man/systemd-dissect.xml

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   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>--list</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>--mtree</option> <arg choice="plain"><replaceable>IMAGE</replaceable></arg></command>
  40     </cmdsynopsis>
  41     <cmdsynopsis>
  42       <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>
  43     </cmdsynopsis>
  44     <cmdsynopsis>
  45       <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>
  46     </cmdsynopsis>
  47     <cmdsynopsis>
  48       <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>
  49     </cmdsynopsis>
  50   </refsynopsisdiv>
  51
  52   <refsect1>
  53     <title>Description</title>
  54
  55     <para><command>systemd-dissect</command> is a tool for introspecting and interacting with file system OS
  56     disk images, specifically Discoverable Disk Images (DDIs). It supports four different operations:</para>
  57
  58     <orderedlist>
  59       <listitem><para>Show general OS image information, including the image's
  60       <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry> data,
  61       machine ID, partition information and more.</para></listitem>
  62
  63       <listitem><para>Mount an OS image to a local directory. In this mode it will dissect the OS image and
  64       mount the included partitions according to their designation onto a directory and possibly
  65       sub-directories.</para></listitem>
  66
  67       <listitem><para>Unmount an OS image from a local directory. In this mode it will recursively unmount
  68       the mounted partitions and remove the underlying loop device, including all the partition sub-devices.
  69       </para></listitem>
  70
  71       <listitem><para>Copy files and directories in and out of an OS image.</para></listitem>
  72     </orderedlist>
  73
  74     <para>The tool may operate on three types of OS images:</para>
  75
  76     <orderedlist>
  77       <listitem><para>OS disk images containing a GPT partition table envelope, with partitions marked
  78       according to the <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions
  79       Specification</ulink>.</para></listitem>
  80
  81       <listitem><para>OS disk images containing just a plain file-system without an enveloping partition
  82       table. (This file system is assumed to be the root file system of the OS.)</para></listitem>
  83
  84       <listitem><para>OS disk images containing a GPT or MBR partition table, with a single
  85       partition only. (This partition is assumed to contain the root file system of the OS.)</para></listitem>
  86     </orderedlist>
  87
  88     <para>OS images may use any kind of Linux-supported file systems. In addition they may make use of LUKS
  89     disk encryption, and contain Verity integrity information. Note that qualifying OS images may be booted
  90     with <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
  91     <option>--image=</option> switch, and be used as root file system for system service using the
  92     <varname>RootImage=</varname> unit file setting, see
  93     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  94
  95     <para>Note that the partition table shown when invoked without command switch (as listed below) does not
  96     necessarily show all partitions included in the image, but just the partitions that are understood and
  97     considered part of an OS disk image. Specifically, partitions of unknown types are ignored, as well as
  98     duplicate partitions (i.e. more than one per partition type), as are root and <filename>/usr/</filename>
  99     partitions of architectures not compatible with the local system. In other words: this tool will display
 100     what it operates with when mounting the image. To display the complete list of partitions use a tool such
 101     as <citerefentry
 102     project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 103
 104     <para>The <command>systemd-dissect</command> command may be invoked as <command>mount.ddi</command> in
 105     which case it implements the <citerefentry
 106     project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> "external
 107     helper" interface. This ensures disk images compatible with <command>systemd-dissect</command> can be
 108     mounted directly by <command>mount</command> and <citerefentry
 109     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
 110     details see below.</para>
 111   </refsect1>
 112
 113   <refsect1>
 114     <title>Commands</title>
 115
 116     <para>If neither of the command switches listed below are passed the specified disk image is opened and
 117     general information about the image and the contained partitions and their use is shown.</para>
 118
 119     <variablelist>
 120       <varlistentry>
 121         <term><option>--mount</option></term>
 122         <term><option>-m</option></term>
 123
 124         <listitem><para>Mount the specified OS image to the specified directory. This will dissect the image,
 125         determine the OS root file system — as well as possibly other partitions — and mount them to the
 126         specified directory. If the OS image contains multiple partitions marked with the <ulink
 127         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>
 128         multiple nested mounts are established. This command expects two arguments: a path to an image file
 129         and a path to a directory where to mount the image.</para>
 130
 131         <para>To unmount an OS image mounted like this use the <option>--umount</option> operation.</para>
 132
 133         <para>When the OS image contains LUKS encrypted or Verity integrity protected file systems
 134         appropriate volumes are automatically set up and marked for automatic disassembly when the image is
 135         unmounted.</para>
 136
 137         <para>The OS image may either be specified as path to an OS image stored in a regular file or may
 138         refer to block device node (in the latter case the block device must be the "whole" device, i.e. not
 139         a partition device). (The other supported commands described here support this, too.)</para>
 140
 141         <para>All mounted file systems are checked with the appropriate <citerefentry
 142         project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 143         implementation in automatic fixing mode, unless explicitly turned off (<option>--fsck=no</option>) or
 144         read-only operation is requested (<option>--read-only</option>).</para>
 145
 146         <para>Note that this functionality is also available in <citerefentry
 147         project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry> via a
 148         command such as <command>mount -t ddi myimage.raw targetdir/</command>, as well as in <citerefentry
 149         project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. For
 150         details, see below.</para></listitem>
 151       </varlistentry>
 152
 153       <varlistentry>
 154         <term><option>-M</option></term>
 155
 156         <listitem><para>This is a shortcut for <option>--mount --mkdir</option>.</para></listitem>
 157       </varlistentry>
 158
 159       <varlistentry>
 160         <term><option>--umount</option></term>
 161         <term><option>-u</option></term>
 162
 163         <listitem><para>Unmount an OS image from the specified directory. This command expects one argument:
 164         a directory where an OS image was mounted.</para>
 165
 166         <para>All mounted partitions will be recursively unmounted, and the underlying loop device will be
 167         removed, along with all it's partition sub-devices.</para></listitem>
 168       </varlistentry>
 169
 170       <varlistentry>
 171         <term><option>-U</option></term>
 172
 173         <listitem><para>This is a shortcut for <option>--umount --rmdir</option>.</para></listitem>
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term><option>--list</option></term>
 178         <term><option>-l</option></term>
 179
 180         <listitem><para>Prints the paths of all the files and directories in the specified OS image to
 181         standard output.</para></listitem>
 182       </varlistentry>
 183
 184       <varlistentry>
 185         <term><option>--mtree</option></term>
 186         <term><option>-l</option></term>
 187
 188         <listitem><para>Generates a BSD <citerefentry
 189         project='die-net'><refentrytitle>mtree</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 190         compatible file manifest of the specified disk image. This is useful for comparing disk image
 191         contents in detail, including inode information and other metadata. While the generated manifest will
 192         contain detailed inode information, it currently excludes extended attributes, file system
 193         capabilities, MAC labels, <citerefentry
 194         project='man-pages'><refentrytitle>chattr</refentrytitle><manvolnum>1</manvolnum></citerefentry> file
 195         flags, btrfs subvolume information, and various other file metadata. File content information is
 196         shown via a SHA256 digest. Additional fields might be added in future. Note that inode information
 197         such as link counts, inode numbers and timestamps is excluded from the output on purpose, as it
 198         typically complicates reproducibility.</para></listitem>
 199       </varlistentry>
 200
 201       <varlistentry>
 202         <term><option>--with</option></term>
 203
 204         <listitem><para>Runs the specified command with the specified OS image mounted. This will mount the
 205         image to a temporary directory, switch the current working directory to it, and invoke the specified
 206         command line as child process. Once the process ends it will unmount the image again, and remove the
 207         temporary directory. If no command is specified a shell is invoked. The image is mounted writable,
 208         use <option>--read-only</option> to switch to read-only operation. The invoked process will have the
 209         <varname>$SYSTEMD_DISSECT_ROOT</varname> environment variable set, containing the absolute path name
 210         of the temporary mount point, i.e. the same directory that is set as the current working
 211         directory.</para></listitem>
 212       </varlistentry>
 213
 214       <varlistentry>
 215         <term><option>--copy-from</option></term>
 216         <term><option>-x</option></term>
 217
 218         <listitem><para>Copies a file or directory from the specified OS image into the specified location on
 219         the host file system. Expects three arguments: a path to an image file, a source path (relative to
 220         the image's root directory) and a destination path (relative to the current working directory, or an
 221         absolute path, both outside of the image). If the destination path is omitted or specified as dash
 222         (<literal>-</literal>), the specified file is written to standard output. If the source path in the
 223         image file system refers to a regular file it is copied to the destination path. In this case access
 224         mode, extended attributes and timestamps are copied as well, but file ownership is not. If the source
 225         path in the image refers to a directory, it is copied to the destination path, recursively with all
 226         containing files and directories. In this case the file ownership is copied too.</para></listitem>
 227       </varlistentry>
 228
 229       <varlistentry>
 230         <term><option>--copy-to</option></term>
 231         <term><option>-a</option></term>
 232
 233         <listitem><para>Copies a file or directory from the specified location in the host file system into
 234         the specified OS image. Expects three arguments: a path to an image file, a source path (relative to
 235         the current working directory, or an absolute path, both outside of the image) and a destination path
 236         (relative to the image's root directory). If the source path is omitted or specified as dash
 237         (<literal>-</literal>), the data to write is read from standard input. If the source path in the host
 238         file system refers to a regular file, it is copied to the destination path. In this case access mode,
 239         extended attributes and timestamps are copied as well, but file ownership is not. If the source path
 240         in the host file system refers to a directory it is copied to the destination path, recursively with
 241         all containing files and directories. In this case the file ownership is copied
 242         too.</para>
 243
 244         <para>As with <option>--mount</option> file system checks are implicitly run before the copy
 245         operation begins.</para></listitem>
 246       </varlistentry>
 247
 248       <varlistentry>
 249         <term><option>--discover</option></term>
 250
 251         <listitem><para>Show a list of DDIs in well-known directories. This will show machine, portable
 252         service and system extension disk images in the usual directories
 253         <filename>/usr/lib/machines/</filename>, <filename>/usr/lib/portables/</filename>,
 254         <filename>/usr/lib/extensions/</filename>, <filename>/var/lib/machines/</filename>,
 255         <filename>/var/lib/portables/</filename>, <filename>/var/lib/extensions/</filename> and so
 256         on.</para></listitem>
 257       </varlistentry>
 258
 259       <xi:include href="standard-options.xml" xpointer="help" />
 260       <xi:include href="standard-options.xml" xpointer="version" />
 261     </variablelist>
 262
 263   </refsect1>
 264
 265   <refsect1>
 266     <title>Options</title>
 267
 268     <para>The following options are understood:</para>
 269
 270     <variablelist>
 271       <varlistentry>
 272         <term><option>--read-only</option></term>
 273         <term><option>-r</option></term>
 274
 275         <listitem><para>Operate in read-only mode. By default <option>--mount</option> will establish
 276         writable mount points. If this option is specified they are established in read-only mode
 277         instead.</para></listitem>
 278       </varlistentry>
 279
 280       <varlistentry>
 281         <term><option>--fsck=no</option></term>
 282
 283         <listitem><para>Turn off automatic file system checking. By default when an image is accessed for
 284         writing (by <option>--mount</option> or <option>--copy-to</option>) the file systems contained in the
 285         OS image are automatically checked using the appropriate <citerefentry
 286         project='man-pages'><refentrytitle>fsck</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 287         command, in automatic fixing mode. This behavior may be switched off using
 288         <option>--fsck=no</option>.</para></listitem>
 289       </varlistentry>
 290
 291       <varlistentry>
 292         <term><option>--growfs=no</option></term>
 293
 294         <listitem><para>Turn off automatic growing of accessed file systems to their partition size, if
 295         marked for that in the GPT partition table. By default when an image is accessed for writing (by
 296         <option>--mount</option> or <option>--copy-to</option>) the file systems contained in the OS image
 297         are automatically grown to their partition sizes, if bit 59 in the GPT partition flags is set for
 298         partition types that are defined by the <ulink
 299         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>. This
 300         behavior may be switched off using <option>--growfs=no</option>. File systems are grown automatically
 301         on access if all of the following conditions are met:</para>
 302         <orderedlist>
 303           <listitem><para>The file system is mounted writable</para></listitem>
 304           <listitem><para>The file system currently is smaller than the partition it is contained in (and thus can be grown)</para></listitem>
 305           <listitem><para>The image contains a GPT partition table</para></listitem>
 306           <listitem><para>The file system is stored on a partition defined by the Discoverable Partitions Specification</para></listitem>
 307           <listitem><para>Bit 59 of the GPT partition flags for this partition is set, as per specification</para></listitem>
 308           <listitem><para>The <option>--growfs=no</option> option is not passed.</para></listitem>
 309         </orderedlist>
 310         </listitem>
 311       </varlistentry>
 312
 313       <varlistentry>
 314         <term><option>--mkdir</option></term>
 315
 316         <listitem><para>If combined with <option>--mount</option> the directory to mount the OS image to is
 317         created if it is missing. Note that the directory is not automatically removed when the disk image is
 318         unmounted again.</para></listitem>
 319       </varlistentry>
 320
 321       <varlistentry>
 322         <term><option>--rmdir</option></term>
 323
 324         <listitem><para>If combined with <option>--umount</option> the specified directory where the OS image
 325         is mounted is removed after unmounting the OS image.</para></listitem>
 326       </varlistentry>
 327
 328       <varlistentry>
 329         <term><option>--discard=</option></term>
 330
 331         <listitem><para>Takes one of <literal>disabled</literal>, <literal>loop</literal>,
 332         <literal>all</literal>, <literal>crypto</literal>. If <literal>disabled</literal> the image is
 333         accessed with empty block discarding turned off. If <literal>loop</literal> discarding is enabled if
 334         operating on a regular file. If <literal>crypt</literal> discarding is enabled even on encrypted file
 335         systems. If <literal>all</literal> discarding is unconditionally enabled.</para></listitem>
 336       </varlistentry>
 337
 338       <varlistentry>
 339         <term><option>--in-memory</option></term>
 340
 341         <listitem><para>If specified an in-memory copy of the specified disk image is used. This may be used
 342         to operate with write-access on a (possibly read-only) image, without actually modifying the original
 343         file. This may also be used in order to operate on a disk image without keeping the originating file
 344         system busy, in order to allow it to be unmounted.</para></listitem>
 345       </varlistentry>
 346
 347       <varlistentry>
 348         <term><option>--root-hash=</option></term>
 349         <term><option>--root-hash-sig=</option></term>
 350         <term><option>--verity-data=</option></term>
 351
 352         <listitem><para>Configure various aspects of Verity data integrity for the OS image. Option
 353         <option>--root-hash=</option> specifies a hex-encoded top-level Verity hash to use for setting up the
 354         Verity integrity protection. Option <option>--root-hash-sig=</option> specifies the path to a file
 355         containing a PKCS#7 signature for the hash. This signature is passed to the kernel during activation,
 356         which will match it against signature keys available in the kernel keyring.  Option
 357         <option>--verity-data=</option> specifies a path to a file with the Verity data to use for the OS
 358         image, in case it is stored in a detached file. It is recommended to embed the Verity data directly
 359         in the image, using the Verity mechanisms in the <ulink
 360         url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>.
 361         </para></listitem>
 362       </varlistentry>
 363
 364       <xi:include href="standard-options.xml" xpointer="no-pager" />
 365       <xi:include href="standard-options.xml" xpointer="no-legend" />
 366       <xi:include href="standard-options.xml" xpointer="json" />
 367     </variablelist>
 368   </refsect1>
 369
 370   <refsect1>
 371     <title>Exit status</title>
 372
 373     <para>On success, 0 is returned, a non-zero failure code otherwise. If the <option>--with</option>
 374     command is used the exit status of the invoked command is propagated.</para>
 375   </refsect1>
 376
 377   <refsect1>
 378     <title>Invocation as <command>/sbin/mount.ddi</command></title>
 379
 380     <para>The <command>systemd-dissect</command> executable may be symlinked to
 381     <filename>/sbin/mount.ddi</filename>. If invoked through that it implements <citerefentry
 382     project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>'s
 383     "external helper" interface for the (pseudo) file system type <literal>ddi</literal>. This means
 384     conformant disk images may be mounted directly via</para>
 385
 386     <programlisting># mount -t ddi myimage.raw targetdir/</programlisting>
 387
 388     <para>in a fashion mostly equivalent to:</para>
 389
 390     <programlisting># systemd-dissect --mount myimage.raw targetdir/</programlisting>
 391
 392     <para>Note that since a single DDI may contain multiple file systems it should later be unmounted with
 393     <command>umount -R targetdir/</command>, for recursive operation.</para>
 394
 395     <para>This functionality is particularly useful to mount DDIs automatically at boot via simple
 396     <filename>/etc/fstab</filename> entries. For example:</para>
 397
 398     <programlisting>/path/to/myimage.raw /images/myimage/ ddi defaults 0 0</programlisting>
 399
 400     <para>When invoked this way the mount options <literal>ro</literal>, <literal>rw</literal>,
 401     <literal>discard</literal>, <literal>nodiscard</literal> map to the corresponding options listed above
 402     (i.e. <option>--read-only</option>, <option>--discard=all</option>,
 403     <option>--discard=disabled</option>). Mount options are <emphasis>not</emphasis> generically passed on to
 404     the file systems inside the images.</para>
 405   </refsect1>
 406
 407   <refsect1>
 408     <title>Examples</title>
 409
 410     <example>
 411       <title>Generate a tarball from an OS disk image</title>
 412
 413       <programlisting># systemd-dissect --with foo.raw tar cz . >foo.tar.gz</programlisting>
 414     </example>
 415   </refsect1>
 416
 417   <refsect1>
 418     <title>See Also</title>
 419     <para>
 420       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 421       <citerefentry><refentrytitle>systemd-nspawn</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 422       <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 423       <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>,
 424       <citerefentry project='man-pages'><refentrytitle>mount</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 425       <citerefentry project='man-pages'><refentrytitle>umount</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 426       <citerefentry project='man-pages'><refentrytitle>fdisk</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 427     </para>
 428   </refsect1>
 429
 430 </refentry>