1.\" $NetBSD: time_second.9,v 1.1 2006/09/06 18:04:30 gdamore 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 September 6, 2006 36.Dt TIME_SECOND 9 37.Os 38.Sh NAME 39.Nm boottime , 40.Nm time_second , 41.Nm time_uptime 42.Nd system time variables 43.Sh SYNOPSIS 44.Va extern struct timeval boottime; 45.br 46.Va extern time_t time_uptime; 47.br 48.Va extern time_t time_second; 49.Sh DESCRIPTION 50The 51.Va time_second 52variable is the system's 53.Dq wall time 54clock. 55It is set at boot by 56.Xr inittodr 9 , 57and is updated by the 58.Xr settimeofday 2 59system call and by periodic clock interrupts. 60.Pp 61The 62.Va boottime 63variable holds the system boot time. 64It is set from 65.Va time 66at system boot, and is updated when the system time is adjusted 67with 68.Xr settimeofday 2 . 69.Pp 70The 71.Va time_uptime 72variable is a monotonically increasing system clock. 73It is set from 74.Va time_second 75at boot, and is updated by the periodic timer interrupt. 76(It is not updated by 77.Xr settimeofday 2 . ) 78.Pp 79All of these variables contain times 80expressed in seconds and microseconds since midnight (0 hour), 81January 1, 1970. 82.Pp 83Clock interrupts should be blocked 84when reading or writing 85.Va time_second 86or 87.Va time_uptime , 88because those variables are updated by 89.Fn hardclock . 90.Va boottime 91and 92.Va runtime 93may be read and written without special precautions. 94.Sh SEE ALSO 95.Xr settimeofday 2 , 96.Xr hardclock 9 , 97.Xr hz 9 , 98.Xr inittodr 9 , 99.Xr microtime 9 100