How to Clean Install macOS Big Sur

You may want to clean install your macOS because it’s running slow or otherwise not performing in the way you would want it to. Another reason that many people do this is if they suspect their Mac is infected with a virus. In this guide, we’ll be showing you how to clean install with the latest version of macOS, Big Sur. 

Before we get started, you need to note that there are actually two different ways of going about this process. The first is the traditional way, using a bootable copy of the macOS installer on a device such as a USB or another flash drive, which would entail formatting your Mac before installing from the drive. There is however an easier option, which will allow you to complete the entire operation over the internet via macOS Recovery.

How to Clean Install macOS Big Sur with a USB

You will need:

1.  A bootable USB stick or device (15GB or larger)

2.  Admin privileges for the Mac

3.  To create a backup in case anything goes wrong during the process. You can either use Time Machine, if not worried about copying settings and preferences from the old system, or you can sync all of your documents to iCloud before beginning.

Step 1 – Format the External Drive

To format your USB/external drive simply do the following steps.

  • Insert the USB/external drive into your Mac
  • Go to Applications, then to Utilities
  • Open the Disk Utility
  • Click on the drive, then click Erase. Note: you will need to make sure the drive is name ‘Untitled’
  • Select macOS Extended (Journaled) as the format type
  • You should now see scheme options. Select GUID Partition Map
  • Click Erase
  • This will then set up the USB/external drive ready to be used for the rest of the process. It could take a while, so you may need to be patient
  • Click Done

Step 2 – Get The macOS Install File

This part is super easy. Follow this link to get Big Sur (free) on the Apple store.

Once you have clicked to download, you will get a warning message telling you that you already have the version of macOS installed. Simply click Continue.

After entering your Apple ID and password as prompted, the download will begin. Again, this could take a little while, as the download for Big Sur is 12.6GB, so a little patience is required. When the download finishes, you will be prompted to begin the install straight away. Do not do this! Instead, hit Command + Q to quit the installer and locate it in the application folder (or use Searchlight to locate).

Step 3 – Create a Bootable USB Disc

  • First, hit Command + Space Bar and look for Terminal.
  • If it’s not already connected, connect the USB now and make sure once again that the drive is called ‘Untitled’
  • Open Terminal then copy and paste the following:

 sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia –volume /Volumes/MyVolume (MyVolume being the name of your USB/external drive, which should be called Untitled)

  • Press Return, then enter your password, then press Return again
  • Terminal will now run through its process of erasing the drive and copying the installer file to it. Again, this is going to take a while.

Step 4 – Wipe your Mac

At this point in the process, you’re going to want to make sure that everything is backed up that you wish to keep.

 When ready, do the following: 

  • Connect the USB once more
  • Turn on, or reboot your Mac while holding down the option (alt) key. This should take you to the Startup Manager
  • Choose to install the macOS from the drive and click ‘Disk Utility
  • Click your Mac’s startup disk (likely Macintosh HD or Home)
  • Click Erase. The startup disk will now format
  • Go back to Utilities, but this time select Install macOS
  • Choose the startup drive as the location to install
  • Once complete, you can then retrieve your files from backup, and/or redownload anything you want to have.

Step 5 – Install Big Sur

 You can now use your bootable installer to perform a clean install on your Mac

 1.  Plug in your bootable installer and turn on your Mac, once again holding the options (alt) key until you see the bootable volume

2.  Click Continue, then install MacOS, then continue

3.  Follow the onscreen instructions and you will be done!

Let us know if you have any questions in the comments!

Related article: macOS Big Sur Slow or Laggy – Here Is How to Speed it up

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