Mbr

Sixsixsix · 11-03-2002, 01:43 PM

Is there a way to clear the mbr in linux rh 8? I need to clear it so i can do a fresh install of linux and windows. Thanks I really need this help soon too.

acid_kewpie · 11-03-2002, 02:03 PM

just do it with a dos boot disk "fdisk /mbr" about 93 times. i don't really see why you need to clear is necessarily though for a new linux install. always install windows first though.

Sixsixsix · 11-03-2002, 02:32 PM

Anyway to do it in linux I have no floppies and xp doesn't do boot disks anymore.

acid_kewpie · 11-03-2002, 02:39 PM

well not really, as a "clear" MBR in your definition would (well.. i'm assuming) mean a microsoft MBR. A genuinely clear MBR is useless. you should be able to replace the backup that lilo might have kept (normally /boot/boot.0300 or similar afaik. see the lilo manpage for uninstallation information

Sixsixsix · 11-03-2002, 02:48 PM

I forgot to mention I'm running grub boot loader.

acid_kewpie · 11-03-2002, 02:53 PM

well i take it you've just gone away and read the grub manpage?

Sixsixsix · 11-03-2002, 03:09 PM

The man pages don't tell me how to uninstall them. Please Help me.

Half_Elf · 11-04-2002, 05:27 PM

You want to erase you MBR to reinstall windoze, is that right?

Put your Windoze cd in and perform the installation. It will clean the old MBR and replace it with a new one.
If you want to keep Linux (or don't want to reinstall Windoze), I highly suggest you to correctly configurate your actual boot loader (grub?) to be able to boot Win or Nux trought it.

Also, if you have windoze NT (Nt4, 2000, Xp) you can do a "repair" to fix the mbr. Put your cd in, boot, choose repair, get a recovery console, and type : fixmbr (or mbrfix? don't remember, use "help"). This will crush your actual nux boot loader, of course.

mlp68 · 11-04-2002, 11:45 PM

Well, I kinda agree that there are many ways and few reasons to do this, but if you are really really sure you want to do that, first backup the MBR to a floppy (not the harddisk! ! ! )

dd if=/dev/hda of=/mnt/floppy/mbr.dat bs=1 count=512

then

dd if=/dev/zero of=/dev/hda bs=1 count=446

That clears the MBR except for the last 64+2 bytes. That should leave the partition table alone. If you overwrite that, you won't have any partitions left on the disk (that's why you want a backup)

(the backup is dd if=/mnt/floppy/mbr.dat of=/dev/hda )

-- mlp

jglen490 · 11-05-2002, 10:28 AM

If you are doing a clean install, you don't need to "clear" anything out of the MBR. Both Windoze and Linux will set up what is needed, or wanted, in the MBR.

If you clean install Windoze, it will layout default code in the MBR to find its boot sector. If you then come behind that with Linux, it will (when asked) put it's boot loader code on the MBR. Either way, it's O.K., you end up replacing boot code on the MBR.