Calendar Server and Messaging Server both integrate minimally into the Monitoring Framework for Java Enterprise System. While the Monitoring Framework is running, it periodically checks the following attribute, operationalStatus , which can have the status of either OK, which means the system is running, or DOWN, which means the system is not running.
A new process, the Monitoring Framework agent (csmfagent), starts with system start up (start-cal). This is the first process started. The process instantiates an application and asserts its status as OK. It also catches SIGTERM and upon catching one, asserts status DOWN and exits.
Similarly, if the Watcher is configured and running, if any part of the system fails or becomes unresponsive, Watcher signals SIGTERM, which stops csmfagent.