Wiping clean an entire disk in Linux

Note to self (DANGER: running as root will cause the disk to be wiped as soon as this command is executed, so be very sure the target disk is typed in correctly):

To wipe a disk clean, fill with random numbers.

dd if=/dev/urandom of=/dev/sda bs=8b

Or run it seven times to be safe.

for n in `seq 7`; do dd if=/dev/urandom of=/dev/sda bs=8b conv=notrunc; done

(From this article.)