The Complete Guide to an OS X Clean Install of macOS Sierra

| How-To

Apple has designed OS X/macOS so that one can just upgrade to the next version, "over the top," seamlessly. With this kind of upgrade, all user data, settings and accounts remain as before, and that works for most users most times. However, there are occasions when a user needs to do what's called a "Clean Install." This is like setting up a Mac as if it first came out of the box and then personal data is restored. This article, after a brief introduction, will list the steps needed for that Clean Install.

There are some users who suspect that a Clean Install is a good way to approach a complete new version of OS X or macOS. Over time, a lot of cruft, that is, unused extensions, app support files, preferences and other files in your Library folder or System Library folder can become troublesome or even a security issue, like Java. Or just take up too much space. See, for example: "How to Manage the Secret Software That Google Chrome Installs on Your Mac."

In addition, sometimes the normal housecleaning process with apps like Spring Cleaning and App Zapper can't solve a particularly difficult issue, and the only way to get a fresh start is a Clean Install.

But First, Let Me Talk You Out of Doing This

A Clean Install, as you'll see below, can be a time intensive process. On the other hand, over the years, we've learned that OS X is pretty good about ignoring things that are no longer applicable. For example, in OS X Yosemite, unless a kernel extension is digitally signed by Apple it won't load.

Adam Christianson (@MacCast) has written "If you aren’t really having any issues or problems then just download the new OS, install over the top and go on your merry way."

We both agree that an over the top is generally the best idea. Those who still pursue the thought of a Clean Install usually reconsider when they realize that everything they own will be deleted from the Mac.

  • The boot drive is erased.
  • All user accounts are deleted.
  • All the files in all the user accounts (spouse, children, family cat) will be deleted. Every document, movie, song and photo will be deleted.
  • All network settings are deleted.
  • Every application and its license files will be gone.

Forging Ahead

However, there is a way to do a Clean Install and restore all your data if you really want to. That's what this article is all about. In summary, you will:

  • Make thorough backups of your entire boot drive in several ways.
  • Erase your boot drive.
  • Install OS X El Capitan (or macOS Sierra)
  • Restore your network settings, user accounts and all data. That means email, photos, music...everything.

I suggest you read this entire article first, understanding all the steps before you begin. Steps #5 and #6 require some preparation, are particularly tricky and must be handled with care. Ready? Here we go!

The Clean Install Process

Step #1. Prepare and Verify. Disconnect any unnecessary peripherals such as printers, tablets, microphones, etc. Try to work with just attached drives and a wired mouse and keyboard. Identify which items are backed up to iCloud. System Preferences > iCloud.

Use Disk Utility to make sure your boot drive permissions are all repaired and that the disk directory is verified as good. This will make sure your Time Machine backup doesn't get scrambled. Then you're ready for the next step.

Step #2. Backups. I recommend two methods.

Time Machine. Do one last Time Machine backup. (Menu Bar > Time Machine > Backup Now.) Later, if you have a curent Time Machine backup and something goes very wrong, you can boot from the recovery partition (CMD-R) and do a complete erase (Disk Utility) and then restore from your Time Machine archive. You'll be back where you were before you started.

File by file with Carbon Copy Cloner. This is a preferred tool by many for making an exact copy of your boot drive to an external Hard Disk Drive (HDD) or Solid State Drive (SSD). That way, you can always mount that external drive, access and copy over individual files.


2.1 You may want to have a log of all your application licenses in a copyable format so that when you restore your apps, you'll have this information handy and can paste it in. I use BBEdit.

2.2 If you try to take a short cut and just copy back in your Library folder, to make licensing easier, you'll be defeating the idea of a Clean Install. That's because the personal Library folder is one place that typically needs a thorough housecleaning.

2.3 Take note of all your mission critical apps and make sure they're all compatible with El Capitan. A great resource for that is Barring sufficient information there, you'll have to visit the developer's website.

2.4 Some simple apps can be copied back to the Applications folder in El Capitan and run just fine. Others will require an installer that places supporting files on your Mac in various places, for example, your personal Library folder.

Catalog these apps so that you'll know which ones came from the Mac App Store and can be readily recovered and those which require you to download a new installer from the developer's website.

2.5 Note that Carbon Copy Cloner takes care of accounts on your Mac other than your own. For example, your spouse. Dont forget those!

Next page: Steps #3 to #7: Download, Install and Restore.

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But First, Let Me Talk You Out of Doing This

OK, OK you talked me out of it. I was all ready to do ElCap the hard way. I was planning it since July or August. But ya know, overall my 2012 MacBook Pro isn’t running too bad. You’re right, OS-X is pretty good at taking care of itself. I might get SpringCleaning or AppZapper and really strip out the stuff I don’t need. Then just do an upgrade.  I can always Nuke & Pave later.


@ Geoduck ~ >>> Clean My Mac <<<
I run it once per month, and it almost always cleans out a couple of Gigs of dross.


Once upon a time I had a freeware app called *App Cleaner*. I used it successfully for years to remove all the ancillary files an app I was tired of had dropped into my Mac. Last year I got a new iMac so I downloaded *App Cleaner*, expecting it to be as good as it had ever been. I think developers should get paid for their work. This developer turned to hacking my browser for his income. I wasted an afternoon eliminating it piece by piece.

I’m telling this story to ask if *App Zapper*, which looks a lot like *App Cleaner* will have the same bad behavior?


I have an old copy of AppCleaner on my system. Haven’t updated it in years. Thanks for the warning.

Clean My Mac looks good
$40, ouch. I mean yes pay developers for their work, but that seems a bit steeper than I want to go for a cleaner utility.

Richard Button

I need some advice: I was considering a clean install of El Capitan (Currently running v10.11.1) because I have been having issues with Mail and Contacts ever since upgrading. Seeing the comments on this post, I am getting cold feet.
However, I have an issue that was existing before, every since Leopard (maybe before). Periodically my system will lockup for seemingly no reason. The only thing that is working when it does it the cursor. I have to do a reboot by holding down the power button until it shuts down and then restart. At one point about 2 years ago, it was so frequent that I assumed it was the computer. I ordered a new iMac (iMac 11.2, Intel Core i3) Apple refurbished. I did the move from the old system via TimeMachine backup. It seemed to work much better for about 6 months, through one or two OS upgrades. (Flash back, I clean installed on the old computer the original OS from the original purchase disks. It was an first gen Intel iMac. After the clean install, it ran for two weeks without freezing. Then I sold it on eBay)
Now back to my current issues - the system still freezes occasionally, sometimes 2 or three times a day, sometimes it will go for a week. The typical time it freezes is while using Safari or coming up from ‘sleep’. But now I have the added issues of Contacts will not open at all, it just hangs and makes the cursor spin. Mail is snail slow about looking up ‘Previous Recipients’ and takes 30-40 seconds to send even the smallest size message. If I try to add an address that it has to lookup from Contacts - nothing doing. (Probably because Contacts won’t open).
I have searched the Apple Help site without any issues descriptions that match this.


I purchased a 480gb SSD for use in my late-09 MacBook with 10.11.2 (and 8gb memory) on it.

I will be replacing the 250gb HD in the system with the 480gb SSD.

I use an external backup drive with TimeMachine and will be taking one last backup before beginning on my quest.

Should I put the SSD into an external USB case and format it and (somehow) load on 10.11.2 onto it as a bootable image? If so, what is the best way to do this?

Then, would I just swap out the internal HD with the SSD, reboot from the SSD and then recover from the external backup? I’m not so sure of the restore process other than one needs to interrupt the reboot/startup process somewhere, somehow and then select recover/restore from the backup drive.

Or, use the old HD now in the external case and copy everything over to the internal SSD (using CCC or another app or just a copy/paste of each directory?)? I suppose I could tar it over, but my Unix Sys Admin skills are very rusty anymore and I could be more dangerous to myself than I’d like. grin

So, can someone provide me with the actual specifics on the above process? Is this the easiest way to swap out the HD with an SSD and still have everything as it was?

Looking forward to zero moving parts (save the SuperDrive which is rarely ever used anymore) and a lot more storage.


NDGough, hopefully you get an answer to the above.

My Mid-2010 MBP is about to undergo some surgery as well (new battery, new 256GB SSD installed via data doubler w current HDD replacing Optidrive).

I’ll be following to see if it’s indeed better to load El Cap bootable on SSD externally, prior to physical install…

Fingers crossed!

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