I have an old hard disk and I want to waste it. So I want to make sure there is no data left on the device:
Overwrite the hard disk /dev/sdd using 1 run:
sudo shred -vn 1 /dev/sdd
A fast alternative:
sudo sh -c 'cryptsetup -d /dev/urandom -c aes-xts-plain create delete <device> && shred -vzn 0 /dev/mapper/delete && sync && sleep 4 && cryptsetup remove delete'