SYSTEMD-DISSECT(1) systemd-dissect SYSTEMD-DISSECT(1)
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...] --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 five 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.
--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.
-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.
--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.
SEE ALSO
systemd(1), systemd-nspawn(1), systemd.exec(5), Discoverable Partitions
Specification[1], umount(8), fdisk(8)
NOTES
1. Discoverable Partitions Specification
https://systemd.io/DISCOVERABLE_PARTITIONS
systemd 252 SYSTEMD-DISSECT(1)
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