man: put description of Wants= above Requires=
We want users to use Wants, but we'd describe Requires first and ask users to look for Wants instead. While at it, let's split the wall of text into sensible paragraphs: syntax first, followed by semantics and longer description, and finally hints and comparison to other configuration items last.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
parent
3126d64e5f
commit
d19cd71a8a
|
|
@ -555,22 +555,44 @@
|
|||
effect.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>Wants=</varname></term>
|
||||
|
||||
<listitem><para>Configures requirement dependencies on other units. This option may be specified more
|
||||
than once or multiple space-separated units may be specified in one option in which case dependencies
|
||||
for all listed names will be created. Dependencies of this type may also be configured outside of the
|
||||
unit configuration file by adding a symlink to a <filename>.wants/</filename> directory accompanying
|
||||
the unit file. For details, see above.</para>
|
||||
|
||||
<para>Units listed in this option will be started if the configuring unit is. However, if the listed
|
||||
units fail to start or cannot be added to the transaction, this has no impact on the validity of the
|
||||
transaction as a whole, and this unit will still be started. This is the recommended way to hook
|
||||
start-up of one unit to the start-up of another unit.</para>
|
||||
|
||||
<para>Note that requirement dependencies do not influence the order in which services are started or
|
||||
stopped. This has to be configured independently with the <varname>After=</varname> or
|
||||
<varname>Before=</varname> options. If unit <filename>foo.service</filename> pulls in unit
|
||||
<filename>bar.service</filename> as configured with <varname>Wants=</varname> and no ordering is
|
||||
configured with <varname>After=</varname> or <varname>Before=</varname>, then both units will be
|
||||
started simultaneously and without any delay between them if <filename>foo.service</filename> is
|
||||
activated.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>Requires=</varname></term>
|
||||
|
||||
<listitem><para>Configures requirement dependencies on other units. If this unit gets activated, the units
|
||||
listed here will be activated as well. If one of the other units fails to activate, and an ordering dependency
|
||||
<varname>After=</varname> on the failing unit is set, this unit will not be started. Besides, with or without
|
||||
specifying <varname>After=</varname>, this unit will be stopped if one of the other units is explicitly
|
||||
stopped. This option may be specified more than once or multiple space-separated units may be
|
||||
specified in one option in which case requirement dependencies for all listed names will be created. Note that
|
||||
requirement dependencies do not influence the order in which services are started or stopped. This has to be
|
||||
configured independently with the <varname>After=</varname> or <varname>Before=</varname> options. If a unit
|
||||
<filename>foo.service</filename> requires a unit <filename>bar.service</filename> as configured with
|
||||
<varname>Requires=</varname> and no ordering is configured with <varname>After=</varname> or
|
||||
<varname>Before=</varname>, then both units will be started simultaneously and without any delay between them
|
||||
if <filename>foo.service</filename> is activated. Often, it is a better choice to use <varname>Wants=</varname>
|
||||
instead of <varname>Requires=</varname> in order to achieve a system that is more robust when dealing with
|
||||
<listitem><para>Similar to <varname>Wants=</varname>, but declares a stronger
|
||||
dependency. Dependencies of this type may also be configured by adding a symlink to a
|
||||
<filename>.requires/</filename> directory accompanying the unit file.</para>
|
||||
|
||||
<para>If this unit gets activated, the units listed will be activated as well. If one of
|
||||
the other units fails to activate, and an ordering dependency <varname>After=</varname> on the
|
||||
failing unit is set, this unit will not be started. Besides, with or without specifying
|
||||
<varname>After=</varname>, this unit will be stopped if one of the other units is explicitly
|
||||
stopped.</para>
|
||||
|
||||
<para>Often, it is a better choice to use <varname>Wants=</varname> instead of
|
||||
<varname>Requires=</varname> in order to achieve a system that is more robust when dealing with
|
||||
failing services.</para>
|
||||
|
||||
<para>Note that this dependency type does not imply that the other unit always has to be in active state when
|
||||
|
|
@ -580,11 +602,7 @@
|
|||
example, a service process may decide to exit cleanly, or a device may be unplugged by the user), which is not
|
||||
propagated to units having a <varname>Requires=</varname> dependency. Use the <varname>BindsTo=</varname>
|
||||
dependency type together with <varname>After=</varname> to ensure that a unit may never be in active state
|
||||
without a specific other unit also in active state (see below).</para>
|
||||
|
||||
<para>Note that dependencies of this type may also be configured outside of the unit configuration file by
|
||||
adding a symlink to a <filename>.requires/</filename> directory accompanying the unit file. For details, see
|
||||
above.</para></listitem>
|
||||
without a specific other unit also in active state (see below).</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
|
|
@ -605,24 +623,6 @@
|
|||
</listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>Wants=</varname></term>
|
||||
|
||||
<listitem><para>A weaker version of
|
||||
<varname>Requires=</varname>. Units listed in this option will
|
||||
be started if the configuring unit is. However, if the listed
|
||||
units fail to start or cannot be added to the transaction,
|
||||
this has no impact on the validity of the transaction as a
|
||||
whole. This is the recommended way to hook start-up of one
|
||||
unit to the start-up of another unit.</para>
|
||||
|
||||
<para>Note that dependencies of this type may also be
|
||||
configured outside of the unit configuration file by adding
|
||||
symlinks to a <filename>.wants/</filename> directory
|
||||
accompanying the unit file. For details, see
|
||||
above.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
<term><varname>BindsTo=</varname></term>
|
||||
|
||||
|
|
@ -679,7 +679,7 @@
|
|||
<varname>After=</varname> and <varname>Before=</varname>
|
||||
ordering dependencies.</para>
|
||||
|
||||
<para>If a unit A that conflicts with a unit B is scheduled to
|
||||
<para>If unit A that conflicts with unit B is scheduled to
|
||||
be started at the same time as B, the transaction will either
|
||||
fail (in case both are required parts of the transaction) or be
|
||||
modified to be fixed (in case one or both jobs are not a
|
||||
|
|
@ -693,29 +693,36 @@
|
|||
<term><varname>Before=</varname></term>
|
||||
<term><varname>After=</varname></term>
|
||||
|
||||
<listitem><para>These two settings expect a space-separated list of unit names. They configure ordering
|
||||
dependencies between units. If a unit <filename>foo.service</filename> contains a setting
|
||||
<option>Before=bar.service</option> and both units are being started, <filename>bar.service</filename>'s
|
||||
start-up is delayed until <filename>foo.service</filename> has finished starting up. Note that this setting is
|
||||
independent of and orthogonal to the requirement dependencies as configured by <varname>Requires=</varname>,
|
||||
<varname>Wants=</varname> or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both
|
||||
the <varname>After=</varname> and <varname>Requires=</varname> options, in which case the unit listed will be
|
||||
started before the unit that is configured with these options. This option may be specified more than once, in
|
||||
which case ordering dependencies for all listed names are created. <varname>After=</varname> is the inverse of
|
||||
<varname>Before=</varname>, i.e. while <varname>After=</varname> ensures that the configured unit is started
|
||||
after the listed unit finished starting up, <varname>Before=</varname> ensures the opposite, that the
|
||||
configured unit is fully started up before the listed unit is started. Note that when two units with an
|
||||
ordering dependency between them are shut down, the inverse of the start-up order is applied. i.e. if a unit is
|
||||
configured with <varname>After=</varname> on another unit, the former is stopped before the latter if both are
|
||||
shut down. Given two units with any ordering dependency between them, if one unit is shut down and the other is
|
||||
started up, the shutdown is ordered before the start-up. It doesn't matter if the ordering dependency is
|
||||
<varname>After=</varname> or <varname>Before=</varname>, in this case. It also doesn't matter which of the two
|
||||
is shut down, as long as one is shut down and the other is started up. The shutdown is ordered before the
|
||||
start-up in all cases. If two units have no ordering dependencies between them, they are shut down or started
|
||||
up simultaneously, and no ordering takes place. It depends on the unit type when precisely a unit has finished
|
||||
starting up. Most importantly, for service units start-up is considered completed for the purpose of
|
||||
<varname>Before=</varname>/<varname>After=</varname> when all its configured start-up commands have been
|
||||
invoked and they either failed or reported start-up success.</para></listitem>
|
||||
<listitem><para>These two settings expect a space-separated list of unit names. They may be specified
|
||||
more than once, in which case dependencies for all listed names are created.</para>
|
||||
|
||||
<para>Those two setttings configure ordering dependencies between units. If unit
|
||||
<filename>foo.service</filename> contains the setting <option>Before=bar.service</option> and both
|
||||
units are being started, <filename>bar.service</filename>'s start-up is delayed until
|
||||
<filename>foo.service</filename> has finished starting up. <varname>After=</varname> is the inverse
|
||||
of <varname>Before=</varname>, i.e. while <varname>Before=</varname> ensures that the configured unit
|
||||
is started before the listed unit begins starting up, <varname>After=</varname> ensures the opposite,
|
||||
that the listed unit is fully started up before the configured unit is started.</para>
|
||||
|
||||
<para>When two units with an ordering dependency between them are shut down, the inverse of the
|
||||
start-up order is applied. i.e. if a unit is configured with <varname>After=</varname> on another
|
||||
unit, the former is stopped before the latter if both are shut down. Given two units with any
|
||||
ordering dependency between them, if one unit is shut down and the other is started up, the shutdown
|
||||
is ordered before the start-up. It doesn't matter if the ordering dependency is
|
||||
<varname>After=</varname> or <varname>Before=</varname>, in this case. It also doesn't matter which
|
||||
of the two is shut down, as long as one is shut down and the other is started up; the shutdown is
|
||||
ordered before the start-up in all cases. If two units have no ordering dependencies between them,
|
||||
they are shut down or started up simultaneously, and no ordering takes place. It depends on the unit
|
||||
type when precisely a unit has finished starting up. Most importantly, for service units start-up is
|
||||
considered completed for the purpose of <varname>Before=</varname>/<varname>After=</varname> when all
|
||||
its configured start-up commands have been invoked and they either failed or reported start-up
|
||||
success.</para>
|
||||
|
||||
<para>Note that those settings are independent of and orthogonal to the requirement dependencies as
|
||||
configured by <varname>Requires=</varname>, <varname>Wants=</varname>, <varname>Requisite=</varname>,
|
||||
or <varname>BindsTo=</varname>. It is a common pattern to include a unit name in both the
|
||||
<varname>After=</varname> and <varname>Wants=</varname> options, in which case the unit listed will
|
||||
be started before the unit that is configured with these options.</para></listitem>
|
||||
</varlistentry>
|
||||
|
||||
<varlistentry>
|
||||
|
|
|
|||
Loading…
Reference in New Issue