How to wipe your Mac, Watch, iPhone or iPad ready for selling

19 November 2015, 09:00

The big, happy secret of Apple ownership is residuals: there’s a strong chance you can put your your Mac, iPad or iPhone on eBay or Craigslist and get a decent quantity of dollars in return – certainly a lot more than you’re likely to get for the same vintage Dell laptop or Samsung cellphone.

However, you MUST make sure there’s no way for the purchaser to access your data.

Wiping a Mac
Here’s how to wipe a Mac, ready for selling. In the steps below we assume OS X El Capitan is installed. For various reasons to do with a more limited Disk Utility app compared to previous releases, El Capitan makes it difficult to securely wipe the Mac’s boot disk. There are ways around this with third-party utilities but they’re complicated and time-consuming.

Some creative thinking is required. First, we must enable FireVault full disk encryption, if it isn’t already activated. Then we can simply reformat the boot disk and reinstall OS X via the OS X Recovery tool. The Mac will subsequently be ready for setup by its new owner.

Although this will not wipe the disk’s contents, as we’d like for 100% peace of mind, the Mac’s data not overwritten by the new OS X installation remains encrypted and therefore unsalvageable. This encryption is strong enough to annoy the FBI, so there’s really nothing to worry about.

  1. Start by enabling FileVault, if it isn’t already enabled. Open System Preferences, click the Security & Privacy icon, select the FileVault tab, and click Turn On FileVault. You may need to first click the padlock icon at the bottom left, and enter your password. Opt to let Apple store the recovery key in iCloud (it makes no difference here, to be honest) then restart and wait until FileVault has finished encrypting the disk. This could take hours and you can monitor progress in System Preferences.
  2. Restart your Mac (Apple menu > Restart) and, before the Apple logo appears, hold down Cmd+R to boot into OS X Recovery.
  3. Select Disk Utility from the list of OS X Recovery apps, and then select your Mac’s boot disk on the left. Then click the Erase button. The default choices for format and partitioning are fine, so go ahead.
  4. Once erasing has finished (it should be very quick), quit Disk Utility. You’ll be returned to the OS X Recovery menu. Select to reinstall OS X.
  5. When OS X has reinstalled, and it reboots to the welcome/hello screen, click click Apple menu > Quit. The Mac is now ready to be setup by its new owner.

If you really wanted to be absolutely sure the Mac had none of your old data left on it – encrypted or otherwise – you could create a new account within the new OS X installation after following the setup steps, then open a Terminal window (it’s in the Utilities folder of the Applications list), and type the following:

  yes > wipefile

This very rapidly writes a stream of dummy data to a file, and the file will eventually grow in size such that it consumes the entire disk – overwriting any of the old data, of course. The command will probably take an hour or two to complete. The Mac will start to report errors that it’s running out of disk space, and might even crash. However, wait until the command within the Terminal window reports an error. At this point, or when the Mac crashes, reboot the Mac and repeat steps 2 – 5 above to wipe the disk and reinstall OS X, ready for the new user.

UPDATE: I came across this old Macworld article, which points out the secure wipe feature of OS X is present as a command-line tool. Apparently it still works on El Capitan. Take a look if you’ve experience of command-line working. I think I still prefer the more simple method, as discussed above.

Wiping an Apple Watch
On your iPhone open the Watch app, and then the Apple Watch heading. Then tap Unpair Apple Watch. The Watch will eventually reboot and be ready for setup with a new owner.

Note that if you intend to sell your iPhone at the same time as the Watch then you must wipe the Watch first, before wiping the iPhone. If you no longer have the iPhone, or have already wiped it, try this: attach the charger to the Watch, then press and hold the side button (not the digital crown!) until the Power Off option appears. Force touch the Power Off slider’s control (there’s no need to actually slide it!), and upon lifting your finger you should find it changes to an Erase All Contents and Settings option. Tap this.

Wiping an iPhone or iPad
Open the Settings app, tap the iCloud heading, tap Find my iPhone/Find my iPad entry, and turn off this feature by deactivating the switch.

Then tap to go back, and tap the General heading, and then the Reset heading at the bottom of the list. Then tap Erase All Contents and Settings. You’ll need to enter your Apple ID and device passphrase when prompted.

Want to wipe your Apple TV? Apple has you covered.

See also

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