man/systemd-fstab-generator.xml

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