systemd-dissect(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | COMMANDS | OPTIONS | EXIT STATUS | INVOCATION AS /SBIN/MOUNT.DDI | EXAMPLES | SEE ALSO | NOTES | COLOPHON

SYSTEMD-DISSECT(1)           systemd-dissect           SYSTEMD-DISSECT(1)

NAME         top

       systemd-dissect, mount.ddi - Dissect Discoverable Disk Images
       (DDIs)

SYNOPSIS         top

       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 [OPTIONS...] [--shift] IMAGE UIDBASE

DESCRIPTION         top

       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.

COMMANDS         top

       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, merging
           into existing directories and updating already existing files.
           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, merging
           into existing directories and updating already existing
           files.. 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.

       --shift
           Recursively iterates through all inodes of the specified image
           and shifts the UIDs and GIDs the inodes are owned by into the
           specified UID range. Takes an image path and a UID base as
           parameter. The UID base can be specified numerically (in which
           case it must be a multiple of 65536, and either 0 or within
           the container or foreign UID range, as per Users, Groups, UIDs
           and GIDs on systemd Systems[2]), or as the symbolic identifier
           "foreign" which is shorthand to the foreign UID base. This
           command is useful for preparing directory container images for
           unprivileged use. Note that this command is intended for
           images that use the 16bit UIDs/GIDs range only, and it always
           ignores the upper 16bit of the current UID/GID ownership,
           combining the lower 16 bit with the target UID base.

           Use systemd-dissect --shift /some/container/tree foreign to
           shift a container image into the foreign UID range, or
           systemd-dissect --shift /some/container/tree 0 to shift it to
           host UID range.

           Added in version 258.

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

       --version
           Print a short version string and exit.

OPTIONS         top

       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.

       --system, --user
           When used together with --discover controls whether to search
           for images installed system-wide or in the user's directories
           in $HOME. If neither switch is specified, will search within
           both scopes.

           Added in version 258.

       --all
           If combined with --discover, also shows images that start with
           a dot, i.e. hidden images.

           Added in version 258.

       --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).

EXIT STATUS         top

       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.

INVOCATION AS /SBIN/MOUNT.DDI         top

       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.

EXAMPLES         top

       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

SEE ALSO         top

       systemd(1), systemd-nspawn(1), systemd.exec(5), systemd.v(7),
       Discoverable Partitions Specification[1], mount(8), umount(8),
       fdisk(8)

NOTES         top

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

        2. Users, Groups, UIDs and GIDs on systemd Systems
           https://systemd.io/UIDS-GIDS/

COLOPHON         top

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       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 2025-02-02.  (At that
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systemd 258~devel                                      SYSTEMD-DISSECT(1)

Pages that refer to this page: systemd-nspawn(1)systemd.directives(7)systemd.image-policy(7)systemd.index(7)systemd.v(7)systemd-nsresourced.service(8)