Normally when you install a new version of macOS, you just install it over the previous version. It’s quick, easy and means we can be back up and running in no time, with all your apps and data ready to use.
Sometimes, however, it’s best to do a clean install. That may be because your Mac has accumulated so many junk files that it’s performance is badly affected. Or it could be because you’re passing your Mac onto someone else and want to make sure all your data is removed. Or maybe you just want that fresh out of the box Mac experience again.
Whatever your reasons, notice: some High Sierra features require an iCloud storage plan; APFS requires all-flash storage drive; and some features may not be available for all countries or languages. If you're OK with it, here is how to clean install new macOS.
Before you do anything, check that your Mac is able to run Apple's new operating system.
To complete the clean install procedure described below, you'll need:
Once you have everything that's needed, let's begin. Don’t worry, this step-by-step guide will walk you through all you need to do.
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Delete everything you don't need - large and old files and archives, useless apps, cache data and other junk, duplicate files - all these files silently eat up the disk space, duplicate images are especially hard to find out.
You can always use CleanMyMac to cleanup system junk, large and old files, and remove unwanted apps. You could do it manually, but CleanMyMac only all it takes is a few clicks.
Then you can use Gemini to easily find duplicate files and folders on your hard drive, so you can delete them and save precious storage space.
The process of performing a clean install involves wiping your Mac’s main drive clean so it’s essential that you back it up immediately before you start.
To backup everything you need in a secure location you can use Get Backup Pro. It’s a good idea to create a bootable clone, so if anything goes wrong you can go back to where you started easily. Also, a cloned drive makes copying files back to your newly-updated system very easy.
Make sure to create the backup on an external drive or a cloud-based storage like iCloud, Dropbox, or Google Drive. If you save backup files on your startup disk drive, you'll lose these data.
As well as backing up your Mac, you should also take screenshots of settings in any apps you’ve customised so that you can set them up again quickly later. And make sure you have a record of licence codes for apps and passwords for websites. The idea is to plan ahead to make it as easy as possible to get started again after the install.
Download macOS High Sierra from the App Store. Here is a link.
When it’s finished, the installer will launch. As soon as it does, select File and Quit (or keyboard shortcut Command-Q) so it doesn’t install. The installer will remain in your Applications folder.
It’s a good idea to use a USB stick to put the bootable installer onto. It will need to be at least 8GB in size.
Launch Terminal either by searching for it in Spotlight or navigating to the Utilities folder in Applications.
Type, or paste, the following command into Terminal, where [YOUR DRIVE NAME] is the name you gave the installer drive when you formatted it:
sudo /Applications/Install\ macOS\ HighSierra.app/Contents/Resources/createinstallmedia --volume /Volumes/[YOUR DRIVE NAME] --applicationpath /Applications/Install\ macOS\ High\ Sierra.app
Make sure you backup your Mac to keep your important files, before taking next step, that erase your Mac’s Startup drive.
When the macOS Utilities screen appears, follow steps:
When your Mac has restarted, you’ll need to follow the process of setting it up as if it was a brand new Mac. So, you’ll need to connect to your wifi router and type in the password. Then you’ll need to type in the details for your iCloud account. Then you’ll have to set up a new admin user account.
Once you’ve done that, you can start installing apps. In order to re-install Setapp apps, go to setapp.com to get Setapp installer or download Setapp here. You’ll need your username and password.
It’s a good idea to only download those apps you need to use straight away. Other apps can be downloaded as and when you need them. That way you avoid cluttering up your brand new macOS.
If you use a cloud service like Dropbox, now is the time to re-connect. And you can copy any documents, photos or other files you need from the backup you made at the start.