signal(3BSD) (BSD System Compatibility) signal(3BSD)
NAME
signal - (BSD) simplified software signal facilities
SYNOPSIS
/usr/ucb/cc [flag . . . ] file . . .
#include <signal.h>
void (*signal(int sig, void *func))();
DESCRIPTION
signal is a simplified interface to the more general
sigvec(3BSD) facility. Programs that use signal in preference
to sigvec are more likely to be portable to all systems.
A signal is generated by some abnormal event, initiated by a
user at a terminal (quit, interrupt, stop), by a program error
(bus error, and so on), 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 termio(7)].
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 interrupt to a specified location. The following is a
list of all signals with names as in the include file
signal.h:
SIGHUP hangup
SIGINT interrupt
SIGQUIT * quit
SIGILL * illegal instruction
SIGTRAP * trace trap
SIGABRT * abort (generated by abort(3C) routine)
SIGEMT * emulator trap
SIGFPE * arithmetic exception
SIGKILL kill (cannot be caught, blocked, or ignored)
SIGBUS * bus error
SIGSEGV * segmentation violation
SIGSYS * bad argument to system call
SIGPIPE write on a pipe or other socket with no one to read it
SIGALRM alarm clock
Copyright 1994 Novell, Inc. Page 1
signal(3BSD) (BSD System Compatibility) signal(3BSD)
SIGTERM software termination signal
SIGURG o urgent condition present on socket
SIGSTOP - stop (cannot be caught, blocked, or ignored)
SIGTSTP - stop signal generated from keyboard
SIGCONT o continue after stop (cannot be blocked)
SIGCHLD o child status has changed
SIGTTIN - background read attempted from control terminal
SIGTTOU - background write attempted to control terminal
SIGIO o I/O is possible on a descriptor [see fcntl(2)]
SIGPWR o power fail/restart
SIGXCPU * cpu time limit exceeded [see getrlimit(2)
SIGXFSZ * file size limit exceeded [see getrlimit(2)
SIGVTALRM virtual time alarm [see getitimer(3C)
SIGPROF profiling timer alarm [see getitimer(3C)]
SIGWINCH o window changed [see termio(7)]
SIGUSR1 user-defined signal 1
SIGUSR2 user-defined signal 2
The starred signals in the list above cause 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 o or -.
Signals marked with o 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.
If a caught signal occurs during certain system calls,
terminating the call prematurely, the call is automatically
restarted. In particular this can occur during a read(2) 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.
An execve [see exec(2)] resets all caught signals to the
default action; ignored signals remain ignored.
Copyright 1994 Novell, Inc. Page 2
signal(3BSD) (BSD System Compatibility) signal(3BSD)
NOTICES
The handler routine can be declared:
void handler(sig, code, scp, addr)
int sig, code;
struct sigcontext *scp;
char *addr;
Here sig is the signal number; code is a parameter of certain
signals that provides additional detail; scp is a pointer to
the sigcontext structure (defined in signal.h), used to
restore the context from before the signal; and addr is
additional address information. See sigvec(3BSD) for more
details.
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 will fail and no action will take place if one of the
following occur:
EINVAL sig is not a valid signal number, or is
SIGKILL or SIGSTOP.
REFERENCES
exec(2), fork(2), getitimer(3C), getrlimit(2), kill(1),
kill(2), ptrace(2), read(2), setjmp(3BSD), setjmp(3C),
sigaction(2), sigblock(3BSD), sigpause(3BSD),
sigsetmask(3BSD), sigstack(3BSD), sigvec(3BSD), termio(7),
wait(2), wait(3BSD), write(2)
Copyright 1994 Novell, Inc. Page 3