Even the official installer may fail after a certain date due to expired security certificates. If you see “This copy of the Install macOS High Sierra application is damaged”:
Once you have the legitimate installer app, don’t just double-click it. To install on multiple machines or a clean drive, create a bootable USB:
sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyUSBDrive
(Replace MyUSBDrive with your USB’s name.)
Apple maintains a hidden support page for legacy OS downloads. You can find the official macOS High Sierra 10.13.6 installer here (usually redirected from the App Store). The link opens the App Store, which downloads the InstallAssistant.pkg—not a raw DMG, but a package that extracts the DMG to your Applications folder. macos high sierra 10.13 6 dmg
Cause: The DMG is corrupted, or the USB was created incorrectly.
Fix: Re-download the DMG from a verified source. Re-create the bootable USB ensuring the createinstallmedia command ran without errors.
A DMG (Disk Image) file is Apple’s native format for distributing software. When you download the macOS High Sierra 10.13.6 DMG, you are getting a container that holds the Install macOS High Sierra.app bundle.
Inside that application bundle are essential resources: Even the official installer may fail after a
Important Note: A raw DMG is not directly double-clickable for OS installation in most cases. It must either be mounted to extract the .app file or restored to a USB drive using Terminal.
Apple no longer lists High Sierra in the App Store “Purchased” tab for most users. However, they maintain a legacy support page that links directly to the official installer.
Here is the legitimate method:
Note: You need to run this on a Mac that already supports High Sierra. If your Mac is too new (Post-2017), the App Store may block the download.
Cause: Your Mac might have a firmware password, or the target drive is formatted as Windows (FAT32). Fix: Disable firmware password via Recovery Mode. Ensure Disk Utility shows the top-level disk (e.g., "Samsung 850 EVO") not just the volume underneath it.