When system fails to boot up, "Enable/disable rescue mode" allows the user to access the hard disk. 

The Rescue system configured uses Rescatux. After enabling, boot it up, and you will need to find that the original hard disk first by typing command


You should be able to see hard disk devices for example. /dev/sda1 which should match up to your hard disk size ( ex. 50GB )

Then all you need to do is to mount the device to a folder. ex. /mnt by using command

sudo mount /dev/sda1 /mnt

Make any changes required as necessary

Disable rescue mode once you are done.