Ubuntu Manpage: ubuntu-image - Generate a bootable disk image

Provided by: ubuntu-image_2.2+22.04ubuntu3.22.04.2_amd64

NAME

       ubuntu-image - Generate a bootable disk image

SYNOPSIS

       ubuntu-image snap [options] model.assertion

       ubuntu-image classic [options] GADGET_TREE_URI

DESCRIPTION

ubuntu-image is a program for generating a variety of bootable disk images. It currently supports
building snap based and classic preinstalled Ubuntu images.

Snap-based images are built from a model assertion, which is a YAML file describing a particular
combination of core, kernel, and gadget snaps, along with other declarations, signed with a digital
signature asserting its authenticity. The assets defined in the model assertion uniquely describe the
device for which the image is built.

As part of the model assertion, a gadget snap is specified. The gadget contains a gadget.yaml file which
contains the exact description of the disk image's contents, in YAML format. The gadget.yaml file
describes such things as the names of all the volumes to be produced [1], the structures [2] within the
volume, whether the volume contains a bootloader and if so what kind of bootloader, etc.

Note that ubuntu-image communicates with the snap store using the snap prepare-image subcommand. The
model assertion file is passed to snap prepare-image which handles downloading the appropriate gadget and
any extra snaps. See that command's documentation for additional details.

Classic images are built from a local gadget tree path. The gadget tree is nothing more than a primed
gadget snap, containing a gadget.yaml file in the meta directory and all the necessary bootloader gadget
bits built. For instance a gadget tree can be easily prepared by fetching a specially tailored gadget
snap source and running snapcraft prime on it, with the resulting tree ending up in the prime/ directory.

The actual rootfs for a classic image is created by live-build with arguments passed as per the optional
arguments to ubuntu-image. The livecd-rootfs configuration from the host system is used.

OPTIONS

-h, --help
Show the program's message and exit.

--version
Show the program's version number and exit.

Snap command options
These are the options for defining the contents of snap-based images. Can only be used when the
ubuntu-image snap command is used.

model_assertion
Path to the model assertion file. This positional argument must be given for this mode of
operation.

--cloud-init USER-DATA-FILE
cloud-config data to be copied to the image.

--disable-console-conf
Disable console-conf on the resulting image.

--factory-image
Hint that the image is meant to boot in a device factory.

--validation=<ignore|enforce>
Control whether validations should be ignored or enforced.

Classic command options
These are the options for defining the contents of classic preinstalled Ubuntu images. Can only be used
when the ubuntu-image classic command is used.

GADGET_TREE_URI
An URI to the gadget tree to be used to build the image. This positional argument must be given
for this mode of operation. Must be a local path.

-p PROJECT, --project PROJECT
Project name to be passed on to livecd-rootfs. Mutually exclusive with --filesystem

-f FILESYSTEM, --filesystem FILESYSTEM
Unpacked Ubuntu filesystem to be copied to the system partition. Mutually exclusive with
--project.

-s SUITE, --suite SUITE
Distribution name to be passed on to livecd-rootfs.

-a CPU-ARCHITECTURE, --arch CPU-ARCHITECTURE
CPU architecture to be passed on to livecd-rootfs. Default value is the architecture of the host.

--subproject SUBPROJECT
Sub-project name to be passed on livecd-rootfs.

--subarch SUBARCH
Sub-architecture to be passed on to livecd-rootfs.

--with-proposed
Defines if the image should be built with -proposed enabled. This is passed through to
livecd-rootfs.

--extra-ppas EXTRA_PPAS
Extra ppas to install. This is passed through to livecd-rootfs.

Common options
There are two general operational modes to ubuntu-image. The usual mode is to run the script giving the
required model assertion file as a required positional argument, generating a disk image file. These
options are useful in this mode of operation.

The second mode of operation is provided for debugging and testing purposes. It allows you to run the
internal state machine step by step, and is described in more detail below.

-d, --debug
Enable debugging output.

-O DIRECTORY, --output-dir DIRECTORY
Write generated disk image files to this directory. The files will be named after the gadget.yaml
volume names, with .img suffix appended. If not given, the current working directory is used.
This option replaces, and cannot be used with, the deprecated --output option.

-i SIZE, --image-size SIZE
The size of the generated disk image files. If this size is smaller than the minimum calculated
size of the volume, a warning will be issued and --image-size will be ignored. The value is the
size in bytes, with allowable suffixes 'M' for MiB and 'G' for GiB.

An extended syntax is supported for gadget.yaml files which specify multiple volumes (i.e. disk
images). In that case, a single SIZE argument will be used for all the defined volumes, with the
same rules for ignoring values which are too small. You can specify the image size for a single
volume using an indexing prefix on the SIZE parameter, where the index is either a volume name or
an integer index starting at zero. For example, to set the image size only on the second volume,
which might be called sdcard in the gadget.yaml, you could use: --image-size 1:8G since the 1-th
index names the second volume (volumes are 0-indexed). Or you could use --image-size sdcard:8G.

You can also specify multiple volume sizes by separating them with commas, and you can mix and
match integer indexes and volume name indexes. Thus, if the gadget.yaml named three volumes, and
you wanted to set all three to different sizes, you could use --image-size 0:2G,sdcard:8G,eMMC:4G.

In the case of ambiguities, the size hint is ignored and the calculated size for the volume will
be used instead.

--image-file-list FILENAME
Print to FILENAME, a list of the file system paths to all the disk images created by the command,
if any.

--hooks-directory DIRECTORY
Directories in which scripts for build-time hooks will be located. This flag must be specified
once for each hook directory. ubuntu-image will look for hooks in
hooks_directory/name_of_hooks_step.d and a script with the name
hooks_directory/name_of_hooks_step. Currently the only supported hooks step is
populate_rootfs_contents.

--disk-info DISK-INFO-CONTENTS
File to be used as .disk/info on the image's rootfs. This file can contain useful information
about the target image, like image identification data, system name, build timestamp etc.

--snap SNAP
Install an extra snap. This is passed through to snap prepare-image. The snap argument can
include additional information about the channel and/or risk with the following syntax:
<snap>=<channel|risk>

-c CHANNEL, --channel CHANNEL
The snap channel to use.

--sector-size SIZE
When creating the disk image file, use the given sector size. This can be either 512 or 4096 (4k
sector size), defaulting to 512.

State machine options
CAUTION!:
The options described here are primarily for debugging and testing purposes and should not be
considered part of the stable, public API. State machine step numbers and names can change between
releases.

ubuntu-image internally runs a state machine to create the disk image. These are some options for
controlling this state machine. Other than --workdir, these options are mutually exclusive. When
--until or --thru is given, the state machine can be resumed later with --resume, but --workdir must be
given in that case since the state is saved in a .ubuntu-image.pck file in the working directory.

-w DIRECTORY, --workdir DIRECTORY
The working directory in which to download and unpack all the source files for the image. This
directory can exist or not, and it is not removed after this program exits. If not given, a
temporary working directory is used instead, which is deleted after this program exits. Use
--workdir if you want to be able to resume a partial state machine run. As an added bonus, the
gadget.yaml file is copied to the working directory after it's downloaded.

-u STEP, --until STEP
Run the state machine until the given STEP, non-inclusively. STEP is the name of a state machine
method. The list of all steps can be found in the STEPS section of this document.

-t STEP, --thru STEP
Run the state machine through the given STEP, inclusively. STEP is the name of a state machine
method. The list of all steps can be found in the STEPS section of this document.

-r, --resume
Continue the state machine from the previously saved state. It is an error if there is no
previous state.

FILES

       gadget.yaml
              https://github.com/snapcore/snapd/wiki/Gadget-snap#gadget.yaml

       model assertion
              https://developer.ubuntu.com/en/snappy/guides/prepare-image/

       gadget tree (example)
              https://github.com/snapcore/pc-amd64-gadget

       cloud-config
              https://help.ubuntu.com/community/CloudInit

ENVIRONMENT

       The following environment variables are recognized by ubuntu-image.

       UBUNTU_IMAGE_PRESERVE_UNPACK
              When  set,  this names a directory for preserving a pristine copy of the unpacked gadget contents.
              The directory must exist, and an unpack directory will be created under this directory.  The  full
              contents of the <workdir>/unpack directory after the snap prepare-image subcommand has run will be
              copied here.

       UBUNTU_IMAGE_LIVECD_ROOTFS_AUTO_PATH
              ubuntu-image uses livecd-rootfs configuration files for its live-build runs.  If this variable  is
              set,  ubuntu-image  will  use  the  configuration  files  from  the  selected  path  for  its auto
              configuration.  Otherwise it will attempt to localize livecd-rootfs through a call to dpkg.

       UBUNTU_IMAGE_QEMU_USER_STATIC_PATH
              In case of classic image cross-compilation for a different architecture, ubuntu-image will attempt
              to  use the qemu-user-static emulator with live-build.  If set, ubuntu-image will use the selected
              path for the cross-compilation.  Otherwise it will attempt to find a matching emulator  binary  in
              the current $PATH.

       There are a few other environment variables used for building and testing only.

HOOKS

       During  image  build at certain stages of the build process the user can execute custom scripts modifying
       its contents or otherwise affecting the process itself.  Whenever a hook is to be fired, the  directories
       as  listed  in  the  --hooks-directory parameter are scanned for matching scripts.  There can be multiple
       scripts for a  specific  hook  defined.   The  HookManager  will  first  look  for  executable  files  in
       <hookdir>/<name-of-the-hook>.d   and   execute   them   in   an   alphanumerical   order.    Finally  the
       <hookdir>/<name-of-the-hook> file is executed if existing.

       Hook scripts can have various additional data passed onto them through environment variables depending on
       the hook being fired.

       Currently supported hooks:

       post-populate-rootfs
              Executed  after  the  rootfs  directory  has  been  populated, allowing custom modification of its
              contents.  Added in version 1.2.  Environment variables present:

                 UBUNTU_IMAGE_HOOK_ROOTFS
                        Includes the absolute path to the rootfs contents.

STEPS

       The names of steps that can be used with --until and --thru for each image type are listed below

   Classic image steps
       1.  make_temporary_directories

       2.  prepare_gadget_tree

       3.  run_live_build

       4.  load_gadget_yaml

       5.  populate_rootfs_contents

       6.  populate_rootfs_contents_hooks

       7.  generate_disk_info

       8.  calculate_rootfs_size

       9.  populate_bootfs_contents

       10. populate_prepare_partitions

       11. make_disk

       12. generate_manifest

       13. finish

   Snap image steps
       1.  make_temporary_directories

       2.  prepare_image

       3.  load_gadget_yaml

       4.  populate_rootfs_contents

       5.  populate_rootfs_contents_hooks

       6.  generate_disk_info

       7.  calculate_rootfs_size

       8.  populate_bootfs_contents

       9.  populate_prepare_partitions

       10. make_disk

       11. generate_manifest

       12. finish

NOTES

       Sometimes, for various reasons, ubuntu-image may perform specific workarounds  that  might  require  some
       explanation to understand the reasoning behind them.

   Classic swapfile manual unsparsing
       When  building  a  classic  image,  if  ubuntu-image  notices the existence of a /swapfile on the image's
       rootfs, it will proactively attempt to unsparse it.  The reason for that  is  that  ubuntu-image  assumes
       that the /swapfile file will be used as a swapfile on the target system, and due to undocumented behavior
       of mkfs.ext4 -d large empty files  are  converted  into  sparse  files  automatically  during  filesystem
       population.  This essentially makes such files unusable as swapfiles.  So just in case, ubuntu-image does
       an in-place dd call of the hard-coded path swapfile to ensure it's no longer sparse.

FOOTNOTES

       [1]  Volumes are roughly analogous to disk images.

       [2]  Structures define the layout of the volume, including partitions, Master Boot Records, or any  other
            relevant content.

AUTHOR

       Barry  Warsaw  <barry@ubuntu.com>,  Łukasz  'sil2100'  Zemczak <lukasz.zemczak@ubuntu.com> William 'jawn-
       smith' Wilson <william.wilson@canonical.com>

COPYRIGHT

       2016-2021 Canonical Ltd.