How does one put a database into ARCHIVELOG mode?

The main reason for running in archivelog mode is that one can provide 24-hour availability and guarantee complete data recoverability. It is also necessary to enable ARCHIVELOG mode before one can start to use on-line database backups.
Issue the following commands to put a database into ARCHIVELOG mode:
SQL> CONNECT sys AS SYSDBASQL> STARTUP MOUNT EXCLUSIVE;SQL> ALTER DATABASE ARCHIVELOG;SQL> ARCHIVE LOG START;SQL> ALTER DATABASE OPEN;