.\"	$OpenBSD: inittodr.9,v 1.10 2007/05/31 19:20:00 jmc Exp $
.\"	$NetBSD: inittodr.9,v 1.2 1996/03/27 21:16:06 jtc 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: May 31 2007 $
.Dt INITTODR 9
.Os
.Sh NAME
.Nm inittodr
.Nd initialize system time
.Sh SYNOPSIS
.Ft void
.Fn inittodr "time_t base"
.Sh DESCRIPTION
The
.Fn inittodr
function determines the time and sets the system clock.
It tries to pick the correct time using a set of heuristics that examine
the system's battery-backed clock and the time reported by the file
system, as given in
.Fa base .
Those heuristics include:
.Bl -bullet
.It
If the battery-backed clock has a valid time, it is used.
.It
If the battery-backed clock does not have a valid time, and
the time provided in
.Fa base
is within reason,
.Fa base
is used as the current time.
.It
If the battery-backed clock appears invalid, and
.Fa base
appears nonsensical or was not provided (was given as zero),
an arbitrary base (typically some time in the late 1970s)
will be used.
.El
.Pp
Once a system time has been determined, it is stored in the
.Va time
variable.
.Sh DIAGNOSTICS
The
.Fn inittodr
function prints diagnostic messages if it has trouble figuring
out the system time.
Conditions that can cause diagnostic messages to be printed include:
.Bl -bullet
.It
The battery-backed clock's time appears nonsensical.
.It
The
.Fa base
time appears nonsensical.
.It
The
.Fa base
time and the battery-backed clock's time differ by a large amount.
.El
.Sh SEE ALSO
.Xr resettodr 9 ,
.Xr time 9
.Sh BUGS
On many systems,
.Fn inittodr
has to convert from
a time expressed in terms of year, month, day, hours, minutes,
and seconds to
.Va time ,
expressed in seconds.
Many of the implementations could share code, but do not.
.Pp
Each system's heuristics for picking the correct time are slightly
different.