Date: Thu, 24 May 2001 09:47:50 +0930 From: Greg Lehey <grog@lemis.com> To: Bruce Evans <bde@zeta.org.au> Cc: arch@FreeBSD.ORG Subject: Re: Re: http://uptime.netcraft.com/up/accuracy.html#cycle Message-ID: <20010524094750.A74859@wantadilla.lemis.com> In-Reply-To: <Pine.BSF.4.21.0105231936220.67212-100000@besplex.bde.org>; from bde@zeta.org.au on Wed, May 23, 2001 at 07:43:32PM %2B1000 References: <20010523083342.E41189@wantadilla.lemis.com> <Pine.BSF.4.21.0105231936220.67212-100000@besplex.bde.org>
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On Wednesday, 23 May 2001 at 19:43:32 +1000, Bruce Evans wrote: > On Wed, 23 May 2001, Greg Lehey wrote: > >> Comments? >> >> Greg >> >> ----- Forwarded message from Richard Wendland <richard@starburst.demon.co.uk> ----- >> >>> Date: Tue, 22 May 2001 21:51:02 +0100 (BST) >>> From: Richard Wendland <richard@starburst.demon.co.uk> >>> To: grog@FreeBSD.org (Greg Lehey) >>> Cc: webmaster@netcraft.com >>> Subject: Re: http://uptime.netcraft.com/up/accuracy.html#cycle >>> X-Mailer: ELM [version 2.5 PL2] >>> >>>> At this link, you claim: >>>> >>>> Additionally HP-UX, Linux, Solaris and recent releases of FreeBSD >>>> cycle back to zero after 497 days, exactly as if the machine had >>>> been rebooted at that precise point. Thus it is not possible to see >>>> a HP-UX, Linux or Solaris system with an uptime measurement above >>>> 497 days. >>>> >>>> FreeBSD does not suffer from this problem. You'll notice that you >>>> have a large number of FreeBSD systems with uptimes of over 497 days. >>>> I'd appreciate if you would correct this statement. >>> >>> Hi Greg, >>> >>> I think that statement is accurate. Note that we're not talking about >>> the FreeBSD 'uptime' command, but our ability to ascertain uptime remotely >>> by decoding the TCP timestamp option. >>> >>> Prior to FreeBSD 3 the TCP timestamp option was incremented every 500ms, >>> as is traditional with BSD. From FreeBSD 3 it was incremented every >>> 10ms, presumably to improve RTT measurement. But it does have the >>> consequence that the 32-bit TCP timestamp wraps around at 497.1 days. >>> Hence, with our current method at least, we don't detect uptimes above >>> this for FreeBSD 3 and later. >>> >>> So the FreeBSD systems listed > 497 days are running FreeBSD 2. >>> Once everyone has upgraded from FreeBSD 2, FreeBSD will no longer get >>> in that top uptimes list! > > The TCP timestamp is actually incremented every 1/hz seconds, so it > overflows after every 48.5 days on alphas (and on i386's with > "options HZ=1024"). So what's Richard talking about? Greg -- Finger grog@lemis.com for PGP public key See complete headers for address and phone numbers To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
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