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Install Macos Catalina From Big Sur

When you want to provide automated workflows to upgrade to or erase-install macOS Big Sur, you can use the startosinstall tool. You can find this tool inside the “Install macOS Big Sur” application at:

Note: Apple calls the “Install macOS *” application “InstallAssistant.” I find this a useful shorthand and will use it.

Before you can use startosinstall, you need to somehow deploy the InstallAssitant on the client system. And since the “Install macOS Big Sur” application is huge (>12GB) it poses its own set of challenges.

Then, you can select whether you want to update macOS from Catalina to Big Sur (or Big Sur to Big Sur if you are switching from a different patcher) or do a clean install of Big Sur (currently unavailable). After that, your Mac will start downloading @barrykn's micropatcher for kexts and a couple other resources. We are extending you an invitation to join the AppleSeed Program and to take part in shaping Safari 15 for macOS Big Sur and Catalina. As a participant, you’ll get to test-drive pre-release software and provide your feedback. But starting today, Apple has introduced the first Safari 15 beta, available for those who are not on Monterey. 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). For macOS Big Sur, macOS Catalina, macOS Mojave or macOS High Sierra, the links download an installer directly into your app folder. The installer has the name “Install macOS version name”. For Mac OS X El Capitan, the link downloads a disk image file named InstallMacOSX.dmg.

Different management systems have different means of deploying software. If you are using Munki (or one of the management systems that has integrated Munki, like SimpleMDM or Workspace One) you can wrap the application in a dmg. Unfortunately, even though “app in a dmg” has been a means of distributing software on macOS for nearly 20 years, most management systems cannot deal with this and expect an installer package (pkg).

You can use pkgbuild to build an installer package from an application, like this:

This works for all InstallAssistants up to and including Catalina. With a Big Sur installer application this command will start working, but then fail:

The reason for this failure is that the Big Sur installer application contains a single file Contents/SharedSupport/SharedSupport.dmg which is larger than 8GB. While a pkg file can be larger than 8GB, there are limitations in the installer package format which preclude individual files in the pkg payload to be larger than that.

When you want to distribute the “Install macOS Big Sur” application to the clients in your fleet, either to upgrade or for an erase-and-install workflow, this limitation introduces some challenges.

You can use Composer with Jamf to create a Jamf dmg style deployment, but that will only work with Jamf Pro. You could further wrap and split the application in different containers, but that will increase the creation and deployment time.

There are a number of solutions. Each with their own advantages and downsides, some supported and recommended by Apple and some… less so. Different management and deployment styles will require different solutions and approaches.

Install

App Deployment with MDM/VPP

When you have your MDM hooked up to Apple Business Manager or Apple School Manager, you can push applications “purchased” in the “Apps and Books” area with MDM commands. This was formerly known as “VPP” (Volume Purchase Program and I will continue to use that name, because “deploy with Apps and Books from Apple Business Manager or Apple School Manager” is just unwieldly and I don’t care what Apple Marketing wants us to call it.

Since the “Install macOS Big Sur” application is available for free on the Mac App Store, you can use VPP to push it to a client from your MDM/management system.

When you do this, the client will not get the full InstallAssistant application, but a ‘stub’ InstallAssistant. This stub is small in size (20-40MB).

The additional resouces required for the actual system upgrade or installation which are GigaBytes worth of data will be loaded when they are needed. It doesn’t matter whether the process is triggered by the user after opeing the application or by using the startosinstall or createinstallmedia tool. Either workflow will trigger the download of the additional resources.

This has the advantage of being a fast initial installation of the InstallAssistant, but then the actual upgrade or re-installation process will take so much longer, because of the large extra download before the actual installation can even begin. For certain deployment workflows, this is an acceptable or maybe even desireable trade-off.

The extra download will use a Caching Server. This approach is recommended and supported by Apple.

Mac App Store and/or System Preferences

For some user-driven deployment styles, having the user download the InstallAssistant themselves can be part of the workflow. This way, the user can control the timing of the large download and make sure they are on a “good” network and the download will not interfere with video conferences or other work.

You can direct then to the Big Sur entry in the Mac App Store with a link. You cannot search for older versions of macOS Installers in the Mac App Store, but Apple has a kbase article with direct links.

You can also use a link that leads a user directly to the Software Update pane in System Preferences and prompts the user to start the download:

When the InstallAssistant is already installed, this link will open the application. When the Mac is already running a newer version of macOS or doesn’t support the version given, it will display an error.

You can use these links from a script with the open command:

The downloads initiated this way will use a Caching Server. Linking to the Mac App Store is supported and recommended by Apple. The x-apple.systempreferences links are undocumented.

softwareupdate command

Catalina introduced the --fetch-full-installer option for the softwareupdate command. You can add the --full-installer-version option to get a specific version of the installer, for example 10.15.7.

You can run this command from a managed script on the clients to install the application. The download will use a Caching Server.

This would be a really useful method to automate deployment the InstallAssistant on a client, if it were reliable. However, in my experience and that of many MacAdmins, this command is very fragile and will fail in many circumstances. As of this writing, I have not been able to reliably download a Big Sur InstallAssistant with this command. Most of the time I get

This approach is often recommended by Apple employees, however it will have to be much more reliable before I will join their recommendation.

Please, use Feedback Assistant, preferably with an AppleSeed for IT account, to communicate your experience with this tool with Apple. If this command were reliable, then it would be my recommended solution for nearly all kinds of deployments.

InstallAssistant pkg

With these solutions so far, we have actually avoided creating an installer package, because we moved the download of the InstallAssistant to the client. A caching server can help with the network load. Nevertheless for some styles of deployments, like schools and universities, using the local management infrastucture (like repositories or distribution points) has great advantages. For this, we need a package installer for the InstallAssistant.

A “magic” download link has been shared frequently in the MacAdmins Slack that downloads an installation package from an Apple URL which installs the Big Sur InstallAssistant.

This pkg from Apple avoids the file size limit for the package payload by not having the big file in the payload and then moving it in the postinstall script. Smart hack.. er… solution!

The URL is a download link from a software update catalog. You can easily find the link for the current version with the SUS Inspector tool.

But it would be really tedious to do this on every update. You, the regular reader, know the “tedious” is a trigger word for me to write a script. In this case it was less writing a script than looting one. Greg Neagle’s installinstallmacos.py had most of the pieces needed to find the InstallAssistant.pkg in the software update catalog and download it. I merely had to put the pieces together somewhat differently.

Nevertheless, I “made” a script that downloads the latest InstallAssistant.pkg for macOS Big Sur. You can then upload this pkg to your management system and distribute it like any other installation package.

  • GitHub: scriptingosx/fetch-installer-pkg

It works very much like installinstallmacos.py.

When you start the script it will download a lot of data into a content folder in the current working directory, parse through it and determine the Big Sur Installers in the catalog. When it finds more than one installers, it will list them and you can choose one. When it finds only one Installer, it will start downloading that immediately.

Install Macos Catalina From Big Sur Torrent

You can add the --help option for some extra options (all inherited from installinstallmacos.py.

We will have to wait for the 11.1 release to be sure this actually works as expected, but I am confident we can make it work.

This approach is very likely not supported by Apple. But neither was re-packaging the InstallAssitant from disk in Catalina. This deployment method is likely closer to the supported deployment workflows than some common existing methods.

The download does not use a Caching Server, but since the goal is to obtain a pkg that you can upload to your management server, this is not a big downside.

Big Sur signature verification check

You may have noticed that when you launch the Big Sur InstallAssistant on Big Sur for the first time, it will take a long time to “think” before it actually launches. This is due to a new security feature in Big Sur that verifies the application signature and integrity on first launch. Since this is a “big” application this check takes a while. Unfortunately Big Sur shows no progress bar or other indication. This check occurs when the user double-clicks the app to open it and when you start an upgrade or installation with the startosinstall command.

There does not seem to be a way to skip or bypass this check. You can run startosinstall --usage from a script right after installing the InstallAssistant. This will do nothing really, but force the check to happen. Subsequent launches, either from Finder or with startosinstall will be immediate.

New things are always exciting and they definitely give us an adrenaline rush trying them. Somehow, not all new things are a perfect fit for us. This might be the case with macOS 11 Big Sur. You definitely switched from your previous MacOS Catalina to the new enhanced MacOS 11 Big Sur and after your high, you realized that you were perfectly comfortable with MacOS Catalina. It’s not too late, you can still seamlessly downgrade to Catalina without losing any of your data.

Here is how you can downgrade seamlessly in 5 simple steps;

First backup your data

You will need to back up your accumulated data since the upgrade. You might have used the MacOS 11 Big Sur for a short while but this step is important nevertheless and this is something very important when you are doing downgrade from big sur to catalina.

To do this you may first need to clean your system so you can retain only important files. CleanMyMac X can help you accomplish this by getting rid of unseen junk and clearing your accumulated clutter and this is something very important and should be done well. There are many people who are not sure about how it is done and regret it later and you should try and avoid being there and so be careful once you are doing the downgrade from big sur to Catalina.

Once done, you can now backup your cleaned data using the Time machine tool or an external backup tool like getting Backup Pro.

How Do I Install Macos Catalina From Big Sur

Time Machine backup.

  1. Backup your data by opening the system preferences and select Back up and this is something very important and you should never ignore it and if you do that then there could be an issue and that is the last thing that you want. Things need to be done in the right way to avoid any kind of issue and you will not have an issue.
  2. Select the drive for use and you are good to go.

Install macOS Catalina on an external drive

Before you can uninstall Big Sur, you first have to install macOS Catalina on an external drive. Some older models of Mac that do not use M1 chip might have problems with booting files. To surpass this hitch, allow booting from an external media before you downgrade. This is something important and you should look for doing it the correct way and once you do that then there will be no problem at all for anyone which is something very important and should not be ignored at all and one has to take things into consideration in the right way which is something very important and should not be looked anywhere else which is something very important.

Once you have booted your Mac externally, you can get back Catalina by simply downloading it from the App store. Thereafter, install macOS Catalina on a formatted external drive and should be done in the right way for a good result.

Erase macOS Big Sur

You have finally downloaded Catalina? Now it’s time to get back to your comfortable MacOS and say bye to Big Sur. Erase macOS Big Sur from your hard drive.

Reinstall macOS Catalina on your Mac

You can now run a downgrade to Catalina by reinstalling it on Mac. For this to happen you need to ensure you are connected to the internet.

  1. Insert your bootable external drive into your Mac then select restart on the menu.
  2. Hold down options while your Mac restarts, a list of startup disks will appear, choose the bootable drive with macOS Catalina and select continue.
  3. Finally, agree to the licensing T & Cs then wait for Catalina to reinstall

Restore data

The final step is to restore the data that you had backed up. Depending on what you had used, this is how you restore your data:

Time Machine Backup

  1. Restart your Mac then hold down Command + R to initiate recovery.
  2. Access utilities then restore from Time Machine Backup and continue.
  3. Select the backup source then proceed to back up and wait for your data to be restored.

Install Macos Catalina From Big Sur Free

After data restoration, your Mac will reboot.

Install Macos Catalina From Big Sur Windows

For Get Backup Pro, you just have to launch the app then select backup and restore your data to a location of your choice. All your data will be restored on MacOS Catalina and you are all set with a smooth downgrade on your sleeve.