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