1.\" $OpenBSD: alarm.3,v 1.17 2022/08/02 01:23:23 jsg Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993, 1994 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.Dd $Mdocdate: August 2 2022 $ 31.Dt ALARM 3 32.Os 33.Sh NAME 34.Nm alarm 35.Nd schedule SIGALRM delivery 36.Sh SYNOPSIS 37.In unistd.h 38.Ft unsigned int 39.Fn alarm "unsigned int seconds" 40.Sh DESCRIPTION 41.Bf -symbolic 42This is a simplified interface to 43.Xr setitimer 2 . 44.Ef 45.Pp 46The 47.Fn alarm 48function schedules the 49.Dv SIGALRM 50signal for delivery to the calling process after the given number of 51.Fa seconds 52have elapsed. 53.Pp 54If an alarm is already pending, 55another call to 56.Fn alarm 57will supersede the prior call. 58.Pp 59If 60.Fa seconds 61is zero, 62any pending alarm is cancelled. 63.Sh RETURN VALUES 64.Fn alarm 65returns the number of seconds remaining until the pending alarm would have 66expired. 67If the alarm has already expired, 68the alarm was cancelled, 69or no alarm was ever scheduled, 70.Fn alarm 71returns zero. 72.Sh SEE ALSO 73.Xr setitimer 2 , 74.Xr sigaction 2 , 75.Xr sigsuspend 2 , 76.Xr signal 3 , 77.Xr sleep 3 , 78.Xr ualarm 3 79.Sh STANDARDS 80The 81.Fn alarm 82function conforms to 83.St -p1003.1-2008 . 84.Sh HISTORY 85An 86.Fn alarm 87system call first appeared outside of Bell Labs in the 88.Dq 50 changes 89tape for 90.At v6 . 91It was first officially released with PWB/UNIX 1.0. 92For 93.Bx 4.1c , 94it was reimplemented as a wrapper around the 95.Xr setitimer 2 96system call. 97.Sh CAVEATS 98The 99.Fn alarm 100function is implemented with the per-process 101.Dv ITIMER_REAL 102timer described in 103.Xr setitimer 2 . 104Use of both 105.Fn alarm 106and 107.Xr setitimer 2 108in the same program may yield confusing behavior. 109