Mac

macOS installer fails to verify or won't start

A macOS installer that fails verification or won't launch is usually caused by an incomplete download, an incorrect system date/time, or a network issue during Apple's verification step.

Difficulty
Moderate
Time
30–60 minutes
DIY cost
$0
Pro cost
$100–$200

Symptoms

  • Installer shows an error like 'This copy of the Install macOS application can't be verified'
  • Installer quits unexpectedly right after launching
  • Download seemed to complete but the file appears smaller than expected
  • Problem occurs specifically when trying to run the installer, not during download

Likely causes

  • CommonAn incomplete or corrupted installer downloadInterrupted downloads are a frequent cause of verification failures.
  • CommonIncorrect system date and time on the MacmacOS verification relies on accurate date/time to check certificates properly.
  • CommonA network issue preventing the Mac from reaching Apple's verification serversThis step requires an active internet connection.
  • PossibleAn outdated installer no longer supported for verification (older macOS versions)Very old installers can eventually fail to verify as Apple updates its systems.
  • PossibleA temporary issue on Apple's endThis is less common but does happen occasionally.

What to do

  1. Check System Settings > General > Date & Time and make sure 'Set automatically' is enabled and the date/time is correct.
  2. Confirm you have a stable internet connection, since verification requires reaching Apple's servers.
  3. Delete the installer from Applications and download it again fresh from the App Store or Apple's site.
  4. Check that the redownloaded installer's file size looks reasonable (several gigabytes) rather than unexpectedly small.
  5. Restart the Mac and try running the freshly downloaded installer again.
  6. If using an older macOS installer, check Apple's support site to confirm it's still a currently supported download.
  7. Try downloading via a different network if possible, in case a firewall or network restriction is blocking verification.
  8. If verification keeps failing with a fresh download and correct date/time, try creating a bootable installer via Terminal as an alternative method.

Tools and parts

  • None required

When to call a pro

If a fresh download with correct system date/time still fails to verify, an Apple Store or authorized repair shop can help install macOS through other official channels.

Safety

Generally low risk

Generally low risk for a careful person. Stop if anything looks different from what this guide describes.

Related guides

Operator provides AI-generated troubleshooting information. It can be wrong. For safety-critical, electrical, gas, structural, medical, automotive safety, or other high-risk problems, consult a qualified professional.