Fix for the XP dual boot problem

[Gerry Tool]

Greg Miller wrote:
> 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
>>
>>
>>-- 
>>fedora-test-list mailing list
>>fedora-test-list at redhat.com
>>To unsubscribe: 
>>http://www.redhat.com/mailman/listinfo/fedora-test-list
>>
> 
> 
> 
I had a similar thing happen and discovered with fdisk that the 
partition it couldn't find was now labled as type 93 (amoeba) instead of 
83 (linux).  Check it out.  I was able to correct it with the t command 
in fdisk.

Gerry Tool