On certain occasions you may encounter problems resetting your password using the method detailed how-to-reset-ubuntu-root-password.
Follow these steps to reset your password using a live CD such as System Rescue which can be downloaded from their website as a ISO file.
1. Mount the ISO
Once you get booted into the live CD, we must be root to use most of the commands that follow so lets switch to root user.
su - root
2. View your disk/volume configuration.
You may need to determine which device your Linux hard drive is listed as under Linux.
Look for the listing that says Linux it will have the root partition on it.
In this example its /DEV/SDA2 that needs to be used.
3. Create mount point.
4. Mount the drive to the recently created mount
mount /dev/sda2 /mnt/maindrive
5. Change directory, This will change your root directory from the live CD to the one on your hard drive
chroot /mnt/maindrive /bin/bash
6. Now you should have root access and a basic bash shell. You probably know what to do from here.
Your password has now been reset, reboot your server when ready.