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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-or-later -->
6<refentry id="systemd-fstab-generator">
7
8  <refentryinfo>
9    <title>systemd-fstab-generator</title>
10    <productname>systemd</productname>
11  </refentryinfo>
12
13  <refmeta>
14    <refentrytitle>systemd-fstab-generator</refentrytitle>
15    <manvolnum>8</manvolnum>
16  </refmeta>
17
18  <refnamediv>
19    <refname>systemd-fstab-generator</refname>
20    <refpurpose>Unit generator for /etc/fstab</refpurpose>
21  </refnamediv>
22
23  <refsynopsisdiv>
24    <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator</filename></para>
25  </refsynopsisdiv>
26
27  <refsect1>
28    <title>Description</title>
29
30    <para><filename>systemd-fstab-generator</filename> is a generator
31    that translates <filename>/etc/fstab</filename> (see
32    <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
33    for details) into native systemd units early at boot and when
34    configuration of the system manager is reloaded. This will
35    instantiate mount and swap units as necessary.</para>
36
37    <para>The <varname>passno</varname> field is treated like a simple
38    boolean, and the ordering information is discarded. However, if
39    the root file system is checked, it is checked before all the
40    other file systems.</para>
41
42    <para>See
43    <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
44    and
45    <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
46    for more information about special <filename>/etc/fstab</filename>
47    mount options this generator understands.</para>
48
49    <para>One special topic is handling of symbolic links.  Historical init
50    implementations supported symlinks in <filename>/etc/fstab</filename>.
51    Because mount units will refuse mounts where the target is a symbolic link,
52    this generator will resolve any symlinks as far as possible when processing
53    <filename>/etc/fstab</filename> in order to enhance backwards compatibility.
54    If a symlink target does not exist at the time that this generator runs, it
55    is assumed that the symlink target is the final target of the mount.</para>
56
57    <para><filename>systemd-fstab-generator</filename> implements
58    <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
59  </refsect1>
60
61  <refsect1>
62    <title>Kernel Command Line</title>
63
64    <para><filename>systemd-fstab-generator</filename> understands the
65    following kernel command line parameters:</para>
66
67    <variablelist class='kernel-commandline-options'>
68
69      <varlistentry>
70        <term><varname>fstab=</varname></term>
71        <term><varname>rd.fstab=</varname></term>
72
73        <listitem><para>Takes a boolean argument. Defaults to
74        <literal>yes</literal>. If <literal>no</literal>, causes the
75        generator to ignore any mounts or swap devices configured in
76        <filename>/etc/fstab</filename>. <varname>rd.fstab=</varname>
77        is honored only by the initial RAM disk (initrd) while
78        <varname>fstab=</varname> is honored by both the main system
79        and the initrd.</para></listitem>
80      </varlistentry>
81
82      <varlistentry>
83        <term><varname>root=</varname></term>
84
85        <listitem><para>Configures the operating system's root filesystem to mount when running in the
86        initrd. This accepts a device node path (usually <filename>/dev/disk/by-uuid/…</filename> or
87        <filename>/dev/disk/by-label/…</filename> or similar), or the special values <literal>gpt-auto</literal>
88        and <literal>tmpfs</literal>.</para>
89
90        <para>Use <literal>gpt-auto</literal> to explicitly request automatic root file system discovery via
91        <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
92
93        <para>Use <literal>tmpfs</literal> in order to mount a <citerefentry
94        project='man-pages'><refentrytitle>tmpfs</refentrytitle><manvolnum>5</manvolnum></citerefentry> file
95        system as root file system of the OS. This is useful in combination with
96        <varname>mount.usr=</varname> (see below) in order to combine a volatile root file system with a
97        separate, immutable <filename>/usr/</filename> file system. Also see
98        <varname>systemd.volatile=</varname> below.</para></listitem>
99      </varlistentry>
100
101      <varlistentry>
102        <term><varname>rootfstype=</varname></term>
103
104        <listitem><para>Takes the root filesystem type that will be
105        passed to the mount command. <varname>rootfstype=</varname> is
106        honored by the initrd.</para></listitem>
107      </varlistentry>
108
109      <varlistentry>
110        <term><varname>rootflags=</varname></term>
111
112        <listitem><para>Takes the root filesystem mount options to use. <varname>rootflags=</varname> is
113        honored by the initrd.</para>
114
115        <para>Note that unlike most kernel command line options this setting does not override settings made
116        in configuration files (specifically: the mount option string in
117        <filename>/etc/fstab</filename>). See
118        <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem>
119      </varlistentry>
120
121      <varlistentry>
122        <term><varname>mount.usr=</varname></term>
123
124        <listitem><para>Takes the <filename>/usr/</filename> filesystem
125        to be mounted by the initrd. If
126        <varname>mount.usrfstype=</varname> or
127        <varname>mount.usrflags=</varname> is set, then
128        <varname>mount.usr=</varname> will default to the value set in
129        <varname>root=</varname>.</para>
130
131        <para>Otherwise, this parameter defaults to the
132        <filename>/usr/</filename> entry found in
133        <filename>/etc/fstab</filename> on the root filesystem.</para>
134
135        <para><varname>mount.usr=</varname> is honored by the initrd.
136        </para></listitem>
137      </varlistentry>
138
139      <varlistentry>
140        <term><varname>mount.usrfstype=</varname></term>
141
142        <listitem><para>Takes the <filename>/usr/</filename> filesystem
143        type that will be passed to the mount command. If
144        <varname>mount.usr=</varname> or
145        <varname>mount.usrflags=</varname> is set, then
146        <varname>mount.usrfstype=</varname> will default to the value
147        set in <varname>rootfstype=</varname>.</para>
148
149        <para>Otherwise, this value will be read from the
150        <filename>/usr/</filename> entry in
151        <filename>/etc/fstab</filename> on the root filesystem.</para>
152
153        <para><varname>mount.usrfstype=</varname> is honored by the
154        initrd.</para></listitem>
155      </varlistentry>
156
157      <varlistentry>
158        <term><varname>mount.usrflags=</varname></term>
159
160        <listitem><para>Takes the <filename>/usr/</filename> filesystem
161        mount options to use. If <varname>mount.usr=</varname> or
162        <varname>mount.usrfstype=</varname> is set, then
163        <varname>mount.usrflags=</varname> will default to the value
164        set in <varname>rootflags=</varname>.</para>
165
166        <para>Otherwise, this value will be read from the
167        <filename>/usr/</filename> entry in
168        <filename>/etc/fstab</filename> on the root filesystem.</para>
169
170        <para><varname>mount.usrflags=</varname> is honored by the
171        initrd.</para></listitem>
172      </varlistentry>
173
174      <varlistentry>
175        <term><varname>roothash=</varname></term>
176        <term><varname>usrhash=</varname></term>
177
178        <listitem><para>These options are primarily read by
179        <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>. When
180        set this indicates that the root file system (or <filename>/usr/</filename>) shall be mounted from
181        Verity volumes with the specified hashes. If these kernel command line options are set the root (or
182        <filename>/usr/</filename>) file system is thus mounted from a device mapper volume
183        <filename>/dev/mapper/root</filename> (or <filename>/dev/mapper/usr</filename>).</para></listitem>
184      </varlistentry>
185
186      <varlistentry>
187        <term><varname>systemd.volatile=</varname></term>
188
189        <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
190        special value <option>state</option>.</para>
191
192        <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
193        normal mode.</para>
194
195        <para>If true the generator ensures
196        <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
197        is run as part of the initial RAM disk ("initrd"). This service changes the mount table before transitioning to
198        the host system, so that a volatile memory file system (<literal>tmpfs</literal>) is used as root directory,
199        with only <filename>/usr/</filename> mounted into it from the configured root file system, in read-only
200        mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
201        lost at shutdown, as <filename>/etc/</filename> and <filename>/var/</filename> will be served from the (initially
202        unpopulated) volatile memory file system.</para>
203
204        <para>If set to <option>state</option> the generator will leave the root directory mount point unaltered,
205        however will mount a <literal>tmpfs</literal> file system to <filename>/var/</filename>. In this mode the normal
206        system configuration (i.e. the contents of <literal>/etc/</literal>) is in effect (and may be modified during
207        system runtime), however the system state (i.e. the contents of <literal>/var/</literal>) is reset at boot and
208        lost at shutdown.</para>
209
210        <para>If this setting is set to <literal>overlay</literal> the root file system is set up as
211        <literal>overlayfs</literal> mount combining the read-only root directory with a writable
212        <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified
213        nonetheless with all changes being lost at reboot.</para>
214
215        <para>Note that in none of these modes the root directory, <filename>/etc/</filename>, <filename>/var/</filename>
216        or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
217        that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para>
218
219        <para>Note that with the exception of <literal>overlay</literal> mode, enabling this setting will
220        only work correctly on operating systems that can boot up with only <filename>/usr/</filename>
221        mounted, and are able to automatically populate <filename>/etc/</filename>, and also
222        <filename>/var/</filename> in case of <literal>systemd.volatile=yes</literal>.</para>
223
224        <para>Also see <varname>root=tmpfs</varname> above, for a method to combine a
225        <literal>tmpfs</literal> file system with a regular <filename>/usr/</filename> file system (as
226        configured via <varname>mount.usr=</varname>). The main distinction between
227        <varname>systemd.volatile=yes</varname>, and <varname>root=tmpfs</varname> in combination
228        <varname>mount.usr=</varname> is that the former operates on top of a regular root file system and
229        temporarily obstructs the files and directories above its <filename>/usr/</filename> subdirectory,
230        while the latter does not hide any files, but simply mounts a unpopulated tmpfs as root file system
231        and combines it with a user picked <filename>/usr/</filename> file system.</para></listitem>
232      </varlistentry>
233
234      <varlistentry>
235        <term><varname>systemd.swap</varname></term>
236
237        <listitem><para>Takes a boolean argument or enables the option if specified
238        without an argument. If disabled, causes the generator to ignore
239        any swap devices configured in <filename>/etc/fstab</filename>.
240        Defaults to enabled.</para></listitem>
241      </varlistentry>
242    </variablelist>
243  </refsect1>
244
245  <refsect1>
246    <title>See Also</title>
247    <para>
248      <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
249      <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
250      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
251      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
252      <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
253      <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
254      <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
255    </para>
256  </refsect1>
257
258</refentry>
259