NetBSD-5.0.2/share/man/man9/time_second.9

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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 November 28, 2008
.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
.Pp
.Va extern time_t time_second;
.br
.Va extern time_t time_uptime;
.Pp
.In sys/kernel.h
.Pp
.Va extern struct timeval 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 .
.Pp
All of these variables contain times
expressed in seconds and microseconds since midnight (0 hour),
January 1, 1970.
.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.
.Pp
.Va boottime
may be read and written without special precautions.
.Sh SEE ALSO
.Xr clock_settime 2 ,
.Xr ntp_adjtime 2 ,
.Xr settimeofday 2 ,
.Xr bintime 9 ,
.Xr binuptime 9 ,
.Xr getbintime 9 ,
.Xr getbinuptime 9 ,
.Xr getmicrotime 9 ,
.Xr getmicrouptime 9 ,
.Xr getnanotime 9 ,
.Xr getnanouptime 9 ,
.Xr hardclock 9 ,
.Xr hz 9 ,
.Xr inittodr 9 ,
.Xr microtime 9 ,
.Xr microuptime 9 ,
.Xr nanotime 9 ,
.Xr nanouptime 9 ,
.Xr timecounter 9