From owner-freebsd-questions@FreeBSD.ORG Fri Dec 21 18:51:31 2007 Return-Path: Delivered-To: questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 9DD6016A419 for ; Fri, 21 Dec 2007 18:51:31 +0000 (UTC) (envelope-from wmoran@potentialtech.com) Received: from mail.potentialtech.com (internet.potentialtech.com [66.167.251.6]) by mx1.freebsd.org (Postfix) with ESMTP id 56CB413C448 for ; Fri, 21 Dec 2007 18:51:31 +0000 (UTC) (envelope-from wmoran@potentialtech.com) Received: from vanquish.pitbpa0.priv.collaborativefusion.com (pr40.pitbpa0.pub.collaborativefusion.com [206.210.89.202]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.potentialtech.com (Postfix) with ESMTP id 9FAB5EBC3B; Fri, 21 Dec 2007 13:51:30 -0500 (EST) Date: Fri, 21 Dec 2007 13:51:29 -0500 From: Bill Moran To: John Webster Message-Id: <20071221135129.ee20677e.wmoran@potentialtech.com> In-Reply-To: <62F8888810A130657FBCAF47@vortex.es.net> References: <20071218165521.GA37529@bewilderbeast.blackhelicopters.org> <343753.78466.qm@web44811.mail.sp1.yahoo.com> <20071221112303.19619c39.wmoran@potentialtech.com> <7BEE288E7C218E96DB9E8AA0@jw-laptop.dhcp.lbnl.us> <20071221132440.31ded74f.wmoran@potentialtech.com> <62F8888810A130657FBCAF47@vortex.es.net> X-Mailer: Sylpheed 2.4.7 (GTK+ 2.12.1; i386-portbld-freebsd6.2) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: questions@freebsd.org, "Michael W. Lucas" , shinny knight Subject: Re: timekeeping on jail servers X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 21 Dec 2007 18:51:31 -0000 In response to John Webster : > > --On Friday, December 21, 2007 13:24:40 -0500 Bill Moran wrote: > > > In response to John Webster : > >> > >> --On December 21, 2007 11:23:03 AM -0500 Bill Moran wrote: > >> > >> > In response to shinny knight : > >> > > >> > The reason that is not recommended is that it results in sudden steps > >> > of the clock. Occasionally, these steps go backwards. Software that > >> > is very sensitive to time changes (make processes, database servers, > >> > anything doing calculations WRT time) can break, crash, or work > >> > inaccurately. > >> > >> ntpdate -B should slew the time slowly. (According to the manpage.) > > > > Not generally suitable for cron because it can take longer to slew > > than it does for the next cron execution to occur, which would then > > result in multiple ntpdate programs fighting each other (not sure > > what the effect of this would be). > > If I were doing it I would write a script with locking in order > to ensure multiple jobs don't fight. Simple. Umm .... At that point, why not just run ntpd? You've basically replaced it with a script anyway. Besides, it's not that easy. As Chuck pointed out, ntpdate calls adjtime() and exits, which means an adjustment might already be in progress when you you call it again. I don't know if ntpdate checks the return pointer from adjtime() to avoid multiple adjustment requests. -- Bill Moran http://www.potentialtech.com