Oracle® Database 11g / 12c / 18c error codes ORA-01147: SYSTEM tablespace file [string] is offline

ORA-01147: SYSTEM tablespace file [string] is offline

Oracle Error Code: ORA-01147

Cause: A file belonging to the SYSTEM tablespace has been marked offline by the DBA. The database cannot be started until all SYSTEM tablespace files are online and openable.

Action: Bring the file online.