# systemd-dissect

## NAME



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


## SYNOPSIS



    
           **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



           **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 withsystemd-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



           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 --partscan** , 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
               and attempts to enable direct IO mode, if possible. Takes a
               path to a disk image file.
    
               If combined with **--quiet** output of the block device name is
               suppressed.
    
               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



           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.**--usr-hash=** , **--usr-hash-sig=**
               Similar to **--root-hash=** and **--root-hash-sig=** , but specifies
               hash and signature for the /usr/ partition. Note that either
               the options for the root partition may be used or the ones for
               the /usr/, but not both in combination.
    
               Added in version 258.
    
           **--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.
    
           **--loop-ref-auto**
               Similar to **--loop-ref=** , but automatically derive the reference
               string from the specified backing filename, truncating it if
               necessary.
    
               Added in version 258.
    
           **--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.
    
           **--quiet** , **-q**
               If combined with **--attach** , suppresses output of the used
               loopback block device path.
    
               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.
    
           **--image-filter=**_filter_
               Takes an image filter string as argument, as per
               systemd.image-filter(7). The filter is taken into
               consideration when operating on the disk image specified via
               **--image=** , see above. If not specified no filtering is applied.
    
           **--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.
    


## INVOCATION AS /SBIN/MOUNT.DDI



           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



           **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
    


## NOTES



            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/
    


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