[grub #11] chainloading did not work as published after installing GRUB on a dual boot machine.

[B.]

Reporter: Jaime B.
Summary: chainloading did not work as published after installing GRUB on a dual 
boot machine.
Version: binary: 0.91,  documentation:0.92
Type: documentation bug

Message:
First of all let me thank all involved for such a great piece of software. 
Despite minor issues, I cannot think of another bootloader I'd rather use. 
Simple, elegant and very powerful. You have done an excellent job so far. 
Congratulations.



Now my experience (hope somebody can use the "debugging/rescue" tips):

A while ago I got my hands on an old IBM E390 ThinkPad for free. I used IBM's 
Rescue CD to revive it and later made it a dual-boot machine. Debian 3.0 
(woody) and its swap file where installed in partitions above the first one, 
which was in use by Win98. I had installed and been booting into Debian using 
loadlin from a DOS prompt. Kind of a pain to boot, but worked ok.

I recently updated my kernel from a 2.2.20 to a 2.4.18 using .debs from stable. 
Problem was that the 2.4 kernel now came with a corresponding intird image. I 
couldn't get the new kernel to boot up using loadlin, and I wanted to use a 
bootloader anyways (skip the extra step of booting into a DOS emulation on 
power up).

So I followed the GRUB's manual to create a boot floppy. As a sanity check 
measure before modifying my hard drive (and to learn how to use GRUB manually) 
I booted up from floopy and into both Win and Debian successfully. 
Specifically, using chainloader +1 to boot into Win worked as advertised.

I then installed GRUB using the setup command (as recommended by the manual) 
into the MBR and tried to boot into Win again. This time using chainloader +1 
only brought me back to GRUB. Tried it with +2 also; same result.
FDISK /MBR from a Win98 install diskette did _not_ restore the MBR as 
advertised in the documentation. Should I have used the Linux version of fdisk 
([note the use of lowercase)? Since the manual did not specify which version 
and it used uppercase to state the name of the program, I understood it to mean 
the MS version.
After several trials and errors I eventually used the Win98 floppy to boot into 
DOS, did a SYS A: C: from within C:\WINDOWS\COMMAND, and got my system back to 
its initial state. At least in appearance -- I don't know of (nor care much 
about) a way to be sure under DOS, short of full backups. 

I carefully re-read both the online and documented help for the setup command. 
I was willing to issue an install command manually. So, to learn how setup was 
using the install command, I issued it again (now that I knew how to restore my 
system). This was when I noticed that setup first called embed to write a 
*stage1_5 onto the first 16 blocks after the MBR of my HD. And then install was 
invoked with a parameter that took into account the 16 block offset. Eureka.

- What worked for me (first try):
Following the procedure for booting a chainloaded OS, but specifying the 
following command:

chainloading +17

instead of the documented one.


Maybe the documentation needs clarification and/or more detail into what 
happens when setup runs and how to chainload. Maybe the details can be in 
subsections clearly labelled as 'safe to skip'. Also, it could certainly use 
more detail regarding the difference between installing GRUB into the MBR or 
into the boot sector of a partition, for the sake of those of us who do not 
deal with partitions and drive organization on a regular basis.
I did not read the developer's section of the document -- I needed to be up and 
running fast and the introductory sections seemed detailed enough. Little did I 
suspect that Murphy's Laws where ready and willing to bite me in the butt.


Hope my memory of the events was accurate enough and that this information is 
useful to somebody. I would have contributed a patch to the documentation, but 
I don't know enough about GRUB's internals to do a proper job.

'till next time ...

Jaime.


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