Rescue System

When the system won't boot, the "Enable/disable rescue mode" option lets you access the hard disk. 

The rescue system relies on Rescatux. After you enable it, boot up and first find the original hard disk by running the command:

lsblk

You should see the hard disk devices — for example, /dev/sda1, which should match your disk's size (e.g., 50GB).

Next, mount that device to a folder, like /mnt, with the command:

sudo mount /dev/sda1 /mnt

Make any necessary changes.

Once you're finished, disable rescue mode.