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

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.

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.

       -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.

       --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.

       --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.

       --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/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.

       --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.

       -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.

       --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].

       --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/loop/by-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/loop/by-ref/quux.

       --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

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

SEE ALSO         top

       systemd(1), systemd-nspawn(1), systemd.exec(5), 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

COLOPHON         top

       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 2023-06-23.  (At that
       time, the date of the most recent commit that was found in the
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       is a better or more up-to-date source for the page, or you have
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 253                                           SYSTEMD-DISSECT(1)

Pages that refer to this page: systemd.directives(7)systemd.image-policy(7)systemd.index(7)