In this article, we explain how to perform a clean install of macOS. Without a doubt, this is a very useful option if your Mac has gotten slow or behaving strangely, crashes some apps, or slows down tasks.
This is also something that we generally resort to, believing that the computer may have a virus (although there is a lot of debate as to whether there are viruses and malware on the Mac that can cause it to malfunction. operating system).
We will start by showing step by step how to do this for the latest version of macOS Catalina (at the time of writing the article), before showing how to install a clean copy of a previous version such as High Sierra, Sierra, El Capitan, Mojave, Yosemite or an earlier version of OS X.
You can find here a full article on how to install macOS High Sierra on your Mac.
In the following tutorial, we explain how to install macOS on your Mac by updating the operating system, but if you want to learn how to reinstall it from scratch, or download older versions of macOS X, you can also refer to this article.
What tools do i need
Before you begin, you should know that there are two ways to perform a clean install of macOS. The traditional way was to create a bootable copy of macOS installer on a Flash drive, then format your drive before installing the bootable copy on your Mac.
There is also an even easier method that allows you to use macOS Recovery to reinstall the Mac operating system from the web. This is something that we will see throughout the article as well.
A word of warning, if you want to do a clean install of macOS Catalina and you’re already running Catalina, the process is different from previous versions of macOS. You will now find two volumes to delete: Macintosh HD-Data and Macintosh HD. We will tell you what to do about it.
How to do a clean install of macOS using a bootable USB drive
Before you begin, you will need the following:
- A removable USB drive of at least 15 GB or more to contain the installation file for the chosen version of macOS. We are going to remove it from the system, so we recommend that you make sure you don’t have any valuable data.
- Administrator privileges for the Mac
- Make a backup so that if something goes wrong you can revert to a previous version of the system. We encourage you to consult in this report, how to backup a Mac.
When it comes to backups, you probably don’t want to recover a Time Machine backup if you don’t want to copy all the settings and preferences associated with your old system.
You can also sync all your documents and desktop with iCloud instead of running a full backup, but make sure everything you need is in the cloud and keep in mind that you might lose the settings. system and application installation.
You’re ready? We have started
Step 1: Format the external drive
We will re-download the installation file for the chosen version of macOS and store it on a USB stick or external drive. The USB drive you use must be formatted as a macOS Extended volume with a GUID partition table.
Here we explain how to properly format your USB drive:
- Plug in the USB stick
- Go to Applications> Utilities’
- Open System Disk Utility
- Select the drive and click Erase. (The disk name must be “Unnamed” if the following terminal commands work, so change the name if necessary.)
- Select macOS Extended (Journaled) as the format type.
- Choose the GUID Partition Map from the scheme options. If you don’t see these options, you’d be in the wrong place. You must select the external drive, not the container below.
- Click delete-
- Disk Utility will create the partition and configure the drive (this may take a long time).
- Click done and you will have it.
Step 2a: Obtain the macOS installer file
If you’re reinstalling the latest version of macOS or installing a new version of macOS, the next step is relatively straightforward, although the process for getting the installer is different.
If you are running Mojave and want to do a clean install of macOS Catalina, you can download the installation package through “System Preferences”, it will be the same if you are running Catalina and want to do a clean install of Big Sur (once started ):
- Open system preferences.
- Choose “Software Update”.
- Download the Catalina installation files or the Big Sur files.
If you want to install Catalina and you’re already running the operating system, or if you’re not running Mojave, the best way to access Catalina installer is through the Mac App Store. Here’s a direct link, but you can also open the Mac App Store and search for Catalina.
Once you’ve located Catalina in the Mac App Store, follow these instructions:
- Tap “Download or Get” (depending on which version of the Mac App Store you are using).
- You may receive a warning message at this point, telling you that this version of macOS ‘is already installed on this computer. Do you want to continue? ‘Click on Continue.
- Enter your Apple ID and password.
- The Catalina installation files will begin to download.
The installation file will be several GB, Mojave was 5.7 GB for example, so the download may take a while.
- Once the macOS installer download is complete, the installer will start automatically, but we don’t want to use it yet, so don’t click start install yet.
- Press Command + Q to exit the installer
- Look for the installer file (it will be located in your Applications folder, or you can find it using Spotlight (command space and start typing Catalina or Big Sur, whichever applies).
If you just want to install Catalina, you can skip the next step, where we’ll show you how to extract the installer file from an older version of macOS or macOS X.
Step 2b: Obtain the installer file for an earlier version of macOS
For older versions of macOS and Mac OS X it is a bit more difficult to get the installer file – Apple does not offer downloads of outdated versions of the operating system through the usual store, and by searching for the name , you will not find what you are looking for.
Depending on the version of macOS you are using, installers for some versions of macOS can be found in the “Purchased” section of the App Store.
Try signing into the Mac App Store with the Apple ID you used and clicking “Purchased” from the menu bar at the top. Scan the list of apps you bought or downloaded for free and find the name of the version you chose. Click on download.
There are several reasons why this may not work for you:
- If you’ve already installed Mojave or Catalina on your Mac, you won’t be able to easily find older versions of macOS on the Mac App Store.
- You won’t find the version of macOS your Mac came with in the “Purchased” section of the App Store.
- You also won’t find macOS versions in the purchased section if you have never installed that version.
Fortunately, it’s still possible to get certain versions of macOS if you’re using a version newer than Sierra.
As in the previous step, once you have downloaded the installer, don’t run it, just close the installer if it opens.
Step 3: Create a bootable USB disk
Next, we need to create a bootable USB drive so that we can install a fresh copy of macOS on your Mac from USB. We’re going to create the startup drive with Terminal, which you can open by pressing “Command + spacebar” and typing “Terminal”.
Connect the removable drive to your Mac and make sure it has the same name you gave it when you created it.
Create bootable USB disk with Terminal
Open the ‘Terminal’ application on your Mac using the ‘Command + space bar’ key combination and type the word Terminal.
Now copy and paste the following text into Terminal (command line):
sudo / Applications / Install macOS Mojave.app/Contents/Resources/createinstallmedia –volume / Volumes / Untitled – / Applications / Install macOS Mojave.app
Enter your password (you will not see it appear). When the boot drive is ready, you will see the word Done. This may take some time. Be patient.
How to install from a DVD drive
Finally, we’ll show you how to install a copy of macOS from a drive or disk drive.
With the startup drive connected, start or restart your Mac while holding down the Option key (also known as Alt). This will take you to the “Administrator” home screen. Choose to install the macOS version from the external drive.
Select “Disk Utility” and the disk where it will be installed. It will be deleted. Go back to the main menu and choose Install macOS.
After installation is complete, you can restore apps and other settings from the backup you created, or download them manually.
Remember not to recover a Time Machine backup if it is a different version of the operating system, so as not to copy all associated settings and preferences.
Step 4: Clean up your Mac and install macOS
We are now ready to install the copy of macOS from the install drive on our Mac. If you want to do a clean install (and completely erase your Mac), it’s time to reformat your Mac’s startup drive.
Here’s how to do a clean install of macOS if you’re not already running Catalina:
- Plug in your boot drive.
- Start or restart your Mac while holding down the “Option” (Alt) key. This will take you to the “Startup Manager”.
- Choose to install your chosen version of macOS from the external drive.
- Select “Disk Utility”.
- Select your Mac’s startup disk, probably the one called Macintosh HD or Home.
- Click on ‘Remove’.
- Wait for your startup disk to format
- Go back to the main “Utilities” menu and choose “Install macOS”.
- Choose your startup drive as the location to install macOS
After installation is complete, you can restore apps and settings from your backup or manually download them again.