Fix for the XP dual boot problem

[Greg Miller]

It looks like I may have a similar but different problem.

I wiped FC2test3 and winXP. I then re-installed XP (to solve other problems), then re-installed FC2. It looks like GRUB is screwed up and can not boot linux, but Win XP boots fine. I get an error message that indicates it can't find the partition abd to press a key to continue. The screen is barely readable and I can just select other to go to the XP/dos boot selection.

I'm thinking I need to re-install grub from a rescue boot.

AMD3200
K8T800 chipset
SATA drive
Radeon 9200 Video

Greg.

----- Original Message -----
From: Radu Cornea <ccradu at yahoo.com>
Date: Wednesday, May 19, 2004 5:25 pm
Subject: Re: Fix for the XP dual boot problem

> Michal Jaegermann wrote:
> 
> > The problem is that there is no "wrong geometry".  For quite a while
> > these "geometries" are just inventions and illusions.  Many years
> > ago hard disks indeed had all these head and cylinder geometries,
> > physical ones, but this is a bygone era.  The trouble here is that
> > here XP invents one geometry and your kernel another and XP refuses
> > to work with what it decided it likes.  Linux kernel is more
> > forgiving than that and anaconda should just read what an existing
> > partition table said and do not bother with any alerts.
> > 
> 
> Well, not exactly. What I call "wrong geometry" is when the two 
> values 
> (physical and logical) don't match. I know the same disk can be 
> seen as 
> having different geometries (e.g. 16 heads vs 255) but in the 
> final 
> C*H*S should be the same. As I mentioned in another post I get 
> very 
> different values from the 2.6 kernel, while 2.4 returns the 
> correct ones:
> 
> These are examples from FC2:
> $ more /proc/ide/hda/geometry
> physical     16383/16/63
> logical      19841/16/63
> 
> On another FC2 machine:
> $ more /proc/ide/hda/geometry
> physical     16383/16/63
> logical      16383/255/63
> 
> On a FC1 machine (2.4 kernel) the numbers are ok:
> $ more /proc/ide/hda/geometry
> physical     155009/16/63
> logical      9726/255/63
> 
> The product C*H*S should be the same (or close at least)...
> But they are different (even for the same OS, not even talking 
> about XP 
> here).
> 
> > Strictly speaking the bug is on an XP side but you are not likely
> > fare that well pursuing that.
> 
> I agree this may be fixed on the XP side too. But still the 
> installer 
> has a problem. Why will it otherwise offer without any warning to 
> change 
> the mbr, when I did not select any partitioning and I chose to put 
> Grub 
> in the Linux partition. This reminds me of another OS (guess:)) 
> which 
> overwrites mbr on install again without asking.
> Plus, there are report on bugzilla of people that did run 
> partition 
> magic after installing FC2 and got a lot of errors (mismatch) in 
> the 
> partition table.
> From the fdisk manual, the mbr stores the info in two ways: as an 
> absolute number of sectors and as C/H/S. Windows uses both, while 
> Linux 
> never uses C/H/S. That's why I think Linux can still boot, and 
> Windows 
> not. Only C/H/S are changed during installation. That's why it is 
> also 
> possible to restore the original aprtition table.
> Fedora 2 is not the only one affected by it, but also Mandrake 10 
> and 
> Suse 9.1. See:
> 
> https://qa.mandrakesoft.com/show_bug.cgi?id=7959
> http://www.eweek.com/article2/0,1759,1585840,00.asp
> 
> So far this post by Alan Cox seems to be the best explanation why 
> this 
> problem occurs with 2.6 kernels:
> 
> https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=113201#c13
> 
> "This seems to be a bug in the FC2 tools. The Linux kernel no longer
> does partition guessing (its a heuristic and policy at best), as a
> result the  parted tools should be honouring existing partition table
> claims when they are present. Failure to do so causes very bad things
> to happen.
> 
> Previously these situations the kernel itself would report the
> partition table or BIOS guess it made, now its firmly in userspace."
> 
> 
> --
> Radu
> 
> 
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