rescuing system after MBR overwrite; root on EVM-ed ReiserFS / root on standalone ext3

[Thomas Kaiser]

If you have your bootloader (grub) installed in the MBR, just save the 
MBR before you install windows. And put your backup MBR back after 
windows install has finished.

I would do something like this:
- Boot into Linux
- dd if=/dev/hda of=mbr.bin bs=512 count=1 -> save MBR to the curent 
directory
- install windows
- after windows install is finished, boot from any live/rescue Linux
- mount the partition where you put mbr.bin
- dd if=/path_to_your_backup/mbr.bin of=/dev/hda
- reboot and Linux should boot like it did before the windows install
- open /boot/grub/menu.lst in a text editor and add the following:
   # This entry is for a non-linux OS
   # on /dev/hda1
   title           Windows NT/2000/XP
   root            (hd0,0)
   savedefault
   makeactive
   chainloader     +1
- reboot again and you should have a new menu entry in the grub boot 
menu for your M$ windows

I hope this helps

Regards, Thomas



Shot (Piotr Szotkowski) wrote:
> Hello.
> 
> I have to reinstall the Windows partition on my laptop, but this
> will overwrite the Master Boot Record. Thinking it's better to be
> safe than sorry I tested the scenario on my spare machine: Windows
> goes to /dev/hda1, Ubuntu Hoary Preview to /dev/hda{2,6,7,8,...}
> (the multipartiton setup), all partitions ReiserFS, all on EVM.
> 
> After some googling I reinstalled Windows on /dev/hda1, booted from
> the Hoary Preview with `rescue root=/dev/hda2` and got kernel panic:
> 
> VFS: Mounted root (ext2 filesystem).
> VFS: Cannot open root device "hda2" or unknown-block(0,0)
> Please append a correct "root=" boot option
> Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
> 
> which is not really surprising as the kernel looks for a standalone
> root on ext2, but there's only an EVM-ed root on ReiserFS.
> 
> Thus, I have a couple of questions:
> 
> My testing machine's case: As far as I understand, I need a CD with
> a rescue kernel with compiled in (not just as a module) EVM support
> and ReiserFS support. Do you know about such a rescue CD?
> 
> My laptop's case: It currently runs Debian sid (but will run Hoary in
> near future, after I sort out this Windows reinstall), and has root on
> a standalone ext3 partition (other partitions are on LVM). Do you know
> about a rescue CD with support for an ext3 root? Do I get it right
> thinking this kernel doesn't have to have LVM support (with the root
> partition not being on LVM)?
> 
> In either case: what parameters should I pass at the
> boot prompt for the rescue kernel to do its magic?
> 
> Cheers,
> -- Shot
>