With GRUB bootloader

• If you have a GRUB password configured, type 'p' and enter the password.
• Select your linux kernel, and type 'e' for edit.
• Select the line that starts with 'kernel' and type 'e' to edit the line.
• Go to the end of the line and type 'single' and press 'Enter'.
• Type 'b' to boot into single user mode.
• Use 'passwd' command to change root password.
• Type 'exit'.
• Login with new password.

With Bootable CD

• Boot with your bootable CD.
• Type 'linux rescue' after 'boot:' prompt and press 'Enter'.
• In 'CD Found' window, choose 'skip'.
• In 'Choose Language' window, choose 'English'.
• In 'Keyboard Type' window, choose 'us'.
• In 'Rescue' window, choose 'continue'.
• In second 'Rescue' window, choose 'OK'.
• Use 'chroot /mnt/sysimage' command to change root file system.
• Use 'passwd' command to change root password.
• Use 'exit' command to exit from chroot mode.
• Use 'exit' command again for reboot.
• Remove bootable CD.
• Login with new password