How to perform a clean install of macOS High Sierra (even if you’ve already installed it)

“Downloading and installing a new OS gives you the opportunity to do some major house cleaning if you so desire,” Luke Filipowicz and Lory Gil report for iMore. “If you feel like you’d like a fresh start with macOS High Sierra, you can always opt to do a clean install: Just follow the steps below, even if you’ve already installed macOS High Sierra.”

“Make sure you understand the difference between a clean install and a standard install before you get started,” Filipowicz and Gil report. “This process will erase whichever OS you’re currently using from your hard drive entirely. That means any files, programs, or documents you have will be deleted. To save your files, put them on an external hard drive or a cloud-based program like Dropbox, OneDrive, or iCloud. If you don’t save these important files off your computer, you will lose them.”

“Before you erase your current operating system, download macOS High Sierra from the Mac App Store,” Filipowicz and Gil report. “Create a bootable drive of macOS High Sierra…”

Read more in the full article here.

MacDailyNews Take: It’s more time-consuming, but it can be worth it if it’s been awhile since your last clean install. We’ve done it to multiple 2011 iMacs and the difference before and after is night and day!


  1. If you are using a compatible Mac with a conventional HD, then for the moment you won’t be able to utilize the new APFS file system. That system is compatible with SSD drives. Earlier betas of HS’s file system included conventional drives, such as found in the iMac’s Fusion drive. However, that feature was removed in later betas. Rumor says Apple will add it back at some stage (undetermined).

  2. would be nice if MDN told us what the night and day difference actually is! Did you make a direct comparison?
    I updated both my 2017 iMac and my 2010 MacBook Air, both SSD, and both feel snappier, Safari in particular. no bugs so far. happy camper here.

  3. Don’t bother reading the article. It’s like the other 99% out there.
    Backup your drive, create bootable installer drive, erase your drive, install. Done.

    – What about all my saved email in “On your Mac”?
    – What about all my bookmarks from three different browsers?
    – What about all my application custom preferences that I setup?
    – How do I get my 60GB of music back into iTunes and my 100GB of photos into the photos app?

    Those of us that are computer geeks have our ways of doing this. I’d like to see others and how they accomplish it.
    As to the common person doing this, no way.

    1. I decided to do a clean install just because I wanted to start fresh. To answer Think’s hypotheticals….

      – What about all my saved email in “On your Mac”?
      A lot of people use a web based email service. As such, no problem because the email will still be there when you’re reformatted and reinstalled. For others, they’d have to learn how to copy their email directory(ies) to a backup drive.

      – What about all my bookmarks from three different browsers?
      I don’t think most users use three different browsers. Don’t most browsers now have a cloud bookmark sync option?

      – What about all my application custom preferences that I setup?
      Dunno – maybe a Time Machine Backup? I just usually go back and set up my app prefs as I want ’em.

      – How do I get my 60GB of music back into iTunes and my 100GB of photos into the photos app?

      Using Apple Music/iTunes Match and iCloud Photo Library completely negates this issue. As an alternative, storing iTunes and Photos libraries on an external drive also negates the issue. Just launch iTunes/Photos while holding the Option key, select your libraries from external drives and done. Easy Peasy.

      1. And for those that aren’t “most of us”, the answer is of little help.

        Restoring from Time Machine significantly diminishes the benefits of “clean install”, since it restores all the gunk that was there in the first place. The only way is to manually bring back only the stuff that is actually needed, and this may be a major headache. The best way to go would be as follows:

        • Backup on Time Machine (as an ultimate fail-safe, if all else fails).
        • Copy the entire home folder for every user on the Mac. That includes the libraries, documents, photos, music, etc.
        • Wipe and reinstall Mac OS. Re-create users, log into respective Apple IDs
        • Reinstall all third-party apps you need and re-activate / register, whatever necessary

        Restoring data will now depend on what needs to be recovered, and what isn’t that necessary. For each application that you want to restore to previous state, you would have to copy its preferences (both from the /library/preferences/ as well as from /user/library/preferences ). You may need to re-install plug-ins or add-ons as well.

        For e-mails that were stored locally, you will need to copy whatever is in /user/library/mail/ . This is needed ONLY if any of your mail is not on the server. Most people have iCloud, G-mail or Outlook/Hotmail service, which keeps all messages on the server, and using IMAP to access them offloads them all to the cloud, without keeping anything permanently local.

        For personal files, people usually put them inside /Documents/ or /Desktop/ (inside their home folder). These are easy to copy over without issues. Same goes for anything that is inside Music, Movies or Photos. If you keep anything in there, you can manually copy over.

        The one possible issue that can arise from this manual copying from an external drive is permissions. When you copy stuff from outside into the /user/library/preferences/ folder, permissions may not be set correctly, which can cause colossal problems later on. The first thing to do is repair them using Disk Utility. If that doesn’t work, you may need to manually set permissions on your home folders, making sure you ‘apply to enclosed folders’ whatever you select (read and write for yourself).

        The main purpose of this exercise (“clean install”) is to get rid of all the gunk that accumulates inside /library/ and /user/library/ folders (especially logs, preferences, Application Support stuff) from old versions of existing apps, as well as from apps we deleted long ago, but which left debris in various places. Time Machine will diligently backup and restore all that gunk, so the only solution is to do wipe and re-install, with manual restoration of personal data. The main risk there is forgetting something that you may need later.

        1. I think i’d almost be guaranteed to mess something up or run into a problem that proves to be more of a headache than whatever benefit I would gain. With a 2013 Macbook Air with the best specs I think I stick to a normal upgrade, clean installs are probably most worthwhile for older machines.

      2. Steve — as a “computer geek”, Think wasn’t asking how to do this.
        He was saying that these “how to do a clean install” articles are all useless unless they tell the average (i.e. fairly ignorant) computer user how to do all these things.

        For those people, your answers such as, “For others, they’d have to learn how to copy their email directory(ies) to a backup drive” are not useful. That’s the point! Who’s going to tell them how to do that – and much more?

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