iMac will not boot after 10.15.5 update

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kevinfarrell Author

Level 1

8 points

iMac will not boot after 10.15.5 update

iMac (Retina 4k, 21.5", 2017)

3.6 GHz quad core i7, 16 GB ram

Radeon Pro 560, 4 GB

Mac OS Catalina 10.15.4

After an attempt to install 10.15.5, when attempting to start up on the internal drive, I see a zero with a slash thru it for about 10 seconds, then the Apple logo. The computer is stuck there and will not boot.

System Preferences still shows the 10.15.5 update pending, but attempts to install it do not work and the Mac will not boot.

Am using Carbon Copy Cloner to back up to an external drive which will boot if it is selected using the option key on startup. Attempts to restore the OS from the CCC backup do not work.

Is there a way to clear out the 10.15.5 update files, and go back to using 10.15.4 and simply waiting for the next major OS release? Not having use of my internal drive and relying on my external backup is disturbing.

Having that red flag on my system preferences that an update is pending makes me nervous as well.

Ideas?

iMac 21.5″ 4K, macOS 10.15

Posted on Aug 14, 2020 8:15 AM

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Answer 1

Best reply

BDAqua

Level 10

239,813 points

Aug 14, 2020 11:47 AM in response to kevinfarrell

Do you have a Time Machine backup to Restore to/from?

https://support.apple.com/guide/mac-help/revert-to-a-previous-macos-version-mh15216/mac

If not…

1. Start up from macOS Recovery

To start up from macOS Recovery, turn on your Mac and immediately press and hold one of the following combinations on your keyboard. Command-R is generally recommended, especially if you never installed macOS Sierra 10.12.4 or later… https://support.apple.com/en-us/HT204904#notupdated

Command (⌘)-R

Install the latest macOS that was installed on your Mac.

Option-⌘-R

Upgrade to the latest macOS compatible with your Mac.

Shift-Option-⌘-R

Install the macOS that came with your Mac, or the closest version still available.

2. Decide whether to erase (format) your disk

If you need to erase your disk before installing macOS, select Disk Utility from the Utilities window, then click Continue. You probably don't need to erase, unless you're selling or giving away your Mac or have an issue that requires you to erase. Learn more about when and how to erase.

3. Install macOS

After starting up from macOS Recovery, follow these steps to install macOS:

Choose Reinstall macOS (or Reinstall OS X) from the Utilities window.
Click Continue, then follow the onscreen instructions to choose your disk and begin installation.
If the installer asks to unlock your disk, enter the password you use to log in to your Mac. If it doesn't see your disk, or it says that it can't install on your computer or volume, you might need to erase your disk.

Please allow installation to complete without putting your Mac to sleep or closing its lid. During installation, your Mac might restart and show a progress bar several times, and the screen might be empty for minutes at a time.

If your Mac restarts to a setup assistant, but you're selling or giving it away, press Command-Q to quit the assistant without completing setup. Then click Shut Down. When the new owner starts up the Mac, they can use their own information to complete setup.

If you never installed macOS Sierra 10.12.4

If macOS Sierra 10.12.4 or later was never installed on your Mac, macOS Recovery works differently:

Command-R is still the recommended way to start up from macOS Recovery. This combination makes sure that the installation isn't associated with your Apple ID, which is important if you're selling or giving away your Mac.
Option-Command-R installs the macOS that came with your Mac, or the closest version still available.
Shift-Option-Command-R isn't available.

https://support.apple.com/en-us/HT204904

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Answer 2

Aug 14, 2020 11:53 AM in response to kevinfarrell

There have been issues like that on Catalina 10.15.5 and 10.15.6 where the Mac won’t charge/boot.

Please restore from a Time Machine backup; in macOS Recovery Mode, like BD said.

Shift-Option-⌘-R may be the smartest, then you can choose to reinstall whatever newer macOS you’d like.

I would say upgrade to Mojave 10.14 as it is more stable and includes x86 support..

This is IF YOU backup. You would just have to reinstall the OS if you don’t have a backup, also you’d be losing your data.

Good luck,

-Christian

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Answer 3

kevinfarrell Author

Level 1

8 points

Aug 19, 2020 7:50 AM in response to BDAqua

Sorry for the delay in replying. Life got in the way.

To recap, I am currently running Catalina 10.15.4

When I tried to install the 10.15.5 update, something happened that caused the internal boot drive to display a zero with a slash thru it for about 10 seconds. Then the Apple logo appears, but nothing else happens. It will sit like that forever and not boot.

I do have an external backup drive, but I don't use Time Machine. I use Carbon Copy Cloner which creates and replicates the entire internal drive to the external drive every night.

When the initial problem with the internal drive occurred, I was able to boot the Mac while holding the Option key down while pressing the power button. This allowed me to select the CCC external backup drive and boot from it.

Before attempting to start up from MacOS Recovery, I will use CCC to back up the files that have changed on my external drive to the internal.

I have already run disk utility on the internal drive (twice), and it showed no issues. I will be doing it again as well as running CleanMyMac X before attempting Shift-Option-Command-R to install the latest version of Catalina.

Does this sound like a good plan?

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Answer 4

kevinfarrell Author

Level 1

8 points

Aug 19, 2020 9:01 AM in response to kevinfarrell

Well, that didn't work.

While in recovery, Disk Utility would not check the internal drive and when I tried to re-install the OS, my only option was Sahara. Thinking I could upgrade back to Catalina later I selected that option and then recovery told me that the internal drive was locked.

So now I'm back and booted on my external backup drive.

Are Mac OD install DVD's still available? I do have a Superdrive connected.

Or... can I go to the store and install a clean copy of Catalina on the internal drive while booted on the external?

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