From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261851AbUKUXkR (ORCPT ); Sun, 21 Nov 2004 18:40:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261849AbUKUXkR (ORCPT ); Sun, 21 Nov 2004 18:40:17 -0500 Received: from fw.osdl.org ([65.172.181.6]:52387 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S261860AbUKUXkF (ORCPT ); Sun, 21 Nov 2004 18:40:05 -0500 Date: Sun, 21 Nov 2004 15:39:40 -0800 From: Andrew Morton To: Eyal Lebedinsky Cc: linux-kernel@vger.kernel.org Subject: Re: help: sysrq and X Message-Id: <20041121153940.035ffc08.akpm@osdl.org> In-Reply-To: <41A122E0.8070307@eyal.emu.id.au> References: <41A122E0.8070307@eyal.emu.id.au> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Eyal Lebedinsky wrote: > > I am trying to diagnose a hard lockup. The only way I can reproduce it is > with mythtv. When the system locks up (no mouse, no activity in X, no message > logged) I can use magic sysrq, but I cannot see the output. > > Using 'r' does not enable console switching. However 'b' will boot the > system, and I hope 's' and 'u' did something blindly. > > I there a way to regain a text console in order to inspect the kernel? > > I can connect a machine to the serial port if this will help - does > sysrq work though the serial port? Which software should I use on > the serial port (on the 'other' machine) for this purpose then? Yes, serial console is the best way to do this. Add `console=ttyS0' to the kernel boot command line and use `t' to get an all-task backtrace. If you're using minicom (spit) on the other end, Control-A F t is the combination to use.