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
  21     and mounting root, <filename>/home</filename> and
  22     <filename>/srv</filename> partitions, as well as
  23     discovering and enabling swap partitions, based on GPT
  24     partition type GUIDs.</refpurpose>
  25   </refnamediv>
  26
  27   <refsynopsisdiv>
  28     <para><filename>/usr/lib/systemd/system-generators/systemd-gpt-auto-generator</filename></para>
  29   </refsynopsisdiv>
  30
  31   <refsect1>
  32     <title>Description</title>
  33
  34     <para><filename>systemd-gpt-auto-generator</filename> is a unit generator that automatically discovers
  35     root, <filename>/home/</filename>, <filename>/srv/</filename>, the EFI System Partition, the Extended
  36     Boot Loader Partition and swap partitions and creates mount and swap units for them, based on the
  37     partition type GUIDs of GUID partition tables (GPT), see <ulink
  38     url="https://uefi.org/specifications">UEFI Specification</ulink>, chapter 5. It implements the <ulink
  39     url="https://www.freedesktop.org/wiki/Specifications/DiscoverablePartitionsSpec/">Discoverable Partitions
  40     Specification</ulink>. Note that this generator has no effect on non-GPT systems, and on specific mount
  41     points that are directories already containing files. Also, on systems where the units are explicitly
  42     configured (for example, listed in <citerefentry
  43     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>), the
  44     units this generator creates are overridden, but additional implicit dependencies might be
  45     created.</para>
  46
  47     <para>This generator will only look for the root partition on the same physical disk the EFI System
  48     Partition (ESP) is located on. Note that support from the boot loader is required: EFI variable
  49     <varname>LoaderDevicePartUUID-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f</varname> is used to determine from
  50     which partition, and hence the disk from which the system was booted. If the boot loader does not set
  51     this variable, this generator will not be able to autodetect the root partition.</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>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
 126             <entry>Swap</entry>
 127             <entry>n/a</entry>
 128             <entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
 129           </row>
 130           <row>
 131             <entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
 132             <entry>EFI System Partition (ESP)</entry>
 133             <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
 134             <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>
 135           </row>
 136           <row>
 137             <entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
 138             <entry>Extended Boot Loader Partition</entry>
 139             <entry><filename>/boot/</filename></entry>
 140             <entry>The first Extended Boot Loader Partition is mounted to <filename>/boot</filename>, see below.</entry>
 141           </row>
 142         </tbody>
 143       </tgroup>
 144     </table>
 145
 146     <para>This generator understands the following attribute flags for partitions:</para>
 147
 148     <table>
 149       <title>Partition Attributes</title>
 150       <tgroup cols='4' align='left' colsep='1' rowsep='1'>
 151         <colspec colname="attribute" />
 152         <colspec colname="value" />
 153         <colspec colname="where" />
 154         <colspec colname="explanation" />
 155         <thead>
 156           <row>
 157             <entry>Name</entry>
 158             <entry>Value</entry>
 159             <entry>Applicable to</entry>
 160             <entry>Explanation</entry>
 161           </row>
 162         </thead>
 163         <tbody>
 164           <row>
 165             <entry><constant>GPT_FLAG_READ_ONLY</constant></entry>
 166             <entry>0x1000000000000000</entry>
 167             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, Extended Boot Loader Partition</entry>
 168             <entry>Partition is mounted read-only</entry>
 169           </row>
 170
 171           <row>
 172             <entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
 173             <entry>0x8000000000000000</entry>
 174             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, Extended Boot Loader Partition</entry>
 175             <entry>Partition is not mounted automatically</entry>
 176           </row>
 177
 178           <row>
 179             <entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
 180             <entry>0x0000000000000002</entry>
 181             <entry>EFI System Partition (ESP)</entry>
 182             <entry>Partition is not mounted automatically</entry>
 183           </row>
 184         </tbody>
 185       </tgroup>
 186     </table>
 187
 188     <para>The <filename>/home/</filename> and <filename>/srv/</filename> partitions may be encrypted in LUKS
 189     format. In this case, a device mapper device is set up under the names
 190     <filename>/dev/mapper/home</filename> and <filename>/dev/mapper/srv</filename>. Note that this might
 191     create conflicts if the same partition is listed in <filename>/etc/crypttab</filename> with a different
 192     device mapper device name.</para>
 193
 194     <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
 195       format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
 196       and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
 197       For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 198     </para>
 199
 200     <para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
 201     is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
 202     below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
 203     there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
 204     accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
 205     explicitly configured mount (for example, listed in <citerefentry
 206     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
 207     the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
 208     are generated.</para>
 209
 210     <para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
 211     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
 212     available at <filename>/boot</filename> (by means of an automount point, similar to the ESP, see
 213     above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
 214     preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
 215     and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
 216
 217     <para>When using this generator in conjunction with btrfs file
 218     systems, make sure to set the correct default subvolumes on them,
 219     using <command>btrfs subvolume set-default</command>.</para>
 220
 221     <para><filename>systemd-gpt-auto-generator</filename> implements
 222     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 223   </refsect1>
 224
 225   <refsect1>
 226     <title>Kernel Command Line</title>
 227
 228     <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
 229     parameters:</para>
 230
 231     <variablelist class='kernel-commandline-options'>
 232
 233       <varlistentry>
 234         <term><varname>systemd.gpt_auto</varname></term>
 235         <term><varname>rd.systemd.gpt_auto</varname></term>
 236
 237         <listitem><para>Those options take an optional boolean argument, and default to yes.
 238         The generator is enabled by default, and a negative value may be used to disable it.
 239         </para></listitem>
 240       </varlistentry>
 241
 242       <varlistentry>
 243         <term><varname>root=</varname></term>
 244
 245         <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
 246         the root partition based on the GPT partition type is enabled.  Any other value disables this
 247         generator.</para></listitem>
 248       </varlistentry>
 249
 250       <varlistentry>
 251         <term><varname>rw</varname></term>
 252         <term><varname>ro</varname></term>
 253
 254         <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
 255
 256         <para>Note that unlike most kernel command line options these settings do not override configuration
 257         in the file system, and the file system may be remounted later. See
 258         <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 259         </para></listitem>
 260       </varlistentry>
 261     </variablelist>
 262   </refsect1>
 263
 264   <refsect1>
 265     <title>See Also</title>
 266     <para>
 267       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 268       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 269       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 270       <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 271       <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 272       <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 273       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 274       <citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 275     </para>
 276   </refsect1>
 277
 278 </refentry>