1.\" $OpenBSD: sigprocmask.2,v 1.13 2017/05/29 09:40:02 deraadt Exp $ 2.\" $NetBSD: sigprocmask.2,v 1.6 1995/02/27 12:37:33 cgd Exp $ 3.\" 4.\" Copyright (c) 1983, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)sigprocmask.2 8.1 (Berkeley) 6/4/93 32.\" 33.Dd $Mdocdate: May 29 2017 $ 34.Dt SIGPROCMASK 2 35.Os 36.Sh NAME 37.Nm sigprocmask 38.Nd manipulate current signal mask 39.Sh SYNOPSIS 40.In signal.h 41.Ft int 42.Fn sigprocmask "int how" "const sigset_t *set" "sigset_t *oset" 43.Sh DESCRIPTION 44The 45.Fn sigprocmask 46function examines and/or changes the current signal mask (those signals 47that are blocked from delivery). 48Signals are blocked if they are members of the current signal mask set. 49.Pp 50If 51.Fa set 52is not null, the action of 53.Fn sigprocmask 54depends on the value of the parameter 55.Fa how , 56which can be one of the following values: 57.Bl -tag -width SIG_UNBLOCK 58.It Dv SIG_BLOCK 59The new mask is the union of the current mask and the specified 60.Fa set . 61.It Dv SIG_UNBLOCK 62The new mask is the intersection of the current mask 63and the complement of the specified 64.Fa set . 65.It Dv SIG_SETMASK 66The current mask is replaced by the specified 67.Fa set . 68.El 69.Pp 70If 71.Fa oset 72is not null, it is set to 73the previous value of the signal mask. 74When 75.Fa set 76is null, 77the value of 78.Fa how 79is insignificant and the mask remains unchanged, 80providing a way to examine the signal mask without modification. 81.Pp 82The system 83quietly disallows 84.Dv SIGKILL 85or 86.Dv SIGSTOP 87to be blocked. 88.Pp 89Only signals which are in the pending state will be blocked. 90Signals that are explicitly ignored or for which no handler has 91been installed and where the default action is to discard the signal 92are not held as pending and will be discarded regardless of the 93signal mask. 94.Pp 95Blocked signals remain in the pending state until another call to 96.Fn sigprocmask 97removes the pending signal(s) from the mask. 98If there are unblocked signals that are pending after the signal 99mask is updated, at least one will be delivered before 100.Fn sigprocmask 101returns. 102.Sh RETURN VALUES 103.Rv -std 104.Sh ERRORS 105The 106.Fn sigprocmask 107call will fail and the signal mask will be unchanged if one 108of the following occurs: 109.Bl -tag -width Er 110.It Bq Er EINVAL 111.Fa how 112has a value other than those listed here. 113.El 114.Sh SEE ALSO 115.Xr kill 2 , 116.Xr sigaction 2 , 117.Xr sigpending 2 , 118.Xr sigsuspend 2 , 119.Xr sigaddset 3 120.Sh STANDARDS 121The 122.Fn sigprocmask 123function conforms to 124.St -p1003.1-2008 . 125