Oracle 11gR2: ORA-01102: cannot mount database in EXCLUSIVE mode

ORA-01102 cannot mount database in EXCLUSIVE mode

Cause: Some other instance has the database mounted exclusive or shared.
Action: Shut down the other instance or mount in a compatible mode.

Find whether you have any running Oracle process.

$ ps -ef | grep smon

Kill the process then try to start again.

Since I dont have the procedure which you have followed to perform DB rename and DBID change I can not say whether there is problem with your procedure.

I would recommend to follow Oracle Knowledge Document to perform such task.
How to Change the DBID and the DBNAME by using NID

Thanks for JSapkato's response. This made me thinking to find that elusive database instance that prevented me from mounting my database.

It turns out that I made a mistake and used the 1st DB's control file name in the 2nd DB's pfile. I changed the control file names according to the "real" ones in ASM. Now I do not get this "exclusive" mounting errors.

Note: I was following the Oracle document on how to change DB name:

http://docs.oracle.com/cd/B28359_01/server.111/b28319/dbnewid.htm