1.\"	$OpenBSD: alarm.3,v 1.16 2021/06/18 22:21:29 cheloha 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: June 18 2021 $
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 appeared in the Programmer's Workbench (PWB/UNIX)
88and was ported to
89.At v7 .
90For
91.Bx 4.1c ,
92it was reimplemented as a wrapper around the
93.Xr setitimer 2
94system call.
95.Sh CAVEATS
96The
97.Fn alarm
98function is implemented with the per-process
99.Dv ITIMER_REAL
100timer described in
101.Xr setitimer 2 .
102Use of both
103.Fn alarm
104and
105.Xr setitimer 2
106in the same program may yield confusing behavior.
107