Wiping a HardDrive is a common task at the workplace or whenever you’re getting ready to sell a PC. There is a utility to do just such a thing in almost all Linux Bootdisks called shred.
Shred can be used to wipe files, or whole drives. To wipe a drive, the following parameters are good to know
-z After shredding, one more pass will be made to write all zeros to the drive, not necessary, but it hides the fact that the disk has been shredded
-v Display messages about progress, which is handy since shredding a drive takes a fair deal of time
-n x x is the number of passes you wish to make. 3 is a good number, and if you use the -z option it will be 3 shredding passes followed by a 4th pass to zero out all the data
Put it together and pass it a drive to wipe:
shred -zvn 3 /dev/sda
And voila, all your private data goes bye-bye