My current start-up drive runs 10.13.6. After a couple of system freezes involving full screen movies and VLC 3.0.6, I thought I'd refresh things by running the 10.13.6 combo update.

The dialogue box came up: "macOS High Sierra 10.13.6 Update can't be installed on this disk. This volume does not meet the requirements for this update."

I've run combo installers before over systems that don't actually update. Why not 10.13.6?

Thanks.

Oops. I've just thought of a possible reason: I have converted my SSD from APFS to HFS+ after the last upgrade. Could that be it?

That particular, and very annoying, error has been around for a long time and a number of causes and solutions have been posited but I have never seen anything conclusive.

As to your speculation that changing your SSD from APFS to HFS+, how did you make the conversion without erasing/reformatting the SSD and re-installing High Sierra? I would think that should have taken care of any compatibility issues — unless perhaps the reinstall was cloned from another drive.

In either case your best bet may be to re-install MacOS from the Recovery Drive. When running a re-install from the Recovery Drive the key combination you use to boot the Recovery Drive is critical. According to Apple Support Article HT204904...

• Command+ R (⌘-R) Install the latest macOS that was installed on your Mac.
• Option+Command+R (⌥⌘R) Upgrade to the latest macOS compatible with your Mac.
• Shift+Option+Cpmmand+R (⇧⌥⌘R) Install the macOS that came with your Mac, or the closest version still available.

CAVEAT: I have not verified this for myself but I am taking Apple's word this will work. As with any OS change/upgrade/update a known good backup/clone is HIGHLY recommended.

That's exactly how I did it: installed High Sierra, set up all my apps, cloned the lot to another drive. Then, erased/reformatted and cloned the new system back to the SSD.


With this method (Option+Command+R), do you lose your User data? I presume I would not be offered Mojave, as I do not have a Metal-compatible graphics card.

Since posting, I have run OnyX. The VLC system freezing problem did not reoccur, so now this just becomes idle curiosity.

Thanks, though, for your help!

The only ways you might lose your data would be an SSD failure or you launch Disk Utility from the Recovery drive and erase the SSD. This would be true of ⌘R, ⌥⌘R, and ⇧⌥⌘R re-installations. However, you might find your SSD changed from HFS+ to APFS in cases where that is a normal part of the installation process.

I have done several ⌘R re-installs and have yet to lose any data.