Here is a good article on processes and signals on a Unix/Linux system. This also shows why sending a ‘kill -9′ to terminate a normal process is a bad idea. It doesn’t give the process a chance to clean up after itself.

Wizard Boot Camp, Part Five: Control Processes Using Signals | Linux Magazine

This month we’ll dig into process control: signals sent to processes and how a shell handles processes, including some details on job control.