From owner-freebsd-usb@FreeBSD.ORG Sat Nov 20 07:02:42 2010 Return-Path: Delivered-To: freebsd-usb@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DAEBC106564A for ; Sat, 20 Nov 2010 07:02:42 +0000 (UTC) (envelope-from guru@unixarea.de) Received: from ms16-1.1blu.de (ms16-1.1blu.de [89.202.0.34]) by mx1.freebsd.org (Postfix) with ESMTP id 694868FC0A for ; Sat, 20 Nov 2010 07:02:42 +0000 (UTC) Received: from [93.104.73.12] (helo=current.Sisis.de) by ms16-1.1blu.de with esmtpsa (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.69) (envelope-from ) id 1PJhT1-00039g-W8; Sat, 20 Nov 2010 08:02:36 +0100 Received: from current.Sisis.de (current [127.0.0.1]) by current.Sisis.de (8.14.3/8.14.3) with ESMTP id oAK72a35002108; Sat, 20 Nov 2010 08:02:36 +0100 (CET) (envelope-from guru@unixarea.de) Received: (from guru@localhost) by current.Sisis.de (8.14.3/8.14.3/Submit) id oAK72ZIE002107; Sat, 20 Nov 2010 08:02:35 +0100 (CET) (envelope-from guru@unixarea.de) X-Authentication-Warning: current.Sisis.de: guru set sender to guru@unixarea.de using -f Date: Sat, 20 Nov 2010 08:02:35 +0100 From: Matthias Apitz To: Warren Block Message-ID: <20101120070235.GA2091@current.Sisis.de> References: <20101119143337.GA3023@current.Sisis.de> <201011191821.09308.hselasky@c2i.net> <20101119173519.GA3933@current.Sisis.de> <201011191916.53655.hselasky@c2i.net> <20101119183900.GA1221@tiny.Sisis.de> <20101119204639.GA1521@tiny.Sisis.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Operating-System: FreeBSD 8.0-CURRENT (i386) User-Agent: Mutt/1.5.19 (2009-01-05) X-Con-Id: 51246 X-Originating-IP: 93.104.73.12 Cc: freebsd-usb@freebsd.org Subject: Re: copying /dev/da0 with dd(1) to file: output differs X-BeenThere: freebsd-usb@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Matthias Apitz List-Id: FreeBSD support for USB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 20 Nov 2010 07:02:43 -0000 El día Friday, November 19, 2010 a las 05:42:57PM -0700, Warren Block escribió: > On Fri, 19 Nov 2010, Matthias Apitz wrote: > > El d?a Friday, November 19, 2010 a las 12:39:13PM -0700, Warren Block escribi?: > > > >>> Should I overwrite the full USB key from /dev/zero? > >> > >> Possibly there would still be differences. Filesystem metadata like > >> date last mounted, for example. If you want a block-by-block duplicate, > >> the brute-force method is to just dd the whole drive. Use bs=64k or > >> bs=1m to help reduce overhead. > > > > Warren, perhaps you missed my point. I have a prepared boot-able key and > > I want to give away a copy of it as a file on DVD. So I dd(1)'ed the key > > to disk and did this twice to ensure that the copy was fine, but the two > > files differ. How can I make sure that the file on disk (or DVD) is a > > exact copy of the key? > > Okay, that makes more sense. Did you mount the key in between the two > times it was dd-ed? No. I just fired up the dd(1) a 2nd time to another file to check if it would produce two times the same result. And, surprise, they differ, they differ each time and in laptops differentes as well. matthias -- Matthias Apitz t +49-89-61308 351 - f +49-89-61308 399 - m +49-170-4527211 e - w http://www.unixarea.de/