If some datafiles are lost or become damaged then when we try start the database then database will not start and it will throw error while opening the database. If we were taking backups using RMAN then we recover the database using RMAN.
Recover from the loss of a datafile assuming the following
To recover from the damaged or lost datafile using RMAN do the following
Try to start the database using SQL Plus
$ export ORACLE_SID=test
When we try to open, Oracle will show an error that a datafile is missing as shown below
From the above the above output we can clearly see that '/u02/oracle/testdb/test/users01.dbf' datafile is not found or damaged.
Now we need to recover it.
To perform a Complete Recovery of this datafile follow the next step
Exit from SQL Plus and start RMAN by typing the following command
$ rman target / nocatalog