This is something many people and especially businesses worry about, or at least they should. Before throwing away a hard drive, returning a hard drive, or especially Warrantying/RMAing it, you should wipe the drive.
Linux provides the "shred" and "dd" utlities which work quite well. It seems even a single pass is good enough but by default shred will do 3 passes.
Here\'s an example of using shred in Linux (I use a custom made distribution from a USB key):
/shred -v /dev/sdd
./shred: /dev/sdd: pass 1/3 (random)...
./shred: /dev/sdd: pass 1/3 (random)...585MiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...1.0GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...1.4GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...1.8GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...2.3GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...2.7GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...3.1GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...3.6GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...4.0GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...4.5GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...4.9GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...5.4GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...5.8GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...6.3GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...6.7GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...7.2GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...7.6GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...8.0GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...8.5GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...8.9GiB/932GiB 0%
./shred: /dev/sdd: pass 1/3 (random)...9.4GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...9.8GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...10GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...11GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...12GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...13GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...14GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...15GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...16GiB/932GiB 1%
./shred: /dev/sdd: pass 1/3 (random)...17GiB/932GiB 1%
You can also use dd and some suggest it works just as well even once:
dd if=/dev/zero of=/dev/sdyourdrivedevice bs=16M
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