Securely erase hard drive using dd
Published by Joe Lovick on June 8th, 2015
head -c 32 /dev/urandom | openssl enc -rc4 -nosalt -in /dev/zero -pass stdin | dd of=/dev/sda bs=1M
to wipe hard drive at a reasonable speed from the command prompt.
http://askubuntu.com/questions/359540/securely-erase-hard-drive-using-the-disk-utility