#include <signal.h> 
 sigsetmask(mask);  int mask; 
 mask = sigmask(signum) 
 DESCRIPTION
 Sigsetmask sets the current signal mask (those signals
that are blocked from delivery).
Signals are blocked if the
corresponding bit in 
 mask is a 1; the macro
 sigmask is provided to construct the mask for a given
 signum . 

The system
quietly disallows SIGKILL, SIGSTOP, or SIGCONT to
be blocked.
 "RETURN VALUE
The previous set of masked signals is returned.
 "SEE ALSO"
kill(2), sigvec(2), sigblock(2), sigpause(2)