Installing new versions of macOS on a Mac should be a pretty simple exercise. The Mac tells you there's an update available via a pop up in Notification Centre - in some cases (depending on your settings) it's even downloaded it already and just needs your go-ahead to install. However, sometimes when you click Go on an update things go a bit pear-shaped. In this tutorial we'll look at what to do if your Mac stalls or freezes during an operating system software update.

If you've seen the warning: "The macOS installation couldn’t be completed " we're here to help.

We'll also explain what to do if you see the message: "macOS could not be installed on your computer" below.

There are a few reasons why the macOS installation process might be interrupted. Perhaps there's been a power cut; maybe there isn't adequate space available on your Mac (we always recommend that you don't install with less than 10GB of space free or your Mac may struggle with the installation); maybe there are other problems with your Mac - it's worth running Disk Utility (you'll find it in Applications > Utilities) prior to updating just in case.

It's always wise to run through a standard series of checks before you perform an operating system update on a Mac. (We cover preparation steps in the first section of our guide showing How to update macOS on a Mac.) But in this article, we cover possible solutions to try if your Mac freezes up in the middle of an update.

macOS installationcouldnt be completed

Can't download the macOS update

If you haven't even got past the download stage there are a few things to try.

1. Check Apple's servers

When Apple releases a new macOS update a lot of people will rush to grab it, which can cause problems with Apple's servers. So your first port of call could be to check the System Status page and check macOS Software Update to see if there are any known issues.

How to fix a Mac that won't finish a macOS update: System Status

2. Switch to a wired connection

You might find that things are quicker if you move from a WiFi to a wired connection. If you have a Ethernet cable and the necessary adaptor if your Mac only has a USB-C port, plug yourself directly into the hub.

Read more: How to fix WiFi problems on Mac

3. Cancel the download, stop a Mac update

You might be able to cancel the download, but the method will depend on what version of macOS you have installed.

In Mojave Apple changed the route users take to download a macOS Software Updates. They are now accessed via System Preferences > Software Update, where previously they were downloaded via the Mac App Store.

If you want to stop the download, you can click on the x that appears beside the bar that shows the download progress, as shown in the screenshot below.

Cancel macOS download

Pre-Mojave, you may be able to fix a stuck update by going to the Mac App Store, finding the software you are downloading, and pressing Option/Alt. When you do so you should see the option to Cancel the download.

Having cancelled the download you should be able to start it again, hopefully without any problems this time.

4. Download the software from Apple's support website

If you're having problems downloading the update via the Mac App Store, you can use Apple's website instead. For example, you can find the latest macOS updates here. To find any software update on the site, just search for it.

How to tell if a macOS update has stalled

Generally, if there's a problem with your software installation it will get stuck on the updating screen, showing an Apple logo with a status bar showing the progress as the software is loading. There may be what people refer to as a 'spinning beach ball'.

How to fix a Mac that won't finish a macOS update: Beach ball

Alternatively, you may see a white, grey or black screen. On many Macs the screen may be so dark that you might not even be able to tell if the Mac is turned on.

However, you want to be absolutely sure that the installation isn't still running in the background because forcibly rebooting the Mac during an installation will interrupt the installation process and potentially cause you to lose data. It's one reason why it's recommended that you back up your Mac before you install new software.

Alternatively, you might find that your Mac gets stuck in the installer with a message that "macOS could not be installed on your computer". When we clicked Restart the same thing happened, in the end, the only way we were able to fix it was by starting in Safe Mode and downloading the installer again. Find out exactly what we did below.

If your Mac appears to have frozen during the install, it's worth listening to your Mac for signs of life - you may be able to hear whiring - and following the below advice.

1. Find out if your Mac has really frozen

Before you conclude that your Mac has frozen during the installation, you need to be aware of the following.

Sometimes updating the software on a Mac can take a Very. Long. Time. You may be confronted by what looks like a frozen update, but if you leave it for a few hours it could finally get to the end of its task. Sometimes it's worth leaving the Mac overnight to finish the job it's started. Sometimes updates can take 16 hours or more - especially on the days when Apple releases a new version of its Mac operating system.

Remember, the progress bar you see during installation is just a best guess at how long it will take. In our experience one minute it tells us there will be a two-hour wait, then 45 minutes, then an hour, before jumping down to 20 minutes. Sometimes things get slowed down because the Mac is taking a while to install one file behind the scenes and that's thrown the whole update time prediction out the window.

The Mac might have been stuck on 20 minutes remaining for the past two hours, but this doesn't necessarily mean it's not busy trying to install the software.

2. Look at the Log to see if your Mac is still installing macOS

Press Command + L. This brings up additional information and more details about the amount of time still remaining for the install. It may give you a better indication of what files are being installed and the amount of time left.

3. Wait

If it turns out that the installation hasn't stalled be patient and wait for a few more hours.

One key thing to remember: Apple indicates how much time is apparently left for an installation... Don't pay this any attention because it is NEVER RIGHT!

What to do if your Mac freezes during software installation

If you're positive that the Mac isn't still working on updating your software then run through the following steps:

1. Shut down, wait a few seconds, then restart your Mac

Press and hold the power button to shut down and start your Mac back up.

2. Go to System Preferences > Software Update

Or, if you are on an older macOS verison, go to the Mac App Store and open Updates.

You should find that the update/installation process carries on from where it left off.

3. Check the Log screen to see if files are being installed

When the progress bar appears, press Command + L again to check the Log screen and ensure files are being installed. If the Log screen shows that nothing is happening move on to the next step.

4. Try installing the Combo update

As we mentioned earlier, Apple hosts software on its website, so you can download it from there if you are having problems with the usual method.

There's good reason to get your software from Apple's website if you're encountering problems: the version of the software available from Software Update or the Mac App Store will only include the files necessary to update your Mac.

If you go to Apple's support website you can find a Combo updater which includes all the files required to update the macOS. This version of the update will replace all the system files and thereby ensure the update is complete.

How to fix a Mac that won't finish a macOS update: Downloads

5. Install in Safe Mode

Press the power button and hold down the Shift key to start the Mac up in Safe Mode. Open App Store and update your apps while in Safe mode. Reboot.

Here's how to use Safe Mode on a Mac.

6. Make some room

If the reason the update was failing was that there wasn't enough storage available to perform the installation then you might be able to delete some files if you enter your Mac via Safe Mode.

We have a tutorial on using Safe Mode here. To access Safe Mode press and hold the Shift key when you start up your Mac. Wait while the Apple logo appears, and then, when the login window appears release the Shift key.

Once you are in, delete anything you can spare and make more space for the update.

7. Reset the NVRAM

If Safe Mode doesn't work, restart the Mac and hold down Command, Option/Alt, P and R. This will reset the NVRAM. Wait until the computer restarts and wait to see if it starts updating.

For more information read How to reset the PRAM/NVRAM here.

8. Use Recovery Mode to reinstall macOS

As a final option you could restart the Mac in Recovery Mode (hold down Command + R at startup). There are a number of options to choose from here - you could recover your Mac from your last Time Machine backup, or perform a disk repair - but we recommend choosing the 'Install new OS' option. We have a separate tutorial on how to reinstall MacOS using Recovery Mode.

When it reinstalls macOS your Mac will replace all the Apple system files overwriting any problematic ones that may be contributing to this error - hopefully. This update won't include the latest version of the software so after performing the update, check Software Update and apply the latest macOS update.

9. Install the OS from an external drive

If you're still having issues with the install you could try installing the OS from an external drive. Read this tutorial to find out how to create a bootable installer and install macOS from an external drive.

10. Run Disk Utility once you've updated

When you finally get the software up and running we advise that you run Disk Utility to correct any issues that might have caused the problem in the first place.

What to do if macOS could not be installed on your computer

When we started up our Mac and saw the message macOS could not be installed on your computer we were initially a little confused - as far as we were concerned we hadn't been trying to install macOS. But, regardless, we were stuck in a loop. When we clicked Restart our Mac restarted, but was still stuck in the installer.

macos couldnt be installed

We tried to quit the installer - we clicked on the Installer window and then from the menu above choose Quit MacOS Installer (alternatively Command + Q). Unfortunately for us when we booted up our Mac again we had the same problem with it opening the installer.

We then ran through the following options and had more success:

  1. Start in Safe Mode: We held down the shift key while we started up our Mac. This way we were able to boot up in Safe Mode. In Safe Mode you will find the Mac is a bit glitchy but you should be able to do what you need to do to fix the problem.
  2. Once in Safe Mode we opened the Mac App Store and searched for Mojave. In later versions of macOS you should be able to find the update in System Preferences Software Update.
  3. We clicked download and waited while the Mojave installer downloaded in the background.
  4. Once the installer was downloaded and we were ready to install we continued with the installation.

It's also possible that macOS is not able to be installed on your Mac because your Mac is too old: you can see which Macs can run Mojave here. The Macs that can run Catalina are listed here.

Read next: How to fix a frozen Mac. We also have a complete guide to fixing some of the most common Mac issues.