What the ‘Legacy System Extension’ Mac Message Means & What To Do About It

Aug 8, 2020 - 11 Comments

macOS legacy system extension warning

If you’re using a Mac running MacOS Catalina 10.15.4 or later (including Big Sur), you might have seen a new and somewhat cryptic message pop up when your Mac is turned on, or when you use certain apps.

Titled “Legacy System Extension”, the message goes on to note that “existing software on your system loaded a legacy system extension by (developer) which will be incompatible with a future version of macOS” and while that might not mean much to most people, it is something you should take note of.


So, what exactly does this message mean? Not a lot right now, but come the arrival of macOS Big Sur 11 / 10.16 – towards the end of 2020 – it’s going to mean a lot.

What Are Legacy System Extensions on Mac?

Legacy system extensions are basically kernel extensions which will no longer work soon on the Mac. Apple makes a better job of explaining things in a knowledge base article, describing system extensions as follows:

System extensions are a category of software that works in the background to extend the functionality of your Mac. Some apps install kernel extensions, which are a kind of system extension that work using older methods that aren’t as secure or reliable as modern alternatives. Your Mac identifies these as legacy system extensions.

Or to put it another way, an app you are using has its tentacles in the underpinnings of how macOS works via a kernel extension. And Apple isn’t going to let it happen much longer for security purposes.

Apple began telling app developers that it planned to deprecate system extensions in 2019 and it’s now up to them to use other methods. The outcome will be a more secure macOS which, we can all agree, is only a good thing for users.

What Do I Need To Do with Legacy System Extensions on the Mac?

If the app has been updated by the developer, often simply installing that available update will resolve the issue by removing the dependency on the kernel extension.

Beyond that, there isn’t much you can do at this point other than making sure the developer of the flagged app knows that you need a solution to be in place by the end of this year for macOS Big Sur and alter.

Another option is that you could decide not to update to macOS Big Sur 11 / 10.16 once it becomes available, but that has its own security implications since newer versions of Mac system software tend to be the most secure.

If the app that the message mentions is no longer in development, things get trickier. The option of not updating to future macOS version remains, but it may be better to look at alternative apps rather than going that route, particularly if you want to take advantage of new features available in upcoming macOS releases. That might not be so easy if you’re using something bespoke or designed for the enterprise, but reach out to your company’s IT support team if that’s the case. They’ll be able to advise further.

In the meantime, you may continue to see that error message, and you will see it until the mentioned app is updated or removed from the Mac. For now, make sure to disable automatic software updates to avoid accidentally installing something, and instead you may want to manually install specific macOS updates for a while too.

Have you seen this error message with a particular Mac app? Did you update the app and resolve the issue, or did you find another solution? Let us know your experiences in the comments.

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Posted by: Oliver Haslam in Mac OS X, Tips & Tricks, Troubleshooting

11 Comments

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  1. Andrea says:

    Hi people… i don’t possible open Clean My mac after installen Catalina 10.15.6
    :(
    trying to open the app tells me:
    You cannot open the “CleanMyMac X” application because it may be damaged or incomplete
    Somebody can Help me?
    tenx
    Andrea:)))

  2. Bobby says:

    How do you find out which of your software uses legacy system extensions? I would like to know so I can tell if I want to update my computer to Big Sur. If it is a software app that I use daily and there is no update, then I won’t update my computer. It is bad enough that I can no longer run my Big Fish games on Catalina.

  3. Sebby says:

    Apple began telling app developers that it planned to deprecate system extensions in 2019 and it’s now up to them to use other methods. The outcome will be a more secure macOS which, we can all agree, is only a good thing for users.

    We can? Security is a wonderful thing, for sure. But for whom? Certainly, if “Security” merely benefits Apple’s increasing control freakery, I’m not interested, and Mojave (on my brand new iMac 2019) is where I’m at for at least another year. It’s bad enough already that kernel extensions need to be signed–having software break for absolutely no reason other than that Apple believe they have an adequate substitute functionality, with absolutely no tangible user-facing benefit and very good odds of decreased functionality, does not endear me at all. I already know, for instance, that VMWare Fusion (my virtualisation solution of choice) will be impacted by this change, and that does appear to include functionality that was only available in the kext which is continuing to be used in Catalina (Mojave has been deprecated).

    My advice: keep your options wide open, including Windows. If you can, archive installers for old releases of the macOS so you’ll be able to run them in partitions on compatible hardware or in a VM.

    Rant over for today … :)

  4. Dave says:

    I rolled back to Mojave and will keep that running with my old apps. Next thing, new Mac. Keep the old one to run old but needed software

  5. RM says:

    This was foreseen in Mojave (which I still use) with the “this will be incompatible in future OSes message.

    It’s amazing to think I still have software over a decade old that still works perfectly well. Expensive software I can’t afford to upgrade at the moment.

    Good luck to all you adventurers in the bold new world of Catalina and Big Sur, someday I will join you.

    • Mac-cy says:

      I also use Mojave which works fine with very old Mac software thanks to 32-bit support.

      I will never use Catalina. I will try Big Sur on a new Mac but the iOS-ification does not interest me.

      All of my current Macs will stay on Mojave, they can run old games and apps and they work great.

      If it ain’t broke, don’t fix it!

  6. Ian T says:

    Re John Merrill

    Don’t install Sophos. If you read about it in any of the reputable journals, you will see that it does a great deal more harm with no benefits. It has been fairly widely condemned even for Windows and AV is most certainly not required for Macs. Anti malware, yes,but not AV.

  7. Al Norbryhn says:

    I get the message with Malware Bytes. Vendor says they are aware of the issue and are working on it

  8. Nishimark says:

    Yes, I get the message when restarting these days. But, it only gives the developer’s name, not the name of the software. How am supposed to figure which application it’s referring to?

  9. John Merrill says:

    I got the message when I tried to install Sophos on Big Sur.

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