How to Enable Archive log in a Primary database which is in No Archive Mode | Oracle Database

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First  Check if the Database is in Archive Log or No Archive Log mode:

 Log in as sys or system (sqlplus / as sysdba):

SQL> archive log list

 Database log mode No Archive Mode

 Automatic archival Disabled

 Archive destination USE_DB_RECOVERY_FILE_DEST

 Oldest online log sequence 3

 Current log sequence 5

Now that we have confirmed database to be in No Archive mode, bring the database down:

 SQL> SHUTDOWN IMMEDIATE;

Now enable Archive log mode, steps to do that are:

Start up database in mount mode and enable archive-log and then open database 

SQL> STARTUP MOUNT;

SQL> ALTER DATABASE ARCHIVELOG;

SQL> ALTER DATABASE OPEN;

Check if archive log is now enabled or not:

 SQL> archive log list;

 Database log mode Archive Mode

 Automatic archival Enabled

 Archive destination USE_DB_RECOVERY_FILE_DEST

 Oldest online log sequence 3

 Next log sequence to archive 5

 Current log sequence 5