Installing macOS High Sierra on a MacBook Pro or other Mac that is not supported by High Sierra

By: (plus.google.com) +David Herron; Date: April 12, 2018

Tags: Mac OS X

Apple has declared certain older Mac computers unsupported by newer versions of macOS. In my case, I attempted to install macOS High Sierra on a mid-2009 MacBook Pro, but the installer failed in a very strange way. I constructed a USB installer using the normal process to make a macOS installer, then rebooted the computer to run the installation, but instead the screen simply went blank and the computer turned itself off. In other words installing macOS High Sierra on this mid-2009 MacBook Pro failed in a strange way. After a couple dozen macOS installs on different computers under my belt, I'd never seen this behavior. After some duckduckgoing the cause was found to be this screen capture - that the computer was not supported by High Sierra - and fortunately there was a relatively simple solution.

Getting to see that message took some digging.

The initial behavior was - insert the USB drive holding the macOS Installer in the USB port, reboot the computer, hold down the Option key, and select the installer drive. Normally booting off the installer this way launches the installation program, and we would then proceed with the installation.

Instead - the computer showed a grey screen with this symbol:

The macOS Prohibitory symbol

According to (support.apple.com) the Apple support knowledge base, the Prohibitory Symbol is shown when "your Mac couldn't find a valid System Folder to start up from." This didn't make sense since the installer USB drive does have a System folder.

Initially the suggestions I found said to reset the NVRAM, the PRAM or the SMC, and even to do a complete reset of the computer. A complete reset is performed by unplugging the battery pack, the power supply, and then holding down the power button for awhile, presumably to drain off any held energy in capacitors. None of that resetting made any changes - the macOS High Sierra installer still failed to start in a strange way.

After some additional searching I found a suggestion to boot by using Command+S ...

Booting that way showed the above screen, telling me "This version of Mac OS X is not supported on this platform!"

I don't know what "Reason: Mac-F2268AC8" means, but the other message clearly means the mid-2009 MacBook Pro is not supported by macOS High Sierra.

By coincidence I had watched a video yesterday concerning the (dosdude1.com) macOS High Sierra Patcher Tool for Unsupported Macs As the name suggests, it an application which patches a macOS High Sierra installer to allow installing High Sierra on an unsupported Mac.

Click through to that link, and you'll find a complete set of instructions. The basic idea is to:

  • Download the macOS High Sierra Installer using the Apple App Store
  • Insert a USB drive into a USB port
  • Execute the Patcher tool, and perform these steps
    • Select the Installer
    • Select the USB drive
    • Click the START button - this builds the installer drive, and applies the necessary patches
  • Boot off the installer USB drive as normal for a macOS installation
  • Perform an installation using the installer
    • Notice there is an extra window on the screen
    • If desired you can use that window to launch Disk Utility to reformat the hard drive
  • After installation, boot again off the installer drive. You'll find a window that can launch a Post-Install Tool that applies patches. Run this tool.

An issue that arose during those machinations is that after running the installation I got a screen saying macOS could not be installed on your computer. That was solved by resetting the system clock, see: Installing MacOSX when the installer says: OS X could not be installed on your computer. No packages were eligible for install.

Afterwards, reboot the computer normally, and you'll be greeted with the normal macOS setup screens.

The following video gives an overview and some results.