1- Log in as user oracle and enter the following commands:

$ export ORACLE_SID=<MYDB>

where <MYDB> is the name of the database

$ sqlplus /nolog
SQL> connect / as sysdba

2- To enable ARCHIVELOG mode status, enter the following SQL commands:

SQL> Shutdown
SQL> Startup mount
SQL> Alter database archivelog;
SQL> alter database open;

3- To check the ARCHIVELOG mode status, enter the following SQL command:

SQL> archive log list;
Database log mode 						Archive Mode
Automatic archival 					Enabled
Archive destination 					/oradump/<MYDB>
Oldest online log sequence 		7
Next log sequence to archive 	7
Current log sequence