man/systemd-fstab-generator.xml

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   4 <!--
   5   SPDX-License-Identifier: LGPL-2.1+
   6
   7   This file is part of systemd.
   8
   9   Copyright 2012 Lennart Poettering
  10 -->
  11 <refentry id="systemd-fstab-generator">
  12
  13   <refentryinfo>
  14     <title>systemd-fstab-generator</title>
  15     <productname>systemd</productname>
  16
  17     <authorgroup>
  18       <author>
  19         <contrib>Developer</contrib>
  20         <firstname>Lennart</firstname>
  21         <surname>Poettering</surname>
  22         <email>lennart@poettering.net</email>
  23       </author>
  24     </authorgroup>
  25   </refentryinfo>
  26
  27   <refmeta>
  28     <refentrytitle>systemd-fstab-generator</refentrytitle>
  29     <manvolnum>8</manvolnum>
  30   </refmeta>
  31
  32   <refnamediv>
  33     <refname>systemd-fstab-generator</refname>
  34     <refpurpose>Unit generator for /etc/fstab</refpurpose>
  35   </refnamediv>
  36
  37   <refsynopsisdiv>
  38     <para><filename>/usr/lib/systemd/system-generators/systemd-fstab-generator</filename></para>
  39   </refsynopsisdiv>
  40
  41   <refsect1>
  42     <title>Description</title>
  43
  44     <para><filename>systemd-fstab-generator</filename> is a generator
  45     that translates <filename>/etc/fstab</filename> (see
  46     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  47     for details) into native systemd units early at boot and when
  48     configuration of the system manager is reloaded. This will
  49     instantiate mount and swap units as necessary.</para>
  50
  51     <para>The <varname>passno</varname> field is treated like a simple
  52     boolean, and the ordering information is discarded. However, if
  53     the root file system is checked, it is checked before all the
  54     other file systems.</para>
  55
  56     <para>See
  57     <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  58     and
  59     <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  60     for more information about special <filename>/etc/fstab</filename>
  61     mount options this generator understands.</para>
  62
  63     <para>One special topic is handling of symbolic links.  Historical init
  64     implementations supported symlinks in <filename>/etc/fstab</filename>.
  65     Because mount units will refuse mounts where the target is a symbolic link,
  66     this generator will resolve any symlinks as far as possible when processing
  67     <filename>/etc/fstab</filename> in order to enhance backwards compatibility.
  68     If a symlink target does not exist at the time that this generator runs, it
  69     is assumed that the symlink target is the final target of the mount.</para>
  70
  71     <para><filename>systemd-fstab-generator</filename> implements
  72     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
  73   </refsect1>
  74
  75   <refsect1>
  76     <title>Kernel Command Line</title>
  77
  78     <para><filename>systemd-fstab-generator</filename> understands the
  79     following kernel command line parameters:</para>
  80
  81     <variablelist class='kernel-commandline-options'>
  82
  83       <varlistentry>
  84         <term><varname>fstab=</varname></term>
  85         <term><varname>rd.fstab=</varname></term>
  86
  87         <listitem><para>Takes a boolean argument. Defaults to
  88         <literal>yes</literal>. If <literal>no</literal>, causes the
  89         generator to ignore any mounts or swap devices configured in
  90         <filename>/etc/fstab</filename>. <varname>rd.fstab=</varname>
  91         is honored only by the initial RAM disk (initrd) while
  92         <varname>fstab=</varname> is honored by both the main system
  93         and the initrd.</para></listitem>
  94       </varlistentry>
  95
  96       <varlistentry>
  97         <term><varname>root=</varname></term>
  98
  99         <listitem><para>Takes the root filesystem to mount in the
 100         initrd. <varname>root=</varname> is honored by the
 101         initrd.</para></listitem>
 102       </varlistentry>
 103
 104       <varlistentry>
 105         <term><varname>rootfstype=</varname></term>
 106
 107         <listitem><para>Takes the root filesystem type that will be
 108         passed to the mount command. <varname>rootfstype=</varname> is
 109         honored by the initrd.</para></listitem>
 110       </varlistentry>
 111
 112       <varlistentry>
 113         <term><varname>rootflags=</varname></term>
 114
 115         <listitem><para>Takes the root filesystem mount options to
 116         use. <varname>rootflags=</varname> is honored by the
 117         initrd.</para></listitem>
 118       </varlistentry>
 119
 120       <varlistentry>
 121         <term><varname>mount.usr=</varname></term>
 122
 123         <listitem><para>Takes the <filename>/usr</filename> filesystem
 124         to be mounted by the initrd. If
 125         <varname>mount.usrfstype=</varname> or
 126         <varname>mount.usrflags=</varname> is set, then
 127         <varname>mount.usr=</varname> will default to the value set in
 128         <varname>root=</varname>.</para>
 129
 130         <para>Otherwise, this parameter defaults to the
 131         <filename>/usr</filename> entry found in
 132         <filename>/etc/fstab</filename> on the root filesystem.</para>
 133
 134         <para><varname>mount.usr=</varname> is honored by the initrd.
 135         </para></listitem>
 136       </varlistentry>
 137
 138       <varlistentry>
 139         <term><varname>mount.usrfstype=</varname></term>
 140
 141         <listitem><para>Takes the <filename>/usr</filename> filesystem
 142         type that will be passed to the mount command. If
 143         <varname>mount.usr=</varname> or
 144         <varname>mount.usrflags=</varname> is set, then
 145         <varname>mount.usrfstype=</varname> will default to the value
 146         set in <varname>rootfstype=</varname>.</para>
 147
 148         <para>Otherwise, this value will be read from the
 149         <filename>/usr</filename> entry in
 150         <filename>/etc/fstab</filename> on the root filesystem.</para>
 151
 152         <para><varname>mount.usrfstype=</varname> is honored by the
 153         initrd.</para></listitem>
 154       </varlistentry>
 155
 156       <varlistentry>
 157         <term><varname>mount.usrflags=</varname></term>
 158
 159         <listitem><para>Takes the <filename>/usr</filename> filesystem
 160         mount options to use. If <varname>mount.usr=</varname> or
 161         <varname>mount.usrfstype=</varname> is set, then
 162         <varname>mount.usrflags=</varname> will default to the value
 163         set in <varname>rootflags=</varname>.</para>
 164
 165         <para>Otherwise, this value will be read from the
 166         <filename>/usr</filename> entry in
 167         <filename>/etc/fstab</filename> on the root filesystem.</para>
 168
 169         <para><varname>mount.usrflags=</varname> is honored by the
 170         initrd.</para></listitem>
 171       </varlistentry>
 172
 173       <varlistentry>
 174         <term><varname>systemd.volatile=</varname></term>
 175
 176         <listitem><para>Controls whether the system shall boot up in volatile mode. Takes a boolean argument or the
 177         special value <option>state</option>.</para>
 178
 179         <para>If false (the default), this generator makes no changes to the mount tree and the system is booted up in
 180         normal mode.</para>
 181
 182         <para>If true the generator ensures
 183         <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 184         is run as part of the initial RAM disk ("initrd"). This service changes the mount table before transitioning to
 185         the host system, so that a volatile memory file system (<literal>tmpfs</literal>) is used as root directory,
 186         with only <filename>/usr</filename> mounted into it from the configured root file system, in read-only
 187         mode. This way the system operates in fully stateless mode, with all configuration and state reset at boot and
 188         lost at shutdown, as <filename>/etc</filename> and <filename>/var</filename> will be served from the (initially
 189         unpopulated) volatile memory file system.</para>
 190
 191         <para>If set to <option>state</option> the generator will leave the root
 192         directory mount point unaltered, however will mount a <literal>tmpfs</literal> file system to
 193         <filename>/var</filename>. In this mode the normal system configuration (i.e. the contents of
 194         <literal>/etc</literal>) is in effect (and may be modified during system runtime), however the system state
 195         (i.e. the contents of <literal>/var</literal>) is reset at boot and lost at shutdown.</para>
 196
 197         <para>Note that in none of these modes the root directory, <filename>/etc</filename>, <filename>/var</filename>
 198         or any other resources stored in the root file system are physically removed. It's thus safe to boot a system
 199         that is normally operated in non-volatile mode temporarily into volatile mode, without losing data.</para>
 200
 201         <para>Note that enabling this setting will only work correctly on operating systems that can boot up with only
 202         <filename>/usr</filename> mounted, and are able to automatically populate <filename>/etc</filename>, and also
 203         <filename>/var</filename> in case of <literal>systemd.volatile=yes</literal>.</para></listitem>
 204       </varlistentry>
 205     </variablelist>
 206   </refsect1>
 207
 208   <refsect1>
 209     <title>See Also</title>
 210     <para>
 211       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 212       <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 213       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 214       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 215       <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 216       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 217     </para>
 218   </refsect1>
 219
 220 </refentry>