I’m going to donate my old desktop computer. To be safe, I wanted to wipe the hard drive. I figured an Ubuntu Live CD would do the trick, and I almost got it to work by guessing the command, but I had mistakenly specified the partition (sda5) instead of the drive itself (sda). It worked like a charm. Here’s how I did it:
sudo swapoff -a
sudo shred -vfz /dev/sda