Sometimes when we trying to start “Online Backup” on our ORACLE/SAP system we get an error like “ORA-01123: cannot start online backup; media recovery not enabled”

For Oracle Version 10g and 11g please use the following syntax on SQLPlus ;
 SQL>alter database begin backup;

For Oracle version 8 and 9 , you have to change your backup mode for each tablespace thats why you have to use following syntax for each tablespace;

example

SQL>alter tablespace users begin backup;

After this step you may get following message shown below ;

ORA-01123 appears after you have run one of the begin backup commands having the following message:

ORA-01123: cannot start online backup; media recovery not enabled.

Then first you have to check your Oracle database status is “ENABLE ONLINE MODE” or Not ?

You can use the following syntax for this info;

SQL> ARCHIVE LOG LIST;

If your database is not working with ONLINE MODE status then you will get the following message;

Database is in non archive mode

Then you have to change your Oracle Database Mode with following syntax , you have to know that “Shutting Down the Database” is MUST for this operation

SQL>shutdown immediate;

SQL>startup mount;

SQL>alter database archivelog;

SQL>Alter database open;

After all,  your ONLINE BACKUP will be Started without any problem…