What Signals Are Available?

Different systems define different signals. The available signals and their names are defined in the header file

signal.h

Note that signal.h is a header file of ANSI C. However, not all signals listed below are supported by the ANSI C standard.

Under Unix, all signal names start with SIG. The following are some examples:

SIGALRM (non-ANSI C)
Alarm clock goes off. To set alarm clock, use system call alarm(n) where n is an integer. After n seconds, the alarm goes off and signal SIGALRM is generated.
SIGBUS (non-ANSI C)
Bus error. You know what it means.
SIGFPE
An arithmetic exception (e.g., division by zero, overflow and underflow) has occurred.
SIGINT
An interrupt (e.g., Ctrl-C) has occurred.
SIGTERM
Software termination.
SIGQUIT (non-ANSI C)
Quit execution (e.g., Ctrl-\).
SIGUSR1 and SIGUSR2 (e.g., non-ANSI C)
User-defined signal 1 and 2.
SIGKILL (non-ANSI C)
Kill the process (cannot be caught or ignored)

A program can take action when a signal is generated. The actual action taken, however, depends on the current signal handler. Some signals can be ignored, while some other cannot (e.g., SIGKILL). When you want to handle a particular signal, a signal handler must be installed. Continue with the next page to learn the way of handling signals.