SQL> select ARCHIVER from v$instance;

ARCHIVE
-------
STOPPED

SQL>
SQL>
SQL>
SQL>
SQL> -- Convert to Archived log mode..!
SQL> -- 1. shutdown
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> -- 2. startup mount..!
SQL> startup mount
ORACLE instance started.

Total System Global Area  285212672 bytes
Fixed Size                  1218992 bytes
Variable Size             100664912 bytes
Database Buffers          180355072 bytes
Redo Buffers                2973696 bytes
Database mounted.
SQL> -- 3. Convert to Archived log mode.
SQL> alter database archivelog;

Database altered.

SQL> -- 4. open
SQL> alter database open;

Database altered.

SQL> -- 5. Confirm!!
SQL> select ARCHIVER from v$instance;

ARCHIVE
-------
STARTED

SQL> -- 6. view the new archvie file
SQL> show parameter recovery_file_dest

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest                string      /u01/app/oracle/flash_recovery_area
db_recovery_file_dest_size           big integer 2G
SQL>
SQL> host ls /u01/app/oracle/flash_recovery_area/ORCL/archivelog/2008_03_16
SQL> alter system switch logfile;

System altered.

SQL> host ls /u01/app/oracle/flash_recovery_area/ORCL/archivelog/2008_03_16
o1_mf_1_7_3xs8mkqf_.arc