= Securely Wipe a drive =

Low - Zero-out a drive. Write 0's onto every block on the hard disk.
{{{
sudo dd if=/dev/zero of=/dev/sdb bs=4K
}}}

Med - Scans disk to detect an early failure and overwrites with random data. Takes Hours.
{{{
sudo badblocks -c 10240 -s -w -t random -v /dev/sdb
}}}

Paranoid - Secure but long method to fill the disk with random binary bits. Takes Days.
{{{
sudo dd if=/dev/urandom of=/dev/sdb bs=4K
# Or when /dev/urandom does not work use /dev/random
sudo dd if=/dev/random of=/dev/sdb bs=4K
}}}