Ubuntu Manpage: systemd-dissect - Dissect Discoverable Disk Images (DDIs)

Provided by: systemd-container_253.5-1ubuntu6.1_amd64

NAME

       systemd-dissect - Dissect Discoverable Disk Images (DDIs)

SYNOPSIS

       systemd-dissect [OPTIONS...] IMAGE

       systemd-dissect [OPTIONS...] --mount IMAGE PATH

       systemd-dissect [OPTIONS...] --umount PATH

       systemd-dissect [OPTIONS...] --list IMAGE

       systemd-dissect [OPTIONS...] --mtree IMAGE

       systemd-dissect [OPTIONS...] --with IMAGE [COMMAND...]

       systemd-dissect [OPTIONS...] --copy-from IMAGE PATH [TARGET]

       systemd-dissect [OPTIONS...] --copy-to IMAGE [SOURCE] PATH

DESCRIPTION

systemd-dissect is a tool for introspecting and interacting with file system OS disk
images, specifically Discoverable Disk Images (DDIs). It supports four different
operations:

1. Show general OS image information, including the image's os-release(5) data, machine
ID, partition information and more.

2. Mount an OS image to a local directory. In this mode it will dissect the OS image and
mount the included partitions according to their designation onto a directory and
possibly sub-directories.

3. Unmount an OS image from a local directory. In this mode it will recursively unmount
the mounted partitions and remove the underlying loop device, including all the
partition sub-devices.

4. Copy files and directories in and out of an OS image.

The tool may operate on three types of OS images:

1. OS disk images containing a GPT partition table envelope, with partitions marked
according to the Discoverable Partitions Specification[1].

2. OS disk images containing just a plain file-system without an enveloping partition
table. (This file system is assumed to be the root file system of the OS.)

3. OS disk images containing a GPT or MBR partition table, with a single partition only.
(This partition is assumed to contain the root file system of the OS.)

OS images may use any kind of Linux-supported file systems. In addition they may make use
of LUKS disk encryption, and contain Verity integrity information. Note that qualifying OS
images may be booted with systemd-nspawn(1)'s --image= switch, and be used as root file
system for system service using the RootImage= unit file setting, see systemd.exec(5).

Note that the partition table shown when invoked without command switch (as listed below)
does not necessarily show all partitions included in the image, but just the partitions
that are understood and considered part of an OS disk image. Specifically, partitions of
unknown types are ignored, as well as duplicate partitions (i.e. more than one per
partition type), as are root and /usr/ partitions of architectures not compatible with the
local system. In other words: this tool will display what it operates with when mounting
the image. To display the complete list of partitions use a tool such as fdisk(8).

COMMANDS

If neither of the command switches listed below are passed the specified disk image is
opened and general information about the image and the contained partitions and their use
is shown.

--mount, -m
Mount the specified OS image to the specified directory. This will dissect the image,
determine the OS root file system — as well as possibly other partitions — and mount
them to the specified directory. If the OS image contains multiple partitions marked
with the Discoverable Partitions Specification[1] multiple nested mounts are
established. This command expects two arguments: a path to an image file and a path to
a directory where to mount the image.

To unmount an OS image mounted like this use the --umount operation.

When the OS image contains LUKS encrypted or Verity integrity protected file systems
appropriate volumes are automatically set up and marked for automatic disassembly when
the image is unmounted.

The OS image may either be specified as path to an OS image stored in a regular file
or may refer to block device node (in the latter case the block device must be the
"whole" device, i.e. not a partition device). (The other supported commands described
here support this, too.)

All mounted file systems are checked with the appropriate fsck(8) implementation in
automatic fixing mode, unless explicitly turned off (--fsck=no) or read-only operation
is requested (--read-only).

-M
This is a shortcut for --mount --mkdir.

--umount, -u
Unmount an OS image from the specified directory. This command expects one argument: a
directory where an OS image was mounted.

All mounted partitions will be recursively unmounted, and the underlying loop device
will be removed, along with all its partition sub-devices.

-U
This is a shortcut for --umount --rmdir.

--list, -l
Prints the paths of all the files and directories in the specified OS image to
standard output.

--mtree, -l
Generates a BSD mtree(8) compatible file manifest of the specified disk image. This is
useful for comparing disk image contents in detail, including inode information and
other metadata. While the generated manifest will contain detailed inode information,
it currently excludes extended attributes, file system capabilities, MAC labels,
chattr(1) file flags, btrfs(5) subvolume information, and various other file metadata.
File content information is shown via a SHA256 digest. Additional fields might be
added in future. Note that inode information such as link counts, inode numbers and
timestamps is excluded from the output on purpose, as it typically complicates
reproducibility.

--with
Runs the specified command with the specified OS image mounted. This will mount the
image to a temporary directory, switch the current working directory to it, and invoke
the specified command line as child process. Once the process ends it will unmount the
image again, and remove the temporary directory. If no command is specified a shell is
invoked. The image is mounted writable, use --read-only to switch to read-only
operation. The invoked process will have the $SYSTEMD_DISSECT_ROOT environment
variable set, containing the absolute path name of the temporary mount point, i.e. the
same directory that is set as the current working directory.

--copy-from, -x
Copies a file or directory from the specified OS image into the specified location on
the host file system. Expects three arguments: a path to an image file, a source path
(relative to the image's root directory) and a destination path (relative to the
current working directory, or an absolute path, both outside of the image). If the
destination path is omitted or specified as dash ("-"), the specified file is written
to standard output. If the source path in the image file system refers to a regular
file it is copied to the destination path. In this case access mode, extended
attributes and timestamps are copied as well, but file ownership is not. If the source
path in the image refers to a directory, it is copied to the destination path,
recursively with all containing files and directories. In this case the file ownership
is copied too.

--copy-to, -a
Copies a file or directory from the specified location in the host file system into
the specified OS image. Expects three arguments: a path to an image file, a source
path (relative to the current working directory, or an absolute path, both outside of
the image) and a destination path (relative to the image's root directory). If the
source path is omitted or specified as dash ("-"), the data to write is read from
standard input. If the source path in the host file system refers to a regular file,
it is copied to the destination path. In this case access mode, extended attributes
and timestamps are copied as well, but file ownership is not. If the source path in
the host file system refers to a directory it is copied to the destination path,
recursively with all containing files and directories. In this case the file ownership
is copied too.

As with --mount file system checks are implicitly run before the copy operation
begins.

--discover
Show a list of DDIs in well-known directories. This will show machine, portable
service and system extension disk images in the usual directories /usr/lib/machines/,
/usr/lib/portables/, /usr/lib/extensions/, /var/lib/machines/, /var/lib/portables/,
/var/lib/extensions/ and so on.

-h, --help
Print a short help text and exit.

--version
Print a short version string and exit.

OPTIONS

The following options are understood:

--read-only, -r
Operate in read-only mode. By default --mount will establish writable mount points. If
this option is specified they are established in read-only mode instead.

--fsck=no
Turn off automatic file system checking. By default when an image is accessed for
writing (by --mount or --copy-to) the file systems contained in the OS image are
automatically checked using the appropriate fsck(8) command, in automatic fixing mode.
This behavior may be switched off using --fsck=no.

--growfs=no
Turn off automatic growing of accessed file systems to their partition size, if marked
for that in the GPT partition table. By default when an image is accessed for writing
(by --mount or --copy-to) the file systems contained in the OS image are automatically
grown to their partition sizes, if bit 59 in the GPT partition flags is set for
partition types that are defined by the Discoverable Partitions Specification[1]. This
behavior may be switched off using --growfs=no. File systems are grown automatically
on access if all of the following conditions are met:

1. The file system is mounted writable

2. The file system currently is smaller than the partition it is contained in (and
thus can be grown)

3. The image contains a GPT partition table

4. The file system is stored on a partition defined by the Discoverable Partitions
Specification

5. Bit 59 of the GPT partition flags for this partition is set, as per specification

6. The --growfs=no option is not passed.

--mkdir
If combined with --mount the directory to mount the OS image to is created if it is
missing. Note that the directory is not automatically removed when the disk image is
unmounted again.

--rmdir
If combined with --umount the specified directory where the OS image is mounted is
removed after unmounting the OS image.

--discard=
Takes one of "disabled", "loop", "all", "crypto". If "disabled" the image is accessed
with empty block discarding turned off. If "loop" discarding is enabled if operating
on a regular file. If "crypt" discarding is enabled even on encrypted file systems. If
"all" discarding is unconditionally enabled.

--in-memory
If specified an in-memory copy of the specified disk image is used. This may be used
to operate with write-access on a (possibly read-only) image, without actually
modifying the original file. This may also be used in order to operate on a disk image
without keeping the originating file system busy, in order to allow it to be
unmounted.

--root-hash=, --root-hash-sig=, --verity-data=
Configure various aspects of Verity data integrity for the OS image. Option
--root-hash= specifies a hex-encoded top-level Verity hash to use for setting up the
Verity integrity protection. Option --root-hash-sig= specifies the path to a file
containing a PKCS#7 signature for the hash. This signature is passed to the kernel
during activation, which will match it against signature keys available in the kernel
keyring. Option --verity-data= specifies a path to a file with the Verity data to use
for the OS image, in case it is stored in a detached file. It is recommended to embed
the Verity data directly in the image, using the Verity mechanisms in the Discoverable
Partitions Specification[1].

--no-pager
Do not pipe output into a pager.

--no-legend
Do not print the legend, i.e. column headers and the footer with hints.

--json=MODE
Shows output formatted as JSON. Expects one of "short" (for the shortest possible
output without any redundant whitespace or line breaks), "pretty" (for a pretty
version of the same, with indentation and line breaks) or "off" (to turn off JSON
output, the default).

EXIT STATUS

       On success, 0 is returned, a non-zero failure code otherwise. If the --with command is
       used the exit status of the invoked command is propagated.

EXAMPLES

       Example 1. Generate a tarball from an OS disk image

           $ systemd-dissect --with foo.raw tar cz . >foo.tar.gz

NOTES

        1. Discoverable Partitions Specification
           https://uapi-group.org/specifications/specs/discoverable_partitions_specification