NetBSD/share/man/man9/time.9

.\" $NetBSD: time.9,v 1.15 2005/10/01 04:09:06 yamt Exp $
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.\" Copyright (c) 1994 Christopher G. Demetriou
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.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
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.Dd October 1, 2005
.Dt TIME 9
.Os
.Sh NAME
.Nm boottime ,
.Nm mono_time ,
.Nm time
.Nd system time variables
.Sh SYNOPSIS
.Va extern struct timeval boottime;
.br
.Va extern volatile struct timeval mono_time;
.br
.Va extern volatile struct timeval time;
.Sh DESCRIPTION
The
.Va time
variable is the system's
.Dq wall time
clock.
It is set at boot by
.Xr inittodr 9 ,
and is updated by the
.Xr settimeofday 2
system call and by periodic clock interrupts.
.Pp
The
.Va boottime
variable holds the system boot time.
It is set from
.Va time
at system boot, and is updated when the system time is adjusted
with
.Xr settimeofday 2 .
.Pp
The
.Va mono_time
variable is a monotonically increasing system clock.
It is set from
.Va time
at boot, and is updated by the periodic timer interrupt.
(It is not updated by
.Xr settimeofday 2 . )
.Pp
All of these variables contain times
expressed in seconds and microseconds since midnight (0 hour),
January 1, 1970.
.Pp
Clock interrupts should be blocked
when reading or writing
.Va time
or
.Va mono_time ,
because those variables are updated by
.Fn hardclock .
.Va boottime
and
.Va runtime
may be read and written without special precautions.
.Sh SEE ALSO
.Xr settimeofday 2 ,
.Xr hardclock 9 ,
.Xr hz 9 ,
.Xr inittodr 9 ,
.Xr microtime 9