signal(3)          UNIX System V(BSD Compatibility Package)           signal(3)


NAME
      signal - simplified software signal facilities

SYNOPSIS
      cc [ flag. . . ] file . . . -lucb

      #include <signal.h>

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

DESCRIPTION
      signal is a simplified interface to the more general sigvec(2) 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(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 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(3) 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
            SIGTERM        software termination signal
            SIGURG    @    urgent condition present on socket
            SIGSTOP   †    stop (cannot be caught, blocked, or ignored)
            SIGTSTP   †    stop signal generated from keyboard
            SIGCONT   @    continue after stop (cannot be blocked)
            SIGCHLD   @    child status has changed
            SIGTTIN   †    background read attempted from control terminal
            SIGTTOU   †    background write attempted to control terminal


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signal(3)          UNIX System V(BSD Compatibility Package)           signal(3)


            SIGIO     @    I/O is possible on a descriptor [see fcntl(2)]
            SIGXCPU   *    cpu time limit exceeded [see getrlimit(2)
            SIGXFSZ   *    file size limit exceeded [see getrlimit(2)
            SIGVTALRM      virtual time alarm [see getitimer(2)
            SIGPROF        profiling timer alarm [see getitimer(2)]
            SIGWINCH  @    window changed [see termio(4)]
            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 SIGDFL, 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 SIGDFL; signals marked with † cause the process to stop.  If
      func is SIGIGN 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(2)
      resets all caught signals to the default action; ignored signals remain
      ignored.

NOTES
      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(2) 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.


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signal(3)          UNIX System V(BSD Compatibility Package)           signal(3)


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.

SEE ALSO
      setjmp(3), sigblock(3), sigpause(3), sigsetmask(3), sigstack(3),
      sigvec(3), wait(3)

      execve(2), fork(2), getitimer(2), getrlimit(2), kill(2), ptrace(2),
      read(2), sigaction(2) wait(2), write(2), setjmp(3C), in the Programmer's
      Reference Manual
      kill(1), in the User's Reference Manual
      termio(7) in the System Administrator's Reference Manual






































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