A port monitor is responsible for performing the following tasks in addition to its port monitor function:
Writing its process ID into the file _pid and place an advisory lock on the file
Following the protocol for message exchange with the SAC
A port monitor must perform the following tasks during service invocation:
Creating a utmp entry if the requested service has the “-u” flag set in _pmtab
Port monitors might ignore this flag if creating a utmp entry for the service does not make sense because of the manner in which the service is to be invoked. On the other hand, some services might not start properly unless utmp entries have been created for them.