ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode

I am trying to execute the command "backup database" in RMAN prompt, and it fails to execute and display below error.

Error:

RMAN-03009: failure of backup command on ORA_DISK_1 channel at   
ORA-19602: cannot backup or copy active file in NOARCHIVELOG mode


Cause: Your database is running into NOARCHIVELOG mode

Solution: Enable the ARCHIVELOG mode for your database and try agian.


How to enable archivelog mode:

SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;

LOG_MODE
------------
NOARCHIVELOG

execute below query one by one to enable archivelog mode.
SQL> shu immediate
SQL> startup mount
SQL> alter database archivelog;
SQL> alter database open;
 
SQL> SELECT LOG_MODE FROM SYS.V$DATABASE;

LOG_MODE
------------
ARCHIVELOG