<?xml version="1.0"?>
<!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-<!--
- This file is part of systemd.
-
- Copyright 2012 Lennart Poettering
-
- systemd is free software; you can redistribute it and/or modify it
- under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 2.1 of the License, or
- (at your option) any later version.
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- systemd is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- Lesser General Public License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with systemd; If not, see <http://www.gnu.org/licenses/>.
--->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="systemd-fstab-generator">
<refentryinfo>
<title>systemd-fstab-generator</title>
<productname>systemd</productname>
-
- <authorgroup>
- <author>
- <contrib>Developer</contrib>
- <firstname>Lennart</firstname>
- <surname>Poettering</surname>
- <email>lennart@poettering.net</email>
- </author>
- </authorgroup>
</refentryinfo>
<refmeta>
for more information about special <filename>/etc/fstab</filename>
mount options this generator understands.</para>
+ <para>One special topic is handling of symbolic links. Historical init
+ implementations supported symlinks in <filename>/etc/fstab</filename>.
+ Because mount units will refuse mounts where the target is a symbolic link,
+ this generator will resolve any symlinks as far as possible when processing
+ <filename>/etc/fstab</filename> in order to enhance backwards compatibility.
+ If a symlink target does not exist at the time that this generator runs, it
+ is assumed that the symlink target is the final target of the mount.</para>
+
<para><filename>systemd-fstab-generator</filename> implements
<citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
</refsect1>
<listitem><para>Takes a boolean argument. Defaults to
<literal>yes</literal>. If <literal>no</literal>, causes the
- generator to ignore any mounts or swaps configured in
+ generator to ignore any mounts or swap devices configured in
<filename>/etc/fstab</filename>. <varname>rd.fstab=</varname>
- is honored only by initial RAM disk (initrd) while
+ is honored only by the initial RAM disk (initrd) while
<varname>fstab=</varname> is honored by both the main system
and the initrd.</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>root=</varname></term>
initrd. <varname>root=</varname> is honored by the
initrd.</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>rootfstype=</varname></term>
passed to the mount command. <varname>rootfstype=</varname> is
honored by the initrd.</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>rootflags=</varname></term>
- <listitem><para>Takes the root filesystem mount options to
- use. <varname>rootflags=</varname> is honored by the
- initrd.</para></listitem>
+ <listitem><para>Takes the root filesystem mount options to use. <varname>rootflags=</varname> is
+ honored by the initrd.</para>
+
+ <para>Note that unlike most kernel command line options this setting does not override settings made
+ in configuration files (specifically: the mount option string in
+ <filename>/etc/fstab</filename>). See
+ <citerefentry><refentrytitle>systemd-remount-fs.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>mount.usr=</varname></term>
<para><varname>mount.usr=</varname> is honored by the initrd.
</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>mount.usrfstype=</varname></term>
<para><varname>mount.usrfstype=</varname> is honored by the
initrd.</para></listitem>
</varlistentry>
+
<varlistentry>
<term><varname>mount.usrflags=</varname></term>
<para><varname>mount.usrflags=</varname> is honored by the
initrd.</para></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.volatile=</varname></term>
+
+ <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
+ special value <option>state</option>.</para>
+
+ <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
+ normal mode.</para>
+
+ <para>If true the generator ensures
+ <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ is run as part of the initial RAM disk ("initrd"). This service changes the mount table before transitioning to
+ the host system, so that a volatile memory file system (<literal>tmpfs</literal>) is used as root directory,
+ with only <filename>/usr</filename> mounted into it from the configured root file system, in read-only
+ mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
+ lost at shutdown, as <filename>/etc</filename> and <filename>/var</filename> will be served from the (initially
+ unpopulated) volatile memory file system.</para>
+
+ <para>If set to <option>state</option> the generator will leave the root directory mount point unaltered,
+ however will mount a <literal>tmpfs</literal> file system to <filename>/var</filename>. In this mode the normal
+ system configuration (i.e. the contents of <literal>/etc</literal>) is in effect (and may be modified during
+ system runtime), however the system state (i.e. the contents of <literal>/var</literal>) is reset at boot and
+ lost at shutdown.</para>
+
+ <para>If this setting is set to <literal>overlay</literal> the root file system is set up as
+ <literal>overlayfs</literal> mount combining the read-only root directory with a writable
+ <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified
+ nonetheless with all changes being lost at reboot.</para>
+
+ <para>Note that in none of these modes the root directory, <filename>/etc</filename>, <filename>/var</filename>
+ or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
+ that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para>
+
+ <para>Note that with the exception of <literal>overlay</literal> mode, enabling this setting will only work
+ correctly on operating systems that can boot up with only <filename>/usr</filename> mounted, and are able to
+ automatically populate <filename>/etc</filename>, and also <filename>/var</filename> in case of
+ <literal>systemd.volatile=yes</literal>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>systemd.swap</varname></term>
+
+ <listitem><para>Takes a boolean argument or enables the option if specified
+ without an argument. If disabled, causes the generator to ignore
+ any swap devices configured in <filename>/etc/fstab</filename>.
+ Defaults to enabled.</para></listitem>
+ </varlistentry>
</variablelist>
</refsect1>
<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
projects / thirdparty / systemd.git / blobdiff