Reinstall macOS Big Sur or Catalina without Losing Data. Option #1: Reinstall macOS without Losing Data From Internet Recovery. Click the Apple iconRestart. Hold down the key combination: Command+R, you will see the Apple logo. Then choose “Reinstall macOS Big Sur” from utilities window and click “Continue”. Still, it seems completely broken on the latest versions of macOS Catalina and Big Sur. Maybe, this will reliably work in the future. Deploy using Volume Purchasing. The Install macOS Big Sur application is available in Apps and Books when viewing either Apple Business Manager or Apple School Manager and is deployable like other Mac App Store. Steps to install/reinstall a fresh version of Catalina/Big Sur. OK, this is crazy, I had just installed Catalina and wiped everything out to start from scratch and only a couple months into my new install, it was doing some bizarre stuff that I had never seen before. I have a 250G SSD disk drive and doing a df to show the disk usage shows this. Big Sur is a big mess and a big fail! My sister downloaded it and her late 2015 iMac became useless. I tried to reinstall it and it hung up at the dreaded 'Less than one minute remaining' Now I have to do a clean erase and load Catalina. Reminds me of all the bad OS from Microsoft in the early days.

How To Downgrade Macos Big Sur To Catalina

I’ll admit it: I’ve gotten a little used to working at smaller companies, where there’s no monitoring of company computers, and it’s the Wild West as far as what you can install on them.

That’s no longer the case for me. I now work at Auth0, a company with a headcount that’s quickly approaching 800, with unicorn status and Series F funding, and it’s in the security industry. Naturally, there’s a full-fledged security team that monitors company-issued computers.

In my excitement to take the new version of macOS — Big Sur — out for a spin, I’d forgotten that the Security team hasn’t yet approved it for use. They very quickly (and I should add, nicely) contacted me and let me know that I needed to reinstall macOS Catalina as soon as possible.

There are other reasons why you might need to go back to Catalina after installing Big Sur:

• It’s still very new, and very new versions of operating systems always have some set of issues, whose effects can run the gamut from mildly annoying to catastrophic. If you can’t afford to lose time dealing with these issues, you should wait for the updates.
• There are reports that the current version can “brick” MacBook Pros from the 2013 / 2014 era. This isn’t a problem if you’re keeping your old 2013 / 2014 machine around as a backup, but more serious if you’re still using it as your main computer (and yes, a 2013 / 2014 Mac is still a perfectly good machine, even for development work).
• If you’re a DJ or music producer, Big Sur currently has compatibility problems with some of the hardware and software. If you want to keep DJing, producing, or mixing on your Mac, stay on Catalina for a little bit.

For the benefit of any who need to downgrade, here’s a step-by-step guide to reinstalling Catalina after you’ve installed Big Sur. You’ll need a USB key and the better part of an afternoon.

Step 1: The preliminaries

1a: Start downloading the Catalina installer from the App store

The first thing you’ll need is the macOS Catalina installer.

It’ll take up around 9 gigabytes of space on your hard drive, and the App Store will put in your Applications folder.

Once it’s completely downloaded from the App Store, the installer will start automatically. When this happens, close the installer. You’ll make use of it later.

The installer will take some time to download. Apple’s servers will be busier than usual, as many users are downloading Big Sur and other upgrades.

1b: Back up your files!

In the process of reinstalling Catalina, you’ll need to completely erase your Mac’s hard drive. If you have any files that you can’t live without, this is the time to back them up.

I didn’t have to worry about this, since:

• All my work product is either code (which lives on GitHub) or content (which lives on GitHub or Google Docs), and
• I’ve been at Auth0 less than a month, and between onboarding and offsites, there just hasn’t been that much of a chance for me to accumulate that many files on my hard drive!

1c: Get a nice fast USB key that stores at least 16 GB

The process will involve booting your Mac from a USB key containing the macOS Catalina installer, so you’ll need a key with enough space. An 8 GB USB key won’t be big enough. Because digital storage is all about powers of 2, the next size up will be 16 GB.

I strongly recommend that you use a USB 3 key, especially one with read speeds of 300 megabits/second or better, such as the Samsung Fit Plus. Doing so will greatly speed up the process. Don’t use a USB key that you got as conference swag — it may have the space, but more often than not, they tend to be slow, because they’re cheap.

If the USB key contains files that you want to keep, back them up. You’re going to erase the key in the next step.

Step 2: Make a bootable USB key containing the macOS Catalina installer

2a: Format the USB key

Plug the USB key into your Mac, then launch Disk Utility.

Select the USB key in Disk Utility’s left column, then click the Erase button:

You’ll be presented with this dialog box:

Enter MyVolume into the Name field, and for Format, select Mac OS Extended (Journaled). Click the Erase button. This will format the USB key with the volume name of MyVolume.

2b: Install the macOS Catalina installer onto the USB key

In Step 1a, you downloaded the macOS Catalina installer and closed it after it started automatically. In this step, you’ll transfer it to your freshly-formatted USB key.

Open a terminal window and paste the following command into it:

(The command above assumes that you gave the USB key the volume name MyVolume.)

Once you’ve provided sudo with your password, you’ll be asked if you want to erase the USB key. Entering Y in response will start the process of making the USB key a bootable drive and copying the macOS Catalina installer onto it:

The Erasing disk process will be relatively quick, but the Copying to disk process may take a while. This is where using a nice, fast USB 3 key will pay off.

Be patient and let it get to 100%, and wait for the Install media now available message to appear and the command line prompt to return.

2c: If your Mac is from 2018 or later, set it up to boot from external media

Check the year of your Mac’s manufacture by selecting About This Mac under the Apple menu:

• If your Mac year is 2017 or earlier, you don’t need to follow the rest of this step. Proceed to Step 3.
• If your Mac’s year is 2018 or later, you’ll need to change its security settings to allow it to boot from an external drive.

Here’s how you change the security settings:

1. Restart your Mac and hold down the ⌘ and R keys when you see the Apple logo. This puts the computer into recovery mode, which provides many setup options.
2. In the menu bar, select Utilities, and then select Startup Security Utility from the list that appears.
3. The Startup Security Utility window will appear:
   1. Under the Secure Boot section, select Medium Security. This will allow you to install Catalina without having to connect to a network.
   2. Under the External Boot section, select Allow booting from external media. This will allow you to install Catalina from a USB key or disk drive.

Step 3: Install macOS Catalina

How To Reinstall Macos Catalina From Scratch

Restart your Mac, and hold down the Option key while it restarts. Your Mac will present you with a choice of startup disks.

Choose the USB key. Your Mac will boot up and you’ll be presented with the macOS Catalina installer screen:

Go ahead and install Catalina.

Once Catalina is installed, you can proceed reinstalling your other software.

Once that’s complete:

• If your Mac’s year is 2017 or earlier, you’re done installing Catalina. You can now go about reinstalling your software and restoring your backed up files.
• If your Mac’s year is 2018 or later, you’ll need to restore its original security settings. The process is described in Step 4, below.

Step 4: If your Mac is from 2018 or later, restore the original security settings

If your Mac is from 2018 or later, follow these steps to restore the original security settings once Catalina has been installed:

1. Restart your Mac and hold down the ⌘ and R keys when you see the Apple logo. This puts the computer into recovery mode, which provides many setup options.
2. In the menu bar, select Utilities, and then select Startup Security Utility from the list that appears.
3. The Startup Security Utility window will appear:
   1. Under the Secure Boot section, select Full Security.
   2. Under the External Boot section, select Disallow booting from external media.

If you've upgrade to macOS Big Sur but decided to stick with macOS Catalina because of annoying bugs still not resolved in Big Sur, it is easy to roll back or downgrade from Big Sur to Catalina by following the guidelines shared in upcoming section. Before the downgrade starts, please make sure you have backed up important data on your Mac. This can be done with Time Machine, the stock app for file backup on macOS.

Notice: No matter which method you are going to pick up for downgrading Big Sur to Catalina, please backup your data on Mac first. You can sync them to cloud drive or an external backup drive.

Potential Bugs for macOS Big Sur

Operating system is a enormous software project that needs hundreds of developers to work together. So it is inevitable to avoid bugs and errors. This also applies to OS Big Sur, the latest version of macOS. Some of the major issues you may have on Big Sur and may be the main reason to put you back to old versions of macOS like Catalina or Mojave.

• Some apps can not run properly like Dropbox, Google Drive.
• App craches after launch.
• Media import may not work in iMovie and Final Cut Pro.
• Can not sign in iCloud sign-in.
• Some keyboard shortcuts not working on non-English languages.
• Weather widget display incorrect location.

Method 1: Directly Downgrade from Big Sur to Catalina

macOS Catalina is the official app you can use to install Catalina on current Mac on the air. This is the direct way to downgrade from Big Sur to Catalina. You don't need to make additional settings as the whole process is quite straightforward and safe.

Step 1: Search 'Catalina' in App Store on your Mac running with Big Sur.

Step 2: Click 'Get' button at the top to download macOS Catalina install app. When it starts, you will see a progress bar in Launchpad and you have to wait for minutes to fully download the app because the app is pretty big.

Step 3: The installer will be opened automatically when the download is completed. Just follow the screen prompt to install macOS Catalina on your Mac. The process will overwrite Big Sur installation in a safe way.

This method still works till the day we wrote the post. However, macOS Catalina will be no longer available after a period of time according to Apple convention. Please don't worry. You can still apply the following two methods to downgrade macOS from a new version to old one.

Method 2: Downgrade from Big Sur to Catalina by Deleting Big Sur Installtion

If your Mac is originally shipped with macOS Catalina, you can then downgrade from Big Sur to Catalina by removing the current Big Sur installation in Recovery Mode. After that, Mac will start downloading and installing Catalina from Internet (Apple Server).

Step 1: Make sure your power adapter is connected because this could take a while. Now, restart the Mac but hold down the Command+R key combination during boot. Next, choose the Disk Utility app when you see the macOS Utilities window on your screen. The purpose of this is to be able to erase Big Sur installation and re-format it for macOS Catalina.

Step 2: Hit the Continue button and choose the option for Startup Disk. Click the Erase option, then choose APFS as your file system and GUID as your partition scheme.

Step 3: Quite Disk Utility app and back to macOS Utilities. At this time, please choose Reinstall macOS and hit Continue button. After that, follow the screen instructions to install macOS on your Mac.

Your Mac must be connected to Internet if you chose to downgrade from Big Sur to Catalina in this way. And this may take hours to complete if the download speed was too slow.

Method 3: Downgrade from Big Sur to Catalina by Reinstalling Catalina

Another possible solution is to install macOS Catalina over Big Sur partition via a bootable USB drive. If the above two methods do not work, then you can use this trick to downgrade from Big Sur to Catalina. However, you should create a macOS Catalina USB installer first. This can be done with the help of UUByte DMG Editor.

Step 1: Get macOS Catalina DMG file from here.

Step 2: Download and install UUByte DMG Editor onto a Windows PC or Mac.

Step 3: Plug in a USB drive and open UUByte DMG Editor app; then click 'Burn' section. You will be lead to a new window immediately, where you can import Catalina dmg file and select USB drive.

Step 4: When the setting part is done, click 'Burn' button to create a bootable Catalina USB drive. You need to wait about 10 minutes in this step.

Step 5: Turn off your Mac with the bootable USB drive still plugged in. Wait 2-3 minutes and reboot your Mac with Power + Option key. This will open up macOS Startup Manager, where you can choose a temporary booting device this time. Now, click the USB drive name and starts to install macOS Catalina on your Mac.

Summary of the Process

To help you get a clear picture of how to downgrade from macOS Big Sur to macOS Catalina, the steps are summarized below:

1. Erase startup disk and reformat it.


2. Get macOS Catalina Install App.


3. Create bootable macOS Installer USB.


4. Boot your Mac from this USB drive.


5. Start installing macOS Catalina in Recovery mode.

If you want to do this once Big Sur is officially launched, you may not be able to get the installer file from the Mac App Store. In that case, you will need to download a DMG disk image file from a third-party source in order to complete the downgrade. Our recommendation is to get the installer file now while it's available as an official download. That way, even if you decide to downgrade later, it will be much easier.