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 popup 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 a operating system software update.

There are a few reasons why the 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 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. Read next: How to fix a frozen Mac

We also have a complete guide to fixing some of the most common Mac issues.

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. Read more: How to fix WiFi problems on Mac

3. Cancel the download

You may be able to fixing 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 macOS Sierra 10.12.4 update here. To find any software update on the site, just search for it.

How to fix a Mac that won't finish a macOS update: Download from Apple support

How do you know if an 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.

You want to be 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.

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.

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 OS X

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.

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 the Mac App Store and open Updates

If you were installing an app from the App Store, then open the App Store and click 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, the Mac App Store isn't the only place your can download Mac software from. Apple still hosts software on its website, so you can download it from there.

There's good reason to get your software from Apple's website if you're encountering problems: the version of the software available from 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 instillation then you might be able to delete some files in Safe Mode.

7. Reset the NVRAM

If Safe Mode doesn't work, restart the Mac and hold down Command, Option, 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 start up). 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 install macOS Sierra on an external hard 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.