SIGNAL(3C) — Kubota Pacfic Computer Inc. (Compatibility Functions−BSD)

NAME

signal − simplified software signal facilities

SYNOPSIS

#include <signal.h>

(∗signal(sig, func))()
int (∗func)();

DESCRIPTION

signal is a simplified interface to the more general sigvec(2) facility.

A signal is generated by some abnormal event, initiated by a user at a terminal (quit, interrupt, stop), by a program error (bus error, etc.), by request of another program (kill), or when a process is stopped because it wishes to access its control terminal while in the background (see tty(4)). Signals are optionally generated when a process resumes after being stopped, when the status of child processes changes, or when input is ready at the control terminal. Most signals cause termination of the receiving process if no action is taken; some signals instead cause the process receiving them to be stopped, or are simply discarded if the process has not requested otherwise. Except for the SIGKILL and SIGSTOP signals, the signal call allows signals either to be ignored or to cause an interrupt to a specified location. The following list of all signals with names is given in the include file <signal.h>:

IGHUP1hangup
SIGINT2interrupt (rubout)
SIGQUIT3 ∗quit (ASCII FS)
SIGILL4 ∗illegal instruction (not reset when caught)
SIGTRAP5 ∗trace trap (not reset when caught)
SIGIOT6 ∗IOT instruction (obsolete)
SIGABRT6 ∗used by abort, replaces SIGIOT
SIGEMT7 ∗EMT instruction (obsolete)
SIGFPE8 ∗floating point exception
SIGKILL9kill (cannot be caught, blocked, or ignored)
SIGBUS10 ∗ bus error
SIGSEGV11 ∗ segmentation violation
SIGSYS12 ∗ bad argument to system call
SIGPIPE13write on a pipe with no one to read it
SIGALRM14alarm clock
SIGTERM15software termination signal
SIGUSR116user-defined signal 1
SIGUSR217user-defined signal 2
SIGCLD18 • death of a child
SIGPWR19power-fail restart
SIGWIND20 • window change
SIGURG21 • urgent condition on an I/O channel
SIGIO22 • pollable event occured
SIGSTOP23 † sendable stop signal, not from tty
SIGTSTP24 † stop signal from tty
SIGTTIN25 † process stop by background tty read
SIGTTOU26 † process stop by background tty write
SIGCONT27 • continue a stopped process
SIGXCPU28exceeded CPU time limit
SIGXFSZ29exceeded file size limit
SIGVTALRM30virtual time alarm
SIGPROF31profiling time alarm

The starred signals generate a core image if not caught or ignored.

If func is SIG_DFL, the default action for signal sig is reinstated; this default is termination (with a core image for starred signals) except for signals marked with • or †. Signals marked with • are discarded if the action is SIG_DFL; signals marked with † cause the process to stop. If func is SIG_IGN the signal is subsequently ignored and pending instances of the signal are discarded. Otherwise, when the signal occurs further occurrences of the signal are automatically blocked and func is called.

A return from the function unblocks the handled signal and continues the process at the point it was interrupted. Unlike previous signal facilities, the handler func remains installed after a signal has been delivered.

If a caught signal occurs during certain system calls, causing the call to terminate prematurely, the call is automatically restarted. In particular this can occur during a read or write(2) on a slow device (such as a terminal; but not a file) and during a wait(2).

The value of signal is the previous (or initial) value of func for the particular signal.

After a fork(2) or vfork(2) the child inherits all signals. execve(2) resets all caught signals to the default action; ignored signals remain ignored.

RETURN VALUE

The previous action is returned on a successful call. Otherwise, −1 is returned and errno is set to indicate the error.

ERRORS

signal fails and no action takes place if one of the following occur:

[EINVAL] sig is not a valid signal number.

[EINVAL] An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP.

[EINVAL] An attempt is made to ignore SIGCONT (by default SIGCONT is ignored).

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