packages" binary provided by the package management
elements.

This option can be specified multiple times, each time with multiple packages
separated by comma.

--envvar VARIABLE
--envvar VARIABLE=VALUE
Carry or set an environment variable for the elements.

See "ENVIRONMENT VARIABLES" below for more information on the interaction and usage of
environment variables.

This option can be used in two ways:

--envvar VARIABLE
Carry the environment variable "VARIABLE". If it is not set, nothing is exported
to the elements.

--envvar VARIABLE=VALUE
Set the environment variable "VARIABLE" with value "VALUE" for the elements,
regardless whether an environment variable with the same name exists.

This can be useful to pass environment variable without exporting them in the
environment where virt-dib runs.

--exclude-element ELEMENT
Ignore the specified element.

--exclude-script SCRIPT
Ignore any element script named "SCRIPT", whichever element it is in.

This can be useful in case some script does not run well with virt-dib, for example
when they really need "diskimage-builder"'s environment.

--formats FORMAT,...
Set the list of output formats, separating them with comma.

Supported formats are:

"qcow2" (enabled by default)
QEMU's qcow2.

"raw"
Raw disk format.

"tar"
An uncompressed tarball.

"vhd"
"Virtual Hard Disk" disk image. This output format requires the "vhd-util" tool.

Please note that the version of "vhd-util" tool needs to be patched to support the
"convert" subcommand, and to be bootable. The patch is available here:
https://github.com/emonty/vhd-util/blob/master/debian/patches/citrix.

--fs-type FILESYSTEM
Set the filesystem type to use for the root filesystem. The default is "ext4".

See also "guestfs_filesystem_available" in guestfs(3).

--image-cache DIRECTORY
Set the path in the host where cache the resources used by the elements of the
"extra-data.d" phase. The default is ~/.cache/image-create.

Please note that most of the resources fetched after "extra-data" will be cached in
the helper drive specified with --drive; see also "HELPER DRIVE".

--install-type TYPE
Specify the default installation type. Defaults to "source".

Set to "package" to use package based installations by default.

--machine-readable
This option is used to make the output more machine friendly when being parsed by
other programs. See "MACHINE READABLE OUTPUT" below.

-m MB
--memsize MB
Change the amount of memory allocated to the appliance. Increase this if you find that
the virt-dib execution runs out of memory.

The default can be found with this command:

guestfish get-memsize

--mkfs-options "OPTION STRING"
Add the specified options to mkfs(1), to be able to fine-tune the root filesystem
creation. Note that this is not possible to override the filesystem type.

You should use --mkfs-options at most once. To pass multiple options, separate them
with space, eg:

virt-dib ... --mkfs-options '-O someopt -I foo'

--network
--no-network
Enable or disable network access from the guest during the installation.

Enabled is the default. Use --no-network to disable access.

The network only allows outgoing connections and has other minor limitations. See
"NETWORK" in virt-rescue(1).

This does not affect whether the guest can access the network once it has been booted,
because that is controlled by your hypervisor or cloud environment and has nothing to
do with virt-dib.

If you use --no-network, then the environment variable "DIB_OFFLINE" is set to 1,
signaling the elements that they should use only cached resources when available.
Note also that, unlike with "diskimage-builder" where elements may still be able to
access to the network even with "DIB_OFFLINE=", under virt-dib network will be fully
unaccessible.

--name NAME
Set the name of the output image file. The default is "image".

According to the chosen name, there will be the following in the current directory:

$NAME.ext
For each output format, a disk image named after the outout image with the
extension depending on the format; for example: $NAME.qcow2, $NAME.raw, etc.

Not applicable in ramdisk mode, see "RAMDISK BUILDING".

$NAME.d
A directory containing any files created by the elements, for example dib-
manifests directory (created by the "manifests" element), ramdisks and kernels in
ramdisk mode, and so on.

--no-delete-on-failure
Don't delete the output files on failure to build. You can use this to debug failures
to run scripts.

The default is to delete the output file if virt-dib fails (or, for example, some
script that it runs fails).

-q
--quiet
Don't print ordinary progress messages.

--qemu-img-options option[,option,...]
Pass --qemu-img-options option(s) to the qemu-img(1) command to fine-tune the output
format. Options available depend on the output format (see --formats) and the
installed version of the qemu-img program.

You should use --qemu-img-options at most once. To pass multiple options, separate
them with commas, eg:

virt-dib ... --qemu-img-options cluster_size=512,preallocation=metadata ...

--ramdisk
Set the ramdisk building mode.

See "RAMDISK BUILDING".

--ramdisk-element NAME
Set the name for the additional element added in ramdisk building mode. The default
is "ramdisk".

See "RAMDISK BUILDING".

--root-label LABEL
Set the label for the root filesystem in the created image.

Please note that some filesystems have different restrictions on the length of their
labels; for example, on "ext2/3/4" filesystems labels cannot be longer than 16
characters, while on "xfs" they have at most 12 characters.

The default depends on the actual filesystem for the root partition (see --fs-type):
on "xfs" is "img-rootfs", while "cloudimg-rootfs" on any other filesystem.

--size SIZE
Select the size of the output disk, where the size can be specified using common names
such as "32G" (32 gigabytes) etc. The default size is "5G".

To specify size in bytes, the number must be followed by the lowercase letter b, eg:
"--size 10737418240b".

See also virt-resize(1) for resizing partitions of an existing disk image.

--skip-base
Skip the inclusion of the "base" element.

--smp N
Enable N ≥ 2 virtual CPUs for scripts to use.

-u Do not compress resulting qcow2 images. The default is to compress them.

-v
--verbose
Enable debugging messages.

-V
--version
Display version number and exit.

-x Enable tracing of libguestfs API calls.

ENVIRONMENT VARIABLES

Unlike with "diskimage-builder", the environment of the host is not inherited in the
appliance when running most of the elements (i.e. all the ones different than
"extra-data.d").

To set environment for the elements being run, it is necessary to tell virt-dib to use
them, with the option --envvar. Such option allows to selectively export environment
variables when running the elements, and it is the preferred way to pass environment
variables to the elements.

To recap: if you want the environment variable "MYVAR" (and its content) to be available
to the elements, you can do either

export MYVAR # whichever is its value
virt-dib ... --envvar MYVAR ...

or

virt-dib ... --envvar MYVAR=value_of_it ...

HELPER DRIVE

Virt-dib runs most of the element in its own appliance, and thus not on the host. Because
of this, there is no possibility for elements to cache resources directly on the host.

To solve this issue, virt-dib allows the usage of an helper drive where to store cached
resources, like disk images, distribution packages, etc. While this means that there is a
smaller space available for caching, at least it allows to limit the space on the host for
caches, without assuming that elements will do that by themselves.

Currently this disk is either required to have a single partition on it, or the first
partition on it will be used. A disk with the latter configuration can be easily created
with guestfish(1) like the following:

guestfish -N filename.img=fs:ext4:10G

The above will create a disk image called filename.img, 10G big, with a single partition
of type ext4; see "PREPARED DISK IMAGES" in guestfish(1).

It is recommended for it to be ≥ 10G or even more, as elements will cache disk images,
distribution packages, etc. As with any disk image, the helper disk can be easily resized
using virt-resize(1) if more space in it is needed.

The drive can be accessed like any other disk image, for example using other tools of
libguestfs such as guestfish(1):

guestfish -a filename.img -m /dev/sda1

If no helper drive is specified with --drive, all the resources cached during a virt-dib
run will be discarded.

RESOURCES INSIDE THE DRIVE
Inside the helper drive, it is possible to find the following resources:

/home
This directory is set as "HOME" environment variable during the build. It contains
mostly the image cache (saved as /home/.cache/image-create), and whichever other
resource is cached in the home directory of the user running the various tools.

/virt-dib-*.log
These are the logs of the elements being run within the libguestfs appliance, which
means all the hooks except "extra-data.d".

RAMDISK BUILDING

Virt-dib can emulate also "ramdisk-image-create", which is a secondary operation mode of
"diskimage-builder". Instead of being a different tool name, virt-dib provides easy
access to this mode using the --ramdisk switch.

In this mode:

· there is an additional ramdisk element added (see --ramdisk-element)

· no image is produced (so --formats is ignored)

· $NAME.d (see --name) will contain initrd, kernel, etc

TEMPORARY DIRECTORY

Virt-dib uses the standard temporary directory used by libguestfs, see "ENVIRONMENT
VARIABLES" in guestfs(3).

By default this location is /tmp (default value for "TMPDIR"), which on some systems may
be on a tmpfs filesystem, and thus defaulting to a maximum size of half of physical RAM.
If virt-dib exceeds this, it may hang or exit early with an error. The solution is to
point "TMPDIR" to a permanent location used as temporary location, for example:

mkdir local-tmp
env TMPDIR=$PWD/local-tmp virt-dib ...
rm -rf local-tmp

EXTRA DEPENDENCIES

Because of virt-dib runs most of the elements in its own appliance, all the tools and
libraries used by elements running outside the guest (typically "root.d",
"block-device.d", and "cleanup.d") need to be present in the appliance as well. In case
they are not, scripts will fail mostly with a "command not found" error.

For tools and libraries packaged by the distribution, the easy solution is to tell
libguestfs to include additional packages in the appliance. This is doable by e.g.
creating a new file with the additional packages:

# echo wget > /usr/lib64/guestfs/supermin.d/dib-my-extra

The actual path to the supermin.d directory depends on the distribution; additional files
can list more packages, each in its own line.

COMPARISON WITH DISKIMAGE-BUILDER

Virt-dib is intended as safe replacement for "diskimage-builder" and its
"ramdisk-image-create" mode; the user-notable differences consist in:

· the command line arguments; some of the arguments are the same as available in
"diskimage-builder", while some have different names:

disk-image-create virt-dib
----------------- --------
-a ARCH --arch ARCH
--image-size SIZE --size SIZE
--max-online-resize SIZE doable using --mkfs-options
-n --skip-base
-o IMAGENAME --name IMAGENAME
-p PACKAGE(S) --extra-packages PACKAGE(S)
-t FORMAT(S) --formats FORMAT(S)
-x --debug N

· the location of non-image output files (like ramdisks and kernels)

· the way some of the cached resources are saved: using an helper drive, not directly on
the disk where virt-dib is run

· the need to specify a target size for the output disk, as opposed to
"diskimage-builder" calculating an optimal one

· the handling of environment variables, see "ENVIRONMENT VARIABLES".

Furthermore, other than the libguestfs own environment variables (see "ENVIRONMENT
VARIABLES" in guestfs(3)), virt-dib does not read any other environment variable: this
means that all the options and behaviour changes are specified solely using command
line arguments

· "extra-data.d" scripts run in the host environment, before all the other ones (even
"root.d"); this means that, depending on the configuration for the elements, some of
them may fail due to missing content (usually directories) in "TMP_HOOKS_PATH".

Workarounds for this may be either:

· fix the "extra-data.d" scripts to create the missing directories

· create (and use) a simple element with a "extra-data.d" script named e.g.
00-create-missing-dirs to create the missing directories

· extra tools needed on some out-of-chroot phases need to be available in the appliance,
see "EXTRA DEPENDENCIES".

Elements themselves should notice no difference in they way they are run; behaviour
differences may due to wrong assumptions in elements, or not correct virt-dib emulation.

Known issues at the moment:

· (none)

MACHINE READABLE OUTPUT

The --machine-readable option can be used to make the output more machine friendly, which
is useful when calling virt-dib from other programs, GUIs etc.

Use the option on its own to query the capabilities of the virt-dib binary. Typical
output looks like this:

$ virt-dib --machine-readable
virt-dib
output:qcow2
output:tar
output:raw
output:vhd

A list of features is printed, one per line, and the program exits with status 0.

TESTING

Virt-dib has been tested with "diskimage-builder" (and its elements) ≥ 0.1.43; from time
to time also with "tripleo-image-elements" and "sahara-image-elements".

Previous versions may work, but it is not guaranteed.

EXIT STATUS

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

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