Oracle® Database 11g / 12c / 18c error codes ORA-12321: database (link name [string]) is not open and AUTO_MOUNTING=FALSE

ORA-12321: database (link name [string]) is not open and AUTO_MOUNTING=FALSE

Oracle Error Code: ORA-12321

Cause: The secondary database that your instance is attempting to mount is not open and automatic mounting has not been enabled.

Action: Manually mount and open the secondary database using ALTER DATABASE with the OPEN and MOUNT options. Alternately, to allow your instance to automatically mount and open secondary databases, set the AUTO_MOUNTING parameter in the parameter file to TRUE.