.\" $NetBSD: time_second.9,v 1.7 2018/10/30 20:10:23 kre 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>>
.\"
.Dd October 30, 2018
.Dt TIME_SECOND 9
.Os
.Sh NAME
.Nm time_second ,
.Nm time_uptime ,
.Nm boottime
.Nd system time variables
.Sh SYNOPSIS
.In sys/time.h
.Vt extern time_t time_second;
.Vt extern time_t time_uptime;
.In sys/kernel.h
.Vt extern struct timespec boottime;
.Sh DESCRIPTION
The
.Va time_second
variable is the system's
.Dq wall time
clock.
It is set at boot by
.Xr inittodr 9 ,
and is updated periodically via
.Xr timecounter 9
framework, and also updated by the
.Xr settimeofday 2
system call.
.Pp
The
.Va time_uptime
variable is a monotonically increasing system clock.
It is set at boot, and is updated periodically.
(It is not updated by
.Xr settimeofday 2 . )
.Pp
The
.Va boottime
variable holds the system boot time.
It is set at system boot, and is updated when the system time is adjusted
with
.Xr settimeofday 2 .
The variable may be read and written without special precautions.
.Pp
All of these variables contain times
expressed in seconds (and for
.Va boottime ,
nanoseconds) since midnight (0 hour),
January 1, 1970, UTC.
.Pp
The
.Xr bintime 9 ,
.Xr getbintime 9 ,
.Xr microtime 9 ,
.Xr getmicrotime 9 ,
.Xr nanotime 9 ,
and
.Xr getnanotime 9
functions can be used to get the current time more accurately and in an
atomic manner.
.Pp
Similarly, the
.Xr binuptime 9 ,
.Xr getbinuptime 9 ,
.Xr microuptime 9 ,
.Xr getmicrouptime 9 ,
.Xr nanouptime 9 ,
and
.Xr getnanouptime 9
functions can be used to get the time elapsed since boot more accurately
and in an atomic manner.
.Sh SEE ALSO
.Xr clock_settime 2 ,
.Xr ntp_adjtime 2 ,
.Xr timespec 3 ,
.Xr hardclock 9 ,
.Xr hz 9