[conspire] Kubuntu Parted Question

Rick Moen rick at linuxmafia.com
Tue Nov 20 13:38:10 PST 2007

Quoting Tony Godshall (togo at of.net):

> Boot flag is what DOS bootloaders use to distinguish between data
> and OS partitions.  It's irrelevant if your bootloader is grub.

It's irrelevant if your bootloader is GRUB _and_ GRUB's first-stage
code got written to the MBR.  However, correct me if I'm wrong, but:
I got the strong impression that most people install GRUB to the
superblock of the Linux boot partition, not to the MBR.

If my assumption's correct, then the MBR program area (initial 446 bytes
out of 512 total in sector zero) probably still contains Microsoft/IBM's
unnamed MBR bootloader left over from DOS.  That program's just smart 
enough to parse the partition table looking for the first primary
partition with the "boot" (active) flag, and branch to whatever's in its 
initial sector -- which per my understanding is where people tend to put
the GRUB first-stage code, which then takes over and controls the rest
of the boot process, presenting the GRUB boot menu, etc.

Answering John's questions:  

> Is it all right to have 2 partitions marked with boot flag?

It's imprudent to have two entries with the active aka boot flag.  
Just don't.  It's possible that your booting software might not be
confused, but why be in a hurry to find out?  Keep it simple.  Use what
works.  Don't dick around with boot configurations and partitions
without knowing what you're doing and why.

> What does boot flag mean and do?

It doesn't necessarily "mean" anything:  It's just a flag, i.e., a bit,
that can either be set or not on each of the four entries in an
IBM/Microsoft-style partition table in sector zero of a hard drive or
hard drive-like device.

See above for how the unnamed IBM/Microsoft MBR bootloader interprets
the flag if it encounters same.

It doesn't "do" anything:  It's just a flag, i.e., a bit,
that can either be set or not on each of the four entries in an
IBM/Microsoft-style partition table in sector zero of a hard drive or
hard drive-like device.  A first-stage bootloader in a hard drive or
hard drive-like device's sector zero either does or does not pay
attention to the bit, depending on what bootloader it is and how it was

> Should I have the lba flag on other primary partitions?

In the general case, you should leave your partitions the hell alone,
especially if you're fond of their contents.

I'm trying to figure out what this line of questioning's all about.
Several messages ago, you were saying something about problems building
(i.e., compiling from source) GRUB v. 1.95.  You provided no clue about
why you were doing such an extremely odd thing as compiling GRUB, or
in particular why you were compiling it from an upstream source tarball.

Reading further up to prior threads suggests that, first, 
you were trying to install Kubuntu (version unclear but possibly the
rather ancient, i.e., mid-2006, Kubuntu Dapper Drake aka v. 6.06) to a
G3 PPC iMac:  You had problems with a Firewire-attached hard drive, then
succeeded but weren't running X11.  Then, you stopped talking about the
PPC box, and suddenly without explanation started talking about some
other machine -- you didn't really tell us anything about it -- that
cannot possibly be the PPC, because you talked about installing MEPIS
(which lacks PPC support) as well as Kubuntu to it.

On this _second_ box (one infers), you had a series of rather unfocussed
questions about booting MS-Windows and about booting in general.  You
seem unclear about where you installed GRUB:  That would probably be
a big part of your problem.  You talk about MEPIS writing to things, and
PCLinuxOS writing to things, and Kubuntu writing to things -- but you
evidently weren't paying attention to where they were writing.

Maybe you should slow down, stop changing things and thereby continually
introducing yet more variables, boot a maintenance Live-CD Linux
distribution, figure out what's _really_ on your two hard drives'
various partitions, decide what you want bootable and from where,
construct an appropriate grub.conf, and install GRUB's bootloader. 

> Why are both Partition Tables msdos?

They are in the standard IBM/Microsoft partition table format used by 
essentially every commonly encountered OS for x86 except for the BSDs.
This is A Good Thing, in context.

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