SIGNAL(3C)              COMMAND REFERENCE              SIGNAL(3C)



NAME
     signal - simplified software signal facilities

SYNOPSIS
     #include <sys/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, and so forth), 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 is a
     list of all signals with names as in the include file
     <sys/signal.h>.  The signal parameters are listed in the
     first column.

 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
 SIGDISPLAY    7    event/timer
 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 with no one to read it
 SIGALRM      14    alarm clock
 SIGTERM      15    software termination signal from kill
 SIGURG       16•   urgent condition present on socket,
                    exception condition present on device
 SIGSTOP      17†   stop (cannot be caught or ignored)
 SIGTSTP      18†   stop signal generated from keyboard
 SIGCONT      19•   continue after stop (cannot be blocked)



Printed 3/13/89                                                 1

SIGNAL(3C)              COMMAND REFERENCE              SIGNAL(3C)



 SIGCHLD      20•   to parent on child stop or exit
 SIGCLD       20•   synonym for SIGCHLD (for System V compatibility)
 SIGTTIN      21†   background read attempted from control terminal
 SIGTTOU      22†   background write attempted to control terminal
 SIGIO        23•   I/O is possible on a descriptor (see fcntl(2))
 SIGXCPU      24    CPU time limit exceeded (see setrlimit(2))
 SIGXFSZ      25    file size limit exceeded (see setrlimit(2))
 SIGVTALRM    26    virtual time alarm (see setitimer(2))
 SIGPROF      27    profiling timer alarm (see setitimer(2))
 SIGUSR1      28    user-defined signal 1
 SIGUSR2      29    user-defined signal 2
 SIGWINCH     30•   window size changed

     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 @ 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 encounters 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.

                 NOTE:
                 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(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.
     Execve(2) resets all caught signals to the default action;
     ignored signals remain ignored.

DIAGNOSTICS
     Signal will fail and no action will take place if one of the
     following occurs:

     [EINVAL]



Printed 3/13/89                                                 2

SIGNAL(3C)              COMMAND REFERENCE              SIGNAL(3C)



             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).

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

SEE ALSO
     kill(1), kill(2), ptrace(2), sigblock(2), sigpause(2),
     sigsetmask(2), sigstack(2), sigvec(2), setjmp(3c), and
     tty(4).




































Printed 3/13/89                                                 3

%%index%%
na:312,98;
sy:410,728;
de:1138,2613;4135,2620;
di:6755,238;7377,279;
rv:7656,309;
se:7965,393;
%%index%%000000000128