At the menu bar, click Utilities → from the drop-down menu, select Startup Security Utility → enter either the login password, Apple ID password, or a firmware password if prompted → in the External Boot section, select Allow booting from external media to enable options of the macOS installation for the next steps.ģ. When you see the utilities window, release the keys. As soon as you see the Apple logo on the screen, press and hold the Command + R keys until the computer boots into Recovery Mode. So, click on the Apple menu and select Restart. If you have the T2 chip, you need to restart your Mac into Recovery Mode to continue to downgrade macOS.To ensure that you have a T2 controller, press and hold the Option key and click on the Apple menu → from the drop-down menu, select System Information → in the sidebar, choose the Controller (or iBridge) section → if you have the chip, you will see Apple T2 chip in the Controller Information on the right.If you have one, take the following steps: This refers to the iMac Pro, and the MacBook Pro, MacBook Air, and Mac mini models released in 2018 or later. The next step is to check if your Mac has the Apple T2 Security Chip. To make a backup of the information stored on the disk, you can transfer it to an external hard drive or cloud storage like Dropbox, Google Drive, OneDrive, and so on. This is because the next steps include erasing your HD. Even more important is to save your data if you have not already made a backup before installing new macOS. While using your Mac, you have probably created several files, which you want to save. The first thing you should do is to make a backup of your data. We will tell you at what step it will be necessary to connect to a hard drive with a backup or macOS installer. It is advisable to disconnect all additional external devices. For example, if you already launched Mail or Photos under Mojave and those apps already updated their databases, then when you try to use the High Sierra versions of those apps, they might not know what to do with the new format and may just fail to work with it or may corrupt it.Your computer must be connected to a power source and have a stable internet connection. It's just not a thing that enough people need to do often enough to be worth the software engineering work.īeware that for built-in apps like Photos and Mail that store their data in proprietary, undocumented database-like formats, you might have problems downgrading. The problem you're facing is that things like how settings are stored, how user account information is stored, how your Photos.app and Mail.app data is stored, how your Spotlight search metadata is stored, etc., often change from one major OS release to the next.Īpple writes the code in the new OS version to upgrade those settings and data to the new formats as applicable, but it's not cost-effective for anyone to write code for the old OS version to know how to downgrade settings that have already been migrated to the new version. For example, apps sold outside of the App Store often come with installers that install a bunch of stuff in various places under /Library, and it would be hard to find all those files to restore them to your High Sierra environment.įor system settings, just set up all your settings again by hand. You can use the Time Machine UI (in the Finder) to restore your users' home directories.įor most apps, you'd be better off re-installing them from their installers, especially if they might not be self-contained. It's no surprise that Migration Assistant won't help you with this.
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