Date: Fri, 25 Apr 2003 17:48:47 -0400 (EDT) From: Jerry McAllister <jerrymc@clunix.cl.msu.edu> To: blueeskimo@gmx.net (Adam) Cc: freebsd-questions@freebsd.org Subject: Re: Problems setting up dual-boot Message-ID: <200304252148.h3PLmlZu020283@clunix.cl.msu.edu> In-Reply-To: <1051304482.76975.33.camel@jake> from "Adam" at Apr 25, 2003 05:01:22 PM
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> On Fri, 2003-04-25 at 16:07, Jerry McAllister wrote: > > Root needs to be the 'a' partition (maybe not absolutely, but everything > > seems to assume it is). =20 > > Yeah, this is the conclusion I'm arriving at as well. I think I'm going > to try reinstalling FreeBSD and completely redo the partitions. Sounds like that needs to be done. > > Sounds like you need to study the man pages for FreeBSD's fdisk and > > disklabel carefully along with the handbook. > > No doubt .. I've been through page after page of tutorials on how to do > this .. The problem is that the terminology is a bit foreign to me, so I > continuously get sidetracked just trying to figure out what the words > mean.=20 A little base description here with most of the details fudged over - I think I have my terminology sorted out correctly, tho I might have it shifted to the right a position. It does get confusing because similar sounding terms get used over with somewhat similar, but different meanings. One thing that seems to often confuse is that there are two (actually three) boot blocks. There is the Master Boot block (MBR) that is per disk and a boot sector which seems to be per slice. You need both. fdisk will install the MBR for you and disklabel will write the boot sector. The MBR, amongst other things lets you select among bootable slices that have boot sectors written in. This stuff is pretty fixed as per location. The BIOS grabs the MBR sector off the first device that it thinks is configured to be a boot device. It only knows if there is a bootable flag set, not what is really in that sector. And, the MBR doesn't know much about what is there in the slice' boot sector either, just if it has a code in a certain location saying it is bootable. If so, it passes off control to that sector after it gets done with its tinkering around. It can tell if the bootable flag is set even if it doesn't recognize which operating system it is booting (which results in the OS being identified as ??? sometimes). The boot sector code does a little bit and loads some more stuff in (that third piece) and then booting as you see it on the screen finally gets under way for real. > In your experience, is it OK to have dual-boot set up across different > physical disks? LILO was perfectly happy with this setup, but I really > wasn't happy with Linux. Maybe the FreeBSD boot manager simply does not > like switching between disks?=20 Sure, you can do it. But, the MBR still goes on the disk that the BIOS thinks is the boot disk - usually the first one. Then it can be made to point to the boot sectors on the other disk slices. That MBR is pretty limited by space in how fancy it can be and probably in how many things it can point to. Some boot systems take advantage of other space that is not usually being used to do a little nicer looking boot and they probably work with most everything available nowdays, but I don't know if they are strictly 100% compatible with everything. Grub is one of these. You don't need them to make it work, just to make it prettier and/or more convenient. ////jerry
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