Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267405AbUI1LE3 (ORCPT ); Tue, 28 Sep 2004 07:04:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266864AbUI1LE3 (ORCPT ); Tue, 28 Sep 2004 07:04:29 -0400 Received: from scanner2.mail.elte.hu ([157.181.151.9]:12735 "EHLO mx2.elte.hu") by vger.kernel.org with ESMTP id S267405AbUI1LEZ (ORCPT ); Tue, 28 Sep 2004 07:04:25 -0400 Date: Tue, 28 Sep 2004 13:05:41 +0200 From: Ingo Molnar To: Gene Heskett Cc: linux-kernel@vger.kernel.org, Matt Heler Subject: Re: 2.6.9-rc2-mm4 Message-ID: <20040928110541.GA22436@elte.hu> References: <20040926181021.2e1b3fe4.akpm@osdl.org> <200409280626.50167.gene.heskett@verizon.net> <20040928103324.GA21050@elte.hu> <200409280701.06932.gene.heskett@verizon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200409280701.06932.gene.heskett@verizon.net> User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3313 Lines: 82 * Gene Heskett wrote: > That would I assume need a null modem cable, and what do I run on the > firewall? Minicom? Or is there something better that can just grab > and log without being interactive? Its a rh7.3 box with a 2.4.18 era > kernel. I'd update that, but its not broken. :) here's a mini-howto: to set up serial logging: ------------------------- install a null modem cable to one of the serial ports of the server, connect the cable to another box, run a terminal program on that other box (e.g. "minicom -m" - do Alt-L to switch on logging after starting it up) and set up the server's kernel to do serial logging: enable CONFIG_SERIAL_8250_CONSOLE and CONFIG_SERIAL_CORE_CONSOLE, recompile & reinstall the kernel, add "console=ttyS0,38400 console=tty0" to your /etc/grub.conf or /etc/lilo.conf kernel boot line, reboot the server with the new kernel command line - and configure minicom to run with that speed (Alt-S). e.g. my /etc/grub.conf has: title test-2.6 (test-2.6) root (hd0,0) kernel /boot/bzImage root=/dev/sda1 console=ttyS0,38400 console=tty0 nmi_watchdog=1 kernel_preempt=1 if everything is set up correctly then you should see kernel messages showing up in the minicom session when you boot up. When the messages do not show up then typical errors are mismatch between the serial port (or speed) and the device names used - if it's COM2 then use ttyS1, and dont forget to set up the serial speed option of minicom, etc. You can test the serial connection by doing: echo x > /dev/ttyS0 and that should show up in the minicom session on the other box. to set up the NMI watchdog: --------------------------- add nmi_watchdog=1 to your boot parameters and reboot - that should be all to get it active. If all CPU's NMI count increases in /proc/interrupts then it's working fine. If the counts do not increase (or only one CPU increases it) then try nmi_watchdog=2 - this is another type of NMI that might work better. (Very rarely there are boxes that dont have reliable NMI counts with 1 and 2 either - but i dont think your box is one of those.) once the NMI watchdog is up and running it should catch all hard lockups and print backtraces to the serial console - even if you are within X while the lockup happens. You can test hard lockups by running the attached 'lockupcli' userspace code as root - it turns off interrupts and goes into an infinite loop => instant lockup. The NMI watchdog should notice this condition after a couple of seconds and should abort the task, printing a kernel trace as well. Your box should be back in working order after that point. now for the real lockup your box wont be 'fixed' by the NMI watchdog, it will likely stay locked up, but you should get messages on the serial console, giving us an idea where the kernel locked up and why. (Very rarely it happens that not even the NMI watchdog prints anything for a hard lockup - this is often the sign of hardware problems.) Ingo --- lockupcli.c main () { iopl(3); for (;;) asm("cli"); } - 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/