.\"	$OpenBSD: time_second.9,v 1.1 2016/04/03 06:43:59 jsg Exp $
.\"	$NetBSD: time.9,v 1.1 1995/11/25 21:24:53 perry Exp $
.\"
.\" Copyright (c) 1994 Christopher G. Demetriou
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"      This product includes software developed by Christopher G. Demetriou
.\"      for the NetBSD Project.
.\" 3. The name of the author may not be used to endorse or promote products
.\"    derived from this software without specific prior written permission
.\"
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.Dd $Mdocdate: April 3 2016 $
.Dt TIME_SECOND 9
.Os
.Sh NAME
.Nm time_second ,
.Nm time_uptime
.Nd system time variables
.Sh SYNOPSIS
.Vt extern volatile time_t time_second;
.Vt extern volatile time_t time_uptime;
.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 by the
.Xr settimeofday 2
system call and by periodic clock interrupts.
.Pp
The
.Va time_uptime
variable is a monotonically increasing system clock.
It is set 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 since midnight (0 hour),
January 1, 1970.
.Pp
Clock interrupts should be blocked when reading or writing
.Va time_second
or
.Va time_uptime ,
because those variables are updated by
.Xr hardclock 9 .
.Sh SEE ALSO
.Xr settimeofday 2 ,
.Xr hardclock 9 ,
.Xr hz 9 ,
.Xr inittodr 9 ,
.Xr microtime 9