While starting a database in RAC, either using startup or srvctl , got error 

ORA-01102: cannot mount database in EXCLUSIVE mode

 

Solution:

This error comes, when cluster_database parameter is set to false. Change it to TRUE and try to start again.

 

startup nomount
alter system set cluster_database=TRUE scope=spfile sid='*';
shutdown immediate;
srvctl start database -d DB_NAME