http://www.cyberciti.biz/tips/howto-recovering-grub-
boot-loader-password.html
Using a recovery CD, such as RIP Linux or the Knoppix Live CD
like in the How To in the link. This will be showing the RHEL way of doing it.
Step 1. Single user the server.
Step 2. You need to mount a partition where the grub configuration file is stored. D: /boot/grub/grub.conf
Step 3. If you forgot partition name use fdisk -l command to obtained partition list.
# fdisk -l
Step 4. Mount your partition:
# mount /dev/sdb1 /mnt
Step 5. Then modify the /boot/grub/grub.conf file
# cd /mnt/boot/grub
# vi or nano grub.conf
Step 6. Once file opened using text editor, locate password line and remove it:
password --md5 $1$9sdflksdf/sdf44k
Step 7. Save file and reboot the system.
# sync; sync
# cd /
# umount /mnt
# reboot
