Date: Fri, 14 Dec 2012 11:42:19 +0100 From: rank1seeker@gmail.com To: "Dieter BSD" <dieterbsd@engineer.com>, hackers@freebsd.org Subject: Re: NetBSD's boot select MBR Message-ID: <20121214.104219.547.1@DOMY-PC> In-Reply-To: <20121213221145.310760@gmx.com> References: <20121213221145.310760@gmx.com>
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> > > So I use NetBSD's MBR for disks I want
> > > to boot from.
> >
> > Can I have a CMD sequence?
> >
> > First would be ...
> > # fetch ...
>
> Read NetBSD's fdisk(8) and mbr(8).
>
> The MBR is only 512 bytes, and must contain the code and data.
> This is very limiting, so there are multiple versions depending
> on which features you need. IIRC, /usr/mdec/mbr_bootsel is the one I use.
> You can specify a label (up to 7 characters) for each bootable partition
> ("slice" in FreeBSD-speak). When the system executes the MBR code,
> it presents a menu with these labels. You can type '1' for the first
> partition/slice, '2' for the second, and so on. You can also type a
> function key to run the MBR of a different disk. The disk numbering
> can be rather insane, so it must be using the bios disk numbering. If
> you don't type anything it times out and boots the active partition/slice.
>
> Sadly, the FreeBSD bootstrap insists on booting the partition/slice
> marked active in the MBR. (The MBR code should look at the active
> bit, the later bootstraps should not.) So if you want to have
> multiple FreeBSD versions, it works best to put each on its own disk.
>
> The last time I used fdisk, large disks triggered a bug where some
> variable overflowed, giving negative numbers. Hopefully this is fixed
> by now. FreeBSD's fdisk also had some bug, so I had great fun
> handcrafting a MBR.
>
> It's been a long time since I installed NetBSD from scratch, (I usually
> just unpack the tar files, run installboot, and edit some config files.)
> I assume you can just boot a CD and get a shell, and experiment with
> fdisk on a scratch disk without actually installing NetBSD.
> To avoid a disaster, do something like
> dd if=$DISK of=/boot/MBR_backup bs=512 count=1 ; sync
> beforehand, in case you accidently mess up your boot drive.
>
> man pages:
> http://netbsd.gw.com/cgi-bin/man-cgi?++NetBSD-current
>
> isos:
> http://www.netbsd.org/mirrors/
> for example:
> ftp://iso.netbsd.org/pub/NetBSD/iso/5.2/amd64cd-5.2.iso
> or
> ftp://iso.netbsd.org/pub/NetBSD/iso/5.2/i386cd-5.2.iso
MBR supports max of 4 slices/partitions.
Looing at:
http://netbsd.gw.com/cgi-bin/man-cgi?mbr++NetBSD-6.0
The '/usr/mdec/mbr_bootsel', which you've mentioned, is equivalent to FreeBSD's '/boot/boot0', which is tuned via 'boot0cfg' util.
It will also show menu, to choose from, a slice to boot or another drive OR => 'F6' to choose PXE boot.
If nothing has been selected, it will simply boot an active slice.
So I see FreeBSD's, as superior (additionally supports PXE) => 8.0 onward ...
I don't use fdisk at all. Gpart is here ...
;)
Additionally ..., when I said '# fetch ...', I meant to get only 1 file, from ftp pub, which is installed into MBR ('/usr/mdec/mbr_$SOMETHING')
Then I would use FreeBSD's:
# gpart bootcode -b $path_to_netbsd_mbr_code ...
But this won't happen, as I thought NetBSD's had a MBR code, which could be told via a tool, from fully booted and running FreeBSD:
"Active slice is 2, but please, boot slice 4 at a next boot".
After that, I would '# reboot' and without any menu, slice 4 would be booted, for that one time, instaed of an active slice 2.
Am I missing something?
Thanks in advance.
Domagoj Smolčić
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