SIGNAL(II)                   8/5/73                    SIGNAL(II)


     signal - catch or ignore signals


     (signal = 48.)

     sys  signal; sig; label

     (old value in r0)

     signal(sig, func)

     int (*func)();


     When the signal defined  by  sig  is  sent  to  the  current

     process,  it  is  to  be  treated  according to label (resp.

     func.)  The following is the list of signals:

          1     hangup

          2     interrupt

          3*    quit

          4*    illegal instruction

          5*    trace trap

          6*    IOT instruction

          7*    EMT instruction

          8*    floating point exception

          9     kill (cannot be caught or ignored)

          10*   bus error

          11*   segmentation violation

          12*   bad argument to sys call

     If label is 0, the default  system  action  applies  to  the

     signal.   This  is  processes  termination with or without a

     core dump.  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 instruction  will  return

     from  the  interrupt.  As a signal is caught, it is reset to

     0.  Thus if it is desired to catch every  such  signal,  the

     catching routine must issue another signal call.

     In C, if func is 0 or 1, the action is as  described  above.

     If  func  is  even,  it  is  assumed  to be the address of a

     function entry point.  When the signal occurs, the  function

     will  be  called.   A return from the function will simulate

     the RTI.

     The starred signals in the list above cause core  images  if

     not caught and not ignored.

     In assembly  language,  the  old  value  of  the  signal  is

     returned in r0.  In C, that value is retruned.

     After a fork, the child inherits all signals.  The exec call

     resets all caught signals to default action.


     kill (I), kill (II)


     The error bit (c-bit) is set if the given signal is  out  of

     range.  In C, a -1 indicates an error; 0 indicates success.