Oracle® Database 11g / 12c / 18c error codes ORA-00306: limit of [string] instances in this database

ORA-00306: limit of [string] instances in this database

Oracle Error Code: ORA-00306

Cause: Starting this instance would exceed the maximum number of instances allowed for this database. This message occurs only with STARTUP shared and multiple instances.

Action: You cannot start more than the lower of a) port-specific limit as to the number of instances b) the number of instances specified at create-database time