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How do I get past the "do not enter" traffic sign that stops me from installing "Sierra" instead of "High Sierra"?

I booted into rescue mode and deleted the original "High Sierra" installation, but booting from the USB stick with the "Sierra" installer on it still gives me the "no".

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  • I understand that you cant downgrade, but why would you downgrade? Do you have legacy software that won't work in High Sierra? I'm just curious.
    – anonymous
    Jun 10, 2021 at 19:13
  • Exactly that. Legacy product that (back then) wouldn't work w/ "High Sierra". Plus in a sensible office environment one tries to keep the fleet homogenous for maintenance reasons (caveat - from a security perspective heterogenous environments would probably be preferable, but one would need more staff or with a wider range of expertise to cater to that, and I mean that more in the sense of different versions of Unix and Unix-like OSes rather than vendor lock-in). @anonymous
    – tink
    Jun 10, 2021 at 19:51
  • Ok, I understand. Also sorry for posting here, I didn't realise that this thread was so old.
    – anonymous
    Jun 11, 2021 at 1:11

2 Answers 2

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If your MacBook Pro came preinstalled with macOS High Sierra, then you cannot downgrade to older OS as Apple restricted it. You have no other choice. You have to live with it.

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  • That's not entirely true. The MacBook Pro Mid-2017 originally came with macOS 10.12.5 (16F2073). So it should be possible to install Sierra.
    – klanomath
    Dec 4, 2017 at 3:55
  • @klanomath The answer still remains correct that any Mac that comes preinstalled cannot be downgraded any further than it's original OS version.
    – Shiri
    Dec 4, 2017 at 9:43
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You can't downgrade. Instead, back up all your apps and data and wipe the Mac and migrate things back after Sierra is installed.

You might run into problems if some programs or data upgraded to a new storage format or location.

Worst case, you would need to upgrade again to High Sierra and export any problematic data.

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  • I'm not trying to downgrade. The machine refuses to boot the Sierra installer.
    – tink
    Dec 4, 2017 at 2:58
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    @tink If your Mac shipped with macOS High Sierra then there’s no installing any version of macOS lower than the version it shipped with.
    – Monomeeth
    Dec 4, 2017 at 3:28
  • @Monomeeth The MacBook Pro Mid-2017 originally came with macOS 10.12.5 (16F2073). So it should be possible to install Sierra (except some newer firmware prevents this...if possible at all - I don't really know this)
    – klanomath
    Dec 4, 2017 at 3:59
  • @klanomath - the one that landed on my desk today to set-up for a new employee came with High Sierra preinstalled out of a sealed box.
    – tink
    Dec 4, 2017 at 4:11
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    @klanomath The newest models have started shipping with macOS High Sierra and they do have more recent firmware.
    – Monomeeth
    Dec 4, 2017 at 4:15

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