ORA-01092: ORACLE instance terminated

Oracle Database Tips by Donald Burleson

The Oracle docs note details on the ORA-1092 error:

ORA-01092:	ORACLE instance terminated. Disconnection forced
Cause:	The instance connected to was terminated abnormally, probably due to a `SHUTDOWN ABORT`. The current process was forced to disconnect from the instance.
Action:	Examine the alert log for more details. Contact the database administrator to determine when the instance is restarted. Attempt to reconnect after the instance is running again.

The ORA-01092: ORACLE instance terminated Disconnection forced. is a generic error when Oracle detects a serious problem at database start time.

The ORA-01092: ORACLE instance terminated error can be caused by many factors, and I've seen there:

A shutdown abort
Bad permissions of BDUMP, CDUMP or UDUMP directories
Missing datafiles
Renaming files when Oracle is down
and many other OS-related causes

Check your alert log for a more descriptive report of the exact startup problem.

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