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 Forums: macOS High Sierra, macOS Mojave, macOS Catalina, OS X Yosemite, OS X El Capitan, macOS Sierra

Top Rated Comments

gank41 Avatar
gank41
79 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)
chrfr Avatar
chrfr
78 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: 3 Votes (Like | Disagree)
gank41 Avatar
gank41
79 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)
tywebb13 Avatar
tywebb13
79 months ago

Another weird problem I'm having is the error: ''..... is not a valid mount point'' in terminal. It only happens when I want to make a Sierra bootable installer, all the others work fine. Changing the name of the USB drive does not solve the issue and I've checked the path and it's correct. Does anyone else has this issue with the new 10.12 Sierra installer?
Indeed. I was so curious about your post that I downloaded Sierra and attempted to make the bootable usb to see if this bug is reproducible.

I got the same result.

The reproducibility of the bug makes it very suitable to apple for a bug report.

I have submitted the bug report to apple.
Score: 2 Votes (Like | Disagree)
bsbeamer Avatar
bsbeamer
79 months ago
For those having issues downloading, you may want to look into the "installinstallmacos.py" script.
Score: 2 Votes (Like | Disagree)
tywebb13 Avatar
tywebb13
79 months ago

The createinstallmedia command will fail with the new Sierra installer. Some code is munged somewhere. As a workaround, do an actual installation to your flash drive, then just copy the new installer to that drive's Applications folder. At least you can boot and get Sierra installed to an otherwise unbootable drive (or reinstalled over an earlier installation nondestructively).
Thank you. I too have a workaround. Make a bootable DVD installer instead.

To do this copy and paste these into terminal to make the bootable iso file (assuming you have the Sierra installer in your Applications folder):

hdiutil attach /Applications/Install\ macOS\ Sierra.app/Contents/SharedSupport/InstallESD.dmg -noverify -nobrowse -mountpoint /Volumes/install_app

hdiutil create -o /tmp/Sierra.cdr -size 7.85g -layout SPUD -fs HFS+J

hdiutil attach /tmp/Sierra.cdr.dmg -noverify -nobrowse -mountpoint /Volumes/install_build

asr restore -source /Volumes/install_app/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase

rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages

cp -rp /Volumes/install_app/Packages /Volumes/OS\ X\ Base\ System/System/Installation/

cp -rp /Volumes/install_app/BaseSystem.chunklist /Volumes/OS\ X\ Base\ System/BaseSystem.chunklist

cp -rp /Volumes/install_app/BaseSystem.dmg /Volumes/OS\ X\ Base\ System/BaseSystem.dmg

hdiutil detach /Volumes/install_app

hdiutil detach /Volumes/OS\ X\ Base\ System/

hdiutil convert /tmp/Sierra.cdr.dmg -format UDTO -o /tmp/Sierra.iso

mv /tmp/Sierra.iso.cdr ~/Desktop/Sierra.iso

A bootable iso file called Sierra.iso will then appear on your desktop and you can use this to burn it to a dual layer dvd:

sudo drutil burn /Users/YOURNAME/Desktop/Sierra.iso

where you replace "YOURNAME" with the username for the account you are logged into at the time.

and then boot to startup manager with option key to select the dvd.

Just be aware though that a bootable dvd takes a lot longer to boot up than a bootable usb.
Score: 2 Votes (Like | Disagree)
Read All Comments

Popular Stories

2024 iPhone Boxes Feature

Apple Adjusts Trade-In Values for iPhones, iPads, Macs, and More

Thursday November 6, 2025 11:12 am PST by
Apple today updated its trade-in values for select iPhone, iPad, Mac, and Apple Watch models. Trade-ins can be completed on Apple's website, or at an Apple Store. The charts below provide an overview of Apple's current and previous trade-in values in the U.S., according to its website. Maximum values for most devices either decreased or saw no change, but the iPad Air received a slight bump. ...
Read Full Article • 66 comments
Finder Siri Feature

Apple's New Siri Will Be Powered By Google Gemini

Wednesday November 5, 2025 11:57 am PST by
The smarter, more capable version of Siri that Apple is developing will be powered by Google Gemini, reports Bloomberg. Apple will pay Google approximately $1 billion per year for a 1.2 trillion parameter artificial intelligence model that was developed by Google. For context, parameters are a measure of how a model understands and responds to queries. More parameters generally means more...
Read Full Article • 367 comments
iOS 26

iOS 26.1 Available Now With These 8 New Features

Monday November 3, 2025 5:54 am PST by
Following more than a month of beta testing, Apple released iOS 26.1 on Monday, November 3. The update includes a handful of new features and changes, including the ability to adjust the look of Liquid Glass and more. Below, we outline iOS 26.1's key new features. Liquid Glass Toggle iOS 26.1 lets you choose your preferred look for Liquid Glass. In the Settings app, under Display...
Read Full Article
Liquid Glass General Feature

Apple Shares Liquid Glass Design Gallery

Thursday November 6, 2025 2:45 pm PST by
Apple is promoting the new Liquid Glass design in iOS 26, showing off the ways that third-party developers are embracing the aesthetic in their apps. On its developer website, Apple is featuring a visual gallery that demonstrates how "teams of all sizes" are creating Liquid Glass experiences. The gallery features examples of Liquid Glass in apps for iPhone, iPad, Apple Watch, and Mac. Apple...
Read Full Article • 104 comments
airtag purple

Apple's Website Lists AirTag 4-Pack at Shockingly Low Price [Updated]

Friday November 7, 2025 6:40 am PST by
Apple's online store in the U.S. is suddenly offering a pack of four AirTags for just $29, which is the same price as a single AirTag. This is likely a pricing error, and it is unclear if orders will be fulfilled. Apple has not discounted the AirTag four-pack in any other countries that we checked. Delivery estimates are already pushing into late November to early December, suggesting...
Read Full Article • 91 comments
apple watch se 3 always on

Apple to Remove iPhone-Apple Watch Wi-Fi Sync in EU With iOS 26.2

Thursday November 6, 2025 4:37 am PST by
Apple in iOS 26.2 will disable automatic Wi-Fi network syncing between iPhone and Apple Watch in the European Union to comply with the bloc's regulations, suggests a new report. Normally, when an iPhone connects to a new Wi-Fi network, it automatically shares the network credentials with the paired Apple Watch. This allows the watch to connect to the same network independently – for...
Read Full Article • 208 comments
ikea smart home devices

IKEA Debuts 21 HomeKit-Compatible Smart Bulbs, Sensors, and Controls

Thursday November 6, 2025 4:08 pm PST by
IKEA today announced the upcoming launch of 21 new Matter-compatible smart home products that will be able to interface with HomeKit and the Apple Home app. There are sensors, lights, and control options, all of which will be reasonably priced. Some of the products are new, while some are updates to existing lines that IKEA previously offered. There are a series of new smart bulbs that are...
Read Full Article • 73 comments
Home Hub Command Center with Dome Base Feature

Apple's 2026 Smart Home Revamp: All the Rumors

Wednesday November 5, 2025 3:54 pm PST by
It's been over a decade since Apple's HomeKit smart home platform launched, and it is overdue for an update. HomeKit and the Home app can no longer keep up with AI-powered solutions from other companies like Google and Amazon, but that's set to change with a smart home revamp that Apple has planned for 2026. Home Hub Apple is working on a home hub or "command center" that will serve as a...
Read Full Article • 56 comments