Autostart the Oracle DB:
You can also use $ORACLE_HOME/bin/dbstart to startup the database, and $ORACLE_HOME/bin/dbshut to shutdown the database. You can place $ORACLE_HOME/bin/dbstart into the /etc/rc.d/rc.local boot script to automatically bring up the database at system boot time. To get $ORACLE_HOME/bin/dbstart and $ORACLE_HOME/bin/dbshut working, you need to change the third field for your Oracle SID in /etc/oratab from "N" to "Y".

For example, for the Oracle SID "test" I changed the line in /etc/oratab from:

test:/opt/oracle/product/9.2.0:N
to read:
test:/opt/oracle/product/9.2.0:Y
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I have performed the above procedure and when I just execute dbstart it is working fine but I have to do this at each boot of the server. To get the result I have added the line

/opt/oracle/product/9.2.0/bin/dbstart

/etc/rc.d/rc.local

but when I reboot the machine it is not going to be execute so I have to start the db manually.