From owner-freebsd-questions Mon Apr 15 21:27: 4 2002 Delivered-To: freebsd-questions@freebsd.org Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by hub.freebsd.org (Postfix) with ESMTP id 5FE0237B416 for ; Mon, 15 Apr 2002 21:27:01 -0700 (PDT) Received: from dan.emsphone.com (smmsp@localhost [127.0.0.1]) by dan.emsphone.com (8.12.2/8.12.2) with ESMTP id g3G4QxDh002751; Mon, 15 Apr 2002 23:27:00 -0500 (CDT) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.12.2/8.12.2/Submit) id g3G4Qvci002750; Mon, 15 Apr 2002 23:26:57 -0500 (CDT) Date: Mon, 15 Apr 2002 23:26:57 -0500 From: Dan Nelson To: Peter Leftwich Cc: "Patrick O'Reilly" , Mike Meyer , mpd , FreeBSD Questions Subject: Re: MBR, mfsroot.flp, handbook, and list fail me! [dnelson] Message-ID: <20020416042657.GC7238@dan.emsphone.com> References: <20020406195912.GA63541@dan.emsphone.com> <20020415205617.S24688-100000@earl-grey.cloud9.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20020415205617.S24688-100000@earl-grey.cloud9.net> User-Agent: Mutt/1.3.28i X-OS: FreeBSD 5.0-CURRENT X-message-flag: Outlook Error Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In the last episode (Apr 15), Peter Leftwich said: > On Sat, 6 Apr 2002, Dan Nelson wrote: > > > Mike, I must beg to differ : I have recently been trying to get > > > the same thing done. I can confirm that "fdisk -B ad0" is safe, > > > as is "boot0cfg -B", but these install the BSD boot manager, > > > which insists on offereing you a menu during the boot process. > > > Peter's question (and mine too now :) is how to "demote" it to > > > the standard mbr which just boots without pausing? > > fdisk -B -b /boot/mbr ad0 > > Since you are using "ad0" in the command line, must you first `cd > /dev` then run this command? No; fdisk knows that its arguments are devices and will prepend /dev for you. You can give it a full path if you want, though, > > will put a "dumb" mbr on that only knows how to chain to the > > bootblock of the first active partition. > > What does "chain to the bootblock of the first active partition" > mean? Basically, the BIOS searches for the first disk with a valid boot block on block 0 of the media (hard drive or floppy disk). If the boot block also has a partition table, the boot code usually is very simple; it finds the first partition marked active and boots block 0 of the partition. The boot block inside the partition is responsible for finding io.sys (for DOS/win95), or /boot/loader (in FreeBSD's case). This is chaining, where each piece of boot code locates the next one in turn and executes it, until your OS is loaded. http://www.pcguide.com/ref/hdd/file/struct.htm has a good explanation of how it all works. -- Dan Nelson dnelson@allantgroup.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message