1.\" $NetBSD: time_second.9,v 1.3 2008/11/28 22:31:01 wiz 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 for the 17.\" NetBSD Project. See http://www.NetBSD.org/ for 18.\" information about NetBSD. 19.\" 4. The name of the author may not be used to endorse or promote products 20.\" derived from this software without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 23.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 24.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 25.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 26.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 27.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 28.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 29.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 30.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 31.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 32.\" 33.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>> 34.\" 35.Dd November 28, 2008 36.Dt TIME_SECOND 9 37.Os 38.Sh NAME 39.Nm time_second , 40.Nm time_uptime , 41.Nm boottime 42.Nd system time variables 43.Sh SYNOPSIS 44.In sys/time.h 45.Pp 46.Va extern time_t time_second; 47.br 48.Va extern time_t time_uptime; 49.Pp 50.In sys/kernel.h 51.Pp 52.Va extern struct timeval boottime; 53.Sh DESCRIPTION 54The 55.Va time_second 56variable is the system's 57.Dq wall time 58clock. 59It is set at boot by 60.Xr inittodr 9 , 61and is updated periodically via 62.Xr timecounter 9 63framework, and also updated by the 64.Xr settimeofday 2 65system call. 66.Pp 67The 68.Va time_uptime 69variable is a monotonically increasing system clock. 70It is set at boot, and is updated periodically. 71(It is not updated by 72.Xr settimeofday 2 . ) 73.Pp 74The 75.Va boottime 76variable holds the system boot time. 77It is set at system boot, and is updated when the system time is adjusted 78with 79.Xr settimeofday 2 . 80.Pp 81All of these variables contain times 82expressed in seconds and microseconds since midnight (0 hour), 83January 1, 1970. 84.Pp 85The 86.Xr bintime 9 , 87.Xr getbintime 9 , 88.Xr microtime 9 , 89.Xr getmicrotime 9 , 90.Xr nanotime 9 , 91and 92.Xr getnanotime 9 93functions can be used to get the current time more accurately and in an 94atomic manner. 95.Pp 96Similarly, the 97.Xr binuptime 9 , 98.Xr getbinuptime 9 , 99.Xr microuptime 9 , 100.Xr getmicrouptime 9 , 101.Xr nanouptime 9 , 102and 103.Xr getnanouptime 9 104functions can be used to get the time elapsed since boot more accurately 105and in an atomic manner. 106.Pp 107.Va boottime 108may be read and written without special precautions. 109.Sh SEE ALSO 110.Xr clock_settime 2 , 111.Xr ntp_adjtime 2 , 112.Xr settimeofday 2 , 113.Xr bintime 9 , 114.Xr binuptime 9 , 115.Xr getbintime 9 , 116.Xr getbinuptime 9 , 117.Xr getmicrotime 9 , 118.Xr getmicrouptime 9 , 119.Xr getnanotime 9 , 120.Xr getnanouptime 9 , 121.Xr hardclock 9 , 122.Xr hz 9 , 123.Xr inittodr 9 , 124.Xr microtime 9 , 125.Xr microuptime 9 , 126.Xr nanotime 9 , 127.Xr nanouptime 9 , 128.Xr timecounter 9 129