NAME¶
systemd-dissect - Dissect Discoverable Disk Images (DDIs)
SYNOPSIS¶
systemd-dissect [OPTIONS...]
IMAGE
systemd-dissect [OPTIONS...]
--mount IMAGE
PATH
systemd-dissect [OPTIONS...]
--umount 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¶
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).
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).
-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 it's partition
sub-devices.
-U
This is a shortcut for --umount --rmdir.
--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 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 extension disk images in the usual
directories /usr/lib/machines/, /usr/lib/portables/, /usr/lib/extensions/,
/var/lib/machines/, /var/lib/portables/, /var/lib/extensions/ and so on.
-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.
--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].
--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.
EXAMPLES¶
Example 1. Generate a tarball from an OS disk
image
$ systemd-dissect --with foo.raw tar cz . >foo.tar.gz
NOTES¶
- 1.
- Discoverable Partitions Specification
