How to clean install macOS High Sierra

macOS doesn’t really get slow with time, like Windows, however, sometimes you do run into issues where it is best to go for a clean install. Luckily, there are somethings that can be tried before the ultimate clean install like resetting NVRAM or SMC to resolve some issues. We list out all the methods you can try before formatting your Mac and reinstalling everything.  

Clean install macOS High Sierra

Reset NVRAM or PRAM on Mac

If the following issues plague your Mac, it might be better to try reseting NVRAM (nonvolatile random-access memory) or PRAM (Parameter RAM) first.

  • Mac boots from the wrong start up disk, even though you have selected the correct one in System Preferences
  • Sound, display resolution and time zone information keep changing

NVRAM/PRAM is where these settings are stored. To reset it, follow these steps:

  • Shut down your Mac.
  • Turn it on and immediately press and hold the following keys: Option + Command + P + R.
  • Keep the keys pressed for 20 seconds. If you hear the start up sound or see the Apple Logo (on iMac Pro), you can let go of the keys
  • Double check your sound/display and time zone settings and configure them again because resetting NVRAM/PRAM can wipe them out.

Reset System Management Controller on Mac

System Management Controller manages the low-level functionality of your Mac, such as, battery and thermal management (fan speed), sensors (motion, ambient etc) and so on.

If you find that your Mac:

  • is heating up
  • has noisy fans
  • does not charge properly
  • runs slow

You might want to reset your Mac’s SMC.

On a MacBook:

  • Shut down your MacBook.
  • Press the left Shift + Control + Option keys and the power key and hold them down for 10 seconds.
  • Release all keys and press the power button to turn on your MacBook.

On an iMac, Mac Pro Mac Mini:

  • Shut down your Mac.
  • Unplug its power cord and wait for 15 seconds.
  • Plug the power cord back and wait for 5 seconds before pressing the power button on the Mac to turn it on.

On iMac Pro:

  • Shut down your iMac Pro.
  • Press and hold the power button for 8 seconds.
  • Release the power button, wait a few moments and press it again to turn the iMac Pro on.

Clean install macOS High Sierra

If both of the above methods do not fix issues with your Mac, it is time to go ahead with the clean install.

Before you start with the installation process, it is best to back up your data to an external drive. This is the best method to back up your data, compared to cloud back up solutions because they are just slower to restore data from. Thanks to Time Machine, macOS makes it easy to back up all your Mac’s content without you having to manually copy files. No matter which backup method you prefer, just make sure to do it because losing data is the worst thing.

Note that you would need to reinstall all apps after resetting your Mac so make sure to backup any license information and setup files too.

There are two ways to go on with clean installing macOS:

Create bootable macOS USB drive

You can create a bootable macOS High Sierra USB drive and reboot from it to install the operating system. This works great if you have a spare USB drive around and also have a compatible USB port/dongle for your Mac.

Use Internet Recovery

I personally prefer this method because it does not involve downloading macOS setup and creating a USB drive. You can just boot into macOS Recovery over the Internet. To do so, simply restart your Mac and immediately press and hold Option + Command + R keys when the display turns on.

macOS High Sierra Recovery

Once Recovery loads, you can reinstall macOS High Sierra. You can also format your drive and partition it using Disk Utility. The Recovery will always download the latest version of macOS from Apple’s servers so if you are not on the latest version, this process will update you the latest macOS release.

If you do not wish to upgrade to the latest macOS version but instead re-install the version that your Mac shipped with, use this key combination to load Recovery: Shift + Option + Command + R.