I wish to turn cascade on automatically. How do i do this in MySQL?

Ideally Let me edit my.cnf

You cannot switch it on automatically.

You will need to place it like a foreign key constraint on the key-by-key basis. Begin to see the documentation at http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html

The cascade on remove behavior is controlled once the individual foreign key constraints are produced. There's no global setting with this.