1.\" Copyright (c) 1989, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)time.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD$ 34.\" 35.Dd April 14, 2022 36.Dt TIME 3 37.Os 38.Sh NAME 39.Nm time 40.Nd get time of day 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In time.h 45.Ft time_t 46.Fn time "time_t *tloc" 47.Sh DESCRIPTION 48The 49.Fn time 50function 51returns the value of time in seconds since 0 hours, 0 minutes, 520 seconds, January 1, 1970, Coordinated Universal Time (UTC). 53If an error occurs, 54.Fn time 55returns the value 56.Po Vt time_t Pc Ns \-1 . 57.Pp 58The return value is also stored in 59.No \&* Ns Va tloc , 60provided that 61.Va tloc 62is non-null. 63.Sh ERRORS 64The 65.Fn time 66function may fail for any of the reasons described in 67.Xr clock_gettime 2 . 68.Sh SEE ALSO 69.Xr clock_gettime 2 , 70.Xr gettimeofday 2 , 71.Xr ctime 3 72.Sh STANDARDS 73The 74.Nm 75function conforms to 76.St -p1003.1-2008 . 77.Sh HISTORY 78The 79.Fn time 80system call first appeared in 81.At v1 . 82Through the 83.At v3 , 84it returned 60 Hz ticks since an epoch that changed occasionally, because it 85was a 32-bit value that overflowed in a little over 2 years. 86.Pp 87In 88.At v4 89the granularity of the return value was reduced to whole seconds, 90delaying the aforementioned overflow until 2038. 91.Pp 92.At v7 93introduced the 94.Fn ftime 95system call, which returned time at a millisecond level, 96though retained the 97.Fn gtime 98system call (exposed as 99.Fn time 100in userland). 101.Fn time 102could have been implemented as a wrapper around 103.Fn ftime , 104but that wasn't done. 105.Pp 106.Bx 4.1c 107implemented a higher-precision time function 108.Fn gettimeofday 109to replace 110.Fn ftime 111and reimplemented 112.Fn time 113in terms of that. 114.Pp 115Since 116.Fx 9 117the implementation of 118.Fn time 119uses 120.Fn clock_gettime "CLOCK_SECOND" 121instead of 122.Fn gettimeofday 123for performance reasons. 124.Sh BUGS 125Neither 126.St -isoC-99 127nor 128.St -p1003.1-2001 129requires 130.Fn time 131to set 132.Va errno 133on failure; thus, it is impossible for an application to distinguish 134the valid time value \-1 (representing the last UTC second of 1969) 135from the error return value. 136.Pp 137Systems conforming to earlier versions of the C and POSIX 138standards (including older versions of 139.Fx ) 140did not set 141.No \&* Ns Va tloc 142in the error case. 143