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Original poster
Apr 12, 2001
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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.

macos-catalina-upgrade-hero.jpg

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."

macos-damaged-installer-alert.jpg

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.

Article Link: How to Fix a Damaged macOS Installer
 
Last edited:

JosephAW

macrumors 68040
May 14, 2012
3,840
4,569
Why not just set your clock back on your computer to the year you installed it? Worked for older versions of iLife and Photoshop.
 
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Telos101

macrumors regular
Apr 29, 2016
219
886
Ireland
Why not just set your clock back on your computer to the year you installed it? Worked for older versions of iLife and Photoshop.

That doesn’t work all the time, at least not with the Install MacOS Mojave app. Plus it's not really practical to go around adjusting clocks if you're deploying installer apps on multiple Macs.
 
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gank41

macrumors 65816
Mar 25, 2008
1,230
766
Too Bad we can't download older versions of macOS on the App Store now.

¯\_(ツ)_/¯
 

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DeltaMac

macrumors G4
Jul 30, 2003
11,062
3,106
Delaware
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.
 
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gank41

macrumors 65816
Mar 25, 2008
1,230
766
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.
 
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makitango

macrumors regular
Apr 15, 2012
195
278
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.
I feel you. I wanted to download the files on a Catalina-run Mac but can‘t. Had to pull out an older device just to get by those slightly annoying middlefingers from the fruit stand.
 
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Xenomorph

macrumors 65816
Aug 6, 2008
1,332
637
St. Louis
I cannot download macOS Catalina right now.

macOS Catalina, 10.15:


"The requested version of macOS is not available."
 
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jdiamond

macrumors 6502a
Dec 17, 2008
657
510
So at what point can we assume Apple has updated the certificate on those installers and redownload?
 
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bsbeamer

macrumors 68040
Sep 19, 2012
3,983
2,080
So at what point can we assume Apple has updated the certificate on those installers and redownload?

Code:
#    ProductID    Version    Build   Post Date  Title
 1    061-36794      10.15   19A603  2019-10-21  macOS Catalina
 2    041-91758    10.13.6    17G66  2019-10-19  macOS High Sierra
 3    041-88800    10.14.4  18E2034  2019-10-23  macOS Mojave
 4    061-26589    10.14.6   18G103  2019-10-14  macOS Mojave
 5    041-90855    10.13.5   17F66a  2019-10-23  Install macOS High Sierra Beta
 6    061-26578    10.14.5  18F2059  2019-10-14  macOS Mojave
 
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gank41

macrumors 65816
Mar 25, 2008
1,230
766
I feel you. I wanted to download the files on a Catalina-run Mac but can‘t. Had to pull out an older device just to get by those slightly annoying middlefingers from the fruit stand.

I was able to boot into a 10.14 VM and download them all from there..
 
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justperry

macrumors G4
Aug 10, 2007
11,599
8,298
I'm a rolling stone.


How to Fix a Damaged macOS Installer

To fix the damaged installer, you should just download the installer again.

Right, if you happen to live in a country with high internet speeds, not so much in quite a few countries, such a stupid mistake of Apple to let certificates expire way too early.
An easier fix would be to download a new certificate after verifying the downloaded Updater and compere it to Apple's Updater.

As for the comment on a fresh install, why, macOS does not need to be reinstalled, only in very-VERY rare cases it needs a reinstall, I never had to reinstall in the almost 2 decades since OS X launched.
 
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benshive

macrumors demi-god
Feb 26, 2017
668
5,918
United States
Also worth noting that I was trying to install Catalina using a bootable USB drive on a couple of Macs that I had wiped and I got this message. Entered "date" in terminal and it was way off. Fixed the date and time and the installer worked fine.
 
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McLover66

macrumors newbie
Oct 25, 2019
13
7
This might be a stupid question, but I have noticed the installers are .dmg files and not .app files like when they come from the App Store. How do I make a bootable installer with terminal now? Could someone please explain this to me? That would help me out a great deal.
 
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termite

macrumors member
Oct 30, 2003
96
7
Pro tip: This also happens if you install on a Mac that has been on a shelf for awhile such that the realtime clock has forgotten the date. You have to shell out and set the time using the command line before installing.
 
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McLover66

macrumors newbie
Oct 25, 2019
13
7
I just downloaded High Sierra using the Macrumours link and it was an ".app"
Some of the older ones are .dmg :( I don't know how to make them bootable. I'm used to using terminal to make a bootable USB, now I don't know what command line to use.
 
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DeltaMac

macrumors G4
Jul 30, 2003
11,062
3,106
Delaware
The full system installers are apps. Some methods will result in downloading a .dmg.
Double-click to mount the .dmg, and find the app inside the disk image folder.
 
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McLover66

macrumors newbie
Oct 25, 2019
13
7
The full system installers are apps. Some methods will result in downloading a .dmg.
Double-click to mount the .dmg, and find the app inside the disk image folder.
Thanks for the reply, but how do I make those bootable? I can't paste the creat install media terminal command right?
 
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DeltaMac

macrumors G4
Jul 30, 2003
11,062
3,106
Delaware
Thanks for the reply, but how do I make those bootable? I can't paste the creat install media terminal command right?
Why not? Works for me, and is how I normally make installers for anything later than probably Yosemite (10.10)
Or, use one of the apps that are designed to do that. I was using one called Install Disk Creator. You can find that here - https://macdaddy.io/install-disk-creator/
I used that same app on Sierra up to Catalina apps just today, and it works every time. I even tested the bootable USB for each version, and they actually booted (as you might expect)
 
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McLover66

macrumors newbie
Oct 25, 2019
13
7
Why not? Works for me, and is how I normally make installers for anything later than probably Yosemite (10.10)
Or, use one of the apps that are designed to do that. I was using one called Install Disk Creator. You can find that here - https://macdaddy.io/install-disk-creator/
I used that same app on Sierra up to Catalina apps just today, and it works every time. I even tested the bootable USB for each version, and they actually booted (as you might expect)
Ah now I see how it works, it weird you walk trough a little ''installation'' window and it puts the familiar installer inside the application folder like it used to be.
 
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