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Before events can be used the event service has to be installed. It is part of the JobScheduler installation if ordered within the installation procedure.
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But it is also possible to install the event service in an existing JobScheduler instance . For more information have a look at How to install the Event Service feature in JobScheduler
The job chain scheduler_event_service is running in predetermined intervals or whenever an event is created and checks all .xml data files in folder $SCHEDULER_DATA//config/events for information matching the active events which are stored in the data base table .