How to Perform a Clean Installation of macOS 10.15 Catalina

[M.PaulCezanne]

I'm on a higher end 2018 MBP. I don't use any third party apps. I don't have any photos or music files outside of the ecosystem. All of my other files are stored in iCloud Drive one way or another.

I have weird "Relocated Items" on my desktop now and a bloated keychain anyway. Is there any reason I wouldn't want to just nuke the drive and do a clean install?

How do I create a bootable clone/backup of my system? I don't want to necessarily restore from it if something goes wrong. I just want to be able to check it for data or grab files if there actually is something I later realize I still need (e.g., some password I forgot in the keychain or some files I just didn't realize weren't stored in iCloud).

 

[talltree]

It is amazing how people complicate things to install macOS including third-party applications like “Install Disk Creator”, “DiskMaker X” or similar; and even Terminal commands. It is much easier than that. Just 1-2-3:

1. Download the macOS installer and open it.
2. Select the desired destination disk and install.
3. Boot from such disk.

That is! No Terminal commands needed. No third-party applications needed either. The Mac way!

But that doesn't accomplish a clean install. That puts the new OS over the top of what's already there. This is an article about how to create a clean install. The difference in results can be night and day.
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After I do a clean installation I will login to my iCloud and App Store accounts. Will it bring back stuff from 2014 in keychain app?

It will, but what I've always done after that is open up Keychain and simply delete everything. Zero it out. (as long as you have a copy (1Password, etc) of all your passwords.

 

[Sasparilla]

And of course, Mac Pro 2010 and 2012 models with metal compatible video cards, can unofficially install Catalina using tools such as the excellent macOS Catalina Patcher by dosdude1 and others. This tool will create a base installer for you, patch it and allow you do either an upgrade or a clean install.

But, unsupported Mac Pro, you won't be able to do Catalina updates if you do the install with these, right? So if a security update or regular update came out you couldn't install it or it'd hose your system, from what I understand. I've got a 5,1 with a Metal card and have been following some of the threads here. There's another group doing installs without the patch tools, so updates could be applied, but several of the devs there say to stay off Catalina if you use your unsupported Mac Pro for anything important (that doesn't require Catalina) at this point.

 

[talltree]

Fascinating, I had no idea there were so many ways to do a clean install. I've been a believer in doing them since Lion or so, about every 18 months. I don't know if the method I've always used is simpler or more complex, but here's the steps:

1. Wipe the drive completely down to its zeros. Then install the new OS. What you get is exactly like a new computer coming from the Apple store.
2. Create a new User account. I've always used the same name/pass as my old one, to avoid permissions issues, but I don't actually know if that's necessary. You can always change it to something new later.
3. Reinstall all 3rd party apps, and drag over all your docs/pics from your backup.
4. Set up all your parameters the way you want them.

Before doing the above, I do this:
A. Create a complete clone of your entire hard drive. I use Carbon Copy Cloner, but any of the apps will do. I always verify that the clone is true by starting up from that drive and verifying it's all there.
As insurance, I also make sure Time Machine is up-to-date, and I also have an online $50/year Backblaze, but this may be overkill.

B. Take lots of screenshots of the following:
- entire Application Folder (so you know what apps to reinstall)
- All System Preference Windows
- Internet Accounts
- Preference windows of your most customized applications (like Word, Pages, Photoshop) and utilities (such as Default Folder, aText, TextExpander, Keyboard Maestro, etc.

C. Export all customized small databases
This is probably the hardest part, since a lot of these we aren't conscious of. Fortunately, with the clone, it kind of doesn't matter, since all databases are there. I just like to do it to speed up and get going again soon.
I backup
- Mac Custom Dictionary (I have 1000s of custom words)
- 1Password
- aText (or text expanders)
- custom templates in Word/Pages, Keynote
- Safari bookmarks
- Contacts and Calendar (these both autofill from iCloud, but I like having them)

My whole point in doing it this way is to not port over any old plist or other files that might be corrupted. My goal is to have a hard drive that is identical to a brand new Mac, and I never knew any other way to accomplish that. I may try the OP's method this next time!

 

[now i see it]

Catalina is going to be the least adopted Mac OS in history

 

[Marx55]

But that doesn't accomplish a clean install. That puts the new OS over the top of what's already there. This is an article about how to create a clean install. The difference in results can be night and day.

What I said can be used for both clean install, upgrade or update. If you want a clean install, just open Disk Utility and erase the destination disk before installing macOS. No need to use third-party applications or Terminal. The Mac way!

 

[IG88]

You must disable t2 security startup or you can't boot from usb on new MacBooks

Correct, and I remember needing to doing that on my previous 13" MBP with T2.

 

[justperry]

People are wasting their time.

I started using OS X even before the official release, just shy of 2 decades, I never reinstalled, System runs like a charm.

 

[pfarmer]

The somewhat annoying thing about articles on how to do clean installs is that they don't discuss how to get apps and files in place afterwards so that my Mac "acts like it used to" except for the changes brought by Catalina itself.

To have a "true" clean install without losing functionality, I'd reinstall all apps from scratch. Which means I'd have to (1) catalog everything I have and, for those that didn't come from the App Store, (2) make sure I had the installation files or weblinks to install them all.

It might be a good thing to do, but it would be a tedious and non-trivial process, and it'd be easy to fail to install stuff I don't think about but find useful. I have over 120 apps, and the majority did not come from the App Store. And not all apps are in /Applications. Some such as MySQL and Homebrew reside in /usr/local; X11 resides in /opt. RCDefaultApp lives in /Library/PreferencePanes.

Also, the article also does not discuss how to bring back user files. Sure, it tells you to do a backup before wiping the disk and doing the clean install, but it says nothing about restoration afterwards. After the clean install, do I create a user from scratch? Do I then restore files from the Time Machine backup? What do I restore and what do I leave behind?

Restoring ~/Documents, ~/Downloads, ~/Movies, ~/Music, and ~/Pictures seems obvious enough, but what of the rest? There's no doubt that my old ~/Library and /Library/Application Support directories are full of cruft, but they also contains useful settings honed over the years for various apps (e.g. MS Office, iDrive) and, I'm guessing, files pertaining to software licenses. So should I restore them as well? And if I'm restoring files to a new user directory, is there a risk that permissions will get messed up.

To reiterate: it's not trivial to do a clean install and have things work the way I want them to.

What I'm thinking of doing is:

1. Manually remove stuff I never use and other crap from my home directory and from /Applications. Fortunately, I've been pretty good at housekeeping over the years, so this shouldn't be difficult.
2. Make sure that Time Machine runs a full backup after my cleanup.
3. Perform a clean install of Catalina.
4. Use Apple's Migration Assistant tool to restore my applications, documents, and settings.
5. Open up my most recent Time Machine backup and do a cross-check on the following folders to make sure I haven't missed anything important—while being careful not to overwrite any newer files.
   • /Library/Applications Support
   • /Library/Extensions
   • /Library/Fonts
   • /Library/Internet Plug-Ins
   • /Library/LaunchAgents
   • /Library/LaunchDaemons
   • /Library/PreferencePanes
   • /Library/PrivilegedHelperTools
   • /iDriveLocal
   • /usr/local
   • /opt

Does this seem a reasonable approach?

 

[unfunfionn]

I did this yesterday on my 2015 MBP. My first clean install since I bought it. The increase in speed and reduction of annoying little issues has been incredible so far. A lot of my plugins for Logic Pro aren’t working though. Thankfully that’s just a hobby and I can wait a bit.

Catalina itself, however, is nothing to write home about.

 

[chriscrowlee]

So if I go back to a clean new install of Catalina and then when it boots the first time restore from a Mojave time machine backup is that possible? I Know forward recovery like a Catalina time machine restored to Mojave isn’t possible but going forward works right?

 

[Oh-es-Ten]

If people have the spare disk space, using AFPS Volumes / Containers suddenly makes this process very cool. I have not ever clean installed since 10.10, so decided that all of the big changes under the hood (Frameworks and 64bit) meant that this would be the OS to do it. So I created another AFPS Volume and clean installed to that. Then brought over any small bits I wanted to move over like the keychain etc, but I could just grab bits in the Finder and drag them over. My 2018 13 inch MBP has never run better and is now cruft free.

The best part is that I can simply restart into the old boot volume if I get stuck. Now I have all my work apps running and compatible, I can then throw away the old Mojave APFS container when I like and get that space back.

*Glad I went with the 1TB internal SSD option....

 

[Jimmy Bubbles]

Whomever wrote this article should’ve just shared Apple’s Support Article and not confused everyone:
support.apple.com/en-us/HT201372

 

[palmerc]

A clean install of Catalina is unnecessary.

As of macOS Catalina you will have two volumes in the APFS container, a read-only OS partition and a data partition. During upgrade macOS will rename your existing partition to 'Macintosh HD - Data' and delete all OS related portions and create a new read-only volume exclusively for the OS. This migration is non-optional. This is in essence an extension of the System Integrity Protection (SIP) added previously.

So by definition the OS is cleanly installed during an upgrade in its own volume and you have no choice in the matter.

 

[Weaselboy]

So by definition the OS is cleanly installed during an upgrade in its own volume and you have no choice in the matter.

I don't think what you are describing is quite the same thing as a true clean install. If you have old startup items of third party drivers/kexts causing a problem, a normal upgrade install would bring those problems right over to the new install. Where a true erase and clean install would not bring those problems over, unless of course you reinstalled the problematic app or utility.

 

[revmacian]

It is amazing how people complicate things to install macOS including third-party applications like “Install Disk Creator”, “DiskMaker X” or similar; and even Terminal commands. It is much easier than that. Just 1-2-3:

1. Download the macOS installer and open it.
2. Select the desired destination disk and install.
3. Boot from such disk.

That is! No Terminal commands needed. No third-party applications needed either. The Mac way!

Despite what you may think, after ignoring the several people here who have tried to educate you, these instructions will not provide a “clean” installation of macOS. What you have described is an update.. there is no way you can use these instructions to yield a clean install. Do you understand what is meant by “clean install”?

 

[Marx55]

By clean install I understand to format the destination disk and install macOS. That can be done as I said, simply erasing the destination disk before installing.

 

[revmacian]

By clean install I understand to format the destination disk and install macOS.

That is correct.

That can be done as I said, simply erasing the destination disk before installing.

But that is not what you said. As per your original instructions there is no “erasing the destination disk”, so you end up with an update rather than a clean install:

It is amazing how people complicate things to install macOS including third-party applications like “Install Disk Creator”, “DiskMaker X” or similar; and even Terminal commands. It is much easier than that. Just 1-2-3:

1. Download the macOS installer and open it.
2. Select the desired destination disk and install.
3. Boot from such disk.

That is! No Terminal commands needed. No third-party applications needed either. The Mac way!

I’m not trying to be argumentative, I’m just trying to make things clear for someone who is new to a Mac that might have read your original instructions.

 

[unobtainium]

By clean install I understand to format the destination disk and install macOS. That can be done as I said, simply erasing the destination disk before installing.

That would be complicated, since you’d have to download and run the installer on a separate disk or partition then. You cannot erase the destination disk if that’s the one you’re running the installer on.

Internet Recovery is by far the simplest option for T2 Macs.

 

[tnkrmdc]

Clean install was the only way that I could get Catalina to install on my MacMini with too many failures along the way.

 

[dbrewood]

Just skip the "--/Applications/Install macOS Catalina.app" altogether. These instructions are incorrect.
Apple has the correct documentation here: https://support.apple.com/en-us/HT201372

Thanks, sorted. Duly noted for the future.

 

[Marx55]

Well, I have an external SSD with Mac OS and repair tools, etc inside. I boot from it every time that I need to clean-install or repair other disk. Really easy!

 

[Marx55]

Just my method above:
How to Clean Install macOS Catalina

How to Clean Install macOS Catalina

macOS Catalina supports a number of methods for installation. Find out how to perform a clean install of Catalina on your Mac with our step-by-step guide.

blog.macsales.com

 

[Tech198]

I don't understand why it's so complicated nowadays to do an offline clean install.

In contrast, Microsoft is making it ultra easy to do an offline clean install of Windows 10 by providing a straightforward utility to create a generic Windows 10 bootable USB that can be used to install any version of Windows 10. Wish Apple would do the same.

Ya, they probably think, like the reason they never do stuff , is third-party software always fills "that" gap, and would always have more features anyway over any software/tool that Apple brings out.

Apple kinda puts the foot it the dirt with this. At least they have Terminal commands, but this could have gone better. This "not proving our own software" might even stem long before Apple, or could just be Apple.. .

 

[fjfjfjfj]

I just purchased a new MacBook Air. I immediately upgraded the OS to Catalina when I got it. A day later I decided that I wanted to do a clean install instead. I created a bootable USB drive and followed the instructions above. I ran into trouble because of the T2 security thing. I got lost in the instructions and managed to disable the security (I think) and delete the Data drive only. Again lost in the steps after that hiccup, I did install the software and the computer booted to what appeared to be like a new machine. I selected the country, setup my Apple ID, Touch ID, etc. However, when I finally got into the operating system there was an error about the Macintosh HD being locked and it couldn't unlock and when I open Disk Utility I see now I have a greyed out Macintosh HD, and two Macintosh HD- Data drives (one being "Data - Data"). How do I completely erase everything and setup the Catalina operating system (including how to disable any T2 security stuff). I still have the bootable USB. Could someone help me with instructions? Thank you in advance.