add Task scheduler

docs/system/index.rst

@@ -16,4 +16,5 @@ should be ready for further configuration which is described in this chapter.
    host-information
    systemusers
    syslog
+   task-scheduler
    config-management

docs/system/task-scheduler.rst

@@ -0,0 +1,59 @@
+.. _task-scheduler:
+
+
+Task scheduler
+--------------
+
+Task scheduler — allows scheduled task execution. Note that scripts excecuted this way are executed as root user - this may be dangerous.
+
+.. code-block:: sh
+
+  system
+      task-scheduler
+          task <name>
+              cron-spec <UNIX cron time spec>
+              executable
+                  arguments <arguments string>
+                  path <path to executable>
+              interval
+                  <int32>[mhd]
+
+Interval
+********
+
+You are able to set the time as an time interval.
+
+.. code-block:: sh
+
+  set system task-scheduler task <name> interval <value><suffix>
+
+Sets the task to execute every N minutes, hours, or days. Suffixes:
+
+ * m — minutes
+ * h — hours
+ * d — days
+
+If suffix is omitted, minutes are implied.
+
+Or set the execution time in common cron time.
+
+.. code-block:: sh
+
+  set system task-scheduler task TEST crontab-spec "* * * 1 *"
+
+Example
+*******
+
+.. code-block:: sh
+
+  system
+      task-scheduler
+          task mytask
+              interval 2h
+              executable
+                  path /config/scripts/mytask
+                  arguments "arg1 arg2 arg3"
+          task anothertask
+              cron-spec "* * * 1 *"
+              executable
+                  path /config/scripts/anothertask