3 <!DOCTYPE refentry PUBLIC
"-//OASIS//DTD DocBook XML V4.5//EN"
4 "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
5 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
6 <refentry id=
"systemd-fstab-generator">
9 <title>systemd-fstab-generator
</title>
10 <productname>systemd
</productname>
14 <refentrytitle>systemd-fstab-generator
</refentrytitle>
15 <manvolnum>8</manvolnum>
19 <refname>systemd-fstab-generator
</refname>
20 <refpurpose>Unit generator for /etc/fstab
</refpurpose>
24 <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator
</filename></para>
28 <title>Description
</title>
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>
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>
43 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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>
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>
57 <para><filename>systemd-fstab-generator
</filename> implements
58 <citerefentry><refentrytitle>systemd.generator
</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
</para>
62 <title>Kernel Command Line
</title>
64 <para><filename>systemd-fstab-generator
</filename> understands the
65 following kernel command line parameters:
</para>
67 <variablelist class='kernel-commandline-options'
>
70 <term><varname>fstab=
</varname></term>
71 <term><varname>rd.fstab=
</varname></term>
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>
83 <term><varname>root=
</varname></term>
85 <listitem><para>Takes the root filesystem to mount in the
86 initrd.
<varname>root=
</varname> is honored by the
87 initrd.
</para></listitem>
91 <term><varname>rootfstype=
</varname></term>
93 <listitem><para>Takes the root filesystem type that will be
94 passed to the mount command.
<varname>rootfstype=
</varname> is
95 honored by the initrd.
</para></listitem>
99 <term><varname>rootflags=
</varname></term>
101 <listitem><para>Takes the root filesystem mount options to
102 use.
<varname>rootflags=
</varname> is honored by the
103 initrd.
</para></listitem>
107 <term><varname>mount.usr=
</varname></term>
109 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
110 to be mounted by the initrd. If
111 <varname>mount.usrfstype=
</varname> or
112 <varname>mount.usrflags=
</varname> is set, then
113 <varname>mount.usr=
</varname> will default to the value set in
114 <varname>root=
</varname>.
</para>
116 <para>Otherwise, this parameter defaults to the
117 <filename>/usr
</filename> entry found in
118 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
120 <para><varname>mount.usr=
</varname> is honored by the initrd.
125 <term><varname>mount.usrfstype=
</varname></term>
127 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
128 type that will be passed to the mount command. If
129 <varname>mount.usr=
</varname> or
130 <varname>mount.usrflags=
</varname> is set, then
131 <varname>mount.usrfstype=
</varname> will default to the value
132 set in
<varname>rootfstype=
</varname>.
</para>
134 <para>Otherwise, this value will be read from the
135 <filename>/usr
</filename> entry in
136 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
138 <para><varname>mount.usrfstype=
</varname> is honored by the
139 initrd.
</para></listitem>
143 <term><varname>mount.usrflags=
</varname></term>
145 <listitem><para>Takes the
<filename>/usr
</filename> filesystem
146 mount options to use. If
<varname>mount.usr=
</varname> or
147 <varname>mount.usrfstype=
</varname> is set, then
148 <varname>mount.usrflags=
</varname> will default to the value
149 set in
<varname>rootflags=
</varname>.
</para>
151 <para>Otherwise, this value will be read from the
152 <filename>/usr
</filename> entry in
153 <filename>/etc/fstab
</filename> on the root filesystem.
</para>
155 <para><varname>mount.usrflags=
</varname> is honored by the
156 initrd.
</para></listitem>
160 <term><varname>systemd.volatile=
</varname></term>
162 <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
163 special value
<option>state
</option>.
</para>
165 <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
168 <para>If true the generator ensures
169 <citerefentry><refentrytitle>systemd-volatile-root.service
</refentrytitle><manvolnum>8</manvolnum></citerefentry>
170 is run as part of the initial RAM disk (
"initrd"). This service changes the mount table before transitioning to
171 the host system, so that a volatile memory file system (
<literal>tmpfs
</literal>) is used as root directory,
172 with only
<filename>/usr
</filename> mounted into it from the configured root file system, in read-only
173 mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
174 lost at shutdown, as
<filename>/etc
</filename> and
<filename>/var
</filename> will be served from the (initially
175 unpopulated) volatile memory file system.
</para>
177 <para>If set to
<option>state
</option> the generator will leave the root directory mount point unaltered,
178 however will mount a
<literal>tmpfs
</literal> file system to
<filename>/var
</filename>. In this mode the normal
179 system configuration (i.e. the contents of
<literal>/etc
</literal>) is in effect (and may be modified during
180 system runtime), however the system state (i.e. the contents of
<literal>/var
</literal>) is reset at boot and
181 lost at shutdown.
</para>
183 <para>If this setting is set to
<literal>overlay
</literal> the root file system is set up as
184 <literal>overlayfs
</literal> mount combining the read-only root directory with a writable
185 <literal>tmpfs
</literal>, so that no modifications are made to disk, but the file system may be modified
186 nonetheless with all changes being lost at reboot.
</para>
188 <para>Note that in none of these modes the root directory,
<filename>/etc
</filename>,
<filename>/var
</filename>
189 or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
190 that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.
</para>
192 <para>Note that with the exception of
<literal>overlay
</literal> mode, enabling this setting will only work
193 correctly on operating systems that can boot up with only
<filename>/usr
</filename> mounted, and are able to
194 automatically populate
<filename>/etc
</filename>, and also
<filename>/var
</filename> in case of
195 <literal>systemd.volatile=yes
</literal>.
</para></listitem>
201 <title>See Also
</title>
203 <citerefentry><refentrytitle>systemd
</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
204 <citerefentry project='man-pages'
><refentrytitle>fstab
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
205 <citerefentry><refentrytitle>systemd.mount
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
206 <citerefentry><refentrytitle>systemd.swap
</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
207 <citerefentry><refentrytitle>systemd-cryptsetup-generator
</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
208 <citerefentry><refentrytitle>kernel-command-line
</refentrytitle><manvolnum>7</manvolnum></citerefentry>