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<?xml version="1.0"?>
<!--*-nxml-*-->
<!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-or-later -->
<refentry id="systemd-fstab-generator">
<refentryinfo>
<title>systemd-fstab-generator</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-fstab-generator</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-fstab-generator</refname>
<refpurpose>Unit generator for /etc/fstab</refpurpose>
</refnamediv>
<refsynopsisdiv>
<para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator</filename></para>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-fstab-generator</filename> is a generator
that translates <filename>/etc/fstab</filename> (see
<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
for details) into native systemd units early at boot and when
configuration of the system manager is reloaded. This will
instantiate mount and swap units as necessary.</para>
<para>The <varname>passno</varname> field is treated like a simple
boolean, and the ordering information is discarded. However, if
the root file system is checked, it is checked before all the
other file systems.</para>
<para>See
<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
and
<citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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>
<refsect1>
<title>Kernel Command Line</title>
<para><filename>systemd-fstab-generator</filename> understands the
following kernel command line parameters:</para>
<variablelist class='kernel-commandline-options'>
<varlistentry>
<term><varname>fstab=</varname></term>
<term><varname>rd.fstab=</varname></term>
<listitem><para>Takes a boolean argument. Defaults to <literal>yes</literal>. If
<literal>no</literal>, causes the generator to ignore any mounts or swap devices configured in
<filename>/etc/fstab</filename>. <varname>rd.fstab=</varname> is honored only in the initrd, while
<varname>fstab=</varname> is honored by both the main system and the initrd.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>root=</varname></term>
<listitem><para>Configures the operating system's root filesystem to mount when running in the
initrd. This accepts a device node path (usually <filename>/dev/disk/by-uuid/…</filename> or
<filename>/dev/disk/by-label/…</filename> or similar), or the special values <literal>gpt-auto</literal>
and <literal>tmpfs</literal>.</para>
<para>Use <literal>gpt-auto</literal> to explicitly request automatic root file system discovery via
<citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
<para>Use <literal>tmpfs</literal> in order to mount a <citerefentry
project='man-pages'><refentrytitle>tmpfs</refentrytitle><manvolnum>5</manvolnum></citerefentry> file
system as root file system of the OS. This is useful in combination with
<varname>mount.usr=</varname> (see below) in order to combine a volatile root file system with a
separate, immutable <filename>/usr/</filename> file system. Also see
<varname>systemd.volatile=</varname> below.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>rootfstype=</varname></term>
<listitem><para>Takes the root filesystem type that will be
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>
<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>
<listitem><para>Takes the <filename>/usr/</filename> filesystem
to be mounted by the initrd. If
<varname>mount.usrfstype=</varname> or
<varname>mount.usrflags=</varname> is set, then
<varname>mount.usr=</varname> will default to the value set in
<varname>root=</varname>.</para>
<para>Otherwise, this parameter defaults to the
<filename>/usr/</filename> entry found in
<filename>/etc/fstab</filename> on the root filesystem.</para>
<para><varname>mount.usr=</varname> is honored by the initrd.
</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>mount.usrfstype=</varname></term>
<listitem><para>Takes the <filename>/usr/</filename> filesystem
type that will be passed to the mount command. If
<varname>mount.usr=</varname> or
<varname>mount.usrflags=</varname> is set, then
<varname>mount.usrfstype=</varname> will default to the value
set in <varname>rootfstype=</varname>.</para>
<para>Otherwise, this value will be read from the
<filename>/usr/</filename> entry in
<filename>/etc/fstab</filename> on the root filesystem.</para>
<para><varname>mount.usrfstype=</varname> is honored by the
initrd.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>mount.usrflags=</varname></term>
<listitem><para>Takes the <filename>/usr/</filename> filesystem
mount options to use. If <varname>mount.usr=</varname> or
<varname>mount.usrfstype=</varname> is set, then
<varname>mount.usrflags=</varname> will default to the value
set in <varname>rootflags=</varname>.</para>
<para>Otherwise, this value will be read from the
<filename>/usr/</filename> entry in
<filename>/etc/fstab</filename> on the root filesystem.</para>
<para><varname>mount.usrflags=</varname> is honored by the
initrd.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>roothash=</varname></term>
<term><varname>usrhash=</varname></term>
<listitem><para>These options are primarily read by
<citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>. When
set this indicates that the root file system (or <filename>/usr/</filename>) shall be mounted from
Verity volumes with the specified hashes. If these kernel command line options are set the root (or
<filename>/usr/</filename>) file system is thus mounted from a device mapper volume
<filename>/dev/mapper/root</filename> (or <filename>/dev/mapper/usr</filename>).</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 in the 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>
<para>Also see <varname>root=tmpfs</varname> above, for a method to combine a
<literal>tmpfs</literal> file system with a regular <filename>/usr/</filename> file system (as
configured via <varname>mount.usr=</varname>). The main distinction between
<varname>systemd.volatile=yes</varname>, and <varname>root=tmpfs</varname> in combination
<varname>mount.usr=</varname> is that the former operates on top of a regular root file system and
temporarily obstructs the files and directories above its <filename>/usr/</filename> subdirectory,
while the latter does not hide any files, but simply mounts a unpopulated tmpfs as root file system
and combines it with a user picked <filename>/usr/</filename> file system.</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>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<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-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
<ulink url="https://systemd.io/ENVIRONMENT/">Known Environment Variables</ulink>
</para>
</refsect1>
</refentry>
|
