On Windows NT Server, we have two Oracle9i databases installed under same ORACLE_HOME. The setup of listener and tnsnames seems to be right, two SIDs specified. The only thing that is interesting when I look at the registry there is HOME0 is pointing to one database instance. That one does not have problem starting up -- the second one gives the error:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
What else can I try to do to have them both up and running?
You'll have to use the ORADIM utility (in %ORACLE_HOME%bin) to create the service to start the second instance. They can both run with the same ORACLE_HOME directory. The problem is that the services need to be set up with different ORACLE_SID environment variables. ORADIM is pretty easy to use, just type 'oradim' at the command prompt and it will give you all of your options. You can manually set the ORACLE_SID environment variable in a DOS window by typing 'set ORACLE_SID=new_sid'.