man/systemd.swap.xml

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  10   Copyright 2010 Lennart Poettering
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  25
  26 <refentry id="systemd.swap">
  27   <refentryinfo>
  28     <title>systemd.swap</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>systemd.swap</refentrytitle>
  43     <manvolnum>5</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>systemd.swap</refname>
  48     <refpurpose>Swap unit configuration</refpurpose>
  49   </refnamediv>
  50
  51   <refsynopsisdiv>
  52     <para><filename><replaceable>swap</replaceable>.swap</filename></para>
  53   </refsynopsisdiv>
  54
  55   <refsect1>
  56     <title>Description</title>
  57
  58     <para>A unit configuration file whose name ends in
  59     <literal>.swap</literal> encodes information about a swap device
  60     or file for memory paging controlled and supervised by
  61     systemd.</para>
  62
  63     <para>This man page lists the configuration options specific to
  64     this unit type. See
  65     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  66     for the common options of all unit configuration files. The common
  67     configuration items are configured in the generic [Unit] and
  68     [Install] sections. The swap specific configuration options are
  69     configured in the [Swap] section.</para>
  70
  71     <para>Additional options are listed in
  72     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  73     which define the execution environment the <citerefentry
  74     project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  75     program is executed in, in
  76     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  77     which define the way these processes are
  78     terminated, and in
  79     <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  80     which configure resource control settings for these processes of the
  81     unit.</para>
  82
  83     <para>Swap units must be named after the devices or files they control. Example: the swap device <filename
  84     noindex='true'>/dev/sda5</filename> must be configured in a unit file <filename>dev-sda5.swap</filename>. For
  85     details about the escaping logic used to convert a file system path to a unit name, see
  86     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Note that swap
  87     units cannot be templated, nor is possible to add multiple names to a swap unit by creating additional symlinks to
  88     it.</para>
  89   </refsect1>
  90
  91   <refsect1>
  92     <title>Implicit Dependencies</title>
  93
  94     <para>The following dependencies are implicitly added:</para>
  95
  96     <itemizedlist>
  97       <listitem><para>All swap units automatically get the
  98       <varname>BindsTo=</varname> and <varname>After=</varname>
  99       dependencies on the device units or the mount units of the files
 100       they are activated from.</para></listitem>
 101     </itemizedlist>
 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>Default Dependencies</title>
 112
 113     <para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
 114
 115     <itemizedlist>
 116       <listitem><para>Swap units automatically acquire a <varname>Conflicts=</varname> and a
 117       <varname>Before=</varname> dependency on <filename>umount.target</filename> so that they are deactivated at
 118       shutdown as well as a <varname>Before=swap.target</varname> dependency.</para></listitem>
 119     </itemizedlist>
 120   </refsect1>
 121
 122   <refsect1>
 123     <title><filename>fstab</filename></title>
 124
 125     <para>Swap units may either be configured via unit files, or via
 126     <filename>/etc/fstab</filename> (see
 127     <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 128     for details). Swaps listed in <filename>/etc/fstab</filename> will
 129     be converted into native units dynamically at boot and when the
 130     configuration of the system manager is reloaded. See
 131     <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 132     for details about the conversion.</para>
 133
 134     <para>If a swap device or file is configured in both
 135     <filename>/etc/fstab</filename> and a unit file, the configuration
 136     in the latter takes precedence.</para>
 137
 138     <para>When reading <filename>/etc/fstab</filename>, a few special
 139     options are understood by systemd which influence how dependencies
 140     are created for swap units.</para>
 141
 142     <variablelist class='fstab-options'>
 143       <varlistentry>
 144         <term><option>noauto</option></term>
 145         <term><option>auto</option></term>
 146
 147         <listitem><para>With <option>noauto</option>, the swap unit
 148         will not be added as a dependency for
 149         <filename>swap.target</filename>. This means that it will not
 150         be activated automatically during boot, unless it is pulled in
 151         by some other unit. The <option>auto</option> option has the
 152         opposite meaning and is the default.</para>
 153         </listitem>
 154       </varlistentry>
 155
 156       <varlistentry>
 157         <term><option>nofail</option></term>
 158
 159         <listitem><para>With <option>nofail</option>, the swap unit
 160         will be only wanted, not required by
 161         <filename>swap.target</filename>. This means that the boot
 162         will continue even if this swap device is not activated
 163         successfully.</para>
 164         </listitem>
 165       </varlistentry>
 166     </variablelist>
 167   </refsect1>
 168
 169   <refsect1>
 170     <title>Options</title>
 171
 172     <para>Swap files must include a [Swap] section, which carries
 173     information about the swap device it supervises. A number of
 174     options that may be used in this section are shared with other
 175     unit types. These options are documented in
 176     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 177     and
 178     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 179     The options specific to the [Swap] section of swap units are the
 180     following:</para>
 181
 182     <variablelist class='unit-directives'>
 183
 184       <varlistentry>
 185         <term><varname>What=</varname></term>
 186         <listitem><para>Takes an absolute path of a device node or file to use for paging. See <citerefentry
 187         project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
 188         details. If this refers to a device node, a dependency on the respective device unit is automatically
 189         created. (See
 190         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry> for more
 191         information.) If this refers to a file, a dependency on the respective mount unit is automatically
 192         created. (See <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 193         for more information.) This option is mandatory. Note that the usual specifier expansion is applied to this
 194         setting, literal percent characters should hence be written as <literal>%%</literal>.</para></listitem>
 195       </varlistentry>
 196
 197       <varlistentry>
 198         <term><varname>Priority=</varname></term>
 199
 200         <listitem><para>Swap priority to use when activating the swap
 201         device or file. This takes an integer. This setting is
 202         optional and ignored when the priority is set by <option>pri=</option> in the
 203         <varname>Options=</varname> key.</para></listitem>
 204       </varlistentry>
 205
 206       <varlistentry>
 207         <term><varname>Options=</varname></term>
 208
 209         <listitem><para>May contain an option string for the swap device. This may be used for controlling discard
 210         options among other functionality, if the swap backing device supports the discard or trim operation. (See
 211         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 212         for more information.) Note that the usual specifier expansion is applied to this setting, literal percent
 213         characters should hence be written as <literal>%%</literal>.</para></listitem>
 214       </varlistentry>
 215
 216       <varlistentry>
 217         <term><varname>TimeoutSec=</varname></term>
 218         <listitem><para>Configures the time to wait for the swapon
 219         command to finish. If a command does not exit within the
 220         configured time, the swap will be considered failed and be
 221         shut down again. All commands still running will be terminated
 222         forcibly via <constant>SIGTERM</constant>, and after another
 223         delay of this time with <constant>SIGKILL</constant>. (See
 224         <option>KillMode=</option> in
 225         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
 226         Takes a unit-less value in seconds, or a time span value such
 227         as "5min 20s". Pass <literal>0</literal> to disable the
 228         timeout logic. Defaults to
 229         <varname>DefaultTimeoutStartSec=</varname> from the manager
 230         configuration file (see
 231         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
 232         </para></listitem>
 233       </varlistentry>
 234     </variablelist>
 235
 236     <para>Check
 237     <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 238     and
 239     <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 240     for more settings.</para>
 241   </refsect1>
 242
 243   <refsect1>
 244       <title>See Also</title>
 245       <para>
 246         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 247         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 248         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 249         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 250         <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 251         <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 252         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 253         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 254         <citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 255         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 256         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 257       </para>
 258   </refsect1>
 259
 260 </refentry>