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-rw-r--r--man/systemctl.xml35
1 files changed, 30 insertions, 5 deletions
diff --git a/man/systemctl.xml b/man/systemctl.xml
index b4727d9730..94f238041a 100644
--- a/man/systemctl.xml
+++ b/man/systemctl.xml
@@ -371,11 +371,36 @@ along with systemd; If not, see <http://www.gnu.org/licenses/>.
<listitem>
<para>When used with <command>kill</command>, choose which
- processes to kill. Must be one of <option>main</option>,
- <option>control</option> or <option>all</option> to select
- whether to kill only the main process of the unit, the
- control process or all processes of the unit. If omitted,
- defaults to <option>all</option>.</para>
+ processes to send a signal to. Must be one of
+ <option>main</option>, <option>control</option> or
+ <option>all</option> to select whether to kill only the main
+ process, the control process or all processes of the
+ unit. The main process of the unit is the one that defines
+ the life-time of it. A control process of a unit is one that
+ is invoked by the manager to induce state changes of it. For
+ example, all processes started due to the
+ <varname>ExecStartPre=</varname>,
+ <varname>ExecStop=</varname> or
+ <varname>ExecReload=</varname> settings of service units are
+ control processes. Note that there is only one control
+ process per unit at a time, as only one state change is
+ executed at a time. For services of type
+ <varname>Type=forking</varname> the initial process started
+ by the manager for <varname>ExecStart=</varname> is a
+ control process, while the process ultimately forked off by
+ that one is then considered the main process of the unit (if
+ it can be determined). This is different for service units
+ of other types, where the process forked off by the manager
+ for <varname>ExecStart=</varname> is always the main process
+ itself. A service unit consists of no or one main process,
+ no or one control process plus any number of additional
+ processes. Not all unit types manage processes of these
+ types however. For example for mount units control processes
+ are defined (which are the invocations of
+ <filename>/usr/bin/mount</filename> and
+ <filename>/usr/bin/umount</filename>), but no main process
+ is defined. If omitted, defaults to
+ <option>all</option>.</para>
</listitem>
</varlistentry>