All too often I’ve seen people buy a used Mac only to find that the seller did not properly erase the Mac first. Sellers sometimes just delete their documents, leaving poorly configured and obsolete apps lying around. Or worse yet a malicious security threat or connections to their old account. Here is how to properly erase a Macintosh, ensuring that:
- If you are selling or recycling your Mac, none of your personal information remains
- If you are buying a used Mac, none of the previous owner’s configuration will mess things up
Take note of what system version you are running, as some of these instructions will vary depending on the version. You can find that in the Apple menu > About This Mac.
Back up any data
These steps will completely and irrecoverably erase everything on your Mac. If you have anything on this Mac that you want to keep you’ll want to back it up. Photos, contacts, documents, application installers, etc. Many of these things are saved to iCloud but not necessarily. When we are done the only thing left will be a squeaky clean computer as good as from the factory.
Update your software (optional)
If the computer is going to be reused or sold, you probably want to upgrade the software to the latest supported OS if it isn’t already. It’s better to do an upgrade and then erase rather than an erase and then upgrade. If you’re planning to simply recycle the computer it doesn’t matter so you can skip this.
You can view my reference chart to see what version of macOS you can run, and where to get each version.
Log out of your accounts
This isn’t strictly necessary but it will remove one of your five allowed iTunes authorizations and will remove the computer from your iCloud account. In particular, you’ll want to:
- Deauthorize iTunes. Instructions are the same for the Music app in macOS Catalina. You only need to do it for Music or Apple TV, not both.
- Log out of iCloud (in the Apple menu > System Preferences > iCloud), if prompted you can delete the local data, since you have all of this in iCloud already.
- Log out of iMessage (open iMessage, click the iMessage menu, click the Accounts tab, click the iMessage account on the left column, and then click the button to sign out)
- Log out of FaceTime (similar to logging out of iMessage).
- Deactivate any third party software that has a limited number of authorizations. Most consumer-grade software doesn’t do this, but some expensive professional software does. Instructions for this will vary depending on the specific software.
Start up in macOS Recovery Mode
Be sure to remove all devices from your computer except for necessary items like the mouse and keyboard. You don’t want to accidentally erase an external hard drive.
For macOS 10.7 or higher
- Turn your Mac off
- Press the power button to turn the Mac back on and immediately press and hold the Command + R keys on your keyboard
- When you see the Apple logo or globe you can release the keys
- Follow any prompts such as entering your WiFi password or choosing your language
Shortcut: If you are running macOS 10.13 High Sierra or later and you want to install the latest OS your computer supports rather than the currently installed OS, use Command + Option + R instead. You can release the keys when you see the globe, then choose your WiFi network when prompted.
For Mac OS X 10.6 and lower you’ll need to boot using a Mac OS X disc. If you don’t have your disc you may need to upgrade the system software to a newer version first and then try again. Or you’ll need to enter Target Disk Mode and connect it to another Mac to erase with Disk Utility.
- With the computer powered on, insert your Mac OS X install disc or the recovery disc that came with your Mac
- Turn off your Mac
- Press the power button to turn the Mac back on and immediately press and hold the Option key on your keyboard
- Release the Option key when you see the boot selector
- Use your arrow keys on your keyboard or your mouse to select the install disc (it could take up to a minute to appear)
- click the arrow below the install disc or press Return on your keyboard to activate it
Erase your hard drive
- Once in Recovery Mode, click the Disk Utility from the menu and then click “Continue”
- If running macOS 10.5 Catalina you will see two similarly named drives on the left column, one with “Data” on the end. Click the Data drive to highlight it, then click the Minus Volume button above to remove the volume. Choose “Delete” (not Delete Volume Group). If you aren’t running Catalina or if you only see one internal drive skip this step.
- Click to highlight your hard drive name on the left column, Macintosh HD by default. If you are running macOS 10.12 or lower it will be indented slightly behind the model name of the hard drive.
- Click the Erase button. Depending on your OS version this will either be on the top button bar or on a tab to the right.
- If you want to destroy sensitive data, click the “Security Options” button and choose the level you want to run. Each pass takes about two hours depending on the speed of your drive. A single pass is good enough for most people. But consider more if you have any highly sensitive data. If you have an SSD or Fusion Drive you may not have this button because a standard erase is far more destructive.
- If the Format is listed as APFS, leave it as is. Otherwise make sure it says “MacOS Extended (Journaled)”.
- Click Erase and wait for it to complete. Erasing an SSD or an insecure erase takes just a few seconds. A secure hard drive erase can take hours. If it fails pretty much immediately just try again. Sometimes it takes a couple of tries. If it runs for a long time and then fails, you may have a bad hard drive.
- Click OK after it has finished.
- Close Disk Utility with the red dot button.
- Press Command-Q to shut down if you are just disposing of the computer, otherwise continue on to install the OS.
Install the OS (Optional)
If you are only recycling the computer and don’t need to prepare it for another user you can skip this step and shut down your computer by pressing Command-Q.
- Make sure you are connected to your WiFi network by clicking the WiFi icon in the upper right corner of your screen.
- Click the button to reinstall the OS and follow the prompts.
- After the OS is installed you can either go through the account creation process or, if you are selling the computer to someone else, press Command-Q to quit and shut down. The next time the Mac is turned on the new user will be greeted with the same welcome screen.
- Fast internet connection: this will download the OS from the internet. It usually takes 30 to 60 minutes on a cable or fiber connection, or it could take 6 to 12 hours on a DSL connection. The download is about 6 to 8 GB.
- For macOS 10.11 or earlier, the currently installed OS must already be in your Mac App Store account. Check this in the Apple menu > App Store > Purchased. If the currently installed OS is not on your purchase list you must upgrade to at least macOS 10.12 and then do the full erase, or solicit the account of someone who does have the currently installed version in their account.
- Compatible network connection: Most home and small business routers since about 2005 should have the appropriate configuration by default. If you are unsure click the WiFi icon in the top right corner of your screen while holding the “Option” key. In light grey lettering you will see your current security type.
You must be on either:
- wired ethernet connection,
- WiFi connection without a password, or
- WiFi connection with WPA-Personal or WPA2-Personal encryption.
You cannot install via:
- captive WiFi connection (one where you get a popup on connecting such as at a coffee shop or library),
- WiFi with WEP encryption
- WiFi with WPA-Enterprise encryption
- WiFi with certificate-based encryption, or
- a connection that requires a proxy to be configured.