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.\"	$OpenBSD: sigblock.3,v 1.20 2017/08/01 15:38:02 schwarze Exp $
.\"
.Dd $Mdocdate: August 1 2017 $
.Dt SIGBLOCK 3
.Os
.Sh NAME
.Nm sigblock ,
.Nm sigmask
.Nd block signals
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigblock "int mask"
.Ft int
.Fn sigmask "int signum"
.Sh DESCRIPTION
.Bf -symbolic
This interface is made obsolete by
.Ef
.Xr sigprocmask 2 .
.Pp
.Fn sigblock
adds the signals specified in
.Fa mask
to the set of signals currently
being blocked from delivery.
Signals are blocked if the
corresponding bit in
.Fa mask
is a 1; the macro
.Fn sigmask
is provided to construct the mask for a given
.Fa signum .
.Pp
It is not possible to block
.Dv SIGKILL
or
.Dv SIGSTOP ;
this restriction is silently
imposed by the system.
.Sh RETURN VALUES
The previous set of masked signals is returned.
.Sh EXAMPLES
The following example utilizing
.Fn sigblock :
.Bd -literal -offset indent
int omask;

omask = sigblock(sigmask(SIGINT) | sigmask(SIGHUP));
.Ed
.Pp
Becomes:
.Bd -literal -offset indent
sigset_t set, oset;

sigemptyset(&set);
sigaddset(&set, SIGINT);
sigaddset(&set, SIGHUP);
sigprocmask(SIG_BLOCK, &set, &oset);
.Ed
.Pp
Another use of
.Fn sigblock
is to get the current set of masked signals without changing what
is actually blocked.
Instead of:
.Bd -literal -offset indent
int set;

set = sigblock(0);
.Ed
.Pp
Use the following:
.Bd -literal -offset indent
sigset_t set;

sigprocmask(SIG_BLOCK, NULL, &set);
.Ed
.Sh SEE ALSO
.Xr kill 2 ,
.Xr sigaction 2 ,
.Xr sigprocmask 2 ,
.Xr sigaddset 3 ,
.Xr sigsetmask 3
.Sh HISTORY
A
.Fn sigblock
system call first appeared in
.Bx 4.2 .
In
.Bx 4.3 Reno ,
it was reimplemented as a wrapper around
.Xr sigprocmask 2 .
The old system call was kept for compatibility until
.Ox 4.9 .