The macOS Installation Couldn’t Be Completed Error Fix

This short article explains what you can do when you encounter the “The macOS installation couldn’t be completed” error message.

The error message says:

“If you continue having a problem installing macOS, the installation log may help you diagnose the problem. To save the log, click Save log. To start installing macOS again, click Restart. To start up your computer using a different disk, choose Startup Disk from the Utilities menu.” See the image below:

macOS installation could not be completed

The error message has four options: Shut Down, Restart, Save Log and View Log. It is highly likely that restarting your computer will produce the same error message.

Updating your Mac is usually very simple process. However, in some cases, you may encounter errors like this one. Please note that it has been reported that this issue may occur even when no upgrade or update is initiated. Your Mac stuck in the middle of a macOS update and your Mac will not start up? Here is how you can fix it:

Note that before trying anything, you may want to backup your device. 


The first thing you should try is to start your Mac in safe mode. You can do so easily: Simply restart your computer and as soon as your computer begins restarting, press and hold the Shift key, until you see the Apple logo. This will put your computer in safe more. Try to update or upgrade your Mac now.  If this does not work, read on.

The next thing you should try is to start up your Mac using Startup Manager. Here is how:

  1. Turn off your Mac
  2. Turn on your Mac
  3. Immediately after turning on your Mac, press and hold the Option (alt) key
  4. You will see the Startup Manager popup, now you can release the Option key
  5. Select your regular/standard (usually Macintosh HD) disk and click the arrow icon under it and hit Enter.

If you are still having this issue, try repairing your disk. Here is how:

  1. Restart your Mac, and while your computer restarting, immediately press and hold the Command and R keys until you see the Apple logo, then you can release the keys.
  2. macOS Utilities will launch
  3. Select Disk Utility and click Continue
  4. Run First Aid.
  5. If First Aid says the Disk is OK, then, on your computer, go to System Preferences> Users & Groups> and click the Login Items tab, if you see any third party apps there, click the minus icon and remove them. And try again.

If nothing above helps, follow the steps below:

  1. Depending on the macOS version you are trying to install, try using the macOS combo update. These update files are available on Apple websites. They are big files so it will take times to download and install.
  2. Locate the macOS combo update (you can find the downloads here)
    and Click Download
  3. Once the download is completed, double click to run and to see if this completes the installation.

If you are still having problems try this.

  1. Power off your Mac.
  2. Power on your Mac and immediately press and hold Command (⌘)-R (see also: How To Back Up Your Mac That Won’t Boot)
  3. Release the keys when you see the Apple logo or a spinning globe icon
  4. You will see the macOS utilities window
  5. Select “Reinstall macOS“. This will install the latest macOS that was installed on your Mac. And click Continue and follow the onscreen instructions.  See also: Reinstall Mac OSmacOS reinstall


Dr. Serhat Kurt worked as a Senior Technology Director. He holds a doctoral degree (or doctorate) from the University of Illinois at Urbana / Champaign and a master’s degree from Purdue University. Here is his LinkedIn profile.

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36 thoughts on “The macOS Installation Couldn’t Be Completed Error Fix”

  1. Hi. I am trying to reinstall OS X Yosemite in an old MacBook that I just erased the HD so I could give the MacBook to a kid in my neighborhood.
    I fallow all the instructions above, all of them, and I still get : “an error occurred while preparing the installation try running this application again”
    And that is it!
    Wondering if you can give any other advice?!

  2. Thank you soooo much Luis, I don’t have any idea how to fix it and just reading your simple solution and it work’s.. God bless you.thanks👏🏻👏🏻👏🏻👏🏻

  3. This is still happening in Catalina? Does anyone know what is causing this? After having this issue in the MacOs 10.15.2 update, I repartitioned and erased the hard drive and started over. 10.15.3 updated OK. 10.15.4 caused this same problem. Had to boot with cmd R and reinstall MacOs. Now, it works, but it shouldn’t be this hard with a Mac.

  4. Thank you so much, this helped bring an old Mac of ours back to life so that I could play Minecraft with my brother. (I know, I’m just kid)

  5. Safe mode startup succeeded but the next time the (normal) boot ended as before, with the infamous “couldn’t complete” message.
    I followed Luis’ hint then. Actually on my High Sierra macbook it was clicking “apple logo -> startup disk” and then just confirming already selected macos system disk (the only choice). Thanks, Luis.
    Just of curiosity, I wonder how one could follow the “combo update” advice on a computer that won’t boot?
    regards, Michal

  6. Thank you!! I freaked out when, after a usual update, l got error codes and l coukd not get my computer to start up. Your various suggestions got me back to my work, being able to answer clients based on the info in my office, aka macbook pro.

  7. Thank you so much! Restarting from the installation disk worked. I tried all the propositions above and started to be desperate.

    So relieved

  8. Thank you….thank you….thank you! I was so happy to find your list of possible solutions and I was even happier when the first one (safe mode) worked.

  9. Thank you! It returned to normal immediatley after the safe boot- I’m a graphic design student & had no idea if my art files were in jeopardy or not, haha thankfully they were sound 🙂

  10. just close the white window where you see all the written stuff and go up to the bar where the apple logo is. go to “installation” and from there go to either the first or second option (don’t remember which it was) to re-select your Macintosh drive – click on the drive so it is highlighted and then click “restart” so your computer can restart with that drive. Should work then!

  11. So when none of that works it is time to test the partion of the volume being used as startup. This becomes critical if you are changing file systems as High Sierra introduced. Techtool Pro provides a partition test and repair function wbich will correct the error.


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