ORA-12720: operation requires database is in EXCLUSIVE mode

ERROR

CREATE CONTROLFILE .................................
   .................................................
CHARACTER SET AL32UTF8;

ERROR at line 1:
ORA-01503: CREATE CONTROLFILE failed
ORA-12720: operation requires database is in EXCLUSIVE mode

SOLUTION

SQL> alter system set cluster_database=FALSE scope=spfile sid='*';
SQL> shutdown immediate; 
SQL>startup nomount;

Now, re-run script for creating controlfile 

CREATE CONTROLFILE .................................
   .................................................
CHARACTER SET AL32UTF8;

Control file created.

Then, change parameter with its old value and restart database.

SQL>alter system set cluster_database=TRUE scope=spfile sid='*';