Oracle: Create a hidden user for RMAN backups only
In order to do RMAN backups you need the SYSDBA or SYSOPER roles. In order to grant those you need to be able log on as a user with those roles: ie the SYS role.

There are variations where you use OS authentication or if your OS user is a member of the ORA_DBA group.  

Easiest is if you can do this:

CONNECT / AS SYSDBA


from the server then you can run an RMAN script like

RMAN&gt; BACKUP AS BACKUPSET DATABASE PLUS ARCHIVELOG;


This very basic script should be configured with details particular to your setup such as the location to backup the files to, crosscheck existing backups, etc.