man/systemd-dissect.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd-dissect" conditional='HAVE_BLKID'
   7     xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-dissect</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-dissect</refentrytitle>
  16     <manvolnum>1</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-dissect</refname>
  21     <refname>mount.ddi</refname>
  22     <refpurpose>Dissect Discoverable Disk Images (DDIs)</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <cmdsynopsis>
  27       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  28     </cmdsynopsis>
  29     <cmdsynopsis>
  30       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--mount</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg> <arg choice="plain"><replaceable>PATH</replaceable></arg></command>
  31     </cmdsynopsis>
  32     <cmdsynopsis>
  33       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--umount</option> <arg choice="plain"><replaceable>PATH</replaceable></arg></command>
  34     </cmdsynopsis>
  35     <cmdsynopsis>
  36       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--attach</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  37     </cmdsynopsis>
  38     <cmdsynopsis>
  39       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--detach</option> <arg choice="plain"><replaceable>PATH</replaceable></arg></command>
  40     </cmdsynopsis>
  41     <cmdsynopsis>
  42       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--list</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  43     </cmdsynopsis>
  44     <cmdsynopsis>
  45       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--mtree</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  46     </cmdsynopsis>
  47     <cmdsynopsis>
  48       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--with</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg> <arg choice="opt" rep="repeat"><replaceable>COMMAND</replaceable></arg></command>
  49     </cmdsynopsis>
  50     <cmdsynopsis>
  51       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--copy-from</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg> <arg choice="plain"><replaceable>PATH</replaceable></arg> <arg choice="opt"><replaceable>TARGET</replaceable></arg></command>
  52     </cmdsynopsis>
  53     <cmdsynopsis>
  54       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--copy-to</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg> <arg choice="opt"><replaceable>SOURCE</replaceable></arg> <arg choice="plain"><replaceable>PATH</replaceable></arg></command>
  55     </cmdsynopsis>
  56     <cmdsynopsis>
  57       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--discover</option></command>
  58     </cmdsynopsis>
  59     <cmdsynopsis>
  60       <command>systemd-dissect <arg choice="opt" rep="repeat">OPTIONS</arg> <option>--validate</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  61     </cmdsynopsis>
  62   </refsynopsisdiv>
  63
  64   <refsect1>
  65     <title>Description</title>
  66
  67     <para><command>systemd-dissect</command> is a tool for introspecting and interacting with file system OS
  68     disk images, specifically Discoverable Disk Images (DDIs). It supports four different operations:</para>
  69
  70     <orderedlist>
  71       <listitem><para>Show general OS image information, including the image's
  72       <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> data,
  73       machine ID, partition information and more.</para></listitem>
  74
  75       <listitem><para>Mount an OS image to a local directory. In this mode it will dissect the OS image and
  76       mount the included partitions according to their designation onto a directory and possibly
  77       sub-directories.</para></listitem>
  78
  79       <listitem><para>Unmount an OS image from a local directory. In this mode it will recursively unmount
  80       the mounted partitions and remove the underlying loop device, including all the partition sub-devices.
  81       </para></listitem>
  82
  83       <listitem><para>Copy files and directories in and out of an OS image.</para></listitem>
  84     </orderedlist>
  85
  86     <para>The tool may operate on three types of OS images:</para>
  87
  88     <orderedlist>
  89       <listitem><para>OS disk images containing a GPT partition table envelope, with partitions marked
  90       according to the <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions
  91       Specification</ulink>.</para></listitem>
  92
  93       <listitem><para>OS disk images containing just a plain file-system without an enveloping partition
  94       table. (This file system is assumed to be the root file system of the OS.)</para></listitem>
  95
  96       <listitem><para>OS disk images containing a GPT or MBR partition table, with a single
  97       partition only. (This partition is assumed to contain the root file system of the OS.)</para></listitem>
  98     </orderedlist>
  99
 100     <para>OS images may use any kind of Linux-supported file systems. In addition they may make use of LUKS
 101     disk encryption, and contain Verity integrity information. Note that qualifying OS images may be booted
 102     with <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 103     <option>--image=</option> switch, and be used as root file system for system service using the
 104     <varname>RootImage=</varname> unit file setting, see
 105     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 106
 107     <para>Note that the partition table shown when invoked without command switch (as listed below) does not
 108     necessarily show all partitions included in the image, but just the partitions that are understood and
 109     considered part of an OS disk image. Specifically, partitions of unknown types are ignored, as well as
 110     duplicate partitions (i.e. more than one per partition type), as are root and <filename>/usr/</filename>
 111     partitions of architectures not compatible with the local system. In other words: this tool will display
 112     what it operates with when mounting the image. To display the complete list of partitions use a tool such
 113     as <citerefentry
 114     project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 115
 116     <para>The <command>systemd-dissect</command> command may be invoked as <command>mount.ddi</command> in
 117     which case it implements the <citerefentry
 118     project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> "external
 119     helper" interface. This ensures disk images compatible with <command>systemd-dissect</command> can be
 120     mounted directly by <command>mount</command> and <citerefentry
 121     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
 122     details see below.</para>
 123   </refsect1>
 124
 125   <refsect1>
 126     <title>Commands</title>
 127
 128     <para>If neither of the command switches listed below are passed the specified disk image is opened and
 129     general information about the image and the contained partitions and their use is shown.</para>
 130
 131     <variablelist>
 132       <varlistentry>
 133         <term><option>--mount</option></term>
 134         <term><option>-m</option></term>
 135
 136         <listitem><para>Mount the specified OS image to the specified directory. This will dissect the image,
 137         determine the OS root file system — as well as possibly other partitions — and mount them to the
 138         specified directory. If the OS image contains multiple partitions marked with the <ulink
 139         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>
 140         multiple nested mounts are established. This command expects two arguments: a path to an image file
 141         and a path to a directory where to mount the image.</para>
 142
 143         <para>To unmount an OS image mounted like this use the <option>--umount</option> operation.</para>
 144
 145         <para>When the OS image contains LUKS encrypted or Verity integrity protected file systems
 146         appropriate volumes are automatically set up and marked for automatic disassembly when the image is
 147         unmounted.</para>
 148
 149         <para>The OS image may either be specified as path to an OS image stored in a regular file or may
 150         refer to block device node (in the latter case the block device must be the "whole" device, i.e. not
 151         a partition device). (The other supported commands described here support this, too.)</para>
 152
 153         <para>All mounted file systems are checked with the appropriate <citerefentry
 154         project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 155         implementation in automatic fixing mode, unless explicitly turned off (<option>--fsck=no</option>) or
 156         read-only operation is requested (<option>--read-only</option>).</para>
 157
 158         <para>Note that this functionality is also available in <citerefentry
 159         project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> via a
 160         command such as <command>mount -t ddi myimage.raw targetdir/</command>, as well as in <citerefentry
 161         project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
 162         details, see below.</para>
 163
 164         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 165       </varlistentry>
 166
 167       <varlistentry>
 168         <term><option>-M</option></term>
 169
 170         <listitem><para>This is a shortcut for <option>--mount --mkdir</option>.</para>
 171
 172         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 173       </varlistentry>
 174
 175       <varlistentry>
 176         <term><option>--umount</option></term>
 177         <term><option>-u</option></term>
 178
 179         <listitem><para>Unmount an OS image from the specified directory. This command expects one argument:
 180         a directory where an OS image was mounted.</para>
 181
 182         <para>All mounted partitions will be recursively unmounted, and the underlying loop device will be
 183         removed, along with all its partition sub-devices.</para>
 184
 185         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 186       </varlistentry>
 187
 188       <varlistentry>
 189         <term><option>-U</option></term>
 190
 191         <listitem><para>This is a shortcut for <option>--umount --rmdir</option>.</para>
 192
 193         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 194       </varlistentry>
 195
 196       <varlistentry>
 197         <term><option>--attach</option></term>
 198
 199         <listitem><para>Attach the specified disk image to an automatically allocated loopback block device,
 200         and print the path to the loopback block device to standard output. This is similar to an invocation
 201         of <command>losetup --find --show</command>, but will validate the image as DDI before attaching, and
 202         derive the correct sector size to use automatically. Moreover, it ensures the per-partition block
 203         devices are created before returning. Takes a path to a disk image file.</para>
 204
 205         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 206       </varlistentry>
 207
 208       <varlistentry>
 209         <term><option>--detach</option></term>
 210
 211         <listitem><para>Detach the specified disk image from a loopback block device. This undoes the effect
 212         of <option>--attach</option> above. This expects either a path to a loopback block device as an
 213         argument, or the path to the backing image file. In the latter case it will automatically determine
 214         the right device to detach.</para>
 215
 216         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 217       </varlistentry>
 218
 219       <varlistentry>
 220         <term><option>--list</option></term>
 221         <term><option>-l</option></term>
 222
 223         <listitem><para>Prints the paths of all the files and directories in the specified OS image or
 224         directory to standard output.</para>
 225
 226         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 227       </varlistentry>
 228
 229       <varlistentry>
 230         <term><option>--mtree</option></term>
 231
 232         <listitem><para>Generates a BSD
 233         <citerefentry project='die-net'><refentrytitle>mtree</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 234         compatible file manifest of the specified disk image or directory. This is useful for comparing image
 235         contents in detail, including inode information and other metadata. While the generated manifest will
 236         contain detailed inode information, it currently excludes extended attributes, file system
 237         capabilities, MAC labels,
 238         <citerefentry project='man-pages'><refentrytitle>chattr</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 239         file flags,
 240         <citerefentry project='url'><refentrytitle url='https://btrfs.readthedocs.io/en/latest/btrfs-man5.html'>btrfs</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 241         subvolume information, and various other file metadata. File content information is shown via a
 242         SHA256 digest. Additional fields might be added in future. Note that inode information such as link
 243         counts, inode numbers and timestamps is excluded from the output on purpose, as it typically
 244         complicates reproducibility.</para>
 245
 246         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 247       </varlistentry>
 248
 249       <varlistentry>
 250         <term><option>--with</option></term>
 251
 252         <listitem><para>Runs the specified command with the specified OS image mounted. This will mount the
 253         image to a temporary directory, switch the current working directory to it, and invoke the specified
 254         command line as child process. Once the process ends it will unmount the image again, and remove the
 255         temporary directory. If no command is specified a shell is invoked. The image is mounted writable,
 256         use <option>--read-only</option> to switch to read-only operation. The invoked process will have the
 257         <varname>$SYSTEMD_DISSECT_ROOT</varname> environment variable set, containing the absolute path name
 258         of the temporary mount point, i.e. the same directory that is set as the current working
 259         directory. It will also have the <varname>$SYSTEMD_DISSECT_DEVICE</varname> environment variable set,
 260         containing the absolute path name of the loop device the image was attached to.</para>
 261
 262         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 263       </varlistentry>
 264
 265       <varlistentry>
 266         <term><option>--copy-from</option></term>
 267         <term><option>-x</option></term>
 268
 269         <listitem><para>Copies a file or directory from the specified OS image or directory into the
 270         specified location on the host file system. Expects three arguments: a path to an image file or
 271         directory, a source path (relative to the image's root directory) and a destination path (relative to
 272         the current working directory, or an absolute path, both outside of the image). If the destination
 273         path is omitted or specified as dash (<literal>-</literal>), the specified file is written to
 274         standard output. If the source path in the image file system refers to a regular file it is copied to
 275         the destination path. In this case access mode, extended attributes and timestamps are copied as
 276         well, but file ownership is not. If the source path in the image refers to a directory, it is copied
 277         to the destination path, recursively with all containing files and directories. In this case the file
 278         ownership is copied too.</para>
 279
 280         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 281       </varlistentry>
 282
 283       <varlistentry>
 284         <term><option>--copy-to</option></term>
 285         <term><option>-a</option></term>
 286
 287         <listitem><para>Copies a file or directory from the specified location in the host file system into
 288         the specified OS image or directory. Expects three arguments: a path to an image file or directory, a
 289         source path (relative to the current working directory, or an absolute path, both outside of the
 290         image) and a destination path (relative to the image's root directory). If the source path is omitted
 291         or specified as dash (<literal>-</literal>), the data to write is read from standard input. If the
 292         source path in the host file system refers to a regular file, it is copied to the destination path.
 293         In this case access mode, extended attributes and timestamps are copied as well, but file ownership
 294         is not. If the source path in the host file system refers to a directory it is copied to the
 295         destination path, recursively with all containing files and directories. In this case the file
 296         ownership is copied too.</para>
 297
 298         <para>As with <option>--mount</option> file system checks are implicitly run before the copy
 299         operation begins.</para>
 300
 301         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 302       </varlistentry>
 303
 304       <varlistentry>
 305         <term><option>--discover</option></term>
 306
 307         <listitem><para>Show a list of DDIs in well-known directories. This will show machine, portable
 308         service and system/configuration extension disk images in the usual directories
 309         <filename>/usr/lib/machines/</filename>, <filename>/usr/lib/portables/</filename>,
 310         <filename>/usr/lib/confexts/</filename>, <filename>/var/lib/machines/</filename>,
 311         <filename>/var/lib/portables/</filename>, <filename>/var/lib/extensions/</filename> and so
 312         on.</para>
 313
 314         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 315       </varlistentry>
 316
 317       <varlistentry>
 318         <term><option>--validate</option></term>
 319
 320         <listitem><para>Validates the partition arrangement of a disk image (DDI), and ensures it matches the
 321         image policy specified via <option>--image-policy=</option>, if one is specified. This parses the
 322         partition table and probes the file systems in the image, but does not attempt to mount them (nor to
 323         set up disk encryption/authentication via LUKS/Verity). It does this taking the configured image
 324         dissection policy into account. Since this operation does not mount file systems, this command –
 325         unlike all other commands implemented by this tool – requires no privileges other than the ability to
 326         access the specified file. Prints "OK" and returns zero if the image appears to be in order and
 327         matches the specified image dissection policy. Otherwise prints an error message and returns
 328         non-zero.</para>
 329
 330         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 331       </varlistentry>
 332
 333       <xi:include href="standard-options.xml" xpointer="help" />
 334       <xi:include href="standard-options.xml" xpointer="version" />
 335     </variablelist>
 336
 337   </refsect1>
 338
 339   <refsect1>
 340     <title>Options</title>
 341
 342     <para>The following options are understood:</para>
 343
 344     <variablelist>
 345       <varlistentry>
 346         <term><option>--read-only</option></term>
 347         <term><option>-r</option></term>
 348
 349         <listitem><para>Operate in read-only mode. By default <option>--mount</option> will establish
 350         writable mount points. If this option is specified they are established in read-only mode
 351         instead.</para>
 352
 353         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 354       </varlistentry>
 355
 356       <varlistentry>
 357         <term><option>--fsck=no</option></term>
 358
 359         <listitem><para>Turn off automatic file system checking. By default when an image is accessed for
 360         writing (by <option>--mount</option> or <option>--copy-to</option>) the file systems contained in the
 361         OS image are automatically checked using the appropriate <citerefentry
 362         project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 363         command, in automatic fixing mode. This behavior may be switched off using
 364         <option>--fsck=no</option>.</para>
 365
 366         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 367       </varlistentry>
 368
 369       <varlistentry>
 370         <term><option>--growfs=no</option></term>
 371
 372         <listitem><para>Turn off automatic growing of accessed file systems to their partition size, if
 373         marked for that in the GPT partition table. By default when an image is accessed for writing (by
 374         <option>--mount</option> or <option>--copy-to</option>) the file systems contained in the OS image
 375         are automatically grown to their partition sizes, if bit 59 in the GPT partition flags is set for
 376         partition types that are defined by the <ulink
 377         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>. This
 378         behavior may be switched off using <option>--growfs=no</option>. File systems are grown automatically
 379         on access if all of the following conditions are met:</para>
 380         <orderedlist>
 381           <listitem><para>The file system is mounted writable</para></listitem>
 382           <listitem><para>The file system currently is smaller than the partition it is contained in (and thus can be grown)</para></listitem>
 383           <listitem><para>The image contains a GPT partition table</para></listitem>
 384           <listitem><para>The file system is stored on a partition defined by the Discoverable Partitions Specification</para></listitem>
 385           <listitem><para>Bit 59 of the GPT partition flags for this partition is set, as per specification</para></listitem>
 386           <listitem><para>The <option>--growfs=no</option> option is not passed.</para></listitem>
 387         </orderedlist>
 388
 389           <xi:include href="version-info.xml" xpointer="v249"/>
 390         </listitem>
 391       </varlistentry>
 392
 393       <varlistentry>
 394         <term><option>--mkdir</option></term>
 395
 396         <listitem><para>If combined with <option>--mount</option> the directory to mount the OS image to is
 397         created if it is missing. Note that the directory is not automatically removed when the disk image is
 398         unmounted again.</para>
 399
 400         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 401       </varlistentry>
 402
 403       <varlistentry>
 404         <term><option>--rmdir</option></term>
 405
 406         <listitem><para>If combined with <option>--umount</option> the specified directory where the OS image
 407         is mounted is removed after unmounting the OS image.</para>
 408
 409         <xi:include href="version-info.xml" xpointer="v252"/></listitem>
 410       </varlistentry>
 411
 412       <varlistentry>
 413         <term><option>--discard=</option></term>
 414
 415         <listitem><para>Takes one of <literal>disabled</literal>, <literal>loop</literal>,
 416         <literal>all</literal>, <literal>crypto</literal>. If <literal>disabled</literal> the image is
 417         accessed with empty block discarding turned off. If <literal>loop</literal> discarding is enabled if
 418         operating on a regular file. If <literal>crypt</literal> discarding is enabled even on encrypted file
 419         systems. If <literal>all</literal> discarding is unconditionally enabled.</para>
 420
 421         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 422       </varlistentry>
 423
 424       <varlistentry>
 425         <term><option>--in-memory</option></term>
 426
 427         <listitem><para>If specified an in-memory copy of the specified disk image is used. This may be used
 428         to operate with write-access on a (possibly read-only) image, without actually modifying the original
 429         file. This may also be used in order to operate on a disk image without keeping the originating file
 430         system busy, in order to allow it to be unmounted.</para>
 431
 432         <xi:include href="version-info.xml" xpointer="v253"/></listitem>
 433       </varlistentry>
 434
 435       <varlistentry>
 436         <term><option>--root-hash=</option></term>
 437         <term><option>--root-hash-sig=</option></term>
 438         <term><option>--verity-data=</option></term>
 439
 440         <listitem><para>Configure various aspects of Verity data integrity for the OS image. Option
 441         <option>--root-hash=</option> specifies a hex-encoded top-level Verity hash to use for setting up the
 442         Verity integrity protection. Option <option>--root-hash-sig=</option> specifies the path to a file
 443         containing a PKCS#7 signature for the hash. This signature is passed to the kernel during activation,
 444         which will match it against signature keys available in the kernel keyring.  Option
 445         <option>--verity-data=</option> specifies a path to a file with the Verity data to use for the OS
 446         image, in case it is stored in a detached file. It is recommended to embed the Verity data directly
 447         in the image, using the Verity mechanisms in the <ulink
 448         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>.
 449         </para>
 450
 451         <xi:include href="version-info.xml" xpointer="v247"/></listitem>
 452       </varlistentry>
 453
 454       <varlistentry>
 455         <term><option>--loop-ref=</option></term>
 456
 457         <listitem><para>Configures the "reference" string the kernel shall report as backing file for the
 458         loopback block device. While this is supposed to be a path or filename referencing the backing file,
 459         this is not enforced and the kernel accepts arbitrary free-form strings, chosen by the user. Accepts
 460         arbitrary strings up to a length of 63 characters. This sets the kernel's
 461         <literal>.lo_file_name</literal> field for the block device. Note this is distinct from the
 462         <filename>/sys/class/block/loopX/loop/backing_file</filename> attribute file that always reports a
 463         path referring to the actual backing file. The latter is subject to mount namespace translation, the
 464         former is not.</para>
 465
 466         <para>This setting is particularly useful in combination with the <option>--attach</option> command,
 467         as it allows later referencing the allocated loop device via
 468         <filename>/dev/disk/by-loop-ref/…</filename> symlinks. Example: first, set up the loopback device
 469         via <command>systemd-dissect attach --loop-ref=quux foo.raw</command>, and then reference it in a
 470         command via the specified filename: <command>cfdisk /dev/disk/by-loop-ref/quux</command>.
 471         </para>
 472
 473         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 474       </varlistentry>
 475
 476       <varlistentry>
 477         <term><option>--mtree-hash=no</option></term>
 478
 479         <listitem><para>If combined with <option>--mtree</option>, turns off inclusion of file hashes in the
 480         mtree output. This makes the <option>--mtree</option> faster when operating on large images.
 481         </para>
 482
 483         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 484       </varlistentry>
 485
 486       <xi:include href="standard-options.xml" xpointer="image-policy-open" />
 487       <xi:include href="standard-options.xml" xpointer="no-pager" />
 488       <xi:include href="standard-options.xml" xpointer="no-legend" />
 489       <xi:include href="standard-options.xml" xpointer="json" />
 490     </variablelist>
 491   </refsect1>
 492
 493   <refsect1>
 494     <title>Exit status</title>
 495
 496     <para>On success, 0 is returned, a non-zero failure code otherwise. If the <option>--with</option>
 497     command is used the exit status of the invoked command is propagated.</para>
 498   </refsect1>
 499
 500   <refsect1>
 501     <title>Invocation as <command>/sbin/mount.ddi</command></title>
 502
 503     <para>The <command>systemd-dissect</command> executable may be symlinked to
 504     <filename>/sbin/mount.ddi</filename>. If invoked through that it implements <citerefentry
 505     project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 506     "external helper" interface for the (pseudo) file system type <literal>ddi</literal>. This means
 507     conformant disk images may be mounted directly via</para>
 508
 509     <programlisting># mount -t ddi myimage.raw targetdir/</programlisting>
 510
 511     <para>in a fashion mostly equivalent to:</para>
 512
 513     <programlisting># systemd-dissect --mount myimage.raw targetdir/</programlisting>
 514
 515     <para>Note that since a single DDI may contain multiple file systems it should later be unmounted with
 516     <command>umount -R targetdir/</command>, for recursive operation.</para>
 517
 518     <para>This functionality is particularly useful to mount DDIs automatically at boot via simple
 519     <filename>/etc/fstab</filename> entries. For example:</para>
 520
 521     <programlisting>/path/to/myimage.raw /images/myimage/ ddi defaults 0 0</programlisting>
 522
 523     <para>When invoked this way the mount options <literal>ro</literal>, <literal>rw</literal>,
 524     <literal>discard</literal>, <literal>nodiscard</literal> map to the corresponding options listed above
 525     (i.e. <option>--read-only</option>, <option>--discard=all</option>,
 526     <option>--discard=disabled</option>). Mount options are <emphasis>not</emphasis> generically passed on to
 527     the file systems inside the images.</para>
 528   </refsect1>
 529
 530   <refsect1>
 531     <title>Examples</title>
 532
 533     <example>
 534       <title>Generate a tarball from an OS disk image</title>
 535
 536       <programlisting># systemd-dissect --with foo.raw tar cz . >foo.tar.gz</programlisting>
 537     </example>
 538   </refsect1>
 539
 540   <refsect1>
 541     <title>See Also</title>
 542     <para><simplelist type="inline">
 543       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 544       <member><citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 545       <member><citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 546       <member><ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink></member>
 547       <member><citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 548       <member><citerefentry project='man-pages'><refentrytitle>umount</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 549       <member><citerefentry project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 550     </simplelist></para>
 551   </refsect1>
 552
 553 </refentry>