recent kernel upgrades damage mbr

[Mikkel L. Ellertson]

Gene Heskett wrote:
> On Wednesday 18 June 2008, Mikkel L. Ellertson wrote:
>> This is not going to help, because the old MBR will be pointing to
>> the wrong location for stage 1.5, so you will get an error on boot.
>> Remember, the part of GRub that is in the MBR loads from a fixed
>> disk location. It does not read the file system. So, unless stage
>> 1.5 is in the same place on the disk, (head, cylinder, sector) it is
>> not going to be able to load it.
>>
>> Your best bet is to fix the device map, and run grub-install.
>>
>> Mikkel
> 
> I have Mikkel, twice, and grub-install (or one of its friends) overwrote it both 
> times.  Lets just say it was "educational".  I now have backups under other 
> names there.
> 
> --------device.map--------
> # this device map was generated by anaconda
> (hd0)     /dev/sdb
> --------------------------
> No mention of any other drives seems to be allowed, and there are 2 others.
> 
This is strange, because grub-install is not supposed to change the 
device map unless you use the --recheck option.

> Also NDI why it says Anaconda, cuz Anaconda hasn't been exec'ed on this box 
> since last February when (I think nvidia blobs had something to do with it) 
> when something, for the 2nd time in 3 months, wiped the mbr from the boot 
> drive.  Now I'm on an old ATI card running the radeon driver, and no further 
> problem (knock on wood). Maybe, if and when I get around to building another 
> box, the new mobo's bios won't be so fscking brain dead and I won't have to 
> screw around with this anymore.
> 
I forgot - one other thing that may help is to change 
/etc/sysconfig/grub to match what you need in the device map. That 
may be where the changed device map is coming from.

> While we're on the subject of mbr's, how big is it?  The first 512 bytes of the 
> one I just saved is virtually empty.  So I overwrote it with a 4kb version, 
> but that is bearing some resemblance to a list of inodes.
> 
The MBR, including the partition table is normally 512 bytes. If it 
is empty, then you may be using the wrong device. Did you use 
/dev/hda1, and not /dev/hda? Writing 4kb can lead to file system 
corruption.

Mikkel
-- 

   Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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