If you look at the before you install manual for Linux there should be a section on getting databases to automatically startup. There should be a file in $ORACLE_HOME/bin called dbstart. It will look at the /var/optt/oracle/oratab file and determine which databases need to be started based on the third field.

sidname:/usr/oracle/9.2.0.2:Y

Then there is a diectory in /etc, I don't remember which one off hand but you basically create a symbolic link there. It is all spelled out in the manual which you should read before installing Oracle on a new platform anyway in case there is something that you should know or change.