Quick Disk Overwrite Script

by Rob

If you're anything like me, you have old hard disks lying around from old computers.

You don't want to throw them out - they work, so they can be used.  Maybe you want to sell them or give them away.  But what about your precious personal data on them?

You don't want a new user of the disk to get your data and use it in an identity theft scenario against you.  The answer is, of course, to overwrite a disk with garbage that has no use to a would-be identity thief.

You can buy software that does that but, as a hacker, of course you want to do it yourself.

Here's what I've done - maybe it could help you too.

Step 1: Reformat the Disk

I reformat my old disks, setting up a full disk EXT4 partition.  There are many ways to do this in Linux.

Reformatting a Windows NTFS/FAT disk to EXT4 loses the old partition table, making it hard to recover files, but probably not impossible.

Step 2: Write to the Disk Until It Is Full

Reformatting is good, but for further data security you need to overwrite the full disk.

I wrote the following simple Bash script to do it.

First, mount the newly formatted disk, e.g. to: /home/myuser/mount/disk

Then run this script:

overwrite.sh:
#!/bin/bash
#
# use whatever meaningless text you like here:
text="thequickbrownfoxjumpsoverthelazydogthequickbrownfoxjumpsoverthelazydogthequickbrownfoxjumpsoverthelazydog"
# try and write 10000 files, adjust this if required
i=1

while [ $i -le 10000 ]
  do
    # generate a unique filename using the date command
    filename="file-`date +%s.%N`"
    # display progress
    echo "$i $filename"
    # write 1,000,000 lines to each file
    j=1
    while [ $j -le 1000000 ]
      do
        #echo $text >> ~/mount/disk/$filename
		echo $text >> /tmp/fart
        ((j++))
      done

  ((i++))
  done

 exit
Depending on the size of your disk, this script may not get to the maximum 10,000 files.

In my case, I was writing to a 40 gigabyte disk, and my text was 1440 characters long, and writing 30 files filled the disk.

After that, the attempt to write more results in the error message write error: No space left on device, so just Ctrl+C out of the script.

Step 3: Just Delete All Those Files, and Sell or Give the Disk to Someone Who Needs It

I hope this is useful.

I like this because it can extend the lifetime of old hardware with some sense of data security.

Code: overwrite.sh

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