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/4.2/docbookx.dtd">
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>77055800-792c-4f94-b39a-98c91b762bb6</entry>
114            <entry><filename>Root Partition (LoongArch 64)</filename></entry>
115            <entry><filename>/</filename></entry>
116            <entry>On LoongArch 64-bit systems, the first LoongArch 64-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>60d5a7fe-8e7d-435c-b714-3dd8162144e1</entry>
120            <entry><filename>Root Partition (RISCV-V 32)</filename></entry>
121            <entry><filename>/</filename></entry>
122            <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>
123          </row>
124          <row>
125            <entry>72ec70a6-cf74-40e6-bd49-4bda08e8f224</entry>
126            <entry><filename>Root Partition (RISCV-V 64)</filename></entry>
127            <entry><filename>/</filename></entry>
128            <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>
129          </row>
130          <row>
131            <entry>933ac7e1-2eb4-4f13-b844-0e14e2aef915</entry>
132            <entry>Home Partition</entry>
133            <entry><filename>/home/</filename></entry>
134            <entry>The first home partition on the disk the root partition is located on is mounted to <filename>/home/</filename>.</entry>
135          </row>
136          <row>
137            <entry>3b8f8425-20e0-4f3b-907f-1a25a76f98e8</entry>
138            <entry>Server Data Partition</entry>
139            <entry><filename>/srv/</filename></entry>
140            <entry>The first server data partition on the disk the root partition is located on is mounted to <filename>/srv/</filename>.</entry>
141          </row>
142          <row>
143            <entry>4d21b016-b534-45c2-a9fb-5c16e091fd2d</entry>
144            <entry>Variable Data Partition</entry>
145            <entry><filename>/var/</filename></entry>
146            <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>
147          </row>
148          <row>
149            <entry>7ec6f557-3bc5-4aca-b293-16ef5df639d1</entry>
150            <entry>Temporary Data Partition</entry>
151            <entry><filename>/var/tmp/</filename></entry>
152            <entry>The first temporary data partition on the disk the root partition is located on is mounted to <filename>/var/tmp/</filename>.</entry>
153          </row>
154          <row>
155            <entry>0657fd6d-a4ab-43c4-84e5-0933c84b4f4f</entry>
156            <entry>Swap</entry>
157            <entry>n/a</entry>
158            <entry>All swap partitions located on the disk the root partition is located on are enabled.</entry>
159          </row>
160          <row>
161            <entry>c12a7328-f81f-11d2-ba4b-00a0c93ec93b</entry>
162            <entry>EFI System Partition (ESP)</entry>
163            <entry><filename>/efi/</filename> or <filename>/boot/</filename></entry>
164            <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>
165          </row>
166          <row>
167            <entry>bc13c2ff-59e6-4262-a352-b275fd6f7172</entry>
168            <entry>Extended Boot Loader Partition</entry>
169            <entry><filename>/boot/</filename></entry>
170            <entry>The first Extended Boot Loader Partition is mounted to <filename>/boot/</filename>, see below.</entry>
171          </row>
172        </tbody>
173      </tgroup>
174    </table>
175
176    <para>This generator understands the following attribute flags for partitions:</para>
177
178    <table>
179      <title>Partition Attributes</title>
180      <tgroup cols='4' align='left' colsep='1' rowsep='1'>
181        <colspec colname="attribute" />
182        <colspec colname="value" />
183        <colspec colname="where" />
184        <colspec colname="explanation" />
185        <thead>
186          <row>
187            <entry>Name</entry>
188            <entry>Value</entry>
189            <entry>Applicable to</entry>
190            <entry>Explanation</entry>
191          </row>
192        </thead>
193        <tbody>
194          <row>
195            <entry><constant>GPT_FLAG_READ_ONLY</constant></entry>
196            <entry>0x1000000000000000</entry>
197            <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
198            <entry>Partition is mounted read-only</entry>
199          </row>
200
201          <row>
202            <entry><constant>GPT_FLAG_NO_AUTO</constant></entry>
203            <entry>0x8000000000000000</entry>
204            <entry><filename>/</filename>, <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename>, <filename>/var/tmp/</filename>, Extended Boot Loader Partition</entry>
205            <entry>Partition is not mounted automatically</entry>
206          </row>
207
208          <row>
209            <entry><constant>GPT_FLAG_NO_BLOCK_IO_PROTOCOL</constant></entry>
210            <entry>0x0000000000000002</entry>
211            <entry>EFI System Partition (ESP)</entry>
212            <entry>Partition is not mounted automatically</entry>
213          </row>
214        </tbody>
215      </tgroup>
216    </table>
217
218    <para>The <filename>/home/</filename>, <filename>/srv/</filename>, <filename>/var/</filename> and
219    <filename>/var/tmp/</filename> partitions may be encrypted in LUKS format. In this case, a device mapper
220    device is set up under the names <filename>/dev/mapper/home</filename>,
221    <filename>/dev/mapper/srv</filename>, <filename>/dev/mapper/var</filename> and
222    <filename>/dev/mapper/tmp</filename>. Note that this might create conflicts if the same partition is
223    listed in <filename>/etc/crypttab</filename> with a different device mapper device name.</para>
224
225    <para>When systemd is running in the initrd the <filename>/</filename> partition may be encrypted in LUKS
226      format as well. In this case, a device mapper device is set up under the name <filename>/dev/mapper/root</filename>,
227      and a <filename>sysroot.mount</filename> is set up that mounts the device under <filename>/sysroot</filename>.
228      For more information, see <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
229    </para>
230
231    <para>The root partition can be specified by symlinking <filename>/run/systemd/volatile-root</filename>
232    to <filename>/dev/block/$major:$minor</filename>. This is especially useful if the root mount has been
233    replaced by some form of volatile file system (overlayfs).
234    </para>
235
236    <para>Mount and automount units for the EFI System Partition (ESP) are generated on EFI systems. The ESP
237    is mounted to <filename>/boot/</filename> (except if an Extended Boot Loader partition exists, see
238    below), unless a mount point directory <filename>/efi/</filename> exists, in which case it is mounted
239    there. Since this generator creates an automount unit, the mount will only be activated on-demand, when
240    accessed. On systems where <filename>/boot/</filename> (or <filename>/efi/</filename> if it exists) is an
241    explicitly configured mount (for example, listed in <citerefentry
242    project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>) or where
243    the <filename>/boot/</filename> (or <filename>/efi/</filename>) mount point is non-empty, no mount units
244    are generated.</para>
245
246    <para>If the disk contains an Extended Boot Loader partition, as defined in the <ulink
247    url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, it is made
248    available at <filename>/boot/</filename> (by means of an automount point, similar to the ESP, see
249    above). If both an EFI System Partition and an Extended Boot Loader partition exist the latter is
250    preferably mounted to <filename>/boot/</filename>. Make sure to create both <filename>/efi/</filename>
251    and <filename>/boot/</filename> to ensure both partitions are mounted.</para>
252
253    <para>When using this generator in conjunction with btrfs file
254    systems, make sure to set the correct default subvolumes on them,
255    using <command>btrfs subvolume set-default</command>.</para>
256
257    <para><filename>systemd-gpt-auto-generator</filename> implements
258    <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
259  </refsect1>
260
261  <refsect1>
262    <title>Kernel Command Line</title>
263
264    <para><filename>systemd-gpt-auto-generator</filename> understands the following kernel command line
265    parameters:</para>
266
267    <variablelist class='kernel-commandline-options'>
268
269      <varlistentry>
270        <term><varname>systemd.gpt_auto</varname></term>
271        <term><varname>rd.systemd.gpt_auto</varname></term>
272
273        <listitem><para>Those options take an optional boolean argument, and default to yes.
274        The generator is enabled by default, and a negative value may be used to disable it.
275        </para></listitem>
276      </varlistentry>
277
278      <varlistentry>
279        <term><varname>root=</varname></term>
280
281        <listitem><para>When used with the special value <literal>gpt-auto</literal>, automatic discovery of
282        the root partition based on the GPT partition type is enabled.  Any other value disables this
283        generator.</para></listitem>
284      </varlistentry>
285
286      <varlistentry>
287        <term><varname>rw</varname></term>
288        <term><varname>ro</varname></term>
289
290        <listitem><para>Mount the root partition read-write or read-only <emphasis>initially</emphasis>.</para>
291
292        <para>Note that unlike most kernel command line options these settings do not override configuration
293        in the file system, and the file system may be remounted later. See
294        <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
295        </para></listitem>
296      </varlistentry>
297    </variablelist>
298  </refsect1>
299
300  <refsect1>
301    <title>See Also</title>
302    <para>
303      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
304      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
305      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
306      <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
307      <citerefentry><refentrytitle>systemd-cryptsetup@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
308      <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
309      <citerefentry project='die-net'><refentrytitle>cryptsetup</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
310      <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
311      <citerefentry project='man-pages'><refentrytitle>btrfs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
312    </para>
313  </refsect1>
314
315</refentry>
316