Mac hangs in an update loop and keeps rebooting

If the Mac hangs in the boot loop ...

Most Mac problems can be solved easily, even by macOS newbies, with the right guidance. Things get a little more complex when the Mac doesn't start properly - or when it starts over and over again.

This was the last time it happened with a macOS security update that had a built-in bug. The result was that the update started but didn't go through. Instead, the Mac restarted itself during the update.

Then came the update screen again, which did not go through because the Mac had restarted itself beforehand, etc ... Even manually switching the device off and on did not help here, as the Mac kept updating itself every time it was restarted.

If the Mac keeps booting after an update, I'll show you the way out of the boot loop here.
If the Mac keeps booting after an update, I'll show you the way out of the boot loop here.

The way out of the loop: the ALT key

The first step to rescue is to hold down the ALT key while restarting your Mac. As a result, the Mac does not reboot automatically with the faulty update volume, but allows the startup volume to be selected manually.

In the list of displayed volumes you should now avoid the “InstallMacOS” partition and instead boot with the “Macintosh HD”. The name depends on what you called your startup disk, but usually it should be “Macintosh HD”.

Instructions in short form

In order not to lose the thread in long descriptions, I will briefly write down the procedure for you in bullet points. It may be that this looks different under newer macOS systems, but basically little should change in the procedure itself.

  1. Restart your Mac
  2. Hold down the ALT key
  3. in the startup manager select “Macintosh HD” (not the “InstallMacOS” partition!)
  4. once the Mac is up, go to the Finder via the menu “Go to” and select “Computer”
  5. you still switch to the start volume hard drive (presumably "Macintosh HD")
  6. In the main directory of the hard drive there is (hopefully) a folder “macOS Install Data” - if it is there: good, if not, this is the end of the instructions, because then I don't know how to go
  7. Restart the Mac and press the key combination CMD + R for the Recovery mode keep pressed down
  8. When the start-up process is finished, select the item "Terminal" from the menu above in the "Utilities" area
  9. Now enter the following command: csrutil disable (this switches off the System Integrity Protection on the Mac)
  10. in the next line you enter the command “reboot” to restart the Mac
  11. Once the Mac has started, you go back to the computer via "Go" and into the "Macintosh HD" hard drive
  12. the “macOS Install Data” folder can now be deleted
  13. you should also enable System Integrity Protection via the Port re-enable with the following command: csrutil enable

Install update via Internet recovery mode

From now on, the Mac should boot cleanly again. If you still want to install the update, but do not want to use the defective update, you can start the Mac in Internet recovery mode.

To do this, restart the Mac and then hold down the CMD + ALT + R keys until the globe appears. Now follow the installation and iron the latest macOS version, which is available for the respective Mac, over the existing system.

As always with such operations, I would recommend making a backup beforehand. Usually nothing changes to the existing user data when installing macOS.

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