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>Automatic Dependencies</title>
  91
  92     <para>All swap units automatically get the
  93     <varname>BindsTo=</varname> and <varname>After=</varname>
  94     dependencies on the device units or the mount units of the files
  95     they are activated from.</para>
  96
  97     <para>Swap units with <varname>DefaultDependencies=</varname> set to its default <option>yes</option> value in the
  98     <literal>[Unit]</literal> section enabled implicitly acquire a <varname>Conflicts=</varname> and a
  99     <varname>Before=</varname> dependency on <filename>umount.target</filename> so that they are deactivated at
 100     shutdown as well as a <varname>Before=swap.target</varname> dependency.</para>
 101
 102     <para>Additional implicit dependencies may be added as result of
 103     execution and resource control parameters as documented in
 104     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 105     and
 106     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 107   </refsect1>
 108
 109   <refsect1>
 110     <title><filename>fstab</filename></title>
 111
 112     <para>Swap units may either be configured via unit files, or via
 113     <filename>/etc/fstab</filename> (see
 114     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 115     for details). Swaps listed in <filename>/etc/fstab</filename> will
 116     be converted into native units dynamically at boot and when the
 117     configuration of the system manager is reloaded. See
 118     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 119     for details about the conversion.</para>
 120
 121     <para>If a swap device or file is configured in both
 122     <filename>/etc/fstab</filename> and a unit file, the configuration
 123     in the latter takes precedence.</para>
 124
 125     <para>When reading <filename>/etc/fstab</filename>, a few special
 126     options are understood by systemd which influence how dependencies
 127     are created for swap units.</para>
 128
 129     <variablelist class='fstab-options'>
 130       <varlistentry>
 131         <term><option>noauto</option></term>
 132         <term><option>auto</option></term>
 133
 134         <listitem><para>With <option>noauto</option>, the swap unit
 135         will not be added as a dependency for
 136         <filename>swap.target</filename>. This means that it will not
 137         be activated automatically during boot, unless it is pulled in
 138         by some other unit. The <option>auto</option> option has the
 139         opposite meaning and is the default.</para>
 140         </listitem>
 141       </varlistentry>
 142
 143       <varlistentry>
 144         <term><option>nofail</option></term>
 145
 146         <listitem><para>With <option>nofail</option>, the swap unit
 147         will be only wanted, not required by
 148         <filename>swap.target</filename>. This means that the boot
 149         will continue even if this swap device is not activated
 150         successfully.</para>
 151         </listitem>
 152       </varlistentry>
 153     </variablelist>
 154   </refsect1>
 155
 156   <refsect1>
 157     <title>Options</title>
 158
 159     <para>Swap files must include a [Swap] section, which carries
 160     information about the swap device it supervises. A number of
 161     options that may be used in this section are shared with other
 162     unit types. These options are documented in
 163     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 164     and
 165     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 166     The options specific to the [Swap] section of swap units are the
 167     following:</para>
 168
 169     <variablelist class='unit-directives'>
 170
 171       <varlistentry>
 172         <term><varname>What=</varname></term>
 173         <listitem><para>Takes an absolute path of a device node or file to use for paging. See <citerefentry
 174         project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
 175         details. If this refers to a device node, a dependency on the respective device unit is automatically
 176         created. (See
 177         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
 178         information.) If this refers to a file, a dependency on the respective mount unit is automatically
 179         created. (See <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 180         for more information.) This option is mandatory. Note that the usual specifier expansion is applied to this
 181         setting, literal percent characters should hence be written as <literal>%%</literal>.</para></listitem>
 182       </varlistentry>
 183
 184       <varlistentry>
 185         <term><varname>Priority=</varname></term>
 186
 187         <listitem><para>Swap priority to use when activating the swap
 188         device or file. This takes an integer. This setting is
 189         optional and ignored when the priority is set by <option>pri=</option> in the
 190         <varname>Options=</varname> key.</para></listitem>
 191       </varlistentry>
 192
 193       <varlistentry>
 194         <term><varname>Options=</varname></term>
 195
 196         <listitem><para>May contain an option string for the swap device. This may be used for controlling discard
 197         options among other functionality, if the swap backing device supports the discard or trim operation. (See
 198         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 199         for more information.) Note that the usual specifier expansion is applied to this setting, literal percent
 200         characters should hence be written as <literal>%%</literal>.</para></listitem>
 201       </varlistentry>
 202
 203       <varlistentry>
 204         <term><varname>TimeoutSec=</varname></term>
 205         <listitem><para>Configures the time to wait for the swapon
 206         command to finish. If a command does not exit within the
 207         configured time, the swap will be considered failed and be
 208         shut down again. All commands still running will be terminated
 209         forcibly via <constant>SIGTERM</constant>, and after another
 210         delay of this time with <constant>SIGKILL</constant>. (See
 211         <option>KillMode=</option> in
 212         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 213         Takes a unit-less value in seconds, or a time span value such
 214         as "5min 20s". Pass <literal>0</literal> to disable the
 215         timeout logic. Defaults to
 216         <varname>DefaultTimeoutStartSec=</varname> from the manager
 217         configuration file (see
 218         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 219         </para></listitem>
 220       </varlistentry>
 221     </variablelist>
 222
 223     <para>Check
 224     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 225     and
 226     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 227     for more settings.</para>
 228   </refsect1>
 229
 230   <refsect1>
 231       <title>See Also</title>
 232       <para>
 233         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 234         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 235         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 236         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 237         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 238         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 239         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 240         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 241         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 242         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 243         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 244       </para>
 245   </refsect1>
 246
 247 </refentry>