Set FRA to indicate ORA-38706 and ORA-38709 when enabled

Background
 
When installing the Oracle database software, we have a flash recovery area option. If we do not select this option, it means that the quick recovery area is not enabled. We can enable or disable it after the database is installed.
 
To enable or disable FRA, you must enable the database in the mount state and archive mode, and execute alter database flashback on/off;
 
The following error is reported when alter database flashback on is executed:
 
ORA-38706: Cannot turn on flashback database logging.
ORA-38709: Recovery Area is not enabled.
 

Solution:
 
1. query through oerr ora 38709 with the following prompt:
 
38709,000 00, "Recovery Area is not enabled ."
// * Cause: An alter database flashback on command failed because
// Recovery Area was not enabled.
// * Action: Set DB_RECOVERY_FILE_DEST to a location and retry.
 

It is clear from the prompts that oracle requires us to set the DB_RECOVERY_FILE_DEST parameter, which represents the storage path of FRA.
 
2. Before setting the DB_RECOVERY_FILE_DEST parameter, you must set DB_RECOVERY_FILE_DEST_SIZE, which is the FRA space size.
 
3. Set these two parameters
 
SQL> alter system set db_recovery_file_dest_size = 5G;
 

SQL> alter system set db_recovery_file_dest = '/home/oracle/fras ';
 
4. Set the database's FRA to ON
 
SQL> alter database flashback on;
 
This problem is solved.