Howto: Zero out your storage devices using any Linux Distro

[curriegrad2004]

As root, type in the following command in a terminal window:

dd if=/dev/zero of=/dev/[insert your destination drive here] bs=1M

The DD command was orignally designed to copy hard disks, but since it can copy zeroes from /dev/zero, this makes it a very good command to wipe out used hard drives or USB flash drives before you sell 'em on ebay or give 'em away. A format isn't enough to wipe out all data. It only overwrites the partition table. For true erasure, you should consider DBAN, which includes some secure erasure agrothims in that disk.

[subodh]

Very usefull tip. Thanks for it.
Yes, it is possible to retrive data from disk after formatting.