How to Clean Install macOS 10.13 High Sierra

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.

How to prepare your Mac for the clean install

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:

  • macOS High Sierra Installer, available from the Mac App Store.
  • a 16GB or larger USB flash drive 
    Notice: USB drive is needed for a clean install on your Mac’s startup drive. If you plan to clean install macOS on a non-startup drive, you don't need it.
  • go for a system cleanup and backup your data - this will allow you to easily return your Mac to the condition it was in before you installed macOS.
  • and an hour or two to spare.

How to clean install new macOS

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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Start with a system cleanup

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. 

CleanMyMac fast cleanup

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.

Duplicates on your disk drive

Backup your data

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. 

Create backup with Get Backup Pro

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.

Create a bootable installer

Download macOS High Sierra from the App Store. Here is a link.

High Sierra downloading

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.

Find High Sierra installer in Application 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. 

  1. Plug in the USB stick and launch Disk Utilities. 
  2. Click the Erase tab and make sure Mac OS Extended (Journaled) is selected in the format tab. 
  3. Give the USB stick a name then click Erase. 
  4. When it’s finished, click Done and close Disk Utility.

Erase Startup disk

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\ --volume /Volumes/[YOUR DRIVE NAME] --applicationpath /Applications/Install\ macOS\ High\

  • Remember to replace [YOUR DRIVE NAME] with the name of your installer disk.
  • Hit Return.
  • Type in your admin password and wait. 
  • When the process is finished, the word Done will appear in the Terminal window. 
  • You can then quit Terminal.

Create bootable USD in Terminal utility

Clean Install macOS High Sierra

Make sure you backup your Mac to keep your important files, before taking next step, that erase your Mac’s Startup drive.

  • Go to System Preferences
  • Сlick Startup disk and choose the installer you just created. 
  • Restart your Mac and hold down Command-R to boot into recovery mode.Take your bootable USB and connect it to your Mac.

When the macOS Utilities screen appears, follow steps:

  • Select Reinstall a new copy of macOS. 
  • Click Continue, then click Continue again when the next window appears. 
  • Agree to the terms and conditions, then select your Mac’s internal drive. 
  • Click Install. 
  • Wait for macOS High Sierra to install and your Mac to restart.

Check disk drive

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 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.

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