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diff --git a/man/systemd-fstab-generator.xml b/man/systemd-fstab-generator.xml new file mode 100644 index 0000000..29d9bd4 --- /dev/null +++ b/man/systemd-fstab-generator.xml @@ -0,0 +1,255 @@ +<?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> |