ORA-01666 When Activating a Physical Standby Database

You’re waking up a Physical standby database, and are welcomed by the following ORA-Code:

ORA-01666: controlfile is for a standby database

Don’t panick, that’s just because the database has been configured as a Standby one. Therefore, you can only open it as a Standby database. Simply start if with the following commands :

sqlplus / as sysdba
startup nomount;
alter database mount standby database;

The database will then open, and you’ll be able to pursue any operation you were doing, Like starting an automatic recovery session, fixing a gap on redo log sequences, etc.