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.Dd April 14, 2022 33.Dt TIME 3 34.Os 35.Sh NAME 36.Nm time 37.Nd get time of day 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In time.h 42.Ft time_t 43.Fn time "time_t *tloc" 44.Sh DESCRIPTION 45The 46.Fn time 47function 48returns the value of time in seconds since 0 hours, 0 minutes, 490 seconds, January 1, 1970, Coordinated Universal Time (UTC). 50If an error occurs, 51.Fn time 52returns the value 53.Po Vt time_t Pc Ns \-1 . 54.Pp 55The return value is also stored in 56.No \&* Ns Va tloc , 57provided that 58.Va tloc 59is non-null. 60.Sh ERRORS 61The 62.Fn time 63function may fail for any of the reasons described in 64.Xr clock_gettime 2 . 65.Sh SEE ALSO 66.Xr clock_gettime 2 , 67.Xr gettimeofday 2 , 68.Xr ctime 3 69.Sh STANDARDS 70The 71.Nm 72function conforms to 73.St -p1003.1-2008 . 74.Sh HISTORY 75The 76.Fn time 77system call first appeared in 78.At v1 . 79Through the 80.At v3 , 81it returned 60 Hz ticks since an epoch that changed occasionally, because it 82was a 32-bit value that overflowed in a little over 2 years. 83.Pp 84In 85.At v4 86the granularity of the return value was reduced to whole seconds, 87delaying the aforementioned overflow until 2038. 88.Pp 89.At v7 90introduced the 91.Fn ftime 92system call, which returned time at a millisecond level, 93though retained the 94.Fn gtime 95system call (exposed as 96.Fn time 97in userland). 98.Fn time 99could have been implemented as a wrapper around 100.Fn ftime , 101but that wasn't done. 102.Pp 103.Bx 4.1c 104implemented a higher-precision time function 105.Fn gettimeofday 106to replace 107.Fn ftime 108and reimplemented 109.Fn time 110in terms of that. 111.Pp 112Since 113.Fx 9 114the implementation of 115.Fn time 116uses 117.Fn clock_gettime "CLOCK_SECOND" 118instead of 119.Fn gettimeofday 120for performance reasons. 121.Sh BUGS 122Neither 123.St -isoC-99 124nor 125.St -p1003.1-2001 126requires 127.Fn time 128to set 129.Va errno 130on failure; thus, it is impossible for an application to distinguish 131the valid time value \-1 (representing the last UTC second of 1969) 132from the error return value. 133.Pp 134Systems conforming to earlier versions of the C and POSIX 135standards (including older versions of 136.Fx ) 137did not set 138.No \&* Ns Va tloc 139in the error case. 140