From Oracle FAQ
PMON (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 (eg. release database locks).
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.
To speed-up housekeeping, one may also wake-up PMON (process 2 below) manually:
SQL> oradebug setmypid SQL> oradebug wakeup 2
In Oracle releases prior to Oracle 12c, PMON also registered database serviced with the listener. This is now handled by the new LREG progress.
The following Unix/Linux command is used to check if the PMON process is running:
$ ps -ef | grep pmon oracle 31144 1 0 11:10 ? 00:00:00 ora_pmon_orcl
|Glossary of Terms|