| SYSTEMD-DISSECT(1) | systemd-dissect | SYSTEMD-DISSECT(1) |
.SH "NAME" systemd-dissect, mount.ddi - Dissect Discoverable Disk
Images (DDIs)
.SH "SYNOPSIS"
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systemd-dissect [OPTIONS...] IMAGE
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systemd-dissect [OPTIONS...] [--mount] IMAGE PATH
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systemd-dissect [OPTIONS...] [--umount] PATH
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systemd-dissect [OPTIONS...] [--attach] IMAGE
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systemd-dissect [OPTIONS...] [--detach] PATH
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systemd-dissect [OPTIONS...] [--list] IMAGE
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systemd-dissect [OPTIONS...] [--mtree] IMAGE
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systemd-dissect [OPTIONS...] [--with] IMAGE
[COMMAND...]
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systemd-dissect [OPTIONS...] [--copy-from] IMAGE PATH
[TARGET]
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systemd-dissect [OPTIONS...] [--copy-to] IMAGE [SOURCE]
PATH
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systemd-dissect [OPTIONS...] [--make-archive] IMAGE
[TARGET]
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systemd-dissect [OPTIONS...] [--discover]
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systemd-dissect [OPTIONS...] [--validate] IMAGE
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systemd-dissect [OPTIONS...] [--shift] IMAGE UIDBASE
.SH "DESCRIPTION"
.PP 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:
.PP The tool may operate on three types of OS images:
.PP 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).
.PP 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).
.PP 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.
.PP In place of the image path a .v/ versioned directory may be specified,
see systemd.v(7) for details.
.SH "COMMANDS"
.PP 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.
.PP --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 UAPI.2 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.
.RE
.PP -M
This is a shortcut for --mount --mkdir.
Added in version 247.
.RE
.PP --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.
.RE
.PP -U
This is a shortcut for --umount --rmdir.
Added in version 252.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP -h, --help
Print a short help text and exit.
.RE
.PP --version
Print a short version string and exit.
.RE
.SH "OPTIONS"
.PP The following options are understood:
.PP --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.
.RE
.PP --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.
.RE
.PP --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 UAPI.2 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:
.sp
Added in version 249.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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 UAPI.2 Discoverable Partitions Specification[1].
Added in version 247.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --copy-ownership=
Controls whether file ownership (user and group) is preserved when copying
files with --copy-from or --copy-to. Takes a boolean, or
auto. If yes, ownership is always preserved. If no, ownership is
never preserved and the current user's UID/GID is used instead. If not
specified or auto, ownership is preserved when copying directory
trees, but not when copying individual regular files.
Added in version 260.
.RE
.PP --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.
.RE
.PP --all
If combined with --discover, also shows images that start with a dot,
i.e. hidden images.
Added in version 258.
.RE
.PP --quiet, -q
If combined with --attach, suppresses output of the used loopback
block device path.
Added in version 258.
.RE
.PP --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.
.RE
.PP --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.
.RE
.PP --no-pager
Do not pipe output into a pager.
.RE
.PP --no-legend
Do not print the legend, i.e. column headers and the footer with hints.
.RE
.PP --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).
.RE
.SH "EXIT STATUS"
.PP 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.
.SH "INVOCATION AS /SBIN/MOUNT.DDI"
.PP 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/
.PP in a fashion mostly equivalent to:
# systemd-dissect --mount myimage.raw targetdir/
.PP Note that since a single DDI may contain multiple file systems it should
later be unmounted with umount -R targetdir/, for recursive
operation.
.PP 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
.PP 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.
.SH "EXAMPLES"
.PP Example 1. Generate a tarball from an OS disk image
(--with)
# systemd-dissect --with foo.raw tar cz . >foo.tar.gz
.PP or alternatively just:
.PP Example 2. Generate a tarball from an OS disk image
(--make-archive)
# systemd-dissect --make-archive foo.raw foo.tar.gz
.SH "SEE ALSO"
.PP systemd(1), systemd-nspawn(1), systemd.exec(5),
systemd.v(7), UAPI.2 Discoverable Partitions Specification[1],
mount(8), umount(8), fdisk(8)
NOTES
- 1.
- UAPI.2 Discoverable Partitions Specification
- 2.
- Users, Groups, UIDs and GIDs on systemd Systems
| systemd 262.2 |