From owner-freebsd-hackers Sun Sep 15 3:20:16 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 0AF5837B406 for ; Sun, 15 Sep 2002 03:20:13 -0700 (PDT) Received: from rwcrmhc52.attbi.com (rwcrmhc52.attbi.com [216.148.227.88]) by mx1.FreeBSD.org (Postfix) with ESMTP id B83ED43E6E for ; Sun, 15 Sep 2002 03:20:12 -0700 (PDT) (envelope-from julian@elischer.org) Received: from InterJet.elischer.org ([12.232.206.8]) by rwcrmhc52.attbi.com (InterMail vM.4.01.03.27 201-229-121-127-20010626) with ESMTP id <20020915102011.SDWG26805.rwcrmhc52.attbi.com@InterJet.elischer.org>; Sun, 15 Sep 2002 10:20:11 +0000 Received: from localhost (localhost.elischer.org [127.0.0.1]) by InterJet.elischer.org (8.9.1a/8.9.1) with ESMTP id DAA87874; Sun, 15 Sep 2002 03:03:42 -0700 (PDT) Date: Sun, 15 Sep 2002 03:03:41 -0700 (PDT) From: Julian Elischer To: Sean Hamilton Cc: hackers@freebsd.org Subject: Re: dmesg circular buffer In-Reply-To: <000501c25c99$af6b6d40$911de8d8@slugabed.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Sun, 15 Sep 2002, Sean Hamilton wrote: > Greetings, > > As I understand, "dmesg" prints the tail end of a circular buffer stored > someplace on the root partition. Is it possible to have it read back beyond > the last reboot? Occasionaly I see it do this, though I have no idea why. > > In this case, I have a kernel that panicked, and am looking for clues > Nothing in /var/log/messages... The buffer is the last N bytes of ram, and the housekeeping for it is with it.. If the BIOS doesn't clear it, it will last beyond a reboot. The incoming new kernel will recognise a valid buffer and continue to use it without overwriting teh old contents.. very useful after a crash. I often see this. It may be related with the 'quick boot' that some BIOS offer as an option. (takes less time if you do not clear RAM.) julian To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message