Linux Desktop Hacks

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Chapter 1, Booting Linux

#2 Kill and Resurrect the Master Boot Record

HACK

Save the MBR

First, before you attempt anything potentially destructive, back up the current

MBR. Boot into Knoppix, and type the following command into a terminal:

knoppix@ttyp0[knoppix]$ sudo dd if=/dev/hda of=/home/knoppix/mbr_backup

bs=512 count=1

Change /dev/hda to match the drive you wish to back up. In your home direc-

tory, you should now see a 512-byte file called mbr_backup. Dd is used to cre-

ate images of entire hard drives, and in this case, a similar command is used;

however, it contains two new options:

bs and count. The bs (byte size) option

tells dd to input and output 512 bytes at a time, and the count option tells dd

to do this only once. The result of the command is that the first 512 bytes of

the drive (the MBR) are copied into the file. If for some reason you only want

to back up the boot sector (although it’s wise to always back up the partition

table as well), replace 512 with 446. Now that you have backed up the MBR,

copy it to a safe location, such as another computer or a CD-ROM.

The full 512-byte copy of the MBR contains the partition

table, so it gets out of sync whenever you change partitions

on your drive. If you back up the full MBR, be sure to update

your backup whenever you make partition changes.

Kill the MBR

Now you should know how to totally destroy the MBR. To do this, simply

use the same ...