Hard drive shredding on Linux

When we delete a file from a filesystem, the data is not physically removed: the operating system simply marks the area previously occupied by the file, as free and makes it available to store new information. The only way to make sure data is actually removed from a device is to override it with other data. We may want to perform such operation for privacy reasons (maybe we plan to sell the device and we want to be sure the new owner cannot access our data), or maybe to prepare a device for encryption. In this tutorial we will see some tools we can use to completely wipe data on a device