POSIX Signal quick review

1. Signals are a mechanism to notify a process that an eventoccured : expiration of a timer, completion of an asynchronous I/O operation, or any kind of event specific to your application.
2. Signals are also used internally by the system to tell a process that it must be suspended, restarted, stopped, that is has done an invalid memory reference, etc.
3. Each signal is identified by a number : SIGSEGV, SIGKILL, SIGUSR1, etc.
4. An API is available to catch signals, wait for signals, mask signals, etc.
5. See signal(7) for a general description of the signal mechanism.