Message Oracle ORA-12321 - database (link name string) is not open and AUTO_MOUNTING=FALSE

ERROR	database (link name string) is not open and AUTO_MOUNTING=FALSE
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.