From owner-freebsd-arch Wed May 23 17:18: 2 2001 Delivered-To: freebsd-arch@freebsd.org Received: from wantadilla.lemis.com (wantadilla.lemis.com [192.109.197.80]) by hub.freebsd.org (Postfix) with ESMTP id DF5ED37B424 for ; Wed, 23 May 2001 17:17:57 -0700 (PDT) (envelope-from grog@lemis.com) Received: by wantadilla.lemis.com (Postfix, from userid 1004) id 56B6F6ACBC; Thu, 24 May 2001 09:47:50 +0930 (CST) Date: Thu, 24 May 2001 09:47:50 +0930 From: Greg Lehey To: Bruce Evans Cc: arch@FreeBSD.ORG Subject: Re: Re: http://uptime.netcraft.com/up/accuracy.html#cycle Message-ID: <20010524094750.A74859@wantadilla.lemis.com> References: <20010523083342.E41189@wantadilla.lemis.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: ; from bde@zeta.org.au on Wed, May 23, 2001 at 07:43:32PM +1000 Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-418-838-708 WWW-Home-Page: http://www.lemis.com/~grog X-PGP-Fingerprint: 6B 7B C3 8C 61 CD 54 AF 13 24 52 F8 6D A4 95 EF Sender: owner-freebsd-arch@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG 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 ----- >> >>> Date: Tue, 22 May 2001 21:51:02 +0100 (BST) >>> From: Richard Wendland >>> 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