So macOS Sierra was released. Went to download it on my trusty Mac Pro that i've tinkered & upgraded over the years … no dice! Apple has deliberately obsoleted my perfectly good Mac! Not such a big deal but it means that I can't install the latest Xcode.

Some searching around the Web and I found it is actually possible with some hackery.

First step was to hack the firmware so it was running the 2010 Mac Pro firmware. My Mac Pro will now report as MacPro5,1 instead of MacPro4,1 which should allow me to run the macOS Sierra installer.

Someone released a tool in 2011 to do this. It didn't work - gave a 5570 error. More searching showed this was solved simply by downloading the EFI firmware update from Apple ("Mac Pro EFI Firmware Update 1.5", DL1321) and then mounting the DMG. Running the firmware hack tool again was successful as it found the files.

However, the firmware wasn't updated - my Mac Pro still reported as MacPro4,1 after rebooting.

Further searching found the answer. As I am running OS X 10.11 El Capitan it has System Integrity Protection (SIP) enabled which restricts the root account and thus was likely preventing the firmware hack tool from working.

I disabled it as per the instructions - restarted my Mac in recovery mode (holding cmd+R during restart), opening Terminal and executing csrutil.

Rebooting my Mac again and trying the firmware hack tool - success!

My Early 2009 Mac Pro is now reporting as MacPro5,1.





In addition to being able to install macOS Sierra, I can also apparently run hex-core CPUs (so she can keep going for a few years yet!).

I haven't tried running the Sierra installer yet - I want to do a full backup first (need to replace a couple of drives in my external back RAID).