Date: Sun, 25 Oct 1998 12:22:22 -0600 From: Dan Nelson <dnelson@emsphone.com> To: Graeme Tait <graeme@echidna.com>, Studded <Studded@gorean.org>, Greg Lehey <grog@lemis.com>, FreeBSD Questions <freebsd-questions@FreeBSD.ORG> Cc: info@boatbooks.com Subject: Re: Time calibration ? Message-ID: <19981025122222.A8447@emsphone.com> In-Reply-To: <363353AE.2772@echidna.com>; from "Graeme Tait" on Sun Oct 25 08:37:02 GMT 1998 References: <Pine.NEB.3.96.981024182211.363c-100000@ds9.dreamhaven.org> <3632EBDA.FD5F1529@gorean.org> <363353AE.2772@echidna.com>
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In the last episode (Oct 25), Graeme Tait said: > Studded wrote: > > For instance, Bryce could synch ds9 and voyager as peers, while > > synching each to a stratum 2 server outside of his network. It's > > generally considered rude for an "average user" to synch to a > > stratum 1 server without permission. It's also essentially > > unecessary, as a good stratum 2 server will provide more accuracy > > than any of us will ever need. > > That's my question - what does accurate time matter for in a typical > network, and how accurate is good enough? > > I ask because I'm involved in setting up a web/mail/ftp server, and > was wondering whether to use NTP. I notice quite a few Internet hosts > do not maintain accurate time, and are evidently just running on > their internal clocks, being perhaps a few minutes in error. Why not use NTP? It'll keep you from ever having to worry if your clock is set correctly. Depending on the business you run, your required clock accuracy will vary. At work, for example, our turnaround time for files clients FTP to us depends on the time the file hit our system (files sent after business hours get returned a day later). So we need to make sure that we are accurate to at least a minute or two. Same thing for ISP systems, if your billing changes for peak hours, or if you have to argue with a client about exceeding an hours-per-day agreement. If you are doing anything with Make across multiple machines, you'll probably want accuracy to the second. If you are doing any soft-realtime stuff, or need something to execute simultaneously on two different machines, you'll need sub-second resolution. NTP gives you all this, at the cost of less than 5 minutes of CPU-time per month :) The simplest way to NTP-synch a network is to create one or two NTP servers that synch to the same 2-3 NTP servers, and set them to broadcast NTP packets. Then just run "xntpd -b" on all your other machines and they'll stay synched. It's important to use the same set of sources because NTP never averages times. It determines a "best" time source and uses that. So if you have two NTP broadcast servers, each synched to a different strat-2 server, your other clients might flip-flop between those two servers. -Dan Nelson dnelson@emsphone.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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