3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 SPDX-License-Identifier: LGPL-2.1+
7 This file is part of systemd.
9 Copyright 2012 Lennart Poettering
11 systemd is free software; you can redistribute it and/or modify it
12 under the terms of the GNU Lesser General Public License as published by
13 the Free Software Foundation; either version 2.1 of the License, or
14 (at your option) any later version.
16 systemd is distributed in the hope that it will be useful, but
17 WITHOUT ANY WARRANTY; without even the implied warranty of
18 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 Lesser General Public License for more details.
21 You should have received a copy of the GNU Lesser General Public License
22 along with systemd; If not, see <http://www.gnu.org/licenses/>.
24 <refentry id=
"systemd-fstab-generator">
27 <title>systemd-fstab-generator
</title>
28 <productname>systemd
</productname>
32 <contrib>Developer
</contrib>
33 <firstname>Lennart
</firstname>
34 <surname>Poettering
</surname>
35 <email>lennart@poettering.net
</email>
41 <refentrytitle>systemd-fstab-generator
</refentrytitle>
42 <manvolnum>8</manvolnum>
46 <refname>systemd-fstab-generator
</refname>
47 <refpurpose>Unit generator for /etc/fstab
</refpurpose>
51 <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator
</filename></para>
55 <title>Description
</title>
57 <para><filename>systemd-fstab-generator
</filename> is a generator
58 that translates
<filename>/etc/fstab
</filename> (see
59 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
60 for details) into native systemd units early at boot and when
61 configuration of the system manager is reloaded. This will
62 instantiate mount and swap units as necessary.
</para>
64 <para>The
<varname>passno
</varname> field is treated like a simple
65 boolean, and the ordering information is discarded. However, if
66 the root file system is checked, it is checked before all the
67 other file systems.
</para>
70 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
72 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
73 for more information about special
<filename>/etc/fstab
</filename>
74 mount options this generator understands.
</para>
76 <para>One special topic is handling of symbolic links. Historical init
77 implementations supported symlinks in
<filename>/etc/fstab
</filename>.
78 Because mount units will refuse mounts where the target is a symbolic link,
79 this generator will resolve any symlinks as far as possible when processing
80 <filename>/etc/fstab
</filename> in order to enhance backwards compatibility.
81 If a symlink target does not exist at the time that this generator runs, it
82 is assumed that the symlink target is the final target of the mount.
</para>
84 <para><filename>systemd-fstab-generator
</filename> implements
85 <citerefentry><refentrytitle>systemd.generator
</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
89 <title>Kernel Command Line
</title>
91 <para><filename>systemd-fstab-generator
</filename> understands the
92 following kernel command line parameters:
</para>
94 <variablelist class='kernel-commandline-options'
>
97 <term><varname>fstab=
</varname></term>
98 <term><varname>rd.fstab=
</varname></term>
100 <listitem><para>Takes a boolean argument. Defaults to
101 <literal>yes
</literal>. If
<literal>no
</literal>, causes the
102 generator to ignore any mounts or swap devices configured in
103 <filename>/etc/fstab
</filename>.
<varname>rd.fstab=
</varname>
104 is honored only by the initial RAM disk (initrd) while
105 <varname>fstab=
</varname> is honored by both the main system
106 and the initrd.
</para></listitem>
110 <term><varname>root=
</varname></term>
112 <listitem><para>Takes the root filesystem to mount in the
113 initrd.
<varname>root=
</varname> is honored by the
114 initrd.
</para></listitem>
118 <term><varname>rootfstype=
</varname></term>
120 <listitem><para>Takes the root filesystem type that will be
121 passed to the mount command.
<varname>rootfstype=
</varname> is
122 honored by the initrd.
</para></listitem>
126 <term><varname>rootflags=
</varname></term>
128 <listitem><para>Takes the root filesystem mount options to
129 use.
<varname>rootflags=
</varname> is honored by the
130 initrd.
</para></listitem>
134 <term><varname>mount.usr=
</varname></term>
136 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
137 to be mounted by the initrd. If
138 <varname>mount.usrfstype=
</varname> or
139 <varname>mount.usrflags=
</varname> is set, then
140 <varname>mount.usr=
</varname> will default to the value set in
141 <varname>root=
</varname>.
</para>
143 <para>Otherwise, this parameter defaults to the
144 <filename>/usr
</filename> entry found in
145 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
147 <para><varname>mount.usr=
</varname> is honored by the initrd.
152 <term><varname>mount.usrfstype=
</varname></term>
154 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
155 type that will be passed to the mount command. If
156 <varname>mount.usr=
</varname> or
157 <varname>mount.usrflags=
</varname> is set, then
158 <varname>mount.usrfstype=
</varname> will default to the value
159 set in
<varname>rootfstype=
</varname>.
</para>
161 <para>Otherwise, this value will be read from the
162 <filename>/usr
</filename> entry in
163 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
165 <para><varname>mount.usrfstype=
</varname> is honored by the
166 initrd.
</para></listitem>
170 <term><varname>mount.usrflags=
</varname></term>
172 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
173 mount options to use. If
<varname>mount.usr=
</varname> or
174 <varname>mount.usrfstype=
</varname> is set, then
175 <varname>mount.usrflags=
</varname> will default to the value
176 set in
<varname>rootflags=
</varname>.
</para>
178 <para>Otherwise, this value will be read from the
179 <filename>/usr
</filename> entry in
180 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
182 <para><varname>mount.usrflags=
</varname> is honored by the
183 initrd.
</para></listitem>
187 <term><varname>systemd.volatile=
</varname></term>
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>
192 <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
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>
204 <para>If set to
<option>state
</option> the generator will leave the root
205 directory mount point unaltered, however will mount a
<literal>tmpfs
</literal> file system to
206 <filename>/var
</filename>. In this mode the normal system configuration (i.e. the contents of
207 <literal>/etc
</literal>) is in effect (and may be modified during system runtime), however the system state
208 (i.e. the contents of
<literal>/var
</literal>) is reset at boot and lost at shutdown.
</para>
210 <para>Note that in none of these modes the root directory,
<filename>/etc
</filename>,
<filename>/var
</filename>
211 or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
212 that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.
</para>
214 <para>Note that enabling this setting will only work correctly on operating systems that can boot up with only
215 <filename>/usr
</filename> mounted, and are able to automatically populate
<filename>/etc
</filename>, and also
216 <filename>/var
</filename> in case of
<literal>systemd.volatile=yes
</literal>.
</para></listitem>
222 <title>See Also
</title>
224 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
225 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
226 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
227 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
228 <citerefentry><refentrytitle>systemd-cryptsetup-generator
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
229 <citerefentry><refentrytitle>kernel-command-line
</refentrytitle><manvolnum>7</manvolnum></citerefentry>