Most Windows users reinstall their operating system in various ways but this is not a common step for Mac users.
Whether you have a big problem and want to start fresh, or are planning to sell your Mac and need to reset, reinstall macOS
Note: I did this process using a MacBook Pro running OS X 10.7 Lion and ending with macOS High Sierra. The process may look a little different on your machine.
Before You Begin: Backup!
Presumably, you have been using this computer for some time and have personal data on it. Reinstalling macOS will erase everything on your system, so you should back it up first. Before backing up, you may want to free up space by getting rid of old files that you never use.
The easiest way to back up is using Apple’s built-in solution, Time Machine. We’ve covered how to use Time Machine to back up your Mac; You will need an external hard drive to take advantage of it.
If you have very few files, you may want to sync your most important files to Google Drive or other cloud storage. Another alternative is to copy your vitals folder to a USB flash drive.
Whatever you choose to do, keep in mind that this process will erase everything on your Mac.
Exit the App
Before proceeding, you should also take the time to exit the application on your computer. Services like Adobe Creative Cloud limit the number of installations you can use, so you should opt out to avoid wasting on systems that don’t exist.
Sign out of iTunes by opening it and selecting Account > Sign Out. You can exit iMessage by opening Messages and selecting Messages > Preferences. Select your account in the left sidebar and select Sign Out.
Finally, sign out of iCloud by visiting System Preferences > iCloud and selecting Sign Out.
1: Boot into Recovery Mode
In the past, you could reinstall the OS via the DVD that shipped with your Mac. But since new Macs don’t have an optical drive, we’ll be using the built-in Recovery Mode to do it. This will work on any Mac running OS X 10.7 Lion or later.
Shut down your Mac. Hold down Cmd + R keys and turn it back on. Continue holding these buttons until you see the Apple logo. After a few moments, you’ll see a macOS Utilities (or OS X Utilities) page with several options.
If this doesn’t work (maybe your computer freezes on the Apple logo like mine), you’ll need to start Internet Recovery mode. It runs a recovery environment from the internet instead of a partition on your hard drive. Hold down Cmd + Option + R at startup to access it. You will see a globe instead of the Apple logo.
Connect to a Wi-Fi network if you haven’t already. Then wait a moment while your computer downloads the recovery environment. You have to select your language to enter the proper Recovery mode.
When using Internet Recovery mode, the system may reinstall a different version of macOS than the one you are using. Mine installed Mavericks, even though I had Lion running to begin with.
2: Erase Disk
To properly reinstall the OS, you must first wipe the disk. To do this, select Disk Utility from the menu.
Next, select your internal hard drive (usually labeled Macintosh HD) from the left sidebar. Switch to the Delete tab on the right side. Make sure Format is set to Mac OS Extended (Journaled). The Macintosh HD’s default name is fine, unless you prefer something else.
Click Delete and confirm the operation. Once that’s done, you’re ready to install the new MacOS. Press Cmd + Q to exit Disk Utility.
3: Reinstall macOS
Back in the macOS Utilities menu, select Reinstall macOS (or Reinstall OS X). Click Continue to continue; Apple will verify your computer’s eligibility to install the OS. You may see a request to enter your Apple ID as part of this process.
Accept the license agreement, then click on your hard drive to select it for installation. Click Install to start the process. Depending on your computer’s specifications (and internet connection speed if using internet recovery), this will take some time.
Once you see the Welcome screen, your Mac returns to factory defaults. If you are selling or giving away your Mac, you can press Cmd + Q at this point. You’ll get a prompt to shut down your Mac; Subsequent owners can continue with the setup later.
If you keep your Mac, we’ll walk you through the setup.
4: Setting up macOS New
Select your region on the Welcome screen and click Continue.
Next, confirm your keyboard layout and hit Continue again. You should then be connected to a wireless network (you can skip this for now if needed).
Continuing on, you will see the Transfer Information to This Mac screen. Here you can choose From Mac, Time Machine backup, or startup disk to import the data you created earlier. Select Don’t transfer any information now to skip this; You can go through the process later.
Your Mac will then ask you to sign in with your Apple ID. Enter your credentials here to sign in, or select Create a new Apple ID if you don’t have an account yet. If you want to use a local account, select Don’t sign in. However, it will prevent you from using the App Store, FaceTime, and the like.
Accept the terms and conditions, then create your computer account if you’re not signed in with an Apple ID. From here, give your computer some time to set up, and you’ll be greeted with your desktop.
5: Update macOS (If Available)
You should check for macOS updates at this point. Open the Apple Menu at the top left and click Software Update to open the App Store.
You’ll see any available updates for the current version of macOS on the Updates tab, but you should also check on the Featured tab (or search for macOS) for the latest version of macOS available. Click Get and walk through the steps to start the update.
Depending on the age of your Mac, you might not be able to update to the latest version. I was able to upgrade to macOS 10.13 High Sierra on a machine previously running Lion.
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