If you want to delete all data contained in your hard drive so that you render it empty in case you want to sell it or for any other reasons, you need to follow these steps:
1. Turn on your computer and boot from Debian Live CD or any of its variants (Debian, Ubuntu, Xubuntu, Edubuntu, Ubuntulite, Fluxbuntu, etc.).
2. In the terminal, run the command given below to disable the swap partition:
Note: If you don’t execute this command, some data might remain on your hard drive.
3. Now you have to run the command listed below to zero out your hard drive:
sudo dd if=/dev/zero of=/dev/sda
The formatting process might take a long time to finish, this depends on the size of your hard disk. To view remaining time, you have to run this command:
sudo killall -USR1 dd
Upon running the command listed above, you will be shown the disk space “cleaned” in GB.