ORA-01157 | cannot identify/lock data file | ORA-01110 | Oracle Error

 ORA-01157: cannot identify/lock data file 6 - see DBWR trace file ORA-01110: data file 6: '/opt/oracle/db02/nms_index.dbf'
SQL> startup
ORACLE instance started.

Total System Global Area  167772160 bytes
Fixed Size                  1279120 bytes
Variable Size             104860528 bytes
Database Buffers           58720256 bytes
Redo Buffers                2912256 bytes
Database mounted.
ORA-01157: cannot identify/lock data file 6 - see DBWR trace file
ORA-01110: data file 6: '/opt/oracle/db02/nms_index.dbf'


SQL>
SQL>
SQL> shut abort
ORACLE instance shut down.
SQL>
SQL> startup mount
ORACLE instance started

SQL> alter database datafile '/opt/oracle/db02/nms_index.dbf' offline drop;

Drop all such DBF files using above command.

Database altered