When trying to update macOS, some users ended up encountering the error: the macOS installation couldn't be completed. For example:
"I'm installing the 10.13.6 supplemental update on my 2018 MacBook Pro. It seemed to go through fine, but after restarting it was still offering me the update in the App Store... I clicked it again, but this time said 'The macOS installation couldn't be completed'."
Why does your Mac say "macOS installation couldn't be completed"? And how to stop the error and complete the macOS installation.
When your Mac says "the macOS installation couldn't be completed", it could mean:
The installer is corrupted: The macOS installer is corrupted and that's why the macOS installation couldn't be completed.
The installation is interrupted by files from another mounted drive: Sometimes another mounted drive interrupts the procedure of installation of macOS.
There are problems with the disk that you are trying to install macOS to: It could also be the problem with your system disk.
There is not enough space on the disk for the installation: This is one of the most common causes where the disk that is used for installation has little space left. macOS installation requires at least 8GB free disk space.
Before applying any method on the macOS installation problem, you must back up your data to avoid any misadventure. You can back up the data to an external hard drive first since your files may be erased if an update goes wrong.
If the Mac can be restarted normally, you can just copy your significant files to a USB drive;
If the Mac is stuck at the macOS installation error, you can use the steps below, to create a bootable USB drive with Recoverit Data Recovery and then rescue your files from the frozen installation.
First of all, you need to get another MacBook and install Recoverit on the workable MacBook.
Once the software has completely launched, click Recover from Crashed Computer. you need to plug in a USB drive to your new MacBook to create a bootable USB drive.
Once you have selected USB drive as "Bootable media drive", Recoverit will format the drive to ensure free space and create a bootable media. Wait patiently for Recoverit to complete the creation.
Now, you need to connect the bootable USB with your frozen Mac at macOS installation error and boot it from Recoverit USB drive.
After that, connect a healthy hard drive with the troubling Mac and copy the files from the frozen Mac to the healthy hard drive and click "Start Copy". The software will take a few minutes to fetch data from your frozen Mac and save it to the selected hard drive. When the procedure is completed, you will see "Copy files completed!" on your screen.
After you have saved all you needed files, you can go ahead to fic the macOS installation that couldn't be completed with the following methods.
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Most of the time, the issue is solvable only by restarting your Mac. You can go to the Apple menu at the top-right of your screen, and you can select restart. You can also press and hold the power button to shut down Mac and then turn it back on.
Suppose the installer on your Mac is corrupt. You can utilize the combo Installer to avoid the macOS installation error. You can go to Apple's support website and download Combo Installer. Download this installer and complete the installation of your macOS. The combo installer can complete the installation more smoothly.
You can also boot your Mac in Safe mode to tackle the errors.
Many people fixed the macOS installation couldn't be completed error with the First Aid utility of macOS.
This will scan your startup for any error and repair the errors. If everything is fine with your disk, it will surely inform you. This is helpful if the macOS installation error happens because there is something wrong with the startup disk.
You can also remove unneeded login items to ensure the macOS installation won't be interrupted by the login items.
You will see all the login items that are activated. Remove unrequired login items from your macOS to avoid any further errors.
PRAM attains multiple settings and preferences on your Mac, such as screen brightness, sound volume, and display resolutions. Any problem with PRAM can also lead you to these errors of macOS installation couldn't be completed.
You can reset PRAM by restarting your Mac and pressing Option + Cmd + P + R. Hold these buttons till you see the Apple logo.
If all the solutions are useless, you can reinstall macOS by restarting Mac and holding Option + Cmd + R keys. Wait until you hear startup sound and Apple logo. In macOS Utility windows, click Reinstall Mac option. This will install the latest version of macOS.
There is nothing to worry about if your macOS installation isn't completed. The above methods are efficient enough to solve your problem.