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-<!--
- SPDX-License-Identifier: LGPL-2.1+
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+<!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>
<varlistentry>
<term><varname>root=</varname></term>
- <listitem><para>Takes the root filesystem to mount in the
- initrd. <varname>root=</varname> is honored by the
- initrd.</para></listitem>
+ <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>
<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>
- <listitem><para>Takes the <filename>/usr</filename> filesystem
+ <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>root=</varname>.</para>
<para>Otherwise, this parameter defaults to the
- <filename>/usr</filename> entry found in
+ <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.
<varlistentry>
<term><varname>mount.usrfstype=</varname></term>
- <listitem><para>Takes the <filename>/usr</filename> filesystem
+ <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
set in <varname>rootfstype=</varname>.</para>
<para>Otherwise, this value will be read from the
- <filename>/usr</filename> entry in
+ <filename>/usr/</filename> entry in
<filename>/etc/fstab</filename> on the root filesystem.</para>
<para><varname>mount.usrfstype=</varname> is honored by the
<varlistentry>
<term><varname>mount.usrflags=</varname></term>
- <listitem><para>Takes the <filename>/usr</filename> filesystem
+ <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>/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>
<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
+ 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
+ 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 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>
+ <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 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>
+ <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>
<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>
</para>
</refsect1>
projects / thirdparty / systemd.git / blobdiff