How to rename a Datafile with Extension .dbf?

For example we have  added a datafile but we forgot to give the extension .dbf

Step 1. Shut down the Database

SQL> shutdown immediate;

Step 2. Startup the Database in Mount State

SQL> startup mount

Step 3. Now copy the datafile by renaming it with .dbf extension

$cp /u01/app/oracle/user2  /u01/app/oracle/user2.dbf

Step 4. Now rename database file at Database Level

SQL> alter database rename file ‘/u01/app/oracle/user2’ to ‘/u01/app/oracle/user2.dbf’;

Step 5. Now Open the Database

SQL> alter database open;