ORA-01089: immediate shutdown in progress - no operations are permitted while rman backup is running?

Error reported: ORA-01089: immediate shutdown in progress

Cause: when rman backup is running some like dba has shutdown the database might be
because of outage window for patching or maintainance activity.

ORA-01089 occurs when all Oracle operation have been terminated. 

This means someone (likely your DBA) has used the SHUTDOWN IMMEDIATE 

command to shut down an Oracle instance. You will need for your DBA to 

restart the instance in order to resolve ORA-01089.

Solution:Start the database and fire rman backup.