What does PMON do?

PMON (Process Monitor)

• Process Monitor is an Oracle background process created when you start a database instance. 
• The PMON process will free up resources if a user process fails (release database locks).
• Is in charge to perform process recovery when a user process fails (also when killed).
• Rolls back any open transactions for the process.
• PMON normally wakes up every 3 seconds to perform its housekeeping activities. 
• PMON must always be running for an instance. If not, the instance will terminate.

Check process

The following Unix/Linux command is used to check if the PMON process is running:

$ ps -ef | grep pmon

Speed-up PMON

To speed-up housekeeping, one may also wake-up PMON (process 2 below) manually:

SQL> oradebug setmypid

SQL> oradebug wakeup 2