Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 5 Nov 2001 15:41:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 5 Nov 2001 15:41:12 -0500 Received: from alfik.ms.mff.cuni.cz ([195.113.19.71]:16656 "EHLO alfik.ms.mff.cuni.cz") by vger.kernel.org with ESMTP id ; Mon, 5 Nov 2001 15:41:06 -0500 Date: Fri, 2 Nov 2001 12:16:03 +0000 From: Pavel Machek To: Ian Maclaine-cross Cc: linux-kernel@vger.kernel.org, Ian Maclaine-cross Subject: Re: PROBLEM: Linux updates RTC secretly when clock synchronizes Message-ID: <20011102121602.A45@toy.ucw.cz> In-Reply-To: <20011031113312.A8738@ilm.mech.unsw.edu.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: <20011031113312.A8738@ilm.mech.unsw.edu.au>; from iml@ilm.mech.unsw.edu.au on Wed, Oct 31, 2001 at 11:33:12AM +1100 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hi! > PROBLEM: Linux updates RTC secretly when clock synchronizes. > > Please CC replies etc to Ian Maclaine-cross . > > When /usr/sbin/ntpd synchronizes the Linux kernel (or system) clock > using the Network Time Protocol the kernel time is accurate to a few > milliseconds. Linux then sets the Real Time (or Hardware or CMOS) > Clock to this time at approximately 11 minute intervals. Typical RTCs > drift less than 10 s/day so rebooting causes only millisecond errors. > > Linux currently does not record the 11 minute updates to a log file. > Clock programs (like hwclock) cannot correct RTC drift at boot without > knowing when the RTC was last set. If NTP service is available after a > long shutdown, ntpd may step the time. Worse after a longer shutdown > ntpd may drop out or even synchronize to the wrong time zone. The > workarounds are clumsy. > > Please find following my small patch for linux/arch/i386/kernel/time.c > which adds a KERN_NOTICE of each 11 minute update to the RTC. This is > just for i386 machines at present. A script can search the logs for > the last set time of the RTC and update /etc/adjtime. Hwclock can > then correct the RTC for drift and set the kernel clock. That seems as very wrong solution. What about just making kernel only _read_ system clock, and never set it? That looks way cleaner to me. Pavel -- Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt, details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html. - 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/