Merge pull request #13962 from keszybz/man-ordering
Describe ordering in case of Conflicts=
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@ -560,22 +560,44 @@
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effect.</para></listitem>
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effect.</para></listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<term><varname>Wants=</varname></term>
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<listitem><para>Configures requirement dependencies on other units. This option may be specified more
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than once or multiple space-separated units may be specified in one option in which case dependencies
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for all listed names will be created. Dependencies of this type may also be configured outside of the
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unit configuration file by adding a symlink to a <filename>.wants/</filename> directory accompanying
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the unit file. For details, see above.</para>
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<para>Units listed in this option will be started if the configuring unit is. However, if the listed
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units fail to start or cannot be added to the transaction, this has no impact on the validity of the
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transaction as a whole, and this unit will still be started. This is the recommended way to hook
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start-up of one unit to the start-up of another unit.</para>
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<para>Note that requirement dependencies do not influence the order in which services are started or
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stopped. This has to be configured independently with the <varname>After=</varname> or
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<varname>Before=</varname> options. If unit <filename>foo.service</filename> pulls in unit
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<filename>bar.service</filename> as configured with <varname>Wants=</varname> and no ordering is
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configured with <varname>After=</varname> or <varname>Before=</varname>, then both units will be
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started simultaneously and without any delay between them if <filename>foo.service</filename> is
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activated.</para></listitem>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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<term><varname>Requires=</varname></term>
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<term><varname>Requires=</varname></term>
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<listitem><para>Configures requirement dependencies on other units. If this unit gets activated, the units
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<listitem><para>Similar to <varname>Wants=</varname>, but declares a stronger
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listed here will be activated as well. If one of the other units fails to activate, and an ordering dependency
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dependency. Dependencies of this type may also be configured by adding a symlink to a
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<varname>After=</varname> on the failing unit is set, this unit will not be started. Besides, with or without
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<filename>.requires/</filename> directory accompanying the unit file.</para>
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specifying <varname>After=</varname>, this unit will be stopped if one of the other units is explicitly
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stopped. This option may be specified more than once or multiple space-separated units may be
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<para>If this unit gets activated, the units listed will be activated as well. If one of
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specified in one option in which case requirement dependencies for all listed names will be created. Note that
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the other units fails to activate, and an ordering dependency <varname>After=</varname> on the
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requirement dependencies do not influence the order in which services are started or stopped. This has to be
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failing unit is set, this unit will not be started. Besides, with or without specifying
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configured independently with the <varname>After=</varname> or <varname>Before=</varname> options. If a unit
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<varname>After=</varname>, this unit will be stopped if one of the other units is explicitly
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<filename>foo.service</filename> requires a unit <filename>bar.service</filename> as configured with
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stopped.</para>
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<varname>Requires=</varname> and no ordering is configured with <varname>After=</varname> or
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<varname>Before=</varname>, then both units will be started simultaneously and without any delay between them
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<para>Often, it is a better choice to use <varname>Wants=</varname> instead of
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if <filename>foo.service</filename> is activated. Often, it is a better choice to use <varname>Wants=</varname>
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<varname>Requires=</varname> in order to achieve a system that is more robust when dealing with
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instead of <varname>Requires=</varname> in order to achieve a system that is more robust when dealing with
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failing services.</para>
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failing services.</para>
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<para>Note that this dependency type does not imply that the other unit always has to be in active state when
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<para>Note that this dependency type does not imply that the other unit always has to be in active state when
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@ -585,11 +607,7 @@
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example, a service process may decide to exit cleanly, or a device may be unplugged by the user), which is not
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example, a service process may decide to exit cleanly, or a device may be unplugged by the user), which is not
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propagated to units having a <varname>Requires=</varname> dependency. Use the <varname>BindsTo=</varname>
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propagated to units having a <varname>Requires=</varname> dependency. Use the <varname>BindsTo=</varname>
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dependency type together with <varname>After=</varname> to ensure that a unit may never be in active state
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dependency type together with <varname>After=</varname> to ensure that a unit may never be in active state
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without a specific other unit also in active state (see below).</para>
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without a specific other unit also in active state (see below).</para></listitem>
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<para>Note that dependencies of this type may also be configured outside of the unit configuration file by
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adding a symlink to a <filename>.requires/</filename> directory accompanying the unit file. For details, see
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above.</para></listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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@ -610,24 +628,6 @@
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</listitem>
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</listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<term><varname>Wants=</varname></term>
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<listitem><para>A weaker version of
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<varname>Requires=</varname>. Units listed in this option will
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be started if the configuring unit is. However, if the listed
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units fail to start or cannot be added to the transaction,
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this has no impact on the validity of the transaction as a
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whole. This is the recommended way to hook start-up of one
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unit to the start-up of another unit.</para>
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<para>Note that dependencies of this type may also be
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configured outside of the unit configuration file by adding
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symlinks to a <filename>.wants/</filename> directory
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accompanying the unit file. For details, see
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above.</para></listitem>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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<term><varname>BindsTo=</varname></term>
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<term><varname>BindsTo=</varname></term>
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@ -676,15 +676,18 @@
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<varlistentry>
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<varlistentry>
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<term><varname>Conflicts=</varname></term>
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<term><varname>Conflicts=</varname></term>
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<listitem><para>A space-separated list of unit names.
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<listitem><para>A space-separated list of unit names. Configures negative requirement
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Configures negative requirement dependencies. If a unit has a
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dependencies. If a unit has a <varname>Conflicts=</varname> setting on another unit, starting the
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<varname>Conflicts=</varname> setting on another unit,
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former will stop the latter and vice versa.</para>
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starting the former will stop the latter and vice versa. Note
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that this setting is independent of and orthogonal to the
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<varname>After=</varname> and <varname>Before=</varname>
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ordering dependencies.</para>
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<para>If a unit A that conflicts with a unit B is scheduled to
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<para>Note that this setting does not imply an ordering dependency, similarly to the
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<varname>Wants=</varname> and <varname>Requires=</varname> dependencies described above. This means
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that to ensure that the conflicting unit is stopped before the other unit is started, an
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<varname>After=</varname> or <varname>Before=</varname> dependency must be declared. It doesn't
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matter which of the two ordering dependencies is used, because stop jobs are always ordered before
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start jobs, see the discussion in <varname>Before=</varname>/<varname>After=</varname> below.</para>
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<para>If unit A that conflicts with unit B is scheduled to
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be started at the same time as B, the transaction will either
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be started at the same time as B, the transaction will either
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fail (in case both are required parts of the transaction) or be
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fail (in case both are required parts of the transaction) or be
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modified to be fixed (in case one or both jobs are not a
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modified to be fixed (in case one or both jobs are not a
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@ -698,29 +701,36 @@
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<term><varname>Before=</varname></term>
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<term><varname>Before=</varname></term>
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<term><varname>After=</varname></term>
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<term><varname>After=</varname></term>
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<listitem><para>These two settings expect a space-separated list of unit names. They configure ordering
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<listitem><para>These two settings expect a space-separated list of unit names. They may be specified
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dependencies between units. If a unit <filename>foo.service</filename> contains a setting
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more than once, in which case dependencies for all listed names are created.</para>
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<option>Before=bar.service</option> and both units are being started, <filename>bar.service</filename>'s
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start-up is delayed until <filename>foo.service</filename> has finished starting up. Note that this setting is
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<para>Those two setttings configure ordering dependencies between units. If unit
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independent of and orthogonal to the requirement dependencies as configured by <varname>Requires=</varname>,
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<filename>foo.service</filename> contains the setting <option>Before=bar.service</option> and both
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<varname>Wants=</varname> or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both
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units are being started, <filename>bar.service</filename>'s start-up is delayed until
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the <varname>After=</varname> and <varname>Requires=</varname> options, in which case the unit listed will be
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<filename>foo.service</filename> has finished starting up. <varname>After=</varname> is the inverse
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started before the unit that is configured with these options. This option may be specified more than once, in
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of <varname>Before=</varname>, i.e. while <varname>Before=</varname> ensures that the configured unit
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which case ordering dependencies for all listed names are created. <varname>After=</varname> is the inverse of
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is started before the listed unit begins starting up, <varname>After=</varname> ensures the opposite,
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<varname>Before=</varname>, i.e. while <varname>After=</varname> ensures that the configured unit is started
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that the listed unit is fully started up before the configured unit is started.</para>
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after the listed unit finished starting up, <varname>Before=</varname> ensures the opposite, that the
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configured unit is fully started up before the listed unit is started. Note that when two units with an
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<para>When two units with an ordering dependency between them are shut down, the inverse of the
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ordering dependency between them are shut down, the inverse of the start-up order is applied. i.e. if a unit is
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start-up order is applied. i.e. if a unit is configured with <varname>After=</varname> on another
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configured with <varname>After=</varname> on another unit, the former is stopped before the latter if both are
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unit, the former is stopped before the latter if both are shut down. Given two units with any
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shut down. Given two units with any ordering dependency between them, if one unit is shut down and the other is
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ordering dependency between them, if one unit is shut down and the other is started up, the shutdown
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started up, the shutdown is ordered before the start-up. It doesn't matter if the ordering dependency is
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is ordered before the start-up. It doesn't matter if the ordering dependency is
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<varname>After=</varname> or <varname>Before=</varname>, in this case. It also doesn't matter which of the two
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<varname>After=</varname> or <varname>Before=</varname>, in this case. It also doesn't matter which
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is shut down, as long as one is shut down and the other is started up. The shutdown is ordered before the
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of the two is shut down, as long as one is shut down and the other is started up; the shutdown is
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start-up in all cases. If two units have no ordering dependencies between them, they are shut down or started
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ordered before the start-up in all cases. If two units have no ordering dependencies between them,
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up simultaneously, and no ordering takes place. It depends on the unit type when precisely a unit has finished
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they are shut down or started up simultaneously, and no ordering takes place. It depends on the unit
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starting up. Most importantly, for service units start-up is considered completed for the purpose of
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type when precisely a unit has finished starting up. Most importantly, for service units start-up is
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<varname>Before=</varname>/<varname>After=</varname> when all its configured start-up commands have been
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considered completed for the purpose of <varname>Before=</varname>/<varname>After=</varname> when all
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invoked and they either failed or reported start-up success.</para></listitem>
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its configured start-up commands have been invoked and they either failed or reported start-up
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success.</para>
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<para>Note that those settings are independent of and orthogonal to the requirement dependencies as
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configured by <varname>Requires=</varname>, <varname>Wants=</varname>, <varname>Requisite=</varname>,
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or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both the
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<varname>After=</varname> and <varname>Wants=</varname> options, in which case the unit listed will
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be started before the unit that is configured with these options.</para></listitem>
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</varlistentry>
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</varlistentry>
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<varlistentry>
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<varlistentry>
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