respectively. The prefix name here refers to the
string before the @, i.e. "getty" in the example
above, where "tty3" is the instance name.</para>
+
+ <para>If a unit file is empty (i.e. has the file size
+ 0) or is symlinked to <filename>/dev/null</filename>
+ its configuration will not be loaded and it appears
+ with a load state of <literal>masked</literal>, and
+ cannot be activated. Use this as an effective way to
+ fully disable a unit, making it impossible to start it
+ even manually.</para>
+
+ <para>The unit file format is covered by the
+ <ulink
+ url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
+ Stability Promise</ulink>.</para>
</refsect1>
<refsect1>
<listitem><para>Lists one or more
units that are activated when this
- unit fails (i.e. enters maintenance
- state).</para></listitem>
+ unit enters the
+ '<literal>failed</literal>'
+ state.</para></listitem>
</varlistentry>
<varlistentry>
<option>false</option>.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>AllowIsolate=</varname></term>
+
+ <listitem><para>Takes a boolean
+ argument. If <option>true</option>
+ this unit may be used with the
+ <command>systemctl isolate</command>
+ command. Otherwise this will be
+ refused. It probably is a good idea to
+ leave this disabled except for target
+ units that shall be used similar to
+ runlevels in SysV init systems, just
+ as a precaution to avoid unusable
+ system states. This option defaults to
+ <option>false</option>.</para></listitem>
+ </varlistentry>
+
<varlistentry>
<term><varname>DefaultDependencies=</varname></term>
time. If this time limit is reached
the job will be cancelled, the unit
however will not change state or even
- enter maintenance mode. This value
- defaults to 0 (job timeouts disabled),
- except for device units. NB: this
- timeout is independent from any
- unit-specific timeout (for example,
- the timeout set with
+ enter the '<literal>failed</literal>'
+ mode. This value defaults to 0 (job
+ timeouts disabled), except for device
+ units. NB: this timeout is independent
+ from any unit-specific timeout (for
+ example, the timeout set with
<varname>Timeout=</varname> in service
- units) as the job timeout has no effect
- on the unit itself, only on the job
- that might be pending for it. Or in
- other words: unit-specific timeouts
+ units) as the job timeout has no
+ effect on the unit itself, only on the
+ job that might be pending for it. Or
+ in other words: unit-specific timeouts
are useful to abort unit state
changes, and revert them. The job
timeout set with this option however
- is useful to abort only the job waiting
- for the unit state to change.</para></listitem>
+ is useful to abort only the job
+ waiting for the unit state to
+ change.</para></listitem>
</varlistentry>
+ <varlistentry>
+ <term><varname>ConditionPathExists=</varname></term>
+ <term><varname>ConditionKernelCommandLine=</varname></term>
+
+ <listitem><para>Before starting a unit
+ verify that the specified condition is
+ true. With
+ <varname>ConditionPathExists=</varname>
+ a file existance condition can be
+ checked before a unit is started. If
+ the specified absolute path name does
+ not exist startup of a unit will not
+ actually happen, however the unit is
+ still useful for ordering purposes in
+ this case. The condition is checked at
+ the time the queued start job is to be
+ executed. If the absolute path name
+ passed to
+ <varname>ConditionPathExists=</varname>
+ is prefixed with an exclamation mark
+ (!), the test is negated, and the unit
+ only started if the path does not
+ exist. Similarly
+ <varname>ConditionKernelCommandLine=</varname>
+ may be used to check whether a
+ specific kernel command line option is
+ set (or if prefixed with the
+ exclamation mark unset). The argument
+ must either be a single word, or an
+ assignment (i.e. two words, seperated
+ by the equality sign). In the former
+ case the kernel command line is search
+ for the word appearing as is, or as
+ left hand side of an assignment. In
+ the latter case the exact assignment
+ is looked for with right and left hand
+ side matching. If multiple conditions
+ are specified the unit will be
+ executed iff at least one of them
+ apply (i.e. a logical OR is
+ applied).</para></listitem>
+ </varlistentry>
</variablelist>
<para>Unit file may include a [Install] section, which
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