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 <refentry id=
"systemd-fstab-generator">
10 <title>systemd-fstab-generator
</title>
11 <productname>systemd
</productname>
15 <refentrytitle>systemd-fstab-generator
</refentrytitle>
16 <manvolnum>8</manvolnum>
20 <refname>systemd-fstab-generator
</refname>
21 <refpurpose>Unit generator for /etc/fstab
</refpurpose>
25 <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator
</filename></para>
29 <title>Description
</title>
31 <para><filename>systemd-fstab-generator
</filename> is a generator
32 that translates
<filename>/etc/fstab
</filename> (see
33 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
34 for details) into native systemd units early at boot and when
35 configuration of the system manager is reloaded. This will
36 instantiate mount and swap units as necessary.
</para>
38 <para>The
<varname>passno
</varname> field is treated like a simple
39 boolean, and the ordering information is discarded. However, if
40 the root file system is checked, it is checked before all the
41 other file systems.
</para>
44 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
46 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
47 for more information about special
<filename>/etc/fstab
</filename>
48 mount options this generator understands.
</para>
50 <para>One special topic is handling of symbolic links. Historical init
51 implementations supported symlinks in
<filename>/etc/fstab
</filename>.
52 Because mount units will refuse mounts where the target is a symbolic link,
53 this generator will resolve any symlinks as far as possible when processing
54 <filename>/etc/fstab
</filename> in order to enhance backwards compatibility.
55 If a symlink target does not exist at the time that this generator runs, it
56 is assumed that the symlink target is the final target of the mount.
</para>
58 <para><filename>systemd-fstab-generator
</filename> implements
59 <citerefentry><refentrytitle>systemd.generator
</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
63 <title>Kernel Command Line
</title>
65 <para><filename>systemd-fstab-generator
</filename> understands the
66 following kernel command line parameters:
</para>
68 <variablelist class='kernel-commandline-options'
>
71 <term><varname>fstab=
</varname></term>
72 <term><varname>rd.fstab=
</varname></term>
74 <listitem><para>Takes a boolean argument. Defaults to
75 <literal>yes
</literal>. If
<literal>no
</literal>, causes the
76 generator to ignore any mounts or swap devices configured in
77 <filename>/etc/fstab
</filename>.
<varname>rd.fstab=
</varname>
78 is honored only by the initial RAM disk (initrd) while
79 <varname>fstab=
</varname> is honored by both the main system
80 and the initrd.
</para></listitem>
84 <term><varname>root=
</varname></term>
86 <listitem><para>Takes the root filesystem to mount in the
87 initrd.
<varname>root=
</varname> is honored by the
88 initrd.
</para></listitem>
92 <term><varname>rootfstype=
</varname></term>
94 <listitem><para>Takes the root filesystem type that will be
95 passed to the mount command.
<varname>rootfstype=
</varname> is
96 honored by the initrd.
</para></listitem>
100 <term><varname>rootflags=
</varname></term>
102 <listitem><para>Takes the root filesystem mount options to
103 use.
<varname>rootflags=
</varname> is honored by the
104 initrd.
</para></listitem>
108 <term><varname>mount.usr=
</varname></term>
110 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
111 to be mounted by the initrd. If
112 <varname>mount.usrfstype=
</varname> or
113 <varname>mount.usrflags=
</varname> is set, then
114 <varname>mount.usr=
</varname> will default to the value set in
115 <varname>root=
</varname>.
</para>
117 <para>Otherwise, this parameter defaults to the
118 <filename>/usr
</filename> entry found in
119 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
121 <para><varname>mount.usr=
</varname> is honored by the initrd.
126 <term><varname>mount.usrfstype=
</varname></term>
128 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
129 type that will be passed to the mount command. If
130 <varname>mount.usr=
</varname> or
131 <varname>mount.usrflags=
</varname> is set, then
132 <varname>mount.usrfstype=
</varname> will default to the value
133 set in
<varname>rootfstype=
</varname>.
</para>
135 <para>Otherwise, this value will be read from the
136 <filename>/usr
</filename> entry in
137 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
139 <para><varname>mount.usrfstype=
</varname> is honored by the
140 initrd.
</para></listitem>
144 <term><varname>mount.usrflags=
</varname></term>
146 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
147 mount options to use. If
<varname>mount.usr=
</varname> or
148 <varname>mount.usrfstype=
</varname> is set, then
149 <varname>mount.usrflags=
</varname> will default to the value
150 set in
<varname>rootflags=
</varname>.
</para>
152 <para>Otherwise, this value will be read from the
153 <filename>/usr
</filename> entry in
154 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
156 <para><varname>mount.usrflags=
</varname> is honored by the
157 initrd.
</para></listitem>
161 <term><varname>systemd.volatile=
</varname></term>
163 <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
164 special value
<option>state
</option>.
</para>
166 <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
169 <para>If true the generator ensures
170 <citerefentry><refentrytitle>systemd-volatile-root.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
171 is run as part of the initial RAM disk (
"initrd"). This service changes the mount table before transitioning to
172 the host system, so that a volatile memory file system (
<literal>tmpfs
</literal>) is used as root directory,
173 with only
<filename>/usr
</filename> mounted into it from the configured root file system, in read-only
174 mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
175 lost at shutdown, as
<filename>/etc
</filename> and
<filename>/var
</filename> will be served from the (initially
176 unpopulated) volatile memory file system.
</para>
178 <para>If set to
<option>state
</option> the generator will leave the root
179 directory mount point unaltered, however will mount a
<literal>tmpfs
</literal> file system to
180 <filename>/var
</filename>. In this mode the normal system configuration (i.e. the contents of
181 <literal>/etc
</literal>) is in effect (and may be modified during system runtime), however the system state
182 (i.e. the contents of
<literal>/var
</literal>) is reset at boot and lost at shutdown.
</para>
184 <para>Note that in none of these modes the root directory,
<filename>/etc
</filename>,
<filename>/var
</filename>
185 or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
186 that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.
</para>
188 <para>Note that enabling this setting will only work correctly on operating systems that can boot up with only
189 <filename>/usr
</filename> mounted, and are able to automatically populate
<filename>/etc
</filename>, and also
190 <filename>/var
</filename> in case of
<literal>systemd.volatile=yes
</literal>.
</para></listitem>
196 <title>See Also
</title>
198 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
199 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
200 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
201 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
202 <citerefentry><refentrytitle>systemd-cryptsetup-generator
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
203 <citerefentry><refentrytitle>kernel-command-line
</refentrytitle><manvolnum>7</manvolnum></citerefentry>