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I have bunch of old hard disks, USB sticks and memory cards I want to sell / give away. However, there's private content that must be cleared before that.

What is a good, preferably free, software for OS X to wipe the contents so that restoring anything is not reasonably possible?

  • A blowtorch should be enough for most applications. – Deer Hunter Mar 7 '14 at 6:40
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The built-in Disk Utility does everything you want.

To wipe a drive:

  1. Open Disk Utility (It's in ~/Applications/Utilities)
  2. Find the drive you want to be wiped in the sidebar, and select the root drive (not the partition):

    Disk Utility Sidebar

  3. Go to the erase tab:

    Erase Tab

  4. (optional) If you're paranoid about your data, there's a button Security Options. Clicking it brings up a dialog with a slider on it. At the highest security level, the erase mode "meets the US Department of Defense's 5220-22 M standard for erasing magnetic media". It overwrites your files seven times.

    Secure Erase Options

  5. Choose a name for your drive and click the erase button.

    Are you sure you want to erase the drive window

  6. Click erase on the resulting dialog. Disk Utility goes through its process (which may be rather long if there's a lot of space on the drive).
  7. Enjoy your brand newly formatted drive!
  • I'd add that contemporary literature on SSDs is contradictory on whether a SSD can be wiped "properly" superuser.com/a/541913/10165 . It should not be a major issue for your purposes however – Journeyman Geek Feb 15 '14 at 3:12
  • @JourneymanGeek Your comment is correct, of course, and I said the same thing in my answer (with regard to flash memory devices like USB sticks and memory cards). But now that the newer MacBooks are coming out with SSDs, it's good to hit that on the head too. I'll update my answer. – Chris Jester-Young Mar 7 '14 at 4:54
13

For paranoid shredding, install GNU coreutils and use its shred program.

Disclaimer: any solid-state drives, USB sticks, and memory cards that use wear levelling can't be guaranteed to be fully shredded. This applies to pretty much any disk-wiping software unless they can get beyond the wear-levelling layer.

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