From owner-freebsd-bugs Mon Jan 22 06:44:34 1996 Return-Path: owner-bugs Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id GAA17148 for bugs-outgoing; Mon, 22 Jan 1996 06:44:34 -0800 (PST) Received: from mpp.minn.net (root@mpp.Minn.Net [204.157.201.242]) by freefall.freebsd.org (8.7.3/8.7.3) with ESMTP id GAA17135 for ; Mon, 22 Jan 1996 06:44:16 -0800 (PST) Received: (from mpp@localhost) by mpp.minn.net (8.7.3/8.6.9) id IAA00318; Mon, 22 Jan 1996 08:36:00 -0600 (CST) Message-Id: <199601221436.IAA00318@mpp.minn.net> Subject: Re: dd /dev/mem ... To: luigi@labinfo.iet.unipi.it (Luigi Rizzo) Date: Mon, 22 Jan 1996 08:36:00 -0600 (CST) From: "Mike Pritchard" Cc: bugs@FreeBSD.org In-Reply-To: <199601221236.NAA05157@labinfo.iet.unipi.it> from "Luigi Rizzo" at Jan 22, 96 01:36:59 pm X-Mailer: ELM [version 2.4 PL25 ME8b] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-bugs@FreeBSD.org Precedence: bulk Luigi Rizzo wrote: > > Running 2.1R, I tried the following running as root: > > dd if=/dev/mem bs=32k skip=512 count=1 | dd bs=32 count=1 | hexdump > > and my P100 w/ 16MB was frozen: no keyboard, no mouse, everything > still on the X screen. > > the manpage says "Only offsets within the bounds of /dev/mem are > allowed.", and 512*32K is right beyond the physical RAM. However, I > have run C programs which would read beyond the limit with no problems. > > Is it a bug in /dev/mem, "dd" or me ? Funny you should mention this -- I just crashed my machine trying the same thing trying to verify PR# 383. As near as I can tell, it only locks up the machine when you run it from X *and* the current vty is the X window. If you do something like: sleep 30; dd if=/dev/mem ... and then switch to vty0, the machine won't lock up. Running from an ordinary syscons vty doesn't seem to be a problem. -- Mike Pritchard mpp@minn.net "Go that way. Really fast. If something gets in your way, turn"