If you have recently purchased a new Mac, you might be considering selling or donating your old machine. Before getting rid of old faithful, be sure to wipe the hard drive completely clean, and install a fresh version of macOS on it. Here’s how.
Backup Your Old Machine’s Hard Drive
It’s likely that you have already moved your old Mac’s data to your new machine. However, it’s always a good idea to have a backup around, just in case you find something you missed moving over during the transfer. (And, this ALWAYS happens!)
For those of you who have been using Time Machine to backup your old Mac, you’re good to go. Just be sure not to write over your Time Machine backup when you start backing up your new machine.
Other backup options include such utilities as SuperDuper or Carbon Copy Cloner. These utilities can clone your Mac’s hard drive to an external hard drive. If needed, you can even boot your Mac from the clone on the external drive.
If you used iTunes on your old Mac, remember that Apple’s iTunes only allows a certain number of devices to be authorized with any one iTunes account. Remember to deauthorize your old Mac, so you can easily add your new Mac to the account.
To deauthorize a Mac, simply start iTunes, then look for the “Account” menu option. Click it, and then bring your mouse pointer down to “Authorizations” in the pull-down menu. In the fly-out menu that appears, click “Deauthorize This Computer…” You’ll be asked for your iTunes password. Enter it, and then click “Deauthorize.”
Restart Your Mac and Boot Into Recovery Mode
Make sure your Mac is connected to the Internet, (you’ll need an Internet connection to reinstall macOS, unless you have an install disk or USB drive), then restart it by clicking on the Apple in the upper-left hand corner of your Mac’s Desktop. Click “Restart” in the Apple menu.
As your machine begins to reboot, simultaneously hold down the Command + R keys. Hold these two keys down until the “Recovery Mode” screen loads.
Erase Your Hard Drive
Now, Select “Disk Utility,” and then click on “Continue.” Select your Mac’s Startup Disk in the sidebar on the left, and then click your mouse pointer on the “Erase” tab on the right-hand side of the window.
If you are afraid someone might try to recover your data, click on the “Security Options…” button and select a higher form of security for erasing your data. (Note: This WILL take quite a bit longer than a normal erase.) Click the “Erase…” button and the utility will begin to erase your hard drive.
WARNING: Before formatting, be VERY sure you either have a backup, or are sure that you do not want anything that remains on the hard drive. This will permanently erase your Mac’s hard drive.
When the drive is erased, exit the utility by selecting “Disk Utility,” and then “Quit Disk Utility.” (For more information about erasing your hard drive, visit the Apple Support website.)
When you’re back to the main screen, click on “Reinstall macOS” and then select “Install.” This will download and install a fresh copy of macOS on your machine. Continue the installation until you see the prompt to enter your Apple ID and password. Do NOT enter it! This is the spot where you’ll stop, in order to allow the new owner to enter their login information and complete the setup process for themselves.
By following the above steps, you’ll erase all of your apps and personal information from your old Mac, enabling a fresh start for its new owner. (For more information about reinstalling macOS on your machine, visit the Apple Support website.)
(Updated as of: 04/18/2017)