Installing new versions of the macOS software on a Mac should be a pretty simple exercise. The Mac tells you that there is 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 little 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 has 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), or maybe there are some other problems with your Mac (its worth running Disk Utility prior to updating just in case).

It’s always wise to run through these checks before you perform an operating system update on a Mac: How to prepare your Mac for a macOS installation.

Having trouble downloading 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

Its worth bearing in mind that when Apple releases a new update to the macOS a lot of people will rush to update, which can cause problems with Apple’s servers, so your first port of call could be to check the System Status page here and look for macOS Software Update to see if there are any known issues.

2. Move to a wired connection

You might find that things are quicker if you move from a WIFi to a wired connection.

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.

4. Download the software from Apple’s support website

If you are having problems with the download via the Mac App Store you can access the download via Apple’s website, as opposed to the Mac App Store. For example, you can find the latest macOS Sierra 10.12.4 update here, but to find any software update just search for it.

How do you know if a MacOS installation has stalled?

Generally if there is 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 beachball’.

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 its recommended that you back up your Mac before you instal 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 over night to finish the job its started. Some times updates can take 16 or more hours.

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 2 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 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.

What to do if your Mac freezes during software installation

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

1. Shut down, wait a few seconds, and 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 are encountering problems: the version of the software available from the Mac App Store will only includes 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.

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.

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 restart 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 the 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 tutorial on how to reinstall the MacOS using Recovery Mode here.

When it reinstalls the 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 are still having issues with the install you could try installing the OS from an external car drive. Read this tutorial to find out how to install macOS Sierra on an external hard drive.

10. Run Disk Utility once you have 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.