how can i start|stop multiple oracle databases in the same oracle server in RHEL4.
i tried the following method to do what i want but it fails with TNS SERVER NAME ERROR! and when i connect to these database via sqlplus i get connected to an idle instance.

-----------------PROCEDURE I FOLLOWED--------------
1. export ORACLE_SID=dbfirst
2. dbstart
3. lsnrctl start

4. export ORACLE_SID=dbsecond
5. dbstart

6. export ORACLE_SID=dbthird
7. dbstart

------------------------------------------------------

right now i first connect to the idle instance in each database via sqlplus then manually start each of them using `startup` command.

I have googled this topic many times and everybody suggests using the ORACLE_SID changes and doing dbstart but this is not working for me.
what am i missing? is there any other way i can start|stop these three databases simultaneously and automatically? automatically is important because i need to start|stop all three databases automatically at system startup|shutdown.


thankyou!