man/systemd-gpt-auto-generator.xml

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   3 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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   5 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   6 <refentry id="systemd-gpt-auto-generator">
   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>933ac7e1-2eb4-4f13-b844-0e14e2aef915</entry>
 114             <entry>Home Partition</entry>
 115             <entry><filename>/home/</filename></entry>
 116             <entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home/</filename>.</entry>
 117           </row>
 118           <row>
 119             <entry>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</entry>
 120             <entry>Server Data Partition</entry>
 121             <entry><filename>/srv/</filename></entry>
 122             <entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv/</filename>.</entry>
 123           </row>
 124           <row>
 125             <entry>4d21b016-b534-45c2-a9fb-5c16e091fd2d</entry>
 126             <entry>Variable Data Partition</entry>
 127             <entry><filename>/var/</filename></entry>
 128             <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>
 129           </row>
 130           <row>
 131             <entry>7ec6f557-3bc5-4aca-b293-16ef5df639d1</entry>
 132             <entry>Temporary Data Partition</entry>
 133             <entry><filename>/var/tmp/</filename></entry>
 134             <entry>The first temporary data partition on the disk the root partition is located on is mounted to <filename>/var/tmp/</filename>.</entry>
 135           </row>
 136           <row>
 137             <entry>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
 138             <entry>Swap</entry>
 139             <entry>n/a</entry>
 140             <entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
 141           </row>
 142           <row>
 143             <entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
 144             <entry>EFI System Partition (ESP)</entry>
 145             <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
 146             <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>
 147           </row>
 148           <row>
 149             <entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
 150             <entry>Extended Boot Loader Partition</entry>
 151             <entry><filename>/boot/</filename></entry>
 152             <entry>The first Extended Boot Loader Partition is mounted to <filename>/boot/</filename>, see below.</entry>
 153           </row>
 154         </tbody>
 155       </tgroup>
 156     </table>
 157
 158     <para>This generator understands the following attribute flags for partitions:</para>
 159
 160     <table>
 161       <title>Partition Attributes</title>
 162       <tgroup cols='4' align='left' colsep='1' rowsep='1'>
 163         <colspec colname="attribute" />
 164         <colspec colname="value" />
 165         <colspec colname="where" />
 166         <colspec colname="explanation" />
 167         <thead>
 168           <row>
 169             <entry>Name</entry>
 170             <entry>Value</entry>
 171             <entry>Applicable to</entry>
 172             <entry>Explanation</entry>
 173           </row>
 174         </thead>
 175         <tbody>
 176           <row>
 177             <entry><constant>GPT_FLAG_READ_ONLY</constant></entry>
 178             <entry>0x1000000000000000</entry>
 179             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 180             <entry>Partition is mounted read-only</entry>
 181           </row>
 182
 183           <row>
 184             <entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
 185             <entry>0x8000000000000000</entry>
 186             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
 187             <entry>Partition is not mounted automatically</entry>
 188           </row>
 189
 190           <row>
 191             <entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
 192             <entry>0x0000000000000002</entry>
 193             <entry>EFI System Partition (ESP)</entry>
 194             <entry>Partition is not mounted automatically</entry>
 195           </row>
 196         </tbody>
 197       </tgroup>
 198     </table>
 199
 200     <para>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename> and
 201     <filename>/var/tmp/</filename> partitions may be encrypted in LUKS format. In this case, a device mapper
 202     device is set up under the names <filename>/dev/mapper/home</filename>,
 203     <filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename> and
 204     <filename>/dev/mapper/tmp</filename>. Note that this might create conflicts if the same partition is
 205     listed in <filename>/etc/crypttab</filename> with a different device mapper device name.</para>
 206
 207     <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
 208       format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
 209       and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
 210       For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 211     </para>
 212
 213     <para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
 214     is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
 215     below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
 216     there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
 217     accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
 218     explicitly configured mount (for example, listed in <citerefentry
 219     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
 220     the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
 221     are generated.</para>
 222
 223     <para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
 224     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
 225     available at <filename>/boot/</filename> (by means of an automount point, similar to the ESP, see
 226     above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
 227     preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
 228     and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
 229
 230     <para>When using this generator in conjunction with btrfs file
 231     systems, make sure to set the correct default subvolumes on them,
 232     using <command>btrfs subvolume set-default</command>.</para>
 233
 234     <para><filename>systemd-gpt-auto-generator</filename> implements
 235     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 236   </refsect1>
 237
 238   <refsect1>
 239     <title>Kernel Command Line</title>
 240
 241     <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
 242     parameters:</para>
 243
 244     <variablelist class='kernel-commandline-options'>
 245
 246       <varlistentry>
 247         <term><varname>systemd.gpt_auto</varname></term>
 248         <term><varname>rd.systemd.gpt_auto</varname></term>
 249
 250         <listitem><para>Those options take an optional boolean argument, and default to yes.
 251         The generator is enabled by default, and a negative value may be used to disable it.
 252         </para></listitem>
 253       </varlistentry>
 254
 255       <varlistentry>
 256         <term><varname>root=</varname></term>
 257
 258         <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
 259         the root partition based on the GPT partition type is enabled.  Any other value disables this
 260         generator.</para></listitem>
 261       </varlistentry>
 262
 263       <varlistentry>
 264         <term><varname>rw</varname></term>
 265         <term><varname>ro</varname></term>
 266
 267         <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
 268
 269         <para>Note that unlike most kernel command line options these settings do not override configuration
 270         in the file system, and the file system may be remounted later. See
 271         <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 272         </para></listitem>
 273       </varlistentry>
 274     </variablelist>
 275   </refsect1>
 276
 277   <refsect1>
 278     <title>See Also</title>
 279     <para>
 280       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 281       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 282       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 283       <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 284       <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 285       <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 286       <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 287       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 288       <citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 289     </para>
 290   </refsect1>
 291
 292 </refentry>