Dec 7, 2017 - macOS High Sierra 10.13 introduces a new feature that requires user approval before loading newly-installed third-party kernel extensions. From the macOS Sierra license. You are granted a limited, non-exclusive license to install, use and run one (1) copy of the Apple Software on a single Apple-branded computer at any one time. As I mentioned in a comment, various parts of the operating system are open-source and available for download.
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I also hit the problem of getting stuck at the UEFI shell prompt when booting from a viable disk (such as my case where ). I was able to fix the UEFI problems as follows (credit to ):. At UEFI prompt: Type exit. You'll be brought into an EFI text-mode GUI. Select Boot Maintenance Manager and click. Select Boot From File and click You should see two entries in a list (they are cryptic looking PCI bus paths).
The first is the PCI path to a boot partition that isn't working (corrupted or perhaps has no data or OS installed on it). The 2nd partition is the recovery partition, the one you need to boot from to do the macOS installation or other maintenance/administrative tasks (including accessing Disk Utility to work on the System Volume partition without an OS running). Click the 2nd entry, you should see (and then click): macOS Install Data Then click: Locked Files Then (if present), click Boot Files And finally click: boot.efi At that point he installer boot will continue and you should get to the point where you can attempt to repair the volume or reinstall macOS.