System Rescue

If your system won't boot, the "Enable/disable rescue mode" option gives you access to the hard drive. 

This rescue environment relies on Rescatux. Once you enable it and restart, you'll first have to locate the main hard disk by entering the command:

lsblk

You'll see a list of disk devices. For instance, /dev/sda1 should correspond to your hard drive's capacity (e.g., 50GB).

Next, simply mount the device to a directory like /mnt with:

sudo mount /dev/sda1 /mnt

Apply any needed changes.

Once you're finished, turn off rescue mode.