SIGNAL(3F)                                                          SIGNAL(3F)



NAME
       signal - change the action for a signal

SYNOPSIS
       integer function signal(signum, proc, flag)
       integer signum, flag
       external proc

DESCRIPTION
       When  a  process incurs a signal (see _s_i_g_n_a_l(3C)) the default action is
       usually to clean up and abort.  The user may choose to write an  alter‐
       native  signal  handling  routine.   A  call  to _s_i_g_n_a_l is the way this
       alternate action is specified to the system.

       _S_i_g_n_u_m is the signal number (see _s_i_g_n_a_l(3C)).   If  _f_l_a_g  is  negative,
       then  _p_r_o_c  must  be  the name of the user signal handling routine.  If
       _f_l_a_g is zero or positive, then _p_r_o_c is ignored and the value of _f_l_a_g is
       passed  to  the system as the signal action definition.  In particular,
       this is how previously saved signal actions can be restored.  Two  pos‐
       sible  values for _f_l_a_g have specific meanings: 0 means "use the default
       action" (See NOTES below), 1 means "ignore this signal".

       A positive returned value is the previous action definition.   A  value
       greater than 1 is the address of a routine that was to have been called
       on occurrence of the given signal.  The returned value can be  used  in
       subsequent  calls to _s_i_g_n_a_l in order to restore a previous action defi‐
       nition.  A negative returned value is the negation of  a  system  error
       code.  (See _p_e_r_r_o_r(3F))

FILES
       /usr/lib/libU77.a

SEE ALSO
       signal(3C), kill(3F), kill(1)

NOTES
       f77  arranges  to  trap certain signals when a process is started.  The
       only way to restore the default f77 action  is  to  save  the  returned
       value from the first call to _s_i_g_n_a_l_.

       If the user signal handler is called, it will be passed the signal num‐
       ber as an integer argument.



4.2 Berkeley Distribution        May 15, 1985                       SIGNAL(3F)