systemd/man/systemd.swap.xml

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<refentry id="systemd.swap">
        <refentryinfo>
                <title>systemd.swap</title>
                <productname>systemd</productname>

                <authorgroup>
                        <author>
                                <contrib>Developer</contrib>
                                <firstname>Lennart</firstname>
                                <surname>Poettering</surname>
                                <email>lennart@poettering.net</email>
                        </author>
                </authorgroup>
        </refentryinfo>

        <refmeta>
                <refentrytitle>systemd.swap</refentrytitle>
                <manvolnum>5</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>systemd.swap</refname>
                <refpurpose>Swap unit configuration</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <para><filename><replaceable>swap</replaceable>.swap</filename></para>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para>A unit configuration file whose name ends in
                <literal>.swap</literal> encodes information about a
                swap device or file for memory paging controlled and
                supervised by systemd.</para>

                <para>This man page lists the configuration options
                specific to this unit type. See
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for the common options of all unit configuration
                files. The common configuration items are configured
                in the generic [Unit] and [Install] sections. The swap
                specific configuration options are configured in the
                [Swap] section.</para>

                <para>Additional options are listed in
                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                which define the execution environment the
                <citerefentry><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                binary is executed in, and in
                <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                which define the way the processes are
                terminated, and in
                <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                which configure resource control settings for the
                processes of the service.</para>

                <para>Swap units must be named after the devices
                or files they control. Example: the swap device
                <filename noindex='true'>/dev/sda5</filename> must be configured in a
                unit file <filename>dev-sda5.swap</filename>. For
                details about the escaping logic used to convert a
                file system path to a unit name, see
                <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>

                <para>All swap units automatically get the appropriate
                dependencies on the devices or on the mount points
                of the files they are activated from.</para>

                <para>Swap units with
                <varname>DefaultDependencies=</varname> enabled
                implicitly acquire a conflicting dependency to
                <filename>umount.target</filename> so that they are
                deactivated at shutdown.</para>
        </refsect1>

        <refsect1>
                <title><filename>fstab</filename></title>

                <para>Swap units may either be configured via unit
                files, or via <filename>/etc/fstab</filename> (see
                <citerefentry><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for details). Swaps listed in
                <filename>/etc/fstab</filename> will be converted into
                native units dynamically at boot and when the
                configuration of the system manager is
                reloaded. See
                <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                for details about the conversion.</para>

                <para>If a swap device or file is configured in both
                <filename>/etc/fstab</filename> and a unit file, the
                configuration in the latter takes precedence.</para>

                <para>Unless the <option>noauto</option> option is set
                for them all swap units configured in
                <filename>/etc/fstab</filename> are also added as
                requirements to <filename>swap.target</filename>, so
                that they are waited for and activated during
                boot.</para>
        </refsect1>

        <refsect1>
                <title>Options</title>

                <para>Swap files must include a [Swap] section, which
                carries information about the swap device it
                supervises. A number of options that may be used in
                this section are shared with other unit types. These
                options are documented in
                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                and
                <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
                options specific to the [Swap] section of swap units
                are the following:</para>

                <variablelist class='unit-directives'>

                        <varlistentry>
                                <term><varname>What=</varname></term>
                                <listitem><para>Takes an absolute path
                                of a device node or file to use for
                                paging. See
                                <citerefentry><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
                                for details. If this refers to a
                                device node, a dependency on the
                                respective device unit is
                                automatically created. (See
                                <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for more information.) If this refers
                                to a file, a dependency on the
                                respective mount unit is automatically
                                created. (See
                                <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                                for more information.) This option is
                                mandatory.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>Priority=</varname></term>

                                <listitem><para>Swap priority to use
                                when activating the swap device or
                                file. This takes an integer. This
                                setting is optional.</para></listitem>
                        </varlistentry>

                        <varlistentry>
                                <term><varname>TimeoutSec=</varname></term>
                                <listitem><para>Configures the time to
                                wait for the swapon command to
                                finish. If a command does not exit
                                within the configured time, the swap
                                will be considered failed and be shut
                                down again. All commands still running
                                will be terminated forcibly via
                                <constant>SIGTERM</constant>, and after another delay of
                                this time with <constant>SIGKILL</constant>. (See
                                <option>KillMode=</option> in
                                <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
                                Takes a unit-less value in seconds, or
                                a time span value such as "5min
                                20s". Pass 0 to disable the timeout
                                logic. Defaults to <varname>TimeoutStartSec=</varname> from the
                                manager configuration file.</para></listitem>
                        </varlistentry>
                </variablelist>

                <para>Check
                <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                and
                <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
                for more settings.</para>
        </refsect1>

        <refsect1>
                  <title>See Also</title>
                  <para>
                          <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
                          <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
                  </para>
        </refsect1>

</refentry>