How to zero out a disk

Question

What's the easiest way to write over a hard disk (such that you could give it to a friend, etc.) on elementary OS?

Answer 1

1. Run sudo fdisk -l to determine which /dev/sdX drive you will rewrite. (The drives are listed in an order: sda for your main drive, sdb, sdc, etc. for your remaining drives.) Use that path in place of sdX in the next command:
2. Run sudo dd if=/dev/zero of=/dev/sdX status=progress to write zeros to your disk. (status=progress is a recent addition to see the process's status—it might not work on your system.)

If you'd prefer to use a GUI, gdiskdump is relatively straightforward, but I think the above is easier than installing software for a single operation. To install, run sudo apt install gdiskdump.