There are many ways for backing up data stored into your hard drive under Linux/Ubuntu. You may use software or 3rd party to protect your data from being lost or get corrupted.
To create an ISO back up image of your drive just follow this simple steps:
Open the terminal (Ctrl+Alt+T) and run this command to create an ISO copy of your hard drive:
sudo dd if=/dev/sda of=file.iso
Your hard disk will be saved into an iso file having the name “file.iso” in the current folder. If your hard drive is not /dev/sda, then correct it with your own. Here is another command having the same effect:
sudo cat /dev/sda > ~/file.iso
Note: To interrupt the iso file creation, you can simply press Ctrl+C.