If you try to build an Oracle 9i DB from scratch, based upon the instructions in the Oracle 9i DBA Handbook, you've seen this rather cryptic error message,

ORA-01092: ORACLE instance terminated. Disconnection forced

Lucky for me, someone pointed me at the bdump/alert_SID.log, which eventually pointed me to the cure.

Seems you have to pre-create the temporary tablespace's datafile on the drive before you issue your CREATE DATABASE command, something which is confusing because if you put the keyword REUSE in there, it will fail, and usually you have to, if a file exists before Oracle tries to use it.