Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758848AbZACHAo (ORCPT ); Sat, 3 Jan 2009 02:00:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750767AbZACHAg (ORCPT ); Sat, 3 Jan 2009 02:00:36 -0500 Received: from bee.hiwaay.net ([216.180.54.11]:19450 "EHLO bee.hiwaay.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750759AbZACHAf (ORCPT ); Sat, 3 Jan 2009 02:00:35 -0500 Date: Sat, 3 Jan 2009 01:00:22 -0600 From: Chris Adams To: David Newall Cc: Robert Hancock , linux-kernel@vger.kernel.org, linasvepstas@gmail.com, "Jeffrey J. Kosowsky" , MentalMooMan , Travis Crump , Goodgerster Subject: Re: Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009 Message-ID: <20090103070022.GC1538533@hiwaay.net> References: <3ae3aa420901021125n1153053fsdf2378e7d11abbc0@mail.gmail.com> <20090102210430.49649261@diego-desktop> <495E7849.4030706@shaw.ca> <495F0672.6020708@davidnewall.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <495F0672.6020708@davidnewall.com> User-Agent: Mutt/1.4i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1457 Lines: 29 Once upon a time, David Newall said: > I don't understand this idea, nor the patch for the problem. I don't > see why adding a leap second would impact the kernel in any way. > Shouldn't this be a simple zoneinfo change, whereby the last two seconds > of the year (in each timezone) both map to 31dec2008 23:59:59? That's > the way the change has worked in the real world. Why would ntp or the > kernel be involved? The leap second isn't a simple thing like a time zone. Zones account for an offset from UTC, but a leap second is an extra second inserted into (or possibly removed from) UTC itself. There was actually a 61 second minute on Dec. 31. The trouble comes in keeping the "seconds since the epoch" counter sane, meaning (seconds % 86400) == 0 at 00:00:00 UTC. Since there were 86401 seconds Dec. 31, the kernel had to tick the last second twice to keep correct UTC time. NTP is used to distribute and synchronize time information, including leap second info. See Wikipedia and Google for more information. -- Chris Adams Systems and Network Administrator - HiWAAY Internet Services I don't speak for anybody but myself - that's enough trouble. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/