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> in the <literal>[Unit]</literal> section enabled
  99     implicitly acquire a <varname>Conflicts=</varname> and an <varname>After=</varname> dependency on
 100     <filename>umount.target</filename> so that they are deactivated at shutdown, unless
 101     <varname>DefaultDependencies=no</varname> is specified.</para>
 102
 103     <para>Additional implicit dependencies may be added as result of
 104     execution and resource control parameters as documented in
 105     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 106     and
 107     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 108   </refsect1>
 109
 110   <refsect1>
 111     <title><filename>fstab</filename></title>
 112
 113     <para>Swap units may either be configured via unit files, or via
 114     <filename>/etc/fstab</filename> (see
 115     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 116     for details). Swaps listed in <filename>/etc/fstab</filename> will
 117     be converted into native units dynamically at boot and when the
 118     configuration of the system manager is reloaded. See
 119     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 120     for details about the conversion.</para>
 121
 122     <para>If a swap device or file is configured in both
 123     <filename>/etc/fstab</filename> and a unit file, the configuration
 124     in the latter takes precedence.</para>
 125
 126     <para>When reading <filename>/etc/fstab</filename>, a few special
 127     options are understood by systemd which influence how dependencies
 128     are created for swap units.</para>
 129
 130     <variablelist class='fstab-options'>
 131       <varlistentry>
 132         <term><option>noauto</option></term>
 133         <term><option>auto</option></term>
 134
 135         <listitem><para>With <option>noauto</option>, the swap unit
 136         will not be added as a dependency for
 137         <filename>swap.target</filename>. This means that it will not
 138         be activated automatically during boot, unless it is pulled in
 139         by some other unit. The <option>auto</option> option has the
 140         opposite meaning and is the default.</para>
 141         </listitem>
 142       </varlistentry>
 143
 144       <varlistentry>
 145         <term><option>nofail</option></term>
 146
 147         <listitem><para>With <option>nofail</option>, the swap unit
 148         will be only wanted, not required by
 149         <filename>swap.target</filename>. This means that the boot
 150         will continue even if this swap device is not activated
 151         successfully.</para>
 152         </listitem>
 153       </varlistentry>
 154     </variablelist>
 155   </refsect1>
 156
 157   <refsect1>
 158     <title>Options</title>
 159
 160     <para>Swap files must include a [Swap] section, which carries
 161     information about the swap device it supervises. A number of
 162     options that may be used in this section are shared with other
 163     unit types. These options are documented in
 164     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 165     and
 166     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 167     The options specific to the [Swap] section of swap units are the
 168     following:</para>
 169
 170     <variablelist class='unit-directives'>
 171
 172       <varlistentry>
 173         <term><varname>What=</varname></term>
 174         <listitem><para>Takes an absolute path of a device node or
 175         file to use for paging. See
 176         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 177         for details. If this refers to a device node, a dependency on
 178         the respective device unit is automatically created. (See
 179         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 180         for more information.) If this refers to a file, a dependency
 181         on the respective mount unit is automatically created. (See
 182         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 183         for more information.) This option is
 184         mandatory.</para></listitem>
 185       </varlistentry>
 186
 187       <varlistentry>
 188         <term><varname>Priority=</varname></term>
 189
 190         <listitem><para>Swap priority to use when activating the swap
 191         device or file. This takes an integer. This setting is
 192         optional and ignored when the priority is set by <option>pri=</option> in the
 193         <varname>Options=</varname> key.</para></listitem>
 194       </varlistentry>
 195
 196       <varlistentry>
 197         <term><varname>Options=</varname></term>
 198
 199         <listitem><para>May contain an option string for the swap
 200         device. This may be used for controlling discard options among
 201         other functionality, if the swap backing device supports the
 202         discard or trim operation. (See
 203         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 204         for more information.) </para></listitem>
 205       </varlistentry>
 206
 207       <varlistentry>
 208         <term><varname>TimeoutSec=</varname></term>
 209         <listitem><para>Configures the time to wait for the swapon
 210         command to finish. If a command does not exit within the
 211         configured time, the swap will be considered failed and be
 212         shut down again. All commands still running will be terminated
 213         forcibly via <constant>SIGTERM</constant>, and after another
 214         delay of this time with <constant>SIGKILL</constant>. (See
 215         <option>KillMode=</option> in
 216         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 217         Takes a unit-less value in seconds, or a time span value such
 218         as "5min 20s". Pass <literal>0</literal> to disable the
 219         timeout logic. Defaults to
 220         <varname>DefaultTimeoutStartSec=</varname> from the manager
 221         configuration file (see
 222         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 223         </para></listitem>
 224       </varlistentry>
 225     </variablelist>
 226
 227     <para>Check
 228     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 229     and
 230     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 231     for more settings.</para>
 232   </refsect1>
 233
 234   <refsect1>
 235       <title>See Also</title>
 236       <para>
 237         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 238         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 239         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 240         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 241         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 242         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 243         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 244         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 245         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 246         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 247         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 248       </para>
 249   </refsect1>
 250
 251 </refentry>