100 lines
3.1 KiB
Groff
100 lines
3.1 KiB
Groff
.\" $NetBSD: time_second.9,v 1.1 2006/09/06 18:04:30 gdamore Exp $
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.\"
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.\" Copyright (c) 1994 Christopher G. Demetriou
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the
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.\" NetBSD Project. See http://www.NetBSD.org/ for
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.\" information about NetBSD.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
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.\"
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.Dd September 6, 2006
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.Dt TIME_SECOND 9
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.Os
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.Sh NAME
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.Nm boottime ,
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.Nm time_second ,
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.Nm time_uptime
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.Nd system time variables
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.Sh SYNOPSIS
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.Va extern struct timeval boottime;
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.br
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.Va extern time_t time_uptime;
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.br
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.Va extern time_t time_second;
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.Sh DESCRIPTION
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The
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.Va time_second
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variable is the system's
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.Dq wall time
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clock.
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It is set at boot by
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.Xr inittodr 9 ,
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and is updated by the
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.Xr settimeofday 2
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system call and by periodic clock interrupts.
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.Pp
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The
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.Va boottime
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variable holds the system boot time.
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It is set from
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.Va time
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at system boot, and is updated when the system time is adjusted
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with
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.Xr settimeofday 2 .
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.Pp
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The
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.Va time_uptime
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variable is a monotonically increasing system clock.
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It is set from
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.Va time_second
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at boot, and is updated by the periodic timer interrupt.
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(It is not updated by
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.Xr settimeofday 2 . )
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.Pp
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All of these variables contain times
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expressed in seconds and microseconds since midnight (0 hour),
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January 1, 1970.
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.Pp
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Clock interrupts should be blocked
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when reading or writing
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.Va time_second
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or
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.Va time_uptime ,
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because those variables are updated by
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.Fn hardclock .
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.Va boottime
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and
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.Va runtime
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may be read and written without special precautions.
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.Sh SEE ALSO
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.Xr settimeofday 2 ,
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.Xr hardclock 9 ,
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.Xr hz 9 ,
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.Xr inittodr 9 ,
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.Xr microtime 9
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