ORA-00236: snapshot operation disallowed: mounted control file is a backup

If you try to take the backup of a controlfile and it returns ORA-00236, it means that you are trying to take backup of a controlfile that is already a backup. The scenario is that you are performing recovery of a database, and during this process, you restored the backup of controlfile. Before recovery is completed and database is opened, the status of controlfile remains “backup”, and trying to backup the controlfile would return ORA-00236. 

Following is a real time scenario when I faced this problem.

RMAN> backup format '/backup/testdb/control_4jun.bak' current controlfile;    Starting backup at 04-JUN-18  allocated channel: ORA_DISK_1  channel ORA_DISK_1: SID=4201 device type=DISK  channel ORA_DISK_1: starting full datafile backup set  channel ORA_DISK_1: specifying datafile(s) in backup set  RMAN-00571: ===========================================================  RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============  RMAN-00571: ===========================================================  RMAN-03009: failure of backup command on ORA_DISK_1 channel at 06/04/2018 13:01:12  ORA-00236: snapshot operation disallowed: mounted control file is a backup

Following output shows the status of the controlfile   

SQL > select controlfile_type from v$database;    CONTROL  -------------  BACKUP    1 row selected.

If controlfile type is CURRENT or STANDBY, you should be able to take the backup of the control file without any problem.