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 root partitions on the
  48     same physical disk the EFI System Partition (ESP) is located on.
  49     It will only look for the other partitions on the same physical
  50     disk the root file system is located on. These partitions will not
  51     be searched for on systems where the root file system is distributed
  52     on multiple disks, for example via btrfs RAID.</para>
  53
  54     <para><filename>systemd-gpt-auto-generator</filename> is useful
  55     for centralizing file system configuration in the partition table
  56     and making configuration in <filename>/etc/fstab</filename> unnecessary.
  57     </para>
  58
  59     <para>This generator looks for the partitions based on their
  60     partition type GUID. The following partition type GUIDs are
  61     identified:</para>
  62
  63     <table>
  64       <title>Partition Type GUIDs</title>
  65       <tgroup cols='3' align='left' colsep='1' rowsep='1'>
  66         <colspec colname="guid" />
  67         <colspec colname="name" />
  68         <colspec colname="where" />
  69         <colspec colname="explanation" />
  70         <thead>
  71           <row>
  72             <entry>Partition Type GUID</entry>
  73             <entry>Name</entry>
  74             <entry>Mount Point</entry>
  75             <entry>Explanation</entry>
  76           </row>
  77         </thead>
  78         <tbody>
  79           <row>
  80             <entry>44479540-f297-41b2-9af7-d131d5f0458a</entry>
  81             <entry><filename>Root Partition (x86)</filename></entry>
  82             <entry><filename>/</filename></entry>
  83             <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>
  84           </row>
  85           <row>
  86             <entry>4f68bce3-e8cd-4db1-96e7-fbcaf984b709</entry>
  87             <entry><filename>Root Partition (x86-64)</filename></entry>
  88             <entry><filename>/</filename></entry>
  89             <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>
  90           </row>
  91           <row>
  92             <entry>69dad710-2ce4-4e3c-b16c-21a1d49abed3</entry>
  93             <entry><filename>Root Partition (32-bit ARM)</filename></entry>
  94             <entry><filename>/</filename></entry>
  95             <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>
  96           </row>
  97           <row>
  98             <entry>b921b045-1df0-41c3-af44-4c6f280d3fae</entry>
  99             <entry><filename>Root Partition (64-bit ARM)</filename></entry>
 100             <entry><filename>/</filename></entry>
 101             <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>
 102           </row>
 103           <row>
 104             <entry>993d8d3d-f80e-4225-855a-9daf8ed7ea97</entry>
 105             <entry><filename>Root Partition (Itanium/IA-64)</filename></entry>
 106             <entry><filename>/</filename></entry>
 107             <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>
 108           </row>
 109           <row>
 110             <entry>933ac7e1-2eb4-4f13-b844-0e14e2aef915</entry>
 111             <entry>Home Partition</entry>
 112             <entry><filename>/home/</filename></entry>
 113             <entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home</filename>.</entry>
 114           </row>
 115           <row>
 116             <entry>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</entry>
 117             <entry>Server Data Partition</entry>
 118             <entry><filename>/srv/</filename></entry>
 119             <entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv</filename>.</entry>
 120           </row>
 121           <row>
 122             <entry>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
 123             <entry>Swap</entry>
 124             <entry>n/a</entry>
 125             <entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
 126           </row>
 127           <row>
 128             <entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
 129             <entry>EFI System Partition (ESP)</entry>
 130             <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
 131             <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>
 132           </row>
 133           <row>
 134             <entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
 135             <entry>Extended Boot Loader Partition</entry>
 136             <entry><filename>/boot/</filename></entry>
 137             <entry>The first Extended Boot Loader Partition is mounted to <filename>/boot</filename>, see below.</entry>
 138           </row>
 139         </tbody>
 140       </tgroup>
 141     </table>
 142
 143     <para>This generator understands the following attribute flags for partitions:</para>
 144
 145     <table>
 146       <title>Partition Attributes</title>
 147       <tgroup cols='4' align='left' colsep='1' rowsep='1'>
 148         <colspec colname="attribute" />
 149         <colspec colname="value" />
 150         <colspec colname="where" />
 151         <colspec colname="explanation" />
 152         <thead>
 153           <row>
 154             <entry>Name</entry>
 155             <entry>Value</entry>
 156             <entry>Applicable to</entry>
 157             <entry>Explanation</entry>
 158           </row>
 159         </thead>
 160         <tbody>
 161           <row>
 162             <entry><constant>GPT_FLAG_READ_ONLY</constant></entry>
 163             <entry>0x1000000000000000</entry>
 164             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, Extended Boot Loader Partition</entry>
 165             <entry>Partition is mounted read-only</entry>
 166           </row>
 167
 168           <row>
 169             <entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
 170             <entry>0x8000000000000000</entry>
 171             <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, Extended Boot Loader Partition</entry>
 172             <entry>Partition is not mounted automatically</entry>
 173           </row>
 174
 175           <row>
 176             <entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
 177             <entry>0x0000000000000002</entry>
 178             <entry>EFI System Partition (ESP)</entry>
 179             <entry>Partition is not mounted automatically</entry>
 180           </row>
 181         </tbody>
 182       </tgroup>
 183     </table>
 184
 185     <para>The <filename>/home/</filename> and <filename>/srv/</filename> partitions may be encrypted in LUKS
 186     format. In this case, a device mapper device is set up under the names
 187     <filename>/dev/mapper/home</filename> and <filename>/dev/mapper/srv</filename>. Note that this might
 188     create conflicts if the same partition is listed in <filename>/etc/crypttab</filename> with a different
 189     device mapper device name.</para>
 190
 191     <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
 192       format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
 193       and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
 194       For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 195     </para>
 196
 197     <para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
 198     is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
 199     below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
 200     there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
 201     accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
 202     explicitly configured mount (for example, listed in <citerefentry
 203     project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
 204     the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
 205     are generated.</para>
 206
 207     <para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
 208     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
 209     available at <filename>/boot</filename> (by means of an automount point, similar to the ESP, see
 210     above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
 211     preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
 212     and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
 213
 214     <para>When using this generator in conjunction with btrfs file
 215     systems, make sure to set the correct default subvolumes on them,
 216     using <command>btrfs subvolume set-default</command>.</para>
 217
 218     <para><filename>systemd-gpt-auto-generator</filename> implements
 219     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 220   </refsect1>
 221
 222   <refsect1>
 223     <title>Kernel Command Line</title>
 224
 225     <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
 226     parameters:</para>
 227
 228     <variablelist class='kernel-commandline-options'>
 229
 230       <varlistentry>
 231         <term><varname>systemd.gpt_auto</varname></term>
 232         <term><varname>rd.systemd.gpt_auto</varname></term>
 233
 234         <listitem><para>Those options take an optional boolean argument, and default to yes.
 235         The generator is enabled by default, and a negative value may be used to disable it.
 236         </para></listitem>
 237       </varlistentry>
 238
 239       <varlistentry>
 240         <term><varname>root=</varname></term>
 241
 242         <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
 243         the root partition based on the GPT partition type is enabled.  Any other value disables this
 244         generator.</para></listitem>
 245       </varlistentry>
 246
 247       <varlistentry>
 248         <term><varname>rw</varname></term>
 249         <term><varname>ro</varname></term>
 250
 251         <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
 252
 253         <para>Note that unlike most kernel command line options these settings do not override configuration
 254         in the file system, and the file system may be remounted later. See
 255         <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 256         </para></listitem>
 257       </varlistentry>
 258     </variablelist>
 259   </refsect1>
 260
 261   <refsect1>
 262     <title>See Also</title>
 263     <para>
 264       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 265       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 266       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 267       <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 268       <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 269       <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 270       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 271       <citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 272     </para>
 273   </refsect1>
 274
 275 </refentry>