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

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.TH SIGSETMASK 2 "7 July 1983"
.UC 4
.SH NAME
sigsetmask \- set current signal mask
.SH SYNOPSIS
.nf
.B sigsetmask(mask);
.B int mask;
.SH DESCRIPTION
.I Sigsetmask
sets the current signal mask (those signals
which are blocked from delivery).  Signal
.I i
is blocked if the
.IR i -th
bit in 
.I mask
is a 1.
.PP
The system
quietly disallows SIGKILL, SIGSTOP, or SIGCONT to
be blocked.
.SH "RETURN VALUE
The previous set of masked signals is returned.
.SH "SEE ALSO"
kill(2), sigvec(2), sigblock(2), sigpause(2)