man/systemd-fstab-generator.xml

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