PROBLEM:

While renaming a RAC database using NID utility, got below error.

NID-00120: Database should be mounted exclusively

SOLUTION:

This error usually comes, when cluster_database parameter is set to TRUE.

So before running the NID tool, make this parameter FALSE.

(if pfile is used change the cluster_database parameter , if spfile, then run the alter statement to set to FALSE)

Shutdown and startup mount:

Now run the nid tool, it will work fine.