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 or files they control. Example: the swap device <filename
  82     noindex='true'>/dev/sda5</filename> must be configured in a unit file <filename>dev-sda5.swap</filename>. For
  83     details about the escaping logic used to convert a file system path to a unit name, see
  84     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Note that swap
  85     units cannot be templated, nor is possible to add multiple names to a swap unit by creating additional symlinks to
  86     it.</para>
  87   </refsect1>
  88
  89   <refsect1>
  90     <title>Implicit Dependencies</title>
  91
  92     <para>The following dependencies are implicitly added:</para>
  93
  94     <itemizedlist>
  95       <listitem><para>All swap units automatically get the
  96       <varname>BindsTo=</varname> and <varname>After=</varname>
  97       dependencies on the device units or the mount units of the files
  98       they are activated from.</para></listitem>
  99     </itemizedlist>
 100
 101     <para>Additional implicit dependencies may be added as result of
 102     execution and resource control parameters as documented in
 103     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 104     and
 105     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 106   </refsect1>
 107
 108   <refsect1>
 109     <title>Default Dependencies</title>
 110
 111     <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
 112
 113     <itemizedlist>
 114       <listitem><para>Swap units automatically acquire a <varname>Conflicts=</varname> and a
 115       <varname>Before=</varname> dependency on <filename>umount.target</filename> so that they are deactivated at
 116       shutdown as well as a <varname>Before=swap.target</varname> dependency.</para></listitem>
 117     </itemizedlist>
 118   </refsect1>
 119
 120   <refsect1>
 121     <title><filename>fstab</filename></title>
 122
 123     <para>Swap units may either be configured via unit files, or via
 124     <filename>/etc/fstab</filename> (see
 125     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 126     for details). Swaps listed in <filename>/etc/fstab</filename> will
 127     be converted into native units dynamically at boot and when the
 128     configuration of the system manager is reloaded. See
 129     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 130     for details about the conversion.</para>
 131
 132     <para>If a swap device or file is configured in both
 133     <filename>/etc/fstab</filename> and a unit file, the configuration
 134     in the latter takes precedence.</para>
 135
 136     <para>When reading <filename>/etc/fstab</filename>, a few special
 137     options are understood by systemd which influence how dependencies
 138     are created for swap units.</para>
 139
 140     <variablelist class='fstab-options'>
 141       <varlistentry>
 142         <term><option>noauto</option></term>
 143         <term><option>auto</option></term>
 144
 145         <listitem><para>With <option>noauto</option>, the swap unit
 146         will not be added as a dependency for
 147         <filename>swap.target</filename>. This means that it will not
 148         be activated automatically during boot, unless it is pulled in
 149         by some other unit. The <option>auto</option> option has the
 150         opposite meaning and is the default.</para>
 151         </listitem>
 152       </varlistentry>
 153
 154       <varlistentry>
 155         <term><option>nofail</option></term>
 156
 157         <listitem><para>With <option>nofail</option>, the swap unit
 158         will be only wanted, not required by
 159         <filename>swap.target</filename>. This means that the boot
 160         will continue even if this swap device is not activated
 161         successfully.</para>
 162         </listitem>
 163       </varlistentry>
 164     </variablelist>
 165   </refsect1>
 166
 167   <refsect1>
 168     <title>Options</title>
 169
 170     <para>Swap files must include a [Swap] section, which carries
 171     information about the swap device it supervises. A number of
 172     options that may be used in this section are shared with other
 173     unit types. These options are documented in
 174     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 175     and
 176     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 177     The options specific to the [Swap] section of swap units are the
 178     following:</para>
 179
 180     <variablelist class='unit-directives'>
 181
 182       <varlistentry>
 183         <term><varname>What=</varname></term>
 184         <listitem><para>Takes an absolute path of a device node or file to use for paging. See <citerefentry
 185         project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
 186         details. If this refers to a device node, a dependency on the respective device unit is automatically
 187         created. (See
 188         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
 189         information.) If this refers to a file, a dependency on the respective mount unit is automatically
 190         created. (See <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 191         for more information.) This option is mandatory. Note that the usual specifier expansion is applied to this
 192         setting, literal percent characters should hence be written as <literal>%%</literal>.</para></listitem>
 193       </varlistentry>
 194
 195       <varlistentry>
 196         <term><varname>Priority=</varname></term>
 197
 198         <listitem><para>Swap priority to use when activating the swap
 199         device or file. This takes an integer. This setting is
 200         optional and ignored when the priority is set by <option>pri=</option> in the
 201         <varname>Options=</varname> key.</para></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term><varname>Options=</varname></term>
 206
 207         <listitem><para>May contain an option string for the swap device. This may be used for controlling discard
 208         options among other functionality, if the swap backing device supports the discard or trim operation. (See
 209         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 210         for more information.) Note that the usual specifier expansion is applied to this setting, literal percent
 211         characters should hence be written as <literal>%%</literal>.</para></listitem>
 212       </varlistentry>
 213
 214       <varlistentry>
 215         <term><varname>TimeoutSec=</varname></term>
 216         <listitem><para>Configures the time to wait for the swapon
 217         command to finish. If a command does not exit within the
 218         configured time, the swap will be considered failed and be
 219         shut down again. All commands still running will be terminated
 220         forcibly via <constant>SIGTERM</constant>, and after another
 221         delay of this time with <constant>SIGKILL</constant>. (See
 222         <option>KillMode=</option> in
 223         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 224         Takes a unit-less value in seconds, or a time span value such
 225         as "5min 20s". Pass <literal>0</literal> to disable the
 226         timeout logic. Defaults to
 227         <varname>DefaultTimeoutStartSec=</varname> from the manager
 228         configuration file (see
 229         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 230         </para></listitem>
 231       </varlistentry>
 232     </variablelist>
 233
 234     <para>Check
 235     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 236     and
 237     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 238     for more settings.</para>
 239   </refsect1>
 240
 241   <refsect1>
 242       <title>See Also</title>
 243       <para>
 244         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 245         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 246         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 247         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 248         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 249         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 250         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 251         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 252         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 253         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 254         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 255       </para>
 256   </refsect1>
 257
 258 </refentry>