4.2BSD/usr/man/man2/sigblock.2

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.TH SIGBLOCK 2 "15 June 1983"
.UC 4
.SH NAME
sigblock \- block signals
.SH SYNOPSIS
.nf
.B sigblock(mask);
.B int mask;
.SH DESCRIPTION
.I Sigblock
causes the signals specified in
.I mask
to be added to the set of signals currently
being blocked from delivery.  Signal
.I i
is blocked if the
.IR i -th
bit in 
.I mask
is a 1.
.PP
It is not possible to block SIGKILL,
SIGSTOP, or SIGCONT;  this restriction is silently
imposed by the system.
.SH "RETURN VALUE
The previous set of masked signals is returned.
.SH "SEE ALSO"
kill(2), sigvec(2), sigsetmask(2),