man/systemd-gpt-auto-generator.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   4 <!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
   5
   6 <refentry id="systemd-gpt-auto-generator" conditional='HAVE_BLKID'>
   7
   8   <refentryinfo>
   9     <title>systemd-gpt-auto-generator</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd-gpt-auto-generator</refentrytitle>
  15     <manvolnum>8</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd-gpt-auto-generator</refname>
  20     <refpurpose>Generator for automatically discovering and mounting root, <filename>/home/</filename>,
  21     <filename>/srv/</filename>, <filename>/var/</filename> and <filename>/var/tmp/</filename> partitions, as
  22     well as discovering and enabling swap partitions, based on GPT partition type GUIDs</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
  27   </refsynopsisdiv>
  28
  29   <refsect1>
  30     <title>Description</title>
  31
  32     <para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
  33     root, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>,
  34     <filename>/var/tmp/</filename>, the EFI System Partition, the Extended Boot Loader Partition and swap
  35     partitions and creates mount and swap units for them, based on the partition type GUIDs of GUID partition
  36     tables (GPT), see <ulink url="https://uefi.org/specifications">UEFI Specification</ulink>, chapter 5. It
  37     implements the <ulink url="https://systemd.io/DISCOVERABLE_PARTITIONS">Discoverable Partitions
  38     Specification</ulink>. Note that this generator has no effect on non-GPT systems, and on specific mount
  39     points that are directories already containing files. Also, on systems where the units are explicitly
  40     configured (for example, listed in <citerefentry
  41     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>), the
  42     units this generator creates are overridden, but additional implicit dependencies might be
  43     created.</para>
  44
  45     <para>This generator will only look for the root partition on the same physical disk the EFI System
  46     Partition (ESP) is located on. Note that support from the boot loader is required: the EFI variable
  47     <varname>LoaderDevicePartUUID</varname> of the <constant>4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</constant>
  48     vendor UUID is used to determine from which partition, and hence the disk from which the system was
  49     booted. If the boot loader does not set this variable, this generator will not be able to autodetect the
  50     root partition. See the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader
  51     Interface</ulink> for details.</para>
  52
  53     <para>Similarly, this generator will only look for the other partitions on the same physical disk as the
  54     root partition. In this case, boot loader support is not required. These partitions will not be searched
  55     for on systems where the root file system is distributed on multiple disks, for example via btrfs RAID.
  56     </para>
  57
  58     <para><filename>systemd-gpt-auto-generator</filename> is useful for centralizing file system
  59     configuration in the partition table and making configuration in <filename>/etc/fstab</filename> or on
  60     the kernel command line unnecessary.</para>
  61
  62     <para>This generator looks for the partitions based on their
  63     partition type GUID. The following partition type GUIDs are
  64     identified:</para>
  65
  66     <table>
  67       <title>Partition Type GUIDs</title>
  68       <tgroup cols='3' align='left' colsep='1' rowsep='1'>
  69         <colspec colname="guid" />
  70         <colspec colname="name" />
  71         <colspec colname="where" />
  72         <colspec colname="explanation" />
  73         <thead>
  74           <row>
  75             <entry>Partition Type GUID</entry>
  76             <entry>Name</entry>
  77             <entry>Mount Point</entry>
  78             <entry>Explanation</entry>
  79           </row>
  80         </thead>
  81         <tbody>
  82           <row>
  83             <entry>44479540-f297-41b2-9af7-d131d5f0458a</entry>
  84             <entry><filename>Root Partition (x86)</filename></entry>
  85             <entry><filename>/</filename></entry>
  86             <entry>On 32-bit x86 systems, the first x86 root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
  87           </row>
  88           <row>
  89             <entry>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</entry>
  90             <entry><filename>Root Partition (x86-64)</filename></entry>
  91             <entry><filename>/</filename></entry>
  92             <entry>On 64-bit x86 systems, the first x86-64 root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
  93           </row>
  94           <row>
  95             <entry>69dad710-2ce4-4e3c-b16c-21a1d49abed3</entry>
  96             <entry><filename>Root Partition (32-bit ARM)</filename></entry>
  97             <entry><filename>/</filename></entry>
  98             <entry>On 32-bit ARM systems, the first ARM root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
  99           </row>
 100           <row>
 101             <entry>b921b045-1df0-41c3-af44-4c6f280d3fae</entry>
 102             <entry><filename>Root Partition (64-bit ARM)</filename></entry>
 103             <entry><filename>/</filename></entry>
 104             <entry>On 64-bit ARM systems, the first ARM root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
 105           </row>
 106           <row>
 107             <entry>993d8d3d-f80e-4225-855a-9daf8ed7ea97</entry>
 108             <entry><filename>Root Partition (Itanium/IA-64)</filename></entry>
 109             <entry><filename>/</filename></entry>
 110             <entry>On Itanium systems, the first Itanium root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
 111           </row>
 112           <row>
 113             <entry>60d5a7fe-8e7d-435c-b714-3dd8162144e1</entry>
 114             <entry><filename>Root Partition (RISCV-V 32)</filename></entry>
 115             <entry><filename>/</filename></entry>
 116             <entry>On RISC-V 32-bit systems, the first RISCV-V 32-bit root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
 117           </row>
 118           <row>
 119             <entry>72ec70a6-cf74-40e6-bd49-4bda08e8f224</entry>
 120             <entry><filename>Root Partition (RISCV-V 64)</filename></entry>
 121             <entry><filename>/</filename></entry>
 122             <entry>On RISC-V 64-bit systems, the first RISCV-V 64-bit root partition on the disk the EFI ESP is located on is mounted to the root directory <filename>/</filename>.</entry>
 123           </row>
 124           <row>
 125             <entry>933ac7e1-2eb4-4f13-b844-0e14e2aef915</entry>
 126             <entry>Home Partition</entry>
 127             <entry><filename>/home/</filename></entry>
 128             <entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home/</filename>.</entry>
 129           </row>
 130           <row>
 131             <entry>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</entry>
 132             <entry>Server Data Partition</entry>
 133             <entry><filename>/srv/</filename></entry>
 134             <entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv/</filename>.</entry>
 135           </row>
 136           <row>
 137             <entry>4d21b016-b534-45c2-a9fb-5c16e091fd2d</entry>
 138             <entry>Variable Data Partition</entry>
 139             <entry><filename>/var/</filename></entry>
 140             <entry>The first variable data partition on the disk the root partition is located on 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>
 141           </row>
 142           <row>
 143             <entry>7ec6f557-3bc5-4aca-b293-16ef5df639d1</entry>
 144             <entry>Temporary Data Partition</entry>
 145             <entry><filename>/var/tmp/</filename></entry>
 146             <entry>The first temporary data partition on the disk the root partition is located on is mounted to <filename>/var/tmp/</filename>.</entry>
 147           </row>
 148           <row>
 149             <entry>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
 150             <entry>Swap</entry>
 151             <entry>n/a</entry>
 152             <entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
 153           </row>
 154           <row>
 155             <entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
 156             <entry>EFI System Partition (ESP)</entry>
 157             <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
 158             <entry>The first ESP located on the disk the root partition is located on is mounted to <filename>/boot/</filename> or <filename>/efi/</filename>, see below.</entry>
 159           </row>
 160           <row>
 161             <entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
 162             <entry>Extended Boot Loader Partition</entry>
 163             <entry><filename>/boot/</filename></entry>
 164             <entry>The first Extended Boot Loader Partition is mounted to <filename>/boot/</filename>, see below.</entry>
 165           </row>
 166         </tbody>
 167       </tgroup>
 168     </table>
 169
 170     <para>This generator understands the following attribute flags for partitions:</para>
 171
 172     <table>
 173       <title>Partition Attributes</title>
 174       <tgroup cols='4' align='left' colsep='1' rowsep='1'>
 175         <colspec colname="attribute" />
 176         <colspec colname="value" />
 177         <colspec colname="where" />
 178         <colspec colname="explanation" />
 179         <thead>
 180           <row>
 181             <entry>Name</entry>
 182             <entry>Value</entry>
 183             <entry>Applicable to</entry>
 184             <entry>Explanation</entry>
 185           </row>
 186         </thead>
 187         <tbody>
 188           <row>
 189             <entry><constant>GPT_FLAG_READ_ONLY</constant></entry>
 190             <entry>0x1000000000000000</entry>
 191             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 192             <entry>Partition is mounted read-only</entry>
 193           </row>
 194
 195           <row>
 196             <entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
 197             <entry>0x8000000000000000</entry>
 198             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 199             <entry>Partition is not mounted automatically</entry>
 200           </row>
 201
 202           <row>
 203             <entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
 204             <entry>0x0000000000000002</entry>
 205             <entry>EFI System Partition (ESP)</entry>
 206             <entry>Partition is not mounted automatically</entry>
 207           </row>
 208         </tbody>
 209       </tgroup>
 210     </table>
 211
 212     <para>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename> and
 213     <filename>/var/tmp/</filename> partitions may be encrypted in LUKS format. In this case, a device mapper
 214     device is set up under the names <filename>/dev/mapper/home</filename>,
 215     <filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename> and
 216     <filename>/dev/mapper/tmp</filename>. Note that this might create conflicts if the same partition is
 217     listed in <filename>/etc/crypttab</filename> with a different device mapper device name.</para>
 218
 219     <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
 220       format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
 221       and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
 222       For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 223     </para>
 224
 225     <para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
 226     is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
 227     below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
 228     there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
 229     accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
 230     explicitly configured mount (for example, listed in <citerefentry
 231     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
 232     the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
 233     are generated.</para>
 234
 235     <para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
 236     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
 237     available at <filename>/boot/</filename> (by means of an automount point, similar to the ESP, see
 238     above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
 239     preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
 240     and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
 241
 242     <para>When using this generator in conjunction with btrfs file
 243     systems, make sure to set the correct default subvolumes on them,
 244     using <command>btrfs subvolume set-default</command>.</para>
 245
 246     <para><filename>systemd-gpt-auto-generator</filename> implements
 247     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 248   </refsect1>
 249
 250   <refsect1>
 251     <title>Kernel Command Line</title>
 252
 253     <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
 254     parameters:</para>
 255
 256     <variablelist class='kernel-commandline-options'>
 257
 258       <varlistentry>
 259         <term><varname>systemd.gpt_auto</varname></term>
 260         <term><varname>rd.systemd.gpt_auto</varname></term>
 261
 262         <listitem><para>Those options take an optional boolean argument, and default to yes.
 263         The generator is enabled by default, and a negative value may be used to disable it.
 264         </para></listitem>
 265       </varlistentry>
 266
 267       <varlistentry>
 268         <term><varname>root=</varname></term>
 269
 270         <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
 271         the root partition based on the GPT partition type is enabled.  Any other value disables this
 272         generator.</para></listitem>
 273       </varlistentry>
 274
 275       <varlistentry>
 276         <term><varname>rw</varname></term>
 277         <term><varname>ro</varname></term>
 278
 279         <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
 280
 281         <para>Note that unlike most kernel command line options these settings do not override configuration
 282         in the file system, and the file system may be remounted later. See
 283         <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 284         </para></listitem>
 285       </varlistentry>
 286     </variablelist>
 287   </refsect1>
 288
 289   <refsect1>
 290     <title>See Also</title>
 291     <para>
 292       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 293       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 294       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 295       <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 296       <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 297       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 298       <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 299       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 300       <citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 301     </para>
 302   </refsect1>
 303
 304 </refentry>