#include <signal.h> 
 sigblock(mask);  int mask; 
 mask = sigmask(signum) 
 DESCRIPTION
 Sigblock causes the signals specified in
 mask to be added to the set of signals currently
being 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 . 

It is not possible to block SIGKILL,
SIGSTOP, or SIGCONT; this restriction is silently
imposed by the system.
 "RETURN VALUE
The previous set of masked signals is returned.
 "SEE ALSO"
kill(2), sigvec(2), sigsetmask(2)