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NAME | SYNOPSIS | DESCRIPTION | COMMANDS | OPTIONS | EXIT STATUS | INVOCATION AS /SBIN/MOUNT.DDI | EXAMPLES | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-DISSECT(1) systemd-dissect SYSTEMD-DISSECT(1)
systemd-dissect, mount.ddi - Dissect Discoverable Disk Images
(DDIs)
systemd-dissect [OPTIONS...] IMAGE
systemd-dissect [OPTIONS...] [--mount] IMAGE PATH
systemd-dissect [OPTIONS...] [--umount] PATH
systemd-dissect [OPTIONS...] [--attach] IMAGE
systemd-dissect [OPTIONS...] [--detach] 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
systemd-dissect [OPTIONS...] [--make-archive] IMAGE [TARGET]
systemd-dissect [OPTIONS...] [--discover]
systemd-dissect [OPTIONS...] [--validate] IMAGE
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).
The systemd-dissect command may be invoked as mount.ddi in which
case it implements the mount(8) "external helper" interface. This
ensures disk images compatible with systemd-dissect can be
mounted directly by mount and fstab(5). For details see below.
In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.
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).
Note that this functionality is also available in mount(8)
via a command such as mount -t ddi myimage.raw targetdir/, as
well as in fstab(5). For details, see below.
Added in version 247.
-M
This is a shortcut for --mount --mkdir.
Added in version 247.
--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.
Added in version 252.
-U
This is a shortcut for --umount --rmdir.
Added in version 252.
--attach
Attach the specified disk image to an automatically allocated
loopback block device, and print the path to the loopback
block device to standard output. This is similar to an
invocation of losetup --find --show, but will validate the
image as DDI before attaching, and derive the correct sector
size to use automatically. Moreover, it ensures the
per-partition block devices are created before returning.
Takes a path to a disk image file.
Added in version 254.
--detach
Detach the specified disk image from a loopback block device.
This undoes the effect of --attach above. This expects either
a path to a loopback block device as an argument, or the path
to the backing image file. In the latter case it will
automatically determine the right device to detach.
Added in version 254.
--list, -l
Prints the paths of all the files and directories in the
specified OS image or directory to standard output.
Added in version 253.
--mtree
Generates a BSD mtree(8) compatible file manifest of the
specified disk image or directory. This is useful for
comparing 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.
Added in version 253.
--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. It will also have the
$SYSTEMD_DISSECT_DEVICE environment variable set, containing
the absolute path name of the loop device the image was
attached to.
Added in version 253.
--copy-from, -x
Copies a file or directory from the specified OS image or
directory into the specified location on the host file
system. Expects three arguments: a path to an image file or
directory, 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.
Added in version 247.
--copy-to, -a
Copies a file or directory from the specified location in the
host file system into the specified OS image or directory.
Expects three arguments: a path to an image file or
directory, 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.
Added in version 247.
--make-archive
Generates an archive file from the specified disk image.
Expects two arguments: the path to the disk image and
optionally the output archive file path. If the latter is
omitted the archive is written to standard output. The
archive file format is determined automatically from the
specified output archive file name, e.g. any path suffixed
with ".tar.xz" will result in an xz compressed UNIX tarball
(if the path is omitted an uncompressed UNIX tarball is
created). See libarchive(3) for a list of supported archive
formats and compression schemes.
Added in version 256.
--discover
Show a list of DDIs in well-known directories. This will show
machine, portable service and system/configuration extension
disk images in the usual directories /usr/lib/machines/,
/usr/lib/portables/, /usr/lib/confexts/, /var/lib/machines/,
/var/lib/portables/, /var/lib/extensions/ and so on.
Added in version 253.
--validate
Validates the partition arrangement of a disk image (DDI),
and ensures it matches the image policy specified via
--image-policy=, if one is specified. This parses the
partition table and probes the file systems in the image, but
does not attempt to mount them (nor to set up disk
encryption/authentication via LUKS/Verity). It does this
taking the configured image dissection policy into account.
Since this operation does not mount file systems, this
command – unlike all other commands implemented by this tool
– requires no privileges other than the ability to access the
specified file. Prints "OK" and returns zero if the image
appears to be in order and matches the specified image
dissection policy. Otherwise prints an error message and
returns non-zero.
Added in version 254.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
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.
Added in version 247.
--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.
Added in version 247.
--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.
Added in version 249.
--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.
Added in version 247.
--rmdir
If combined with --umount the specified directory where the
OS image is mounted is removed after unmounting the OS image.
Added in version 252.
--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.
Added in version 247.
--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.
Added in version 253.
--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].
Added in version 247.
--loop-ref=
Configures the "reference" string the kernel shall report as
backing file for the loopback block device. While this is
supposed to be a path or filename referencing the backing
file, this is not enforced and the kernel accepts arbitrary
free-form strings, chosen by the user. Accepts arbitrary
strings up to a length of 63 characters. This sets the
kernel's ".lo_file_name" field for the block device. Note
this is distinct from the
/sys/class/block/loopX/loop/backing_file attribute file that
always reports a path referring to the actual backing file.
The latter is subject to mount namespace translation, the
former is not.
This setting is particularly useful in combination with the
--attach command, as it allows later referencing the
allocated loop device via /dev/disk/by-loop-ref/...
symlinks. Example: first, set up the loopback device via
systemd-dissect attach --loop-ref=quux foo.raw, and then
reference it in a command via the specified filename: cfdisk
/dev/disk/by-loop-ref/quux.
Added in version 254.
--mtree-hash=no
If combined with --mtree, turns off inclusion of file hashes
in the mtree output. This makes the --mtree faster when
operating on large images.
Added in version 254.
--image-policy=policy
Takes an image policy string as argument, as per
systemd.image-policy(7). The policy is enforced when
operating on the disk image specified via --image=, see
above. If not specified defaults to the "*" policy, i.e. all
recognized file systems in the image are used.
--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).
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.
The systemd-dissect executable may be symlinked to
/sbin/mount.ddi. If invoked through that it implements mount(8)'s
"external helper" interface for the (pseudo) file system type
"ddi". This means conformant disk images may be mounted directly
via
# mount -t ddi myimage.raw targetdir/
in a fashion mostly equivalent to:
# systemd-dissect --mount myimage.raw targetdir/
Note that since a single DDI may contain multiple file systems it
should later be unmounted with umount -R targetdir/, for
recursive operation.
This functionality is particularly useful to mount DDIs
automatically at boot via simple /etc/fstab entries. For example:
/path/to/myimage.raw /images/myimage/ ddi defaults 0 0
When invoked this way the mount options "ro", "rw", "discard",
"nodiscard" map to the corresponding options listed above (i.e.
--read-only, --discard=all, --discard=disabled). Mount options
are not generically passed on to the file systems inside the
images.
Example 1. Generate a tarball from an OS disk image (--with)
# systemd-dissect --with foo.raw tar cz . >foo.tar.gz
or alternatively just:
Example 2. Generate a tarball from an OS disk image
(--make-archive)
# systemd-dissect --make-archive foo.raw foo.tar.gz
systemd(1), systemd-nspawn(1), systemd.exec(5), systemd.v(7),
Discoverable Partitions Specification[1], mount(8), umount(8),
fdisk(8)
1. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have
a bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SYSTEMD-DISSECT(1)
Pages that refer to this page: systemd.directives(7), systemd.image-policy(7), systemd.index(7), systemd.v(7), systemd-nsresourced.service(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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