Sams Teach Yourself Shell Programming in 24 Hours, Second Edition

How Are Signals Represented?

In UNIX, every type of event that can occur is represented by a separate signal. Every signal is a small positive integer. The signals most commonly encountered in shell script programming are given in Table 19.1. The signals are available on all versions of UNIX.

Table 19.1. Important Signals for Shell Scripts

Name	Value	Description
SIGHUP	1	Hangup detected on controlling terminal or death of controlling process
SIGINT	2	Interrupt from keyboard
SIGQUIT	3	Quit from keyboard
SIGKILL	9	Kill signal
SIGALRM	14	Alarm Clock signal (used for timers)
SIGTERM	15	Termination signal

In addition to the signals listed in Table 19.1, you might see a reference to signal 0. This signal is more of a shell convention than a real signal. ...