[conspire] Kubuntu Parted Question

Rick Moen rick at linuxmafia.com
Tue Nov 20 18:38:50 PST 2007

Quoting Nick Moffitt (nick at zork.net):

> Just for the record, most people don't create separate /boot partitions
> these days.

Worth noting, I guess, though not visibly relevant to the foregoing.

> Surely the superblock of this partition (or even of a separate /boot
> partition) would be an ext3 filesystem superblock, and not some funny
> grub program.

I believe I meant, and should have said, that the first-stage GRUB
bootloader usually goes into simply the initial sector of the
filesystem.  The ext3 (or whatever) superblock copies would then be
after that.  I don't know details of exactly where physically, within a
native-Linux filesystem, the first-stage bootloader goes when it gets
installed there, having not really needed to know.

The distro installer generally offers that choice:  install GRUB into
the MBR, or install it into the /dev/sdb1 or whatever, with the latter
being the default.

> My understanding is that Ubuntu installs the stage 1 grub loader into
> the MBR, complete with the four-entry DOS-style Partition Table at
> 0x01BE.  It then has the device ID, partition number, and offset in
> sectors where stage 2 can be found.

_If_ so, then that first-stage bootloader would seem to be functionally 
identical to the unnamed IBM/Microsoft one carried forward from MS-DOS
to various MS-Windows things -- and it really doesn't make a lot of
difference which one resides there, as long as one of them does.

There are also various other <= 446-byte programs for the same purpose.
Have noticed some in the Debian catalogue.  Point is, though, that for a 
machine that dual-boots MS-Windows, my understanding is that you want 
to leave in the 446-byte first portion of the MBR sector _some_ simple
first-stage bootloader (GRUB's or any other) that emulates the
IBM/Microsoft one's behaviour: find the first primary partition with the
"active" flag, branch to whatever's in its sector zero.

If you were to take any other approach to booting, then any reinstall of
MS-Windows (or, for all I know, maybe installation of service packs,
etc.) will cause the Microsoft installer to overwrite that area anyway,
so you might as well work its behaviour into your boot strategy.

My recollection is:  Those Microsoft installers will both overwrite the
MBR (without asking your leave) _and_ set the "active" flag to the
MS-Windows one.  So, if/when that happens, you correct the latter change
by changing the "active" flag back, using whatever tool you have for
that purpose.  (In olden days, one could fire up MS-DOS media and run
FDISK.EXE, for that purpose.)

Frankly, I neither know nor care personally about the fine details of
such things, since I never dual-boot with MS-Windows, and stick to a
single OS per machine.

We are getting somewhat sidetracked from the main point, however, which
was that John was very likely barking up the wrong tree, and not
addressing his real problem at all.

> I suppose that the task performed by the stage 1 loader *could* be done
> by the old DOS one, but I am fairly confident that most Linuxes these
> days assume that our boot loader technology is always preferable to
> random proprietary cruft found in boot sectors.  

Could be, but that's really kind of irrelevant.  

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