Even if you diligently followed all the instructions in this book, you might encounter problems while upgrading. I can’t anticipate every difficulty you may have (or provide solutions in every case), but here are some of the most likely issues and how to deal with them.
If the Catalina installer icon has a slash through it, or if you try to run it and it quits immediately, the likely causes are:
You’re trying to run it on a Mac whose CPU is incompatible with Catalina (see Model Support for full details). Solution: Buy a new Mac. (Sorry.)
The installer didn’t fully download, or the file was damaged. Solution: First delete the installer. Then open the App Store app, click Purchased, and download Catalina again.
If you see the error message “Installation cannot proceed with Boot Camp configured,” flip back to the sidebar The 3 TB iMac Boot Camp Problem for details.
If you run the Catalina installer, click Show All Disks when asked to choose a destination, and find that the volume on which you want to install Catalina isn’t available, chances are excellent that if you click the volume in question, the installer will tell you why it can’t be used—for example, not enough disk space, wrong partition map scheme, or wrong format—and explain how to fix that problem.
You may also see a message about an “unsupported partition structure,” which means the installer thinks the disk containing the volume where you want to put Catalina isn’t partitioned in one of the officially sanctioned ways. Repartitioning your disk as described in Prepare Your External Drive is the only reliable solution.
Come to mention it, repartitioning is, in fact, the best (if brute-force) way to eliminate almost every possible cause of an unselectable volume. If all else fails, try that.
I’ve heard reports of a situation in which the installer runs, without any error messages or other indications of problems, but when the Mac restarts afterward, it’s still on the old system—the installation didn’t actually take place.
Since I haven’t encountered this personally, I can only speculate about a cause based on what I’ve read, but the leading possibilities appear to be odd disk errors or, perhaps, running the installer from an external drive, rather than from the drive you’re booted from. So, if this happens to you, here’s what I suggest:
Make sure the Catalina installer you’re running is located on the volume you’re currently booted from. If it isn’t, put it there and try again. If it is and you’re still having problems…
Restart your Mac while holding ⌘-Option-R (not just ⌘-R) and—after a considerable delay—select Reinstall macOS (or OS X or Mac OS X, as the case may be); this requires internet access. Then:
If your Mac was previously running macOS 10.12.3 Sierra or earlier, doing this reinstalls the operating system that came with your Mac, or if that’s not available, the nearest one that is. So, after you’ve done this, restart your Mac and repeat the process of upgrading to Catalina.
If your Mac was already running 10.12.4 Sierra or later, doing this installs the latest version of macOS compatible with your Mac—which should be Catalina!
Following installation—either on the first restart or a subsequent restart—if your machine will not start up under Catalina at all, if it gets stuck on a gray or black screen for more than about 15 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. (In fact, wait a little longer than seems necessary—again, 15 minutes is not unreasonable—especially if you’re booting from a mechanical hard drive.)
Disconnect non-essential USB devices: USB devices have been known to interfere with the Mac startup sequence, so if your Mac gets stuck on a gray screen and won’t finish booting, try this:
As in step 1, 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 15 minutes or so—or if it starts but then you experience a kernel panic—move on to the next step.
Try a safe boot: Restart your Mac. As soon as the screen goes black and your Mac begins to restart, press and hold the Shift key until the login window appears. (If the Mac is frozen or you see a kernel panic message, press and hold the power button for about 10 seconds until the Mac shuts down. Then press the power button to turn it back on and immediately hold down the Shift key until the login window appears.) The Mac will complete the startup process, which may take considerably longer than usual. You’ll eventually see the words “Safe Boot” on the screen—likely in red at the top of the login screen.
If Catalina starts up normally after a safe boot, a third-party 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). This may include drivers for audio interfaces and input devices, security software, and certain system enhancements.
If you find any that you explicitly recognize and suspect as a culprit, 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. (Don’t drag these items to the Trash manually unless you can find no other way to remove them.)
Restart and see if 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.
If the problem does not go away after a safe boot, go to…
Try macOS Recovery: Assuming the Catalina installer succeeded in installing the Recovery HD volume (or that your Mac already had one from a previous installation of macOS), you can boot into macOS Recovery by choosing Apple > Restart, clicking Restart, and immediately holding down ⌘-R until the Apple logo appears. A few moments later, you’ll see a macOS Utilities window; that means you’re using macOS Recovery.
Once in macOS Recovery, select Disk Utility and click Continue. When it opens, select the problematic Catalina volume in the sidebar, click First Aid, and follow the prompts to repair any problems that may have appeared on your Catalina volume. Choose Disk Utility > Quit Disk Utility to return to the macOS Utilities window. Then choose Apple > Restart.
Try another startup volume: If you need to run Disk Utility but macOS Recovery isn’t available, try:
A bootable duplicate: The easiest option is to restart from your bootable duplicate (attach the drive, hold down the Option key when restarting, select the duplicate, and press Return), and then run Disk Utility.
Target Disk Mode: Connect your Mac and another Mac you have access to (that can definitely start up correctly) with a Thunderbolt, USB, or FireWire cable. Restart the good Mac, holding down the T key to turn it into a fancy external drive. Then restart the misbehaving Mac, holding down the Option key, and select the good Mac’s startup disk. Once you’ve booted, run Disk Utility from the good Mac to try to fix the boot disk of the misbehaving Mac.
Remove any nonessential hardware: Try restarting with only your Apple-supplied keyboard, mouse, and display attached, and without any third-party PCI or video cards. You may even need to remove extra RAM. If this works, check for driver updates, and then reattach the devices one at a time, restarting after each one.
Reinstall Catalina: If you still can’t start your Mac, consider reinstalling Catalina. Perform a clean install (described in Upgrade Using Plan B: 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 Catalina installation.
Your Mac is likely to be slow for a bit after its first boot into Catalina, but if it’s unusable—as in, you get the Spinning Pinwheel of Doom for 15 minutes and you can’t open any apps—try restarting. (And if you can’t use the Apple > Restart menu command, hold down the power button until your Mac turns off completely, and then press it again to turn it back on.) That has set things right for me on occasion. If that extra restart doesn’t help, however, you could be looking at a software conflict.
Even if you diligently updated all your software before installing Catalina, a third-party app that wasn’t disabled by Setup Assistant could be having problems. One symptom to look for is the Finder repeatedly crashing—that is, your Finder windows and desktop icons keep appearing and disappearing. Another is a Finder hang—even after several minutes, the Finder doesn’t respond to commands such as Finder > Empty Trash or File > New Finder Window.
If you suspect that the Finder is crashing or hanging, open Console (in /Applications/Utilities), and watch the error messages as they flit by. If you see an app or filename repeatedly, that could be the source of the misbehavior. Try disabling it (if you know what and where it is), or follow the instructions in Mac Won’t Start Up Under Catalina….