MBR blown away

Duane Whitty duane at greenmeadow.ca
Sat Feb 11 07:56:30 PST 2006

Jerry McAllister wrote:
>> I need help.
>> I added a slice to a single hard drive dual-boot (windows) system and now
>> I guess that scrambled my MBR.  I get three options from the FreeBSD (5.4)
>> boot manager:
>> 1. DOS
>> 2. FreeBSD
>> 3. FreeBSD
>> I can boot to FreeBSD (the new slice is fine) by choosing option 3 but the
>> windows/dos option is fried.
> The MBR itself looks OK.   According to that piece of menu you posted, you 
> just added another bootable slice.  So, there are now two bootable FreeBSD 
> slices and one bootable Microsloth slice.   
> Are you saying that the MS slice will no longer boot if you select '1' from
> the menu?    If that is the case, it is not the MBR that was messed up.  
> It is something in the MS slice - probably their boot sector.   I don't even 
> pretend to know how MS sets up theirs if it is any different from FreeBSD.
> But, the MBR is doing what it is supposed to do.  It discovers all the
> bootable slices and makes a menu and transfers control to the selected
> slice.  What happens after that is not the problem of the MBR.
> That may be bad news, I suppose.  It might be easier to fix the MBR
> than the MS slice boot code if it is actually messed up.
> It might be as simple as you managed to mark the MS slice as not bootable
> in some way, but in that case, I wouldn't expect the MBR to be able to
> see that slice and put it in the menu as bootable.
> Did you use some utility to shrink the original two slices to fit in
> the new one?  Or was there already unused space (previously unallocated)
> that you were using?    Maybe the utility you used to shrink the other
> slices messed something up.    You might need to go back to it and
> check it out.
> Was the MS slice an NTFS type file system?   Many of the free utilities
> for resizing slices do not work properly on NTFS systems.   So, it is 
> possible, in that case, that the MS slice was not shrunk properly and
> so it got trashed at that stage.
> Just some thing to consider.
> Good luck,
> ////jerry
>> My current strategy is to use boot0cfg:
>> # boot0cfg -B
>> But I'm a little squeemish.  I don't want to be locked out of FreeBSD (I
>> barely use Windows but I still would like it back for Visio).  Any
>> guidance?
> As per my comments above, I don't think rewriting the MBR will help any.
> /jrm
>> --
>> Peter

Just out of curiosity, did you try using 
sysinstall again to take a look at things?  Maybe 
you can mark your Windows partition bootable?

Trying this might at least tell you whether your 
Windows slice is "fried" or not.

I know I seem to have some sort of trouble along 
these lines every time I do a fresh install 
because I'm always trying to run so many different 
systems on one machine.  Windows just doesn't play 
nice.  But so far I have always been able to get 
things straightened out.


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