.\"	$OpenBSD: sigprocmask.2,v 1.6 2003/06/02 20:18:39 millert Exp $
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.\"	@(#)sigprocmask.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt SIGPROCMASK 2
.Os
.Sh NAME
.Nm sigprocmask
.Nd manipulate current signal mask
.Sh SYNOPSIS
.Fd #include <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 .
The signal mask is changed as a function of the specified
.Fa set
and the current mask.
The function is specified by
.Fa how
using one of the following values from
.Aq Pa signal.h :
.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
.Ar how
is insignificant and the mask remains unset
providing a way to examine the signal mask without modification.
.Pp
The system
quietly disallows
.Dv SIGKILL
or
.Dv SIGSTOP
to be blocked.
.Sh RETURN VALUES
A 0 value indicated that the call succeeded.
A \-1 return value indicates an error occurred and
.Va errno
is set to indicated the reason.
.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 sigsuspend 2 ,
.Xr sigsetops 3
.Sh STANDARDS
The
.Fn sigprocmask
function call is expected to conform to
.St -p1003.1-88 .