Enable Flashback Mode In Oracle Database

 To Enable Flashback Database 

shutdown immediate;

startup nomount;

alter database mount;

archive log list;

alter database archivelog;

change FRA size and then dest :-

alter system set db_flashback_retention_target=2880; ----> 2880 minutes 

alter system set db_recovery_file_dest_size=10G;

alter system set db_recovery_file_dest='/path/to/FRA';

alter system set undo_retention=86400; -----------> 86400 seconds

alter database flashback on;

alter database open;

if not open then do "alter database open resetlogs" or "alter database open noresetlogs" 

SQL >

select name, value from gv$parameter where name in ('db_flashback_retention_target','db_recovery_file_dest_size','db_recovery_file_dest','undo_retention');

To Check Flashback on/off :-

select flashback_on from gv$database;