Even if you diligently followed every instruction, you might encounter problems while upgrading. I can’t anticipate every difficulty you may have (or provide solutions in every case), but here are two of the most likely issues and how to deal with them.
When the installation volume can’t be selected
If you run the macOS 27 Golden Gate installer, click Show All Disks when asked to choose a destination, and find that the volume on which you want to install macOS 27 isn’t available, chances are excellent that if you click the volume in question, the installer will usually tell you why it can’t be used and explain how to fix that problem.
When the Mac won’t start up
Following installation, if your machine will not start up under macOS 27 at all, if it gets stuck on a gray or black screen for more than about five minutes, or if you experience a kernel panic upon the first restart, try these steps in order until you are able to start up normally:
- Force a shutdown and restart: Press and hold the power button for about 10 seconds until your Mac shuts down. Then press it again and wait for it to restart. You should give it plenty of time, as it may be performing a lot of disk integrity operations quietly underneath that black screen—again, five minutes is not unreasonable.
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Disconnect non-essential USB devices: If your Mac gets stuck on a gray screen and won’t finish booting, try this:
- Press and hold the power button for about 10 seconds until your Mac shuts down.
- Disconnect all USB cables from your Mac except any that go to a keyboard, mouse, or other pointing device.
- Press the power button again and wait for your Mac to start. If it starts normally, you can then reconnect your USB devices. If it’s still stuck after five minutes or so—or if it starts but then you experience a kernel panic—move on to the next step.
- Try safe mode: Safe mode disables some third-party software and checks your disk for certain types of errors.
To enter safe mode, choose Apple menu > Shut Down and wait until the Mac has fully shut down. Then press and hold the power button until you see “Loading startup options” on the screen. When the Options icon appears, select your startup disk, hold down the Shift key, click Continue in Safe Mode, and then release the Shift key.
If macOS 27 starts up normally after a safe boot, a third-party extension or startup item may be the culprit. Check in /Library/LaunchAgents, /Library/LaunchDaemons, and ~/Library/LaunchAgents for third-party items that haven’t been updated recently (older items are more likely to have compatibility problems).
If you find any that you explicitly recognize and suspect, look for an uninstaller from the developer, and if there is one, use it. If not, consult the documentation that came with the software, or the developer’s website, for removal instructions.
Restart and see whether the problem is still gone. If so, reinstall the uninstalled items one at a time, restarting after each one, until you find the culprit or you’ve installed new copies of them all and your Mac is still working well.
- Try recovery mode: You can boot into recovery mode by shutting your Mac down and then pressing and holding the power button until you see “Loading startup options” on the screen; when the Options icon appears, click it and then click Continue. A few moments later, you’ll see a macOS Utilities window; that means you’re using recovery mode.
Once in recovery mode, select Disk Utility and click Continue. When it opens, select the problematic macOS 27 volume in the sidebar, click First Aid, and follow the prompts to repair any problems that may have appeared on your macOS 27 volume. Choose Disk Utility > Quit Disk Utility to return to the macOS Utilities window. Then choose Apple menu > Restart.
- Remove any nonessential hardware: Try restarting with only your Apple-supplied keyboard, mouse, and display attached, and (if you have a Mac Pro) without any third-party PCI or video cards. If this works, check for driver updates, and then reattach the devices one at a time, restarting after each one.
- Reinstall macOS 27: If you still can’t start your Mac, consider reinstalling macOS 27. Perform a clean install, omitting items in the Applications category when you work your way through the file transfer portion of the installation to eliminate any possibility of software conflicts. (You can add those items later using Migration Assistant.)
In most cases, these steps will lead to a happy macOS 27 installation.
