9 October 2026

How to check a macOS installer is genuine

Found an old “Install macOS” app on a drive or a forum? Two built-in Terminal commands show whether Apple really signed it, before you trust it with your Mac.

Every genuine macOS installer is digitally signed by Apple. If anyone modifies the installer, even by one byte, the signature breaks. That makes it easy to check an installer you didn't download yourself, such as one from an old USB drive, a colleague or a file-sharing site.

Checking an “Install macOS” app

Run this in Terminal, changing the name to match your installer:

codesign --verify --deep --strict --verbose=2 "/Applications/Install macOS Sequoia.app"

A genuine installer reports valid on disk and satisfies its Designated Requirement. Anything else, such as “a sealed resource is missing or invalid”, means the app has been changed. Delete it.

To see who signed it:

codesign -dv --verbose=4 "/Applications/Install macOS Sequoia.app" 2>&1 | grep Authority

Every Authority= line should be an Apple certificate, ending with Apple Root CA. If you see a named developer or company, someone other than Apple signed it.

Checking an InstallAssistant.pkg or .dmg package

Installer packages, such as the InstallAssistant.pkg files in the Mr. Macintosh database or the .pkg inside Apple's older disk images, can be checked with:

pkgutil --check-signature ~/Downloads/InstallAssistant.pkg

Look for Status: signed by a certificate trusted by macOS (older versions of macOS say “signed Apple Software”) and a certificate chain made up only of Apple certificates.

“Expired certificate” isn't the same as fake

Older installers can fail with “this copy of the application is damaged” even when they're genuine, because their signing certificate has since expired. The checks above still show Apple as the signer. Our guide to fixing damaged installer errors explains what to do.

The safest option: get it from Apple

Every download link on this site goes to Apple's servers or the Mac App Store, so you can skip all of this. Find your version on the home page, or check which versions your Mac supports in the Mac lookup.