How do I get Oracle to automatically start when my server boots up?

I have added this entry in oratab file , but still it is not getting started whenever the server boots up. do i need to change in any other file or do i am missing something.

# $ORACLE_SID:$ORACLE_HOME:[N|Y]
#
ORCL:/u01/app/oracle/product/8.1.7:Y

thanks in advance
Gajanan