How to Fix a Damaged macOS Installer

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Creating a macOS installer on a bootable USB drive provides a convenient way of installing a fresh copy of macOS on multiple Macs, and also allows you to perform a clean installation quickly and easily.

Catalina
If you tried to run your installer recently and unexpectedly received an error that it is damaged and can't be used, then don't worry – keep reading for a simple and straightforward way to fix it.

Why is my macOS Installer Damaged?

If you tried to use a macOS installer in the last few days or weeks, you may have been met with an error message saying something like "This copy of the Install macOS Mojave.app application is damaged, and can’t be used to install macOS."

installer
As Apple explains in a newly published support document, the likely reason for the "damaged" error message is an expired certificate. Happily though, the fix is very simple.

How to Fix a Damaged macOS Installer

To fix the damaged installer, you should just download the installer again. Doing so will also ensure that you have all of the macOS updates that have been released since you made the original installer, meaning you won't have to update macOS immediately after the initial installation is complete.

You can find the latest official download links below for the last six versions of Apple's Mac operating system, all of which contain a new certificate that has not expired:

To learn how to perform a clean installation of macOS using the bootable USB drive method, click one of the following links: macOS Catalina, macOS Mojave, macOS Sierra.

Related Roundup: macOS Catalina

Top Rated Comments

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Avatar
9 months ago


That message does not mean you can't download it.
It only means that the installer won't run on that system version.
You will see that message after the download is complete (because the system automatically tries to launch the installer)
And, you have the downloaded installer, in your Applications folder. I would save the installer app to an external drive, and use one of the methods to create a fresh bootable installer from that app.
Finally, delete the downloaded installer from your boot drive.

Actually, I get that message BEFORE it tries to download it. I'm well aware that you can still download the file and create USB Installers and whatnot.. Gotta have the file downloaded first, though. And I'm not able to get that far.
Score: 4 Votes (Like | Disagree)
Avatar
9 months ago


Right this had baffled me and a colleague for a few days. The issue im having, now I understand the cause of the error, is that the links send you to the App Store and it just announces that it cant connect to the store. It will if I go to an app thats there. Any clues folks

The only way I was able to get the App Store installers was by going through a Virtual Machine of 10.14 and downloading them from there, and then copying them over.
Score: 2 Votes (Like | Disagree)
Avatar
8 months ago


I am sure that I already had been looking and can't seem to find and it's puzzles me..

It could be on any drive attached to your computer.
Score: 2 Votes (Like | Disagree)
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13 weeks ago


You are partly correct. This is related to the downloads that Apple offers for El Capitan, and Sierra. There's another step that you can use.
Both of those download as .dmg files, which you would open to mount the images. Both of those images have .pkg files, which is what you noticed. When you open those with the Installer app, you will find that those will simply install the actual macOS installer app - which is used with your normal tools, DiskMakerX, or (my current fav) Install Disk Creator. So, that .pkg file is just used to "assemble" the actual install app, which you would use as normal.
But, I just save the resulting installer app, for later use.


If I remember correctly, installing the .pkg will put the actual installer in your Applications folder. From there you can use the Terminal to make a bootable USB or an app like Install Disk Creator.

https://macdaddy.io/install-disk-creator/

Thank you, DeltaMac and gank41, for both your assistance and your recommendation of Disk Creator! Everything worked great and I now have working bootable USB drive for all my formerly-created ones as well as a new one for Catalina. Disk Creator is a keeper!

Now I only hope the new installers don't have certificates that will expire down the road.
Score: 1 Votes (Like | Disagree)
Avatar
9 months ago


Too Bad we can't download older versions of macOS on the App Store now.

That message does not mean you can't download it.
It only means that the installer won't run on that system version.
You will see that message after the download is complete (because the system automatically tries to launch the installer)
And, you have the downloaded installer, in your Applications folder. I would save the installer app to an external drive, and use one of the methods to create a fresh bootable installer from that app.
Finally, delete the downloaded installer from your boot drive.
Score: 1 Votes (Like | Disagree)
Avatar
8 months ago
Phew.. ! I thought i was going nuts.... I was blaming VMWare fusion for this exact error, which forced me to download a fresh copy every few weeks... of Mojave mostly.

I was wondering why an installer, which worked after downloading, "didn't" work when i came to install again a few "days" later, or so when its just sitting on an external USB drive doing nothing..

Expired certificate in installer huh ? Well, lets hope it's fixed..

Now i'm know i know i'm not crazy, i can sleep better.. :)


Too Bad we can't download older versions of macOS on the App Store now.

Not related, but i got round this by installing Yosemite in VM, then using that to login to App store and download all past OS's :)

Apple's not gonna stop me...
Score: 1 Votes (Like | Disagree)

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