1.\" $NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $ 2.\" 3.\" Copyright (c) 1994 Christopher G. Demetriou 4.\" 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. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by Christopher G. Demetriou 17.\" for the NetBSD Project. 18.\" 3. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.Dd May 4, 2021 33.Dt TIME 9 34.Os 35.Sh NAME 36.Nm boottime , 37.Nm time_second , 38.Nm time_uptime 39.Nd system time variables 40.Sh SYNOPSIS 41.In sys/time.h 42.Pp 43.Vt extern struct timeval boottime ; 44.Vt extern time_t time_second ; 45.Vt extern time_t time_uptime ; 46.Sh DESCRIPTION 47The 48.Va boottime 49variable holds the estimated system boot time. 50This time is initially set when the system boots, either from the RTC, or from a 51time estimated from the system's root filesystem. 52When the current system time is set, stepped by 53.Xr ntpd 8 , 54or a new time is read from the RTC as the system resumes, 55.Va boottime 56is recomputed as new_time - uptime. 57The 58.Xr sysctl 8 59.Va kern.boottime 60returns this value. 61.Pp 62The 63.Va time_second 64variable is the system's 65.Dq wall time 66clock to the second. 67.Pp 68The 69.Va time_uptime 70variable is the number of seconds since boot. 71.Pp 72The 73.Xr bintime 9 , 74.Xr getbintime 9 , 75.Xr microtime 9 , 76.Xr getmicrotime 9 , 77.Xr nanotime 9 , 78and 79.Xr getnanotime 9 80functions can be used to get the current time more accurately and in an 81atomic manner. 82Similarly, the 83.Xr binuptime 9 , 84.Xr getbinuptime 9 , 85.Xr microuptime 9 , 86.Xr getmicrouptime 9 , 87.Xr nanouptime 9 , 88and 89.Xr getnanouptime 9 90functions can be used to get the time elapse since boot more accurately 91and in an atomic manner. 92The 93.Va boottime 94variable may be read and written without special precautions. 95It is adjusted when the phase of the system time changes. 96.Sh SEE ALSO 97.Xr clock_settime 2 , 98.Xr ntp_adjtime 2 , 99.Xr settimeofday 2 , 100.Xr bintime 9 , 101.Xr binuptime 9 , 102.Xr getbintime 9 , 103.Xr getbinuptime 9 , 104.Xr getmicrotime 9 , 105.Xr getmicrouptime 9 , 106.Xr getnanotime 9 , 107.Xr getnanouptime 9 , 108.Xr microtime 9 , 109.Xr microuptime 9 , 110.Xr nanotime 9 , 111.Xr nanouptime 9 112.Rs 113.%A "Poul-Henning Kamp" 114.%T "Timecounters: Efficient and precise timekeeping in SMP kernels" 115.%J "Proceedings of EuroBSDCon 2002, Amsterdam" 116.%O /usr/share/doc/papers/timecounter.ascii.gz 117.Re 118.Rs 119.%A "Marshall Kirk McKusick" 120.%A "George V. Neville-Neil" 121.%B "The Design and Implementation of the FreeBSD Operating System" 122.%D "July 2004" 123.%I "Addison-Wesley" 124.%P "57-61,65-66" 125.Re 126