man/systemd.swap.xml

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   5
   6 <refentry id="systemd.swap" xmlns:xi="http://www.w3.org/2001/XInclude">
   7   <refentryinfo>
   8     <title>systemd.swap</title>
   9     <productname>systemd</productname>
  10   </refentryinfo>
  11
  12   <refmeta>
  13     <refentrytitle>systemd.swap</refentrytitle>
  14     <manvolnum>5</manvolnum>
  15   </refmeta>
  16
  17   <refnamediv>
  18     <refname>systemd.swap</refname>
  19     <refpurpose>Swap unit configuration</refpurpose>
  20   </refnamediv>
  21
  22   <refsynopsisdiv>
  23     <para><filename><replaceable>swap</replaceable>.swap</filename></para>
  24   </refsynopsisdiv>
  25
  26   <refsect1>
  27     <title>Description</title>
  28
  29     <para>A unit configuration file whose name ends in
  30     <literal>.swap</literal> encodes information about a swap device
  31     or file for memory paging controlled and supervised by
  32     systemd.</para>
  33
  34     <para>This man page lists the configuration options specific to
  35     this unit type. See
  36     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  37     for the common options of all unit configuration files. The common
  38     configuration items are configured in the generic [Unit] and
  39     [Install] sections. The swap specific configuration options are
  40     configured in the [Swap] section.</para>
  41
  42     <para>Additional options are listed in
  43     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  44     which define the execution environment the <citerefentry
  45     project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  46     program is executed in, in
  47     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  48     which define the way these processes are
  49     terminated, and in
  50     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  51     which configure resource control settings for these processes of the
  52     unit.</para>
  53
  54     <para>Swap units must be named after the devices or files they control. Example: the swap device <filename
  55     index="false">/dev/sda5</filename> must be configured in a unit file <filename>dev-sda5.swap</filename>. For
  56     details about the escaping logic used to convert a file system path to a unit name, see
  57     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Note that swap
  58     units cannot be templated, nor is possible to add multiple names to a swap unit by creating additional symlinks to
  59     it.</para>
  60
  61     <para>Note that swap support on Linux is privileged, swap units are hence only available in the system
  62     service manager (and root's user service manager), but not in unprivileged user's service manager.</para>
  63   </refsect1>
  64
  65   <refsect1>
  66     <title>Automatic Dependencies</title>
  67
  68     <refsect2>
  69       <title>Implicit Dependencies</title>
  70
  71       <para>The following dependencies are implicitly added:</para>
  72
  73       <itemizedlist>
  74         <listitem><para>All swap units automatically get the
  75         <varname>BindsTo=</varname> and <varname>After=</varname>
  76         dependencies on the device units or the mount units of the files
  77         they are activated from.</para></listitem>
  78       </itemizedlist>
  79
  80       <para>Additional implicit dependencies may be added as result of
  81       execution and resource control parameters as documented in
  82       <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  83       and
  84       <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
  85     </refsect2>
  86
  87     <refsect2>
  88       <title>Default Dependencies</title>
  89
  90       <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
  91
  92       <itemizedlist>
  93         <listitem><para>Swap units automatically acquire a <varname>Conflicts=</varname> and a
  94         <varname>Before=</varname> dependency on <filename>umount.target</filename> so that they are deactivated at
  95         shutdown as well as a <varname>Before=swap.target</varname> dependency.</para></listitem>
  96       </itemizedlist>
  97     </refsect2>
  98   </refsect1>
  99
 100   <refsect1>
 101     <title><filename>fstab</filename></title>
 102
 103     <para>Swap units may either be configured via unit files, or via
 104     <filename>/etc/fstab</filename> (see
 105     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 106     for details). Swaps listed in <filename>/etc/fstab</filename> will
 107     be converted into native units dynamically at boot and when the
 108     configuration of the system manager is reloaded. See
 109     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 110     for details about the conversion.</para>
 111
 112     <para>If a swap device or file is configured in both
 113     <filename>/etc/fstab</filename> and a unit file, the configuration
 114     in the latter takes precedence.</para>
 115
 116     <para>When reading <filename>/etc/fstab</filename>, a few special
 117     options are understood by systemd which influence how dependencies
 118     are created for swap units.</para>
 119
 120     <variablelist class='fstab-options'>
 121       <varlistentry>
 122         <term><option>noauto</option></term>
 123         <term><option>auto</option></term>
 124
 125         <listitem><para>With <option>noauto</option>, the swap unit
 126         will not be added as a dependency for
 127         <filename>swap.target</filename>. This means that it will not
 128         be activated automatically during boot, unless it is pulled in
 129         by some other unit. The <option>auto</option> option has the
 130         opposite meaning and is the default.</para>
 131
 132         <xi:include href="version-info.xml" xpointer="v218"/>
 133         </listitem>
 134       </varlistentry>
 135
 136       <varlistentry>
 137         <term><option>nofail</option></term>
 138
 139         <listitem><para>With <option>nofail</option>, the swap unit
 140         will be only wanted, not required by
 141         <filename>swap.target</filename>. This means that the boot
 142         will continue even if this swap device is not activated
 143         successfully.</para>
 144         </listitem>
 145       </varlistentry>
 146
 147       <xi:include href="systemd.mount.xml" xpointer="device-timeout" />
 148
 149       <varlistentry>
 150         <term><option>x-systemd.makefs</option></term>
 151
 152         <listitem><para>The swap structure will be initialized on the device. If the device is not
 153         "empty", i.e. it contains any signature, the operation will be skipped. It is hence expected
 154         that this option remains set even after the device has been initialized.</para>
 155
 156         <para>Note that this option can only be used in <filename>/etc/fstab</filename>, and will be
 157         ignored when part of the <varname>Options=</varname> setting in a unit file.</para>
 158
 159         <para>See
 160         <citerefentry><refentrytitle>systemd-mkswap@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 161         and the discussion of
 162         <citerefentry project='man-pages'><refentrytitle>wipefs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 163         in <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 164         </para>
 165
 166         <xi:include href="version-info.xml" xpointer="v240"/></listitem>
 167       </varlistentry>
 168     </variablelist>
 169   </refsect1>
 170
 171   <refsect1>
 172     <title>Options</title>
 173
 174     <para>Swap unit files may include [Unit] and [Install] sections, which are described in
 175     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 176     </para>
 177
 178     <para>Swap unit files must include a [Swap] section, which carries
 179     information about the swap device it supervises. A number of
 180     options that may be used in this section are shared with other
 181     unit types. These options are documented in
 182     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 183     and
 184     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 185     The options specific to the [Swap] section of swap units are the
 186     following:</para>
 187
 188     <variablelist class='unit-directives'>
 189
 190       <varlistentry>
 191         <term><varname>What=</varname></term>
 192         <listitem><para>Takes an absolute path of a device node or file to use for paging. See <citerefentry
 193         project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
 194         details. If this refers to a device node, a dependency on the respective device unit is automatically
 195         created. (See
 196         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 197         for more information.) If this refers to a file, a dependency on the respective mount unit is
 198         automatically created. (See
 199         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 200         more information.) This option is mandatory. Note that the usual specifier expansion is applied to
 201         this setting, literal percent characters should hence be written as
 202         <literal class='specifiers'>%%</literal>.</para></listitem>
 203       </varlistentry>
 204
 205       <varlistentry>
 206         <term><varname>Priority=</varname></term>
 207
 208         <listitem><para>Swap priority to use when activating the swap
 209         device or file. This takes an integer. This setting is
 210         optional and ignored when the priority is set by <option>pri=</option> in the
 211         <varname>Options=</varname> key.</para></listitem>
 212       </varlistentry>
 213
 214       <varlistentry>
 215         <term><varname>Options=</varname></term>
 216
 217         <listitem><para>May contain an option string for the swap device. This may be used for controlling discard
 218         options among other functionality, if the swap backing device supports the discard or trim operation. (See
 219         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 220         for more information.) Note that the usual specifier expansion is applied to this setting, literal percent
 221         characters should hence be written as <literal>%%</literal>.</para>
 222
 223         <xi:include href="version-info.xml" xpointer="v217"/></listitem>
 224       </varlistentry>
 225
 226       <varlistentry>
 227         <term><varname>TimeoutSec=</varname></term>
 228         <listitem><para>Configures the time to wait for the swapon
 229         command to finish. If a command does not exit within the
 230         configured time, the swap will be considered failed and be
 231         shut down again. All commands still running will be terminated
 232         forcibly via <constant>SIGTERM</constant>, and after another
 233         delay of this time with <constant>SIGKILL</constant>. (See
 234         <option>KillMode=</option> in
 235         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 236         Takes a unit-less value in seconds, or a time span value such
 237         as "5min 20s". Pass <literal>0</literal> to disable the
 238         timeout logic. Defaults to
 239         <varname>DefaultTimeoutStartSec=</varname> from the manager
 240         configuration file (see
 241         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 242         </para></listitem>
 243       </varlistentry>
 244     </variablelist>
 245
 246     <xi:include href="systemd.service.xml" xpointer="shared-unit-options" />
 247   </refsect1>
 248
 249   <refsect1>
 250       <title>See Also</title>
 251       <para>
 252         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 253         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 254         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 255         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 256         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 257         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 258         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 259         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 260         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 261         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 262         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 263         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 264       </para>
 265   </refsect1>
 266
 267 </refentry>