man/systemd.swap.xml

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  23
  24 <refentry id="systemd.swap">
  25   <refentryinfo>
  26     <title>systemd.swap</title>
  27     <productname>systemd</productname>
  28
  29     <authorgroup>
  30       <author>
  31         <contrib>Developer</contrib>
  32         <firstname>Lennart</firstname>
  33         <surname>Poettering</surname>
  34         <email>lennart@poettering.net</email>
  35       </author>
  36     </authorgroup>
  37   </refentryinfo>
  38
  39   <refmeta>
  40     <refentrytitle>systemd.swap</refentrytitle>
  41     <manvolnum>5</manvolnum>
  42   </refmeta>
  43
  44   <refnamediv>
  45     <refname>systemd.swap</refname>
  46     <refpurpose>Swap unit configuration</refpurpose>
  47   </refnamediv>
  48
  49   <refsynopsisdiv>
  50     <para><filename><replaceable>swap</replaceable>.swap</filename></para>
  51   </refsynopsisdiv>
  52
  53   <refsect1>
  54     <title>Description</title>
  55
  56     <para>A unit configuration file whose name ends in
  57     <literal>.swap</literal> encodes information about a swap device
  58     or file for memory paging controlled and supervised by
  59     systemd.</para>
  60
  61     <para>This man page lists the configuration options specific to
  62     this unit type. See
  63     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  64     for the common options of all unit configuration files. The common
  65     configuration items are configured in the generic [Unit] and
  66     [Install] sections. The swap specific configuration options are
  67     configured in the [Swap] section.</para>
  68
  69     <para>Additional options are listed in
  70     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  71     which define the execution environment the <citerefentry
  72     project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  73     binary is executed in, in
  74     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  75     which define the way these processes are
  76     terminated, and in
  77     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  78     which configure resource control settings for these processes of the
  79     unit.</para>
  80
  81     <para>Swap units must be named after the devices
  82     or files they control. Example: the swap device
  83     <filename noindex='true'>/dev/sda5</filename> must be configured in a
  84     unit file <filename>dev-sda5.swap</filename>. For details about
  85     the escaping logic used to convert a file system path to a unit
  86     name, see
  87     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  88   </refsect1>
  89
  90   <refsect1>
  91     <title>Automatic Dependencies</title>
  92
  93     <para>All swap units automatically get the
  94     <varname>BindsTo=</varname> and <varname>After=</varname>
  95     dependencies on the device units or the mount units of the files
  96     they are activated from.</para>
  97
  98     <para>Swap units with <varname>DefaultDependencies=</varname>
  99     enabled implicitly acquire a <varname>Conflicts=</varname> and an
 100     <varname>After=</varname> dependency on
 101     <filename>umount.target</filename> so that they are deactivated at
 102     shutdown, unless <varname>DefaultDependencies=no</varname> is
 103     specified.</para>
 104
 105     <para>Additional implicit dependencies may be added as result of
 106     execution and resource control parameters as documented in
 107     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 108     and
 109     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 110   </refsect1>
 111
 112   <refsect1>
 113     <title><filename>fstab</filename></title>
 114
 115     <para>Swap units may either be configured via unit files, or via
 116     <filename>/etc/fstab</filename> (see
 117     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 118     for details). Swaps listed in <filename>/etc/fstab</filename> will
 119     be converted into native units dynamically at boot and when the
 120     configuration of the system manager is reloaded. See
 121     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 122     for details about the conversion.</para>
 123
 124     <para>If a swap device or file is configured in both
 125     <filename>/etc/fstab</filename> and a unit file, the configuration
 126     in the latter takes precedence.</para>
 127
 128     <para>When reading <filename>/etc/fstab</filename>, a few special
 129     options are understood by systemd which influence how dependencies
 130     are created for swap units.</para>
 131
 132     <variablelist class='fstab-options'>
 133       <varlistentry>
 134         <term><option>noauto</option></term>
 135         <term><option>auto</option></term>
 136
 137         <listitem><para>With <option>noauto</option>, the swap unit
 138         will not be added as a dependency for
 139         <filename>swap.target</filename>. This means that it will not
 140         be activated automatically during boot, unless it is pulled in
 141         by some other unit. The <option>auto</option> option has the
 142         opposite meaning and is the default.</para>
 143         </listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term><option>nofail</option></term>
 148
 149         <listitem><para>With <option>nofail</option>, the swap unit
 150         will be only wanted, not required by
 151         <filename>swap.target</filename>. This means that the boot
 152         will continue even if this swap device is not activated
 153         successfully.</para>
 154         </listitem>
 155       </varlistentry>
 156     </variablelist>
 157   </refsect1>
 158
 159   <refsect1>
 160     <title>Options</title>
 161
 162     <para>Swap files must include a [Swap] section, which carries
 163     information about the swap device it supervises. A number of
 164     options that may be used in this section are shared with other
 165     unit types. These options are documented in
 166     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 167     and
 168     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 169     The options specific to the [Swap] section of swap units are the
 170     following:</para>
 171
 172     <variablelist class='unit-directives'>
 173
 174       <varlistentry>
 175         <term><varname>What=</varname></term>
 176         <listitem><para>Takes an absolute path of a device node or
 177         file to use for paging. See
 178         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 179         for details. If this refers to a device node, a dependency on
 180         the respective device unit is automatically created. (See
 181         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 182         for more information.) If this refers to a file, a dependency
 183         on the respective mount unit is automatically created. (See
 184         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 185         for more information.) This option is
 186         mandatory.</para></listitem>
 187       </varlistentry>
 188
 189       <varlistentry>
 190         <term><varname>Priority=</varname></term>
 191
 192         <listitem><para>Swap priority to use when activating the swap
 193         device or file. This takes an integer. This setting is
 194         optional and ignored when the priority is set by <option>pri=</option> in the
 195         <varname>Options=</varname> key.</para></listitem>
 196       </varlistentry>
 197
 198       <varlistentry>
 199         <term><varname>Options=</varname></term>
 200
 201         <listitem><para>May contain an option string for the swap
 202         device. This may be used for controlling discard options among
 203         other functionality, if the swap backing device supports the
 204         discard or trim operation. (See
 205         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 206         for more information.) </para></listitem>
 207       </varlistentry>
 208
 209       <varlistentry>
 210         <term><varname>TimeoutSec=</varname></term>
 211         <listitem><para>Configures the time to wait for the swapon
 212         command to finish. If a command does not exit within the
 213         configured time, the swap will be considered failed and be
 214         shut down again. All commands still running will be terminated
 215         forcibly via <constant>SIGTERM</constant>, and after another
 216         delay of this time with <constant>SIGKILL</constant>. (See
 217         <option>KillMode=</option> in
 218         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 219         Takes a unit-less value in seconds, or a time span value such
 220         as "5min 20s". Pass <literal>0</literal> to disable the
 221         timeout logic. Defaults to
 222         <varname>DefaultTimeoutStartSec=</varname> from the manager
 223         configuration file (see
 224         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 225         </para></listitem>
 226       </varlistentry>
 227     </variablelist>
 228
 229     <para>Check
 230     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 231     and
 232     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 233     for more settings.</para>
 234   </refsect1>
 235
 236   <refsect1>
 237       <title>See Also</title>
 238       <para>
 239         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 240         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 241         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 242         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 243         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 244         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 245         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 246         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 247         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 248         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 249         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 250       </para>
 251   </refsect1>
 252
 253 </refentry>