Signals A signal is a notification to a process that an event has occurred.
Signals usually occur asynchronously.
By this we mean that the process doesn't know ahead of time exactly when a signal will occur. Unix supports several signals. The kill system call allows a process to send a signal to another process or to itself. The name kill is somewhat of a misnomer, since a signal does not always terminate a process. Some signals do indeed kill the receiving process, while others are used to inform the process of some condition that the receiving process then handles.