Here is a neat trick. If you want to start a program that always respawns if it gets killed, just put it in /etc/inittab. The init process will respawn the program. That’s what it’s for.

Here’s an example. …

Full article here:
How to run unkillable* programs in Linux (catonmat.net)
* “unkillable” refers to a program that respawns when you kill it.