Using dd to blank a drive

A lot of well-meaning people dumped their leftovers on me when I mentioned I was using a machine with a floppy drive, and had use for some spares. The things are like coat hangers now though — I have about twice as many as I wanted, and 10 times more than I need.

I also don’t really want to know what was on the floppy before it became mine, so I scrounged around a bit and found this as a command to overwrite the disk, until I find time to actually use it. As an alternative to the shred command. …

dd if=/dev/urandom of=/dev/fd0

The drive assignment is for Debian there, so it might be different for your distro. And changing the destination assignment will work for a USB drive or something else too. My primary school maths teacher taught us that we should always check our work, so …

dd if=/dev/fd0 count=1 | hexdump -C

That gives you a quick look at the earliest part of the floppy, so you can check and make sure what’s there is more or less unreadable. I don’t know if it’s a terrifically secure method or proof against forensics efforts, but neither of those is really a concern for me. :)

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10 thoughts on “Using dd to blank a drive

  1. Mehall

    I hate to say wrong to you, but dd is actually by far one of the best ways to blank a drive. However much faith you put into DBaN, dd does the job so well, that if it completes a run (even if using /dev/null instead of /dev/urandom like you suggested) that many professional forensics recovery companies will refuse to try, as it is a waste of their time and your money.

    dd is a fantastic tool. Whenever I get a machine that I may have to return to the original owner, or to someone else significantly clueless about computers, I make a disk image to my external HDD, then wipe the disk (all using a live CD) using dd for both operations. a quick run of gParted later, and the disk is ready to have a new OS installed, but if I need to return it to the condition I got it in, dd will do exactly that given the disk image instead of /dev/null

    Reply
  2. anonymous coward

    and then there’s always the ‘badblocks’ command which comes with the ‘e2fsprogs’ package which allows you to check for … well, bad blocks on a device. I used to use the -w option almost all the time…

    Reply
    1. anonymous coward

      d’oh! ;) here’s what the man page says about the ‘-w’ option:

      With this option, badblocks scans for bad blocks by writing some patterns (0xaa, 0×55, 0xff, 0×00) on every block of the device, reading every block and comparing the contents.

      Reply
      1. Luca

        That sounds like a better way, as it’ll also check the integrity of the device. Depending on how un-random it is, it should also not take much longer.

        Reply
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  4. anonymous coward

    Several passes with /dev/urandom (while syncing in between passes) is by far one of the best methods you can use to destroy data. Even if you’re worried about forensic recovery.

    Whenever I need to destroy a partition, I use:

    for i in {1..5}; do dd if=/dev/urandom of=/dev/sdXX bs=1M && sync; done

    Reply
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