.\"	$OpenBSD: sigprocmask.2,v 1.13 2017/05/29 09:40:02 deraadt Exp $
.\"	$NetBSD: sigprocmask.2,v 1.6 1995/02/27 12:37:33 cgd Exp $
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.\"	@(#)sigprocmask.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: May 29 2017 $
.Dt SIGPROCMASK 2
.Os
.Sh NAME
.Nm sigprocmask
.Nd manipulate current signal mask
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn sigprocmask "int how" "const sigset_t *set" "sigset_t *oset"
.Sh DESCRIPTION
The
.Fn sigprocmask
function examines and/or changes the current signal mask (those signals
that are blocked from delivery).
Signals are blocked if they are members of the current signal mask set.
.Pp
If
.Fa set
is not null, the action of
.Fn sigprocmask
depends on the value of the parameter
.Fa how ,
which can be one of the following values:
.Bl -tag -width SIG_UNBLOCK
.It Dv SIG_BLOCK
The new mask is the union of the current mask and the specified
.Fa set .
.It Dv SIG_UNBLOCK
The new mask is the intersection of the current mask
and the complement of the specified
.Fa set .
.It Dv SIG_SETMASK
The current mask is replaced by the specified
.Fa set .
.El
.Pp
If
.Fa oset
is not null, it is set to
the previous value of the signal mask.
When
.Fa set
is null,
the value of
.Fa how
is insignificant and the mask remains unchanged,
providing a way to examine the signal mask without modification.
.Pp
The system
quietly disallows
.Dv SIGKILL
or
.Dv SIGSTOP
to be blocked.
.Pp
Only signals which are in the pending state will be blocked.
Signals that are explicitly ignored or for which no handler has
been installed and where the default action is to discard the signal
are not held as pending and will be discarded regardless of the
signal mask.
.Pp
Blocked signals remain in the pending state until another call to
.Fn sigprocmask
removes the pending signal(s) from the mask.
If there are unblocked signals that are pending after the signal
mask is updated, at least one will be delivered before
.Fn sigprocmask
returns.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn sigprocmask
call will fail and the signal mask will be unchanged if one
of the following occurs:
.Bl -tag -width Er
.It Bq Er EINVAL
.Fa how
has a value other than those listed here.
.El
.Sh SEE ALSO
.Xr kill 2 ,
.Xr sigaction 2 ,
.Xr sigpending 2 ,
.Xr sigsuspend 2 ,
.Xr sigaddset 3
.Sh STANDARDS
The
.Fn sigprocmask
function conforms to
.St -p1003.1-2008 .