One of the many great things about Linux are the free utilities at your disposal.
If you have old an computer, some disks you want to sell on or give away, you need to wipe clean the disks to ensure all your personal data is erased.
A great Unix utility is Wipe. If your running Debian or Ubuntu, its available in the main repository for download.
You know the routine:
aptitude install wipe
Instantly you have a great utility to securely wipe/erase all data on disk.
Its easy to use. From the man page:
wipe -rcf /home/bark/text/
Wipe every file under /home/bark/text/ including /home/bark/text/. Recursive wipe (-r) and don't ask for confirmation (-f). Files without correct permission will be chmod'd (-c).
wipe -kq /dev/sdb1
Wipes all data from the first partition on the second SCSI/SATA disk drive, using the quick option (-q). Before starting it will ask you to confirm.
On a fast multicore machine, an 18GB SCSI disk took 7 mins to wipe with four passes. A 72GB SCSI disk took 26 mins with four passes. For large size disks you probably want to run the Wipe utility overnight.
Unless you enjoy watching paint dry!