# Use this command to backup your MBR:

dd if=/dev/hda of=/home/hda.boot.mbr bs=512 count=1

#To restore the MBR (from a Live CD), use this command:

dd if=/mnt/hda1/home/hda.boot.mbr of=/dev/hda bs=512 count=1

http://jaredprins.squarespace.com/ubducted/2009/4/2/backup-your-mbr-on-linux.html

About the dd command:

dd if=<source> of=<target> bs=<byte>("USUALLY" some power of 2, not less than 512 bytes(ie, 512, 1024, 2048, 4096, 8192, 16384[/b], but can be ANY reasonable number.) skip= seek= conv=<conversion>.

Source is the data being read. Target is where the data gets written.

Warning!! If you reverse the source and target, you can wipe out a lot of data. This feature has inspired the nickname "dd" Data Destroyer.
Warning!! Caution should be observed when using dd to duplicate encrypted partitions.

Backup your MBR on Linux

backup

Bash