Mojave Downgrade to High Sierra…

1. You're not supposed to be discussing Mojave here.

2. If you didn't make a backup first, the only way to go back is to erase the drive and reinstall the previous OS version. OS versions aren't like applications, they can't be uninstalled.

3. Everyone should maintain a backup even if you're not upgrading or updating.

4. Your issue has nothing to do with the 12" Retina MacBook, yet that's the forum area that you've posted in.

Hi sweenex,

Regarding your screenshot, choose Partition. A Time Machine backup cannot be made on an APFS-formatted volume (as far as I know).

Encrypting the backup isn't necessary for this scenario.

If Internet Recovery Mode offers to install a version of macOS other than High Sierra, verify that you used the correct key combination to start Recovery Mode. To boot the latest publicly available version of Recovery Mode, hold down Option-Command-R as you turn on or restart your Mac. A spinning globe should appear. If you don't see a spinning globe and the Apple logo immediately appears instead, you haven't booted Recovery Mode over the Internet.

You could try creating a bootable installer, but I doubt whether the macOS Mojave beta would permit this. However, it's certainly worth giving a shot, and if you are able to successfully download the macOS High Sierra installer from the App Store, see this article to create the bootable installer: How to create a bootable installer for macOS - Apple Support. If you have another Mac that supports High Sierra, you can also use it to transform your flash drive into a bootable installer. Ultimately, if you are able to create a bootable installer for High Sierra then by all means do so; it will eliminate download times for both Recovery Mode and installing macOS. You can boot your bootable installer by holding down the Option key while you turn on or restart your Mac.

It should be fine to exclude macOS from this backup; however, for future (non-beta) backups macOS should be included. This will give you the ability to restore your entire system from a given point in time using the "Restore from Time Machine" option in Recovery Mode.

Thanks for the info. Based on the screenshot and the output of diskutil list, you appear to have an internal SSD which uses Apple File System (APFS). Follow these steps to safely revert back to macOS High Sierra:

1. If you do not have another device to view this reply, print out these instructions before continuing.
2. Open Disk Utility and select your startup disk.
3. Click the Partition button. If prompted to add an APFS volume instead, click Partition.
4. Select your startup disk, then click the + button. Give the new partition an unique name, and format it as Mac OS Extended (Journaled). It should be larger than your normal startup disk in size.
5. Click Apply to create the new partition. Then, quit Disk Utility.
6. Open System Preferences and click on Time Machine. Check the box next to "Back Up Automatically", then select the new partition you just created. Encrypt the backups if desired.

   WARNING: If you forget the encryption password, it is impossible to restore from encrypted Time Machine backups.

7. Wait for the first backup to fully complete (which may take a long time), then restart your Mac while holding down Option-Command-R. Release the keys when a spinning globe appears, or when you're prompted to connect to a Wi-Fi network. This will boot Recovery Mode over the Internet.
8. When the main Utilities window appears, select Disk Utility and continue. Click the View button, and select "Show Only Volumes".
9. Select your startup disk and click Erase. Be careful NOT to select your backup partition. Format your startup disk as follows:
   1. Name: Whatever you want, but the default name is Macintosh HD
   2. Format: APFS
   3. The Scheme option should NOT appear. If it does, cancel the erase and be sure you're only selecting your startup disk instead of the entire SSD. Erasing with the Scheme option present will wipe out BOTH your startup disk and your backup.
10. Click Erase. When the erase is complete, quit Disk Utility.
11. The main Utilities window should reappear. Select Install macOS, and verify that it is offering to install High Sierra. If so, select your startup disk as the target volume and start the macOS installation.
12. When the installation is complete, Setup Assistant should appear. Progress through the Assistant until you're prompted to transfer data. Choose to transfer "From another Mac, Time Machine backup or startup disk". If successful, your Time Machine backup on your other partition should be detected automatically. You'll then be guided through the data restoration process.
13. If everything is successful, you should end up at either the login window or at the desktop screen. Verify that all accounts, applications and other data are present. If desired, use Disk Utility to delete your backup partition.

Yes, it is possible to avoid buying an external drive at all, given that the amount of used data on your Mac is less than half of the total drive space. In this case, you'd need to have 124 GB or less of stored data on your Mac (although I'd recommend bringing it down to at least 120 GB or lower, if possible).

One last thing I need to know: how is your startup disk currently formatted? To check this, open Terminal (located in /Applications/Utilities) and execute diskutil list. The resulting output will provide this answer. Posting the full output here would be much appreciated.

Note: Do NOT follow the instructions included in my previous post. In your case, it would irreversibly destroy all of the data on your startup disk since you don't have an external drive available.

macOS Sierra: Exclude items from a Time Machine backup

if you choose to exclude system Folder, it will ask if you want to include all System Items.

You are backing up the combination of Your files and Mojave system. Since Mojave is the system you want to walk away from, there is no need to put a copy of it on your backup. The backup will be used after you install High Sierra form other sources.

Hi Sweenex,

Even though your photo shows that migrating from the Time Machine backup failed, not everything is lost. On the contrary, it just means that you can't use Migration Assistant to do the job the easy way. To successfully copy over your user accounts and third-party applications:

1. If you haven't done so already, complete Setup Assistant (choose not to transfer any data) and create a temporary administrator account. I'd recommend giving it a generic or random name in order to avoid conflicts with your previous user account; however, if you already created the account then don't try to rename it.
2. Open two Finder windows. In the first window, navigate to your backup partition and open the folder named "Backups.backupdb". Inside that folder, open the folder that is named after your Mac.
3. Open the folder titled as the date of the backup that you wish to restore, then open the folder named after your startup disk (usually named Macintosh HD). You should now see four folders: Applications, Users, Library and System.
4. In the second Finder window, press Command-Shift-G to open the Go To box. Type in a forward slash, then hit Enter (Return). This will show you the contents of your startup disk.
5. In both windows, open the Users folder. Copy over any user account folders present in the first Finder window into the second Finder window. Take note of the exact name(s) and capitalization of the home folder(s); you will need this later in order to resurrect the user account(s).

   If two or more user accounts share the exact home folder name (including capitalization), stop here and do not copy over the accounts.
   

6. Once all of the user accounts are copied over, click the Back arrow on both Finder windows. Then, open the Applications folder on both windows.
7. Copy over any applications from the first Finder window that don't already exist in the Finder window. However, do not copy over an application if the prohibitory symbol (circle with slash) appears over it.
8. Open System Preferences and go to Users and Groups. To resurrect the user account(s) that were copied over, you'll need to add each account one at a time. For each user account you add, the Account Name must exactly match the name of the corresponding home (user account) folder, including capitalization. If you did this correctly, you will be prompted that the user you're trying to create already exists. Click on "Use Existing Folder" to resurrect the user account.

You don't need to copy over the user named Shared. By copy over, I'm referring to either drag and drop from the first window to the second window, or right-click on the folder you want to copy (and click Copy) in the first window, then right-clicking the second window and selecting Paste.

The first window should contain your backed up user account(s). The second window should contain all of the users currently existing on your Mac, including the temporary administrator account you made.

To wipe out the backup partition:

1. Verify that you've copied over all of your accounts (except Shared) and all applications that you wish to keep. This erasure is irreversible.

   As an extra precaution, do this procedure while normally booted into your Mac. Do NOT boot into Recovery Mode; doing so will add the risk of accidentally erasing your startup disk.

2. Open Disk Utility, which is located in /Applications/Utilities.
3. Select your startup disk and click the Partition button. If prompted to add an APFS volume instead, click on Partition.
4. Select your backup partition, then click the minus sign. Then, click Apply.
5. Your startup disk should now be resized back to the full 256 GB.

Yes, normally booted would refer to just simply turning on or restarting your Mac normally (not booting a secondary device or partition, such as Recovery Mode).

To delete the temporary administrator account (once you've resurrected your own account):

1. Ensure that at least one of the accounts you resurrected is set as an administrator account.
2. Log out of the temporary administrator account.
3. Log into your account that you resurrected. Then, open System Preferences, and select Users and Groups.
4. Click on the padlock icon, and authenticate with your own password (given that your account is an administrator).
5. Select the temporary account, and click on the minus button.

   Note: if you choose to delete the home folder for the temporary account, it will be impossible to resurrect the account afterwards.