SIGNAL(2)							System Calls Manual							 SIGNAL(2)

NAME

       signal - catch or ignore signals

SYNOPSIS

       #include <signal.h>

       (*signal(sig, func))()
       (*func)();

DESCRIPTION

       A  signal  is  generated by some abnormal event, initiated either by user at a typewriter (quit, interrupt), by a program error (bus error,
       etc.), or by request of another program (kill).	Normally all signals cause termination of the receiving process, but a signal call  allows
       them either to be ignored or to cause an interrupt to a specified location.  Here is the list of signals with names as in the include file.

       SIGHUP  1    hangup
       SIGINT  2    interrupt
       SIGQUIT 3*   quit
       SIGILL  4*   illegal instruction (not reset when caught)
       SIGTRAP 5*   trace trap (not reset when caught)
       SIGIOT  6*   IOT instruction
       SIGEMT  7*   EMT instruction
       SIGFPE  8*   floating point exception
       SIGKILL 9    kill (cannot be caught or ignored)
       SIGBUS  10*  bus error
       SIGSEGV 11*  segmentation violation
       SIGSYS  12*  bad argument to system call
       SIGPIPE 13   write on a pipe or link with no one to read it
       SIGALRM 14   alarm clock
       SIGTERM 15   software termination signal
	       16   unassigned

       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, sometimes with a core image.	If func is
       SIG_IGN the signal is ignored.  Otherwise when the signal occurs func will be called with the signal number as argument.  A return from the
       function  will continue the process at the point it was interrupted.  Except as indicated, a signal is reset to SIG_DFL after being caught.
       Thus if it is desired to catch every such signal, the catching routine must issue another signal call.

       When a caught signal occurs during certain system calls, the call terminates prematurely.  In particular this can occur during  a  read	or
       write(2) on a slow device (like a typewriter; but not a file); and during pause or wait(2).  When such a signal occurs, the saved user sta-
       tus is arranged in such a way that when return from the signal-catching takes place, it will appear that the system call returned an  error
       status.	The user's program may then, if it wishes, re-execute the call.

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

       After a fork(2) the child inherits all signals.	Exec(2) resets all caught signals to default action.

SEE ALSO

       kill(1), kill(2), ptrace(2), setjmp(3)

DIAGNOSTICS

       The value (int)-1 is returned if the given signal is out of range.

BUGS

       If a repeated signal arrives before the last one can be reset, there is no chance to catch it.

       The type specification of the routine and its func argument are problematical.

ASSEMBLER

       (signal = 48.)
       sys signal; sig; label
       (old label in r0)

       If  label  is  0,  default action is reinstated.  If label is odd, the signal is ignored.  Any other even label specifies an address in the
       process where an interrupt is simulated.  An RTI or RTT instruction will return from the interrupt.

																	 SIGNAL(2)