To login to the shadow instance with a user account other than SAP* or DDIC you need to unlock it:
1. Log on as useradm
2. Enter the following command (this assumes you use /usr/sap/put as your upgrade directory):
cd /usr/sap/put/bin
./R3up unlockshd
or
./SAPup unlockshd
If shadow instance isn't running you can start it with the following command:
./SAPup startshd
and to stop:
./SAPup stopshd
