man/systemd-gpt-auto-generator.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/4.5/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd-gpt-auto-generator" conditional='HAVE_BLKID'
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-gpt-auto-generator</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-gpt-auto-generator</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-gpt-auto-generator</refname>
  21     <refpurpose>Generator for automatically discovering and mounting root, <filename>/home/</filename>,
  22     <filename>/srv/</filename>, <filename>/var/</filename> and <filename>/var/tmp/</filename> partitions, as
  23     well as discovering and enabling swap partitions, based on GPT partition type GUIDs</refpurpose>
  24   </refnamediv>
  25
  26   <refsynopsisdiv>
  27     <para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
  28   </refsynopsisdiv>
  29
  30   <refsect1>
  31     <title>Description</title>
  32
  33     <para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
  34     the root partition, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
  35     <filename>/var/tmp/</filename>, the EFI System Partition (ESP), the Extended Boot Loader Partition
  36     (XBOOTLDR), and swap partitions and creates mount and swap units for them, based on the partition type
  37     GUIDs of GUID partition tables (GPT). See <ulink url="https://uefi.org/specifications">UEFI
  38     Specification</ulink>, chapter 5 for more details. It implements the <ulink
  39     url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable
  40     Partitions Specification</ulink>.</para>
  41
  42     <para>Note that this generator has no effect on non-GPT systems. It will also not create mount point
  43     configuration for directories which already contain files or if the mount point is explicitly configured
  44     in <citerefentry
  45     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Additionally
  46     no unit will be created for the ESP or the XBOOTLDR partition if mount entries are found in the
  47     <filename>/boot/</filename> or <filename>/efi/</filename> hierarchies in <citerefentry
  48     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  49
  50     <para>If the units this generator creates are overridden, for example by units in directories with higher
  51     precedence, drop-ins and additional dependencies created by this generator might still be used.</para>
  52
  53     <para>This generator will only look for the root partition on the same physical disk where the EFI System
  54     Partition (ESP) is located. Note that support from the boot loader is required: the EFI variable
  55     <varname>LoaderDevicePartUUID</varname> of the <constant>4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</constant>
  56     vendor UUID is used to determine from which partition, and hence the disk, from which the system was
  57     booted. If the boot loader does not set this variable, this generator will not be able to detect the root
  58     partition. See the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
  59     for details.</para>
  60
  61     <para>Similarly, this generator will only look for the other partitions on the same physical disk as the
  62     root partition. In this case, boot loader support is not required. These partitions will not be searched
  63     for on systems where the root file system is distributed on multiple disks, for example via btrfs RAID.
  64     </para>
  65
  66     <para><filename>systemd-gpt-auto-generator</filename> is useful for centralizing file system
  67     configuration in the partition table and making configuration in <filename>/etc/fstab</filename> or on
  68     the kernel command line unnecessary.</para>
  69
  70     <para>This generator looks for the partitions based on their
  71     partition type GUID. The following partition type GUIDs are
  72     identified:</para>
  73
  74     <table>
  75       <title>Partition Type GUIDs</title>
  76       <tgroup cols='5' align='left' colsep='1' rowsep='1'>
  77         <colspec colname="type" />
  78         <colspec colname="guid" />
  79         <colspec colname="name" />
  80         <colspec colname="where" />
  81         <colspec colname="explanation" />
  82         <thead>
  83           <row>
  84             <entry>Partition Type</entry>
  85             <entry>GUID</entry>
  86             <entry>Name</entry>
  87             <entry>Mount Point</entry>
  88             <entry>Explanation</entry>
  89           </row>
  90         </thead>
  91         <tbody>
  92           <row>
  93             <entry><constant>SD_GPT_ROOT_X86_64</constant></entry>
  94             <entry><constant>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</constant></entry>
  95             <entry><filename>Root Partition (x86-64)</filename></entry>
  96             <entry><filename>/</filename></entry>
  97             <entry>The first partition with this type UUID, located on the same disk as the ESP used for booting, is used as the root file system <filename>/</filename> on AMD64 / 64-bit x86 systems.</entry>
  98           </row>
  99           <row>
 100             <entry><constant>SD_GPT_ROOT_ARM64</constant></entry>
 101             <entry><constant>b921b045-1df0-41c3-af44-4c6f280d3fae</constant></entry>
 102             <entry><filename>Root Partition (64-bit ARM)</filename></entry>
 103             <entry><filename>/</filename></entry>
 104             <entry>The first partition with this type UUID, located on the same disk as the ESP used for booting, is used as the root file system <filename>/</filename> on AArch64 / 64-bit ARM systems.</entry>
 105           </row>
 106           <row>
 107             <entry><constant>SD_GPT_ROOT_ALPHA</constant> <constant>SD_GPT_ROOT_ARC</constant> <constant>SD_GPT_ROOT_ARM</constant> <constant>SD_GPT_ROOT_ARM64</constant> <constant>SD_GPT_ROOT_IA64</constant> <constant>SD_GPT_ROOT_LOONGARCH64</constant> <constant>SD_GPT_ROOT_MIPS</constant> <constant>SD_GPT_ROOT_MIPS64</constant> <constant>SD_GPT_ROOT_MIPS_LE</constant> <constant>SD_GPT_ROOT_MIPS64_LE</constant> <constant>SD_GPT_ROOT_PARISC</constant> <constant>SD_GPT_ROOT_PPC</constant> <constant>SD_GPT_ROOT_PPC64</constant> <constant>SD_GPT_ROOT_PPC64_LE</constant> <constant>SD_GPT_ROOT_RISCV32</constant> <constant>SD_GPT_ROOT_RISCV64</constant> <constant>SD_GPT_ROOT_S390</constant> <constant>SD_GPT_ROOT_S390X</constant> <constant>SD_GPT_ROOT_TILEGX</constant> <constant>SD_GPT_ROOT_X86</constant> <constant>SD_GPT_ROOT_X86_64</constant> <constant>SD_GPT_USR_ALPHA</constant> <constant>SD_GPT_USR_ARC</constant> <constant>SD_GPT_USR_ARM</constant> <constant>SD_GPT_USR_IA64</constant> <constant>SD_GPT_USR_LOONGARCH64</constant> <constant>SD_GPT_USR_MIPS_LE</constant> <constant>SD_GPT_USR_MIPS64_LE</constant> <constant>SD_GPT_USR_PARISC</constant> <constant>SD_GPT_USR_PPC</constant> <constant>SD_GPT_USR_PPC64</constant> <constant>SD_GPT_USR_PPC64_LE</constant> <constant>SD_GPT_USR_RISCV32</constant> <constant>SD_GPT_USR_RISCV64</constant> <constant>SD_GPT_USR_S390</constant> <constant>SD_GPT_USR_S390X</constant> <constant>SD_GPT_USR_TILEGX</constant> <constant>SD_GPT_USR_X86</constant></entry>
 108             <entry>…</entry>
 109             <entry>Root partitions for other architectures</entry>
 110             <entry><filename>/</filename></entry>
 111             <entry>The first partition with the type UUID matching the architecture, located on the same disk as the ESP used for booting, is used as the root file system <filename>/</filename>. For the full list and constant values, see <ulink url="https://uapi-group.org/specifications/specs/discoverable_partitions_specification">Discoverable Partitions Specification</ulink>.</entry>
 112           </row>
 113           <row>
 114             <entry><constant>SD_GPT_HOME</constant></entry>
 115             <entry><constant>933ac7e1-2eb4-4f13-b844-0e14e2aef915</constant></entry>
 116             <entry>Home Partition</entry>
 117             <entry><filename>/home/</filename></entry>
 118             <entry>The first partition with this type UUID on the same disk as the root partition is mounted to <filename>/home/</filename>.</entry>
 119           </row>
 120           <row>
 121             <entry><constant>SD_GPT_SRV</constant></entry>
 122             <entry><constant>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</constant></entry>
 123             <entry>Server Data Partition</entry>
 124             <entry><filename>/srv/</filename></entry>
 125             <entry>The first partition with this type UUID on the same disk as the root partition is mounted to <filename>/srv/</filename>.</entry>
 126           </row>
 127           <row>
 128             <entry><constant>SD_GPT_VAR</constant></entry>
 129             <entry><constant>4d21b016-b534-45c2-a9fb-5c16e091fd2d</constant></entry>
 130             <entry>Variable Data Partition</entry>
 131             <entry><filename>/var/</filename></entry>
 132             <entry>The first partition with this type UUID on the same disk as the root partition is mounted to <filename>/var/</filename> — under the condition its partition UUID matches the first 128 bit of the HMAC-SHA256 of the GPT type uuid of this partition keyed by the machine ID of the installation stored in <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</entry>
 133           </row>
 134           <row>
 135             <entry><constant>SD_GPT_TMP</constant></entry>
 136             <entry><constant>7ec6f557-3bc5-4aca-b293-16ef5df639d1</constant></entry>
 137             <entry>Temporary Data Partition</entry>
 138             <entry><filename>/var/tmp/</filename></entry>
 139             <entry>The first partition with this type UUID on the same disk as the root partition is mounted to <filename>/var/tmp/</filename>.</entry>
 140           </row>
 141           <row>
 142             <entry><constant>SD_GPT_SWAP</constant></entry>
 143             <entry><constant>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</constant></entry>
 144             <entry>Swap</entry>
 145             <entry>n/a</entry>
 146             <entry>All partitions with this type UUID on the same disk as the root partition are used as swap.</entry>
 147           </row>
 148           <row>
 149             <entry><constant>SD_GPT_ESP</constant></entry>
 150             <entry><constant>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</constant></entry>
 151             <entry>EFI System Partition (ESP)</entry>
 152             <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
 153             <entry>The first partition with this type UUID located on the same disk as the root partition is mounted to <filename>/boot/</filename> or <filename>/efi/</filename>, see below.</entry>
 154           </row>
 155           <row>
 156             <entry><constant>SD_GPT_XBOOTLDR</constant></entry>
 157             <entry><constant>bc13c2ff-59e6-4262-a352-b275fd6f7172</constant></entry>
 158             <entry>Extended Boot Loader Partition</entry>
 159             <entry><filename>/boot/</filename></entry>
 160             <entry>The first partition with this type UUID located on the same disk as the root partition is mounted to <filename>/boot/</filename>, see below.</entry>
 161           </row>
 162         </tbody>
 163       </tgroup>
 164     </table>
 165
 166     <para>This generator understands the following attribute flags for partitions:</para>
 167
 168     <table>
 169       <title>Partition Attribute Flags</title>
 170       <tgroup cols='4' align='left' colsep='1' rowsep='1'>
 171         <colspec colname="flag" />
 172         <colspec colname="value" />
 173         <colspec colname="where" />
 174         <colspec colname="explanation" />
 175         <thead>
 176           <row>
 177             <entry>Flag</entry>
 178             <entry>Value</entry>
 179             <entry>Applicable to</entry>
 180             <entry>Explanation</entry>
 181           </row>
 182         </thead>
 183         <tbody>
 184           <row>
 185             <entry><constant>SD_GPT_FLAG_READ_ONLY</constant></entry>
 186             <entry><constant>0x1000000000000000</constant></entry>
 187             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 188             <entry>Partition is mounted read-only</entry>
 189           </row>
 190
 191           <row>
 192             <entry><constant>SD_GPT_FLAG_NO_AUTO</constant></entry>
 193             <entry><constant>0x8000000000000000</constant></entry>
 194             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 195             <entry>Partition is not mounted automatically</entry>
 196           </row>
 197
 198           <row>
 199             <entry><constant>SD_GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
 200             <entry><constant>0x0000000000000002</constant></entry>
 201             <entry>EFI System Partition (ESP)</entry>
 202             <entry>Partition is not mounted automatically</entry>
 203           </row>
 204         </tbody>
 205       </tgroup>
 206     </table>
 207
 208     <para>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
 209     <filename>/var/tmp/</filename> and swap partitions may be encrypted in LUKS format. In this case, a
 210     device mapper device is set up under the names <filename>/dev/mapper/home</filename>,
 211     <filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename>,
 212     <filename>/dev/mapper/tmp</filename> or <filename>/dev/mapper/swap</filename>. Note that this might
 213     create conflicts if the same partition is listed in <filename>/etc/crypttab</filename> with a different
 214     device mapper device name.</para>
 215
 216     <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted with
 217     LUKS as well. In this case, a device mapper device is set up under the name
 218     <filename>/dev/mapper/root</filename>, and a <filename>sysroot.mount</filename> is set up that mounts the
 219     device under <filename>/sysroot</filename>. For more information, see
 220     <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 221     </para>
 222
 223     <para>The root partition can be specified by symlinking <filename>/run/systemd/volatile-root</filename>
 224     to <filename>/dev/block/$major:$minor</filename>. This is especially useful if the root mount has been
 225     replaced by some form of volatile file system (overlayfs).
 226     </para>
 227
 228     <para>Mount and automount units for the EFI System Partition (ESP) and Extended Boot Loader Partition
 229     (XBOOTLDR) are generated on EFI systems. If the disk contains an XBOOTLDR partition, as defined in the
 230     <ulink url="https://uapi-group.org/specifications/specs/boot_loader_specification">Boot Loader
 231     Specification</ulink>, it is made available at <filename>/boot/</filename>. This generator creates an
 232     automount unit; the mount will only be activated on-demand when accessed. The mount point will be created
 233     if necessary.</para>
 234
 235     <para>The ESP is mounted to <filename>/boot/</filename> if that directory exists and is not used for
 236     XBOOTLDR, and otherwise to <filename>/efi/</filename>. Same as for <filename>/boot/</filename>, an
 237     automount unit is used. The mount point will be created if necessary.</para>
 238
 239     <para>No configuration is created for mount points that are configured in <citerefentry
 240     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry> or when
 241     the target directory contains files.</para>
 242
 243     <para>When using this generator in conjunction with btrfs file
 244     systems, make sure to set the correct default subvolumes on them,
 245     using <command>btrfs subvolume set-default</command>.</para>
 246
 247     <para>If the system was booted via
 248     <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> and the
 249     stub reported to userspace that the kernel image was measured to a TPM2 PCR, then any discovered root and
 250     <filename>/var/</filename> volume identifiers (and volume encryption key in case it is encrypted) will be
 251     automatically measured into PCR 15 on activation, via
 252     <citerefentry><refentrytitle>systemd-pcrfs@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 253
 254     <para><filename>systemd-gpt-auto-generator</filename> implements
 255     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 256   </refsect1>
 257
 258   <refsect1>
 259     <title>Kernel Command Line</title>
 260
 261     <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
 262     parameters:</para>
 263
 264     <variablelist class='kernel-commandline-options'>
 265
 266       <varlistentry>
 267         <term><varname>systemd.gpt_auto</varname></term>
 268         <term><varname>rd.systemd.gpt_auto</varname></term>
 269
 270         <listitem><para>Those options take an optional boolean argument, and default to yes.
 271         The generator is enabled by default, and a false value may be used to disable it
 272         (e.g. <literal>systemd.gpt_auto=0</literal>).
 273         </para>
 274
 275         <xi:include href="version-info.xml" xpointer="v242"/></listitem>
 276       </varlistentry>
 277
 278       <varlistentry>
 279         <term><varname>systemd.image_policy=</varname></term>
 280         <term><varname>rd.systemd.image_policy=</varname></term>
 281
 282         <listitem><para>Takes an image dissection policy string as argument (as per
 283         <citerefentry><refentrytitle>systemd.image-policy</refentrytitle><manvolnum>7</manvolnum></citerefentry>),
 284         and allows enforcing a policy on dissection and use of the automatically discovered GPT partition
 285         table entries.</para>
 286
 287         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 288       </varlistentry>
 289
 290       <varlistentry>
 291         <term><varname>root=</varname></term>
 292         <term><varname>rootfstype=</varname></term>
 293         <term><varname>rootflags=</varname></term>
 294
 295         <listitem><para>When <varname>root=</varname> is used with the special value
 296         <literal>gpt-auto</literal> (or if the parameter is not used at all), automatic discovery of the root
 297         partition based on the GPT partition type is enabled. Any other value disables this
 298         logic.</para>
 299
 300         <para>The <varname>rootfstype=</varname> and <varname>rootflags=</varname> are used to select the
 301         file system type and options when the root file system is automatically discovered.</para>
 302
 303         <xi:include href="version-info.xml" xpointer="v242"/></listitem>
 304       </varlistentry>
 305
 306       <varlistentry>
 307         <term><varname>rw</varname></term>
 308         <term><varname>ro</varname></term>
 309
 310         <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
 311
 312         <para>Note that unlike most kernel command line options these settings do not override configuration
 313         in the file system, and the file system may be remounted later. See
 314         <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 315         </para>
 316
 317         <xi:include href="version-info.xml" xpointer="v242"/></listitem>
 318       </varlistentry>
 319
 320       <varlistentry>
 321         <term><varname>systemd.swap=</varname></term>
 322
 323         <listitem><para>Takes a boolean argument or enables the option if specified without an argument.
 324         If disabled, automatic discovery of swap partition(s) based on GPT partition type is disabled.
 325         Defaults to enabled.</para>
 326
 327         <xi:include href="version-info.xml" xpointer="v254"/></listitem>
 328       </varlistentry>
 329     </variablelist>
 330   </refsect1>
 331
 332   <refsect1>
 333     <title>See Also</title>
 334     <para><simplelist type="inline">
 335       <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
 336       <member><citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 337       <member><citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 338       <member><citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 339       <member><citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 340       <member><citerefentry><refentrytitle>systemd-pcrfs@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 341       <member><citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 342       <member><citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 343       <member><citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry></member>
 344       <member><citerefentry project='url'><refentrytitle url='https://btrfs.readthedocs.io/en/latest/btrfs.html'>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
 345     </simplelist></para>
 346   </refsect1>
 347
 348 </refentry>