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264 lines
13 KiB
XML
264 lines
13 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="systemd.swap"
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xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>systemd.swap</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd.swap</refentrytitle>
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<manvolnum>5</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd.swap</refname>
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<refpurpose>Swap unit configuration</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename><replaceable>swap</replaceable>.swap</filename></para>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para>A unit configuration file whose name ends in
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<literal>.swap</literal> encodes information about a swap device
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or file for memory paging controlled and supervised by
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systemd.</para>
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<para>This man page lists the configuration options specific to
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this unit type. See
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for the common options of all unit configuration files. The common
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configuration items are configured in the generic [Unit] and
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[Install] sections. The swap specific configuration options are
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configured in the [Swap] section.</para>
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<para>Additional options are listed in
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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which define the execution environment the <citerefentry
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project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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program is executed in, in
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<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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which define the way these processes are
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terminated, and in
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<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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which configure resource control settings for these processes of the
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unit.</para>
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<para>Swap units must be named after the devices or files they control. Example: the swap device <filename
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index="false">/dev/sda5</filename> must be configured in a unit file <filename>dev-sda5.swap</filename>. For
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details about the escaping logic used to convert a file system path to a unit name, see
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Note that swap
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units cannot be templated, nor is possible to add multiple names to a swap unit by creating additional symlinks to
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it.</para>
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<para>Note that swap support on Linux is privileged, swap units are hence only available in the system
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service manager (and root's user service manager), but not in unprivileged user's service manager.</para>
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</refsect1>
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<refsect1>
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<title>Automatic Dependencies</title>
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<refsect2>
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<title>Implicit Dependencies</title>
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<para>The following dependencies are implicitly added:</para>
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<itemizedlist>
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<listitem><para>All swap units automatically get the
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<varname>BindsTo=</varname> and <varname>After=</varname>
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dependencies on the device units or the mount units of the files
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they are activated from.</para></listitem>
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</itemizedlist>
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<para>Additional implicit dependencies may be added as result of
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execution and resource control parameters as documented in
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
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</refsect2>
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<refsect2>
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<title>Default Dependencies</title>
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<para>The following dependencies are added unless <varname>DefaultDependencies=no</varname> is set:</para>
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<itemizedlist>
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<listitem><para>Swap units automatically acquire a <varname>Conflicts=</varname> and a
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<varname>Before=</varname> dependency on <filename>umount.target</filename> so that they are deactivated at
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shutdown as well as a <varname>Before=swap.target</varname> dependency.</para></listitem>
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</itemizedlist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title><filename>fstab</filename></title>
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<para>Swap units may either be configured via unit files, or via
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<filename>/etc/fstab</filename> (see
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<citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for details). Swaps listed in <filename>/etc/fstab</filename> will
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be converted into native units dynamically at boot and when the
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configuration of the system manager is reloaded. See
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<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for details about the conversion.</para>
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<para>If a swap device or file is configured in both
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<filename>/etc/fstab</filename> and a unit file, the configuration
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in the latter takes precedence.</para>
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<para>When reading <filename>/etc/fstab</filename>, a few special
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options are understood by systemd which influence how dependencies
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are created for swap units.</para>
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<variablelist class='fstab-options'>
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<varlistentry>
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<term><option>noauto</option></term>
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<term><option>auto</option></term>
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<listitem><para>With <option>noauto</option>, the swap unit
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will not be added as a dependency for
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<filename>swap.target</filename>. This means that it will not
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be activated automatically during boot, unless it is pulled in
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by some other unit. The <option>auto</option> option has the
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opposite meaning and is the default.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><option>nofail</option></term>
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<listitem><para>With <option>nofail</option>, the swap unit
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will be only wanted, not required by
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<filename>swap.target</filename>. This means that the boot
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will continue even if this swap device is not activated
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successfully.</para>
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</listitem>
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</varlistentry>
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<xi:include href="systemd.mount.xml" xpointer="device-timeout" />
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<varlistentry>
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<term><option>x-systemd.makefs</option></term>
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<listitem><para>The swap structure will be initialized on the device. If the device is not
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"empty", i.e. it contains any signature, the operation will be skipped. It is hence expected
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that this option remains set even after the device has been initialized.</para>
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<para>Note that this option can only be used in <filename>/etc/fstab</filename>, and will be
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ignored when part of the <varname>Options=</varname> setting in a unit file.</para>
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<para>See
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<citerefentry><refentrytitle>systemd-mkswap@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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and the discussion of
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<citerefentry project='man-pages'><refentrytitle>wipefs</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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in <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para>Swap unit files must include a [Swap] section, which carries
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information about the swap device it supervises. A number of
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options that may be used in this section are shared with other
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unit types. These options are documented in
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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The options specific to the [Swap] section of swap units are the
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following:</para>
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<variablelist class='unit-directives'>
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<varlistentry>
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<term><varname>What=</varname></term>
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<listitem><para>Takes an absolute path of a device node or file to use for paging. See <citerefentry
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project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry> for
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details. If this refers to a device node, a dependency on the respective device unit is automatically
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created. (See
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<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for more information.) If this refers to a file, a dependency on the respective mount unit is
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automatically created. (See
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<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
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more information.) This option is mandatory. Note that the usual specifier expansion is applied to
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this setting, literal percent characters should hence be written as
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<literal class='specifiers'>%%</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Priority=</varname></term>
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<listitem><para>Swap priority to use when activating the swap
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device or file. This takes an integer. This setting is
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optional and ignored when the priority is set by <option>pri=</option> in the
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<varname>Options=</varname> key.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>Options=</varname></term>
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<listitem><para>May contain an option string for the swap device. This may be used for controlling discard
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options among other functionality, if the swap backing device supports the discard or trim operation. (See
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<citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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for more information.) Note that the usual specifier expansion is applied to this setting, literal percent
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characters should hence be written as <literal>%%</literal>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>TimeoutSec=</varname></term>
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<listitem><para>Configures the time to wait for the swapon
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command to finish. If a command does not exit within the
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configured time, the swap will be considered failed and be
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shut down again. All commands still running will be terminated
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forcibly via <constant>SIGTERM</constant>, and after another
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delay of this time with <constant>SIGKILL</constant>. (See
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<option>KillMode=</option> in
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<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>.)
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Takes a unit-less value in seconds, or a time span value such
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as "5min 20s". Pass <literal>0</literal> to disable the
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timeout logic. Defaults to
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<varname>DefaultTimeoutStartSec=</varname> from the manager
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configuration file (see
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<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>).
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</para></listitem>
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</varlistentry>
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</variablelist>
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<para>Check
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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and
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<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>
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for more settings.</para>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.kill</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
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<citerefentry project='man-pages'><refentrytitle>swapon</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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