1.\" $OpenBSD: time.3,v 1.18 2021/12/11 13:34:38 tb Exp $ 2.\" 3.\" Copyright (c) 1989, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the American National Standards Committee X3, on Information 8.\" Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.Dd $Mdocdate: December 11 2021 $ 35.Dt TIME 3 36.Os 37.Sh NAME 38.Nm time 39.Nd get time of day 40.Sh SYNOPSIS 41.In time.h 42.Ft time_t 43.Fn time "time_t *now" 44.Sh DESCRIPTION 45The 46.Fn time 47function returns the number of seconds elapsed since 48Jan 1 1970 00:00:00 UTC. 49This value is also written to 50.Fa now 51unless 52.Fa now 53is 54.Dv NULL . 55.Sh RETURN VALUES 56The 57.Fn time 58function is always successful, 59and no return value is reserved to indicate an error. 60.Sh SEE ALSO 61.Xr clock_gettime 2 , 62.Xr gettimeofday 2 , 63.Xr ctime 3 64.Sh STANDARDS 65The 66.Fn time 67function conforms to 68.St -p1003.1-2008 . 69.Sh HISTORY 70A 71.Fn time 72system call first appeared in 73.At v1 . 74That version counted time in sixtieths of a second with a 32-bit return value, 75ensuring an integer overflow crisis every 2.26 years. 76In 77.At v6 78the granularity of the return value was reduced to whole seconds, 79delaying the aforementioned crisis until 2038. 80In 81.Bx 4.1c 82the function was moved out of the kernel into the C standard library and 83reimplemented with 84.Xr gettimeofday 2 . 85