Accurate time without a network connection?

[Bob Johnson]

> Date: Wed, 23 Apr 2003 11:13:58 -0500
> From: David Kelly <dkelly at hiwaay.net>
> Subject: Re: Accurate time without a network connection?
> To: Joel Rees <joel at alpsgiken.gr.jp>
> Cc: FreeBSD-Questions at freebsd.org
> Message-ID: <20030423161358.GA24633 at grumpy.dyndns.org>
> Content-Type: text/plain; charset=us-ascii
> 
> On Wed, Apr 23, 2003 at 05:58:47PM +0900, Joel Rees wrote:
> 
>>>> > On Tue, Apr 22, 2003 at 03:26:19PM -0400, Charles Swiger wrote:
>>>> > 
>>>> > As for exactly what time the systems have, it doesn't much matter as
>>>> > long as they all have the same time.
>>
>>> 
>>> If you're serious about it not mattering exactly what time they have,
>>> what's the problem with letting one machine be the time server, letting
>>> it tune itself and then free run, and syncing all the rest to the
>>> slightly-off-time-server?
> 
> 
> Because the other systems do not have a link to the first.
> 
> I could sync them all to a common source they could *hear* but the
> customer won't allow them to *talk* to anything.
> 
> - David Kelly N4HHE, dkelly at hiwaay.net
> 

The NTP daemon can sync to a variety of external time signals.  These 
days it is very common to use GPS receivers as the reference for an NTP 
server.  If you can afford to spend about $100 per computer for low end 
GPS receivers (that output NMEA-0183 data) AND it is possible to put 
each GPS receiver where it can see the sky, that should work for you. 
If all of the computers are in the same building, it may even be 
possible to have them share a common GPS receiver with appropriate cabling.

There are other options, but I don't remember what they are.  For 
instance, it might be possible to sync the computers to the time 
reference included with most network television signals.

See www.ntp.org for more clues.

- Bob