Even if you dont know the grub password and you can break it.. Yes you have read it right. You can break it. Just simply follow the below instructions..
To break the grub password, follow the below steps
1) Boot from Linux bootable dvd.
2) Type the command linux rescue to switch to rescue mode.
3) Choose Language English
4) Keyboard type US (By Default)
4) Open /boot/grub/grub.conf file and remove the password --md5 line or simple type # in front of this line. Save and exit.
5) Then type exit (It will come out from chroot) and then again type exit (It will reboot the system).
Reboot your system without any bootable cd or dvd and go to the Single User Mode. Now it will not ask you for grub password.
To break the grub password, follow the below steps
1) Boot from Linux bootable dvd.
2) Type the command linux rescue to switch to rescue mode.
3) Choose Language English
4) Keyboard type US (By Default)
5) It will ask "Do You Want To Start The Network Interfaces On This System?" Here select "No" then enter.
6) Then select Continue.
7) Type chroot /mnt/sysimage
6) Then select Continue.
4) Open /boot/grub/grub.conf file and remove the password --md5 line or simple type # in front of this line. Save and exit.
5) Then type exit (It will come out from chroot) and then again type exit (It will reboot the system).
Reboot your system without any bootable cd or dvd and go to the Single User Mode. Now it will not ask you for grub password.