SQL> shutdown immediate

Database closed.

Database dismounted.

ORACLE instance shut down.

SQL>startup mount;

ORACLE instance started.

Total System Global Area 1653518336 bytes

Fixed Size                  2253784 bytes

Variable Size            1207962664 bytes

Database Buffers          436207616 bytes

Redo Buffers                7094272 bytes

Database mounted.

SQL> alter database archivelog;

Database altered.

SQL> archive log list;

Database log mode              Archive Mode

Automatic archival             Enabled

Archive destinationUSE_DB_RECOVERY_FILE_DEST

Oldest online log sequence     18

Next log sequence to archive   20

Current log sequence           20