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‎concepts/systemd-targets.xml‎

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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:trans="http://docbook.org/ns/transclusion">
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<info>
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<title>&systemd; targets</title> <!-- can be changed via merge in the assembly -->
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<title>Understanding &systemd; targets</title> <!-- can be changed via merge in the assembly -->
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<!--add author's email address-->
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<meta name="maintainer" content="[email protected]" its:translate="no"/>
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<abstract> <!-- can be changed via merge in the assembly -->
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<para>
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&systemd; uses units and targets. A &systemd; unit defines a service or action on the system, which consists of a name, type, and configuration file.
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A &systemd; target combines several units and defines which services have to be started to reach the target.
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</para>
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</abstract>
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</info>
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<section xml:id="systemd-what-are-targets">
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<title>What are &systemd; targets?</title>
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<para>
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A &systemd; target combines several units and defines which services have to be started to reach the target.
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On a server, for example, this is a state where the network is running and multiple users can log in.
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These files are identified by the suffix <literal>.target</literal>.
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</para>
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<para>Similar to unit files, different targets may be nested via dependencies. For example, <literal>multi-user.target</literal> requires (among others) the targets
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that set up login and user session services.
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</para>
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</abstract>
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</info>
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<para>
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<para>
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Common &systemd; targets:
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</para>
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<variablelist>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>For more information on &systemd; targets, refer to <emphasis>man 5 systemd.target</emphasis>
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and <emphasis>man 7 systemd.special</emphasis>.
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</section>
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<section xml:id="systemd-set-targets">
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<title>Setting up a &systemd; target</title>
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<para>To set up a &systemd; target, you need to create a new target unit file and define any required dependencies.
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A target is a group of unit files that manages the state of services. A target can be used to control groups of services
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or define system states.</para>
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<procedure>
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<step>
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<para>Create a new file with the <literal>.target</literal> extension in <filename>/etc/systemd/system/</filename>. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>vi /etc/systemd/system/test.target</command></screen>
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</step>
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<step>
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<para>Define the target with basic configuration.</para>
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<para>For example:</para>
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<screen>[Unit]
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Description= Test target
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Requires=multi-user.target
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After=multi-user.target
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[Install]
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WantedBy=multi-user.target
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</screen>
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<itemizedlist>
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<listitem>
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<para>
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<emphasis>Requires:</emphasis> specifies that <literal>multi-user.target</literal> must be reached
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for <literal>test.target</literal> to be active.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>After:</emphasis> specifies that this target starts after the <literal>multi-user.target</literal>.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>WantedBy:</emphasis> specifies that this target should be a part of <literal>multi-user.target</literal>.
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</para>
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</listitem>
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</itemizedlist>
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</step>
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<step>
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<para>Set permissions for the target file. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>chmod 644 /etc/systemd/system/test.target
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</command></screen> </step>
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<step>
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<para>Link the required services to the target file. Create a <literal>.wants</literal> directory and then create
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symbolic links to the services you want to include in your custom target.</para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>mkdir -p /etc/systemd/system/custom.target.wants/ </command></screen>
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<screen>&prompt.sudo; <command>ln -s /etc/systemd/system/test.service /etc/systemd/system/custom.target.wants/
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</command></screen>
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</step>
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<step>
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<para>Reload &systemd;. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>systemctl daemon-reload</command></screen> </step>
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<step>
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<para>Start and enable the target. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>systemctl start test.target</command></screen>
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<screen>&prompt.sudo; <command>systemctl enable test.target</command></screen>
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</step>
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<step>
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<para>Verify the status of the custom target. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>systemctl status test.target</command></screen>
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</step>
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<step>
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<para>Verify all the units that are part of this target. </para>
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<para>For example:</para>
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<screen>&prompt.sudo; <command>systemctl list-dependencies test.target </command></screen>
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</step>
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<step><para>Your custom &systemd; target is set up and configured.</para></step>
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</procedure>
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<para>You can use the following common configuration options: </para>
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<itemizedlist>
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<listitem>
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<para>
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<emphasis>Description:</emphasis> human-readable description of the target.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>Documentation:</emphasis> URIs to documentation.</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>AllowIsolate:</emphasis>
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If set to <literal>true</literal>, this unit can be used with the <command>systemctl isolate</command> command.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>Wants:</emphasis>
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Units that can be started but is not mandatory.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>After/Before:</emphasis>
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the order of the dependency.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis>Conflicts:</emphasis>
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units that should not be active while this target is active.
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</para>
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</listitem>
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</itemizedlist>
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<para>For more information on &systemd; targets, refer to <emphasis>man 5 systemd.target</emphasis>
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and <emphasis>man 7 systemd.special</emphasis>.
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</para>
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</section>
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</topic>

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