How to change Database ID

                      How to change Database ID

Step 1: Backup the database.
Step 2: Mount the database after a clean shutdown:

bash$ SHUTDOWN IMMEDIATE
bash$ STARTUP MOUNT

Step 3 :Invoke the DBNEWID utility (nid) from the command line using a user with SYSDBA privilege. Do not specify a new DBNAME:

bash$ nid TARGET=sys/password@SID

(below out put may expected)
DBNEWID: Release 10.2.0.1.0 - Production on Sat Feb 5 13:56:00 2011
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to database MYDB (DBID=2730365025)
Connected to server version 10.2.0
Control Files in database:
    /export/home/oracle/oradg/oradata/control01.ctl
    /export/home/oracle/oradg/oradata/control02.ctl
    /export/home/oracle/oradg/oradata/control03.ctl
Change database ID of database MYDB? (Y/[N]) => Y
Proceeding with operation
Changing database ID from 2730365025 to 2657293041
    Control File /export/home/oracle/oradg/oradata/control01.ctl - modified
    Control File /export/home/oracle/oradg/oradata/control02.ctl - modified
    Control File /export/home/oracle/oradg/oradata/control03.ctl - modified
    Datafile /export/home/oracle/oradg/oradata/system01.dbf - dbid changed
    Datafile /export/home/oracle/oradg/oradata/undotbs01.dbf - dbid changed
    Datafile /export/home/oracle/oradg/oradata/sysaux01.dbf - dbid changed
    Datafile /export/home/oracle/oradg/oradata/users01.dbf - dbid changed
    Datafile /export/home/oracle/oradg/oradata/temp01.dbf - dbid changed
    Control File /export/home/oracle/oradg/oradata/control01.ctl - dbid changed
    Control File /export/home/oracle/oradg/oradata/control02.ctl - dbid changed
    Control File /export/home/oracle/oradg/oradata/control03.ctl - dbid changed
    Instance shut down
Database ID for database MYDB changed to 2657293041.
All previous backups and archived redo logs for this database are unusable.
Database has been shutdown, open database with RESETLOGS option.
Succesfully changed database ID.
DBNEWID - Completed succesfully.
Step 4 :Shutdown and open the database with RESETLOGS:

bash$ SHUTDOWN IMMEDIATE
bash$ STARTUP MOUNT
bash$ ALTER DATABASE OPEN RESETLOGS;

Step 5 : Backup the database.