I followed a Youtube tutorial to install Mac OS on my T440P but failed, it can't access the internet for some reason, I tried few times the same and I gave up.


Then I check the power settings on the BIOS, to see if anything else available so that I can turn the notebook on by attach the AC, tried everything but failed too, but then I found something changed. There's an Opencore option on the boot menu, as far as I know it's a Mac thing, but the tutorial was not targeted at the Thinkpad, even if it was the BIOS (CMOS) can not be altered easily, or can it ? further more, the Mac install was on a spare HD, not the one I boot to Linux to write this, so how come Opencore exists on the boot menu ?

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Apple has been using EFI for over a decade and if your computer is EFI capable, the attempt to install the Apple system created a boot entry which stored some data on the system board which is why you see OpenCore there. Actually, I've never used any Apple computers so this is a guess based on my knowledge of EFI. I'm not really sure from what you posted if that is the question?

I boot Linux in legacy mode but set to UEFI while installing Mac OS, I don't know the installer will write something on the CMOS (?), this won't hurt me booting Linux I was just curious about what I saw on the BIOS settings.

It won't be written to CMOS, that kind of thing usually resides in the EFI system partition.

EFI boot entries (seen via efibootmgr) are stored in NVRAM on the motherboard and if the OP were to delete the EFI partition, that entry would still be see in the BIOS.

IC, so such space is open to use. I don't know much about UEFI, but I disabled it to boot Linux in legacy mode, I may not want or need to reset the NVRAM as long as Linux boots fine. I learned to live out of the windows, and I don't even dualboot. In before, I simply install Linux on the internal SSD of my Thinkpad and share the free space of windows drive to mount the /home and Swap, then I select boot drive on BIOS to switch, now I completely skip windows and install straight in the internal HD. When I test other distro I will replace the HD, it's just 3 screws to remove the cover and the HD on my TB, I even install to USB SSD if the distro supports that...

Thanks for the correction, I forgot about that. I seem to recall efibootmgr can handle removing these?

Generally, although on most HP computers most of the efibootmgr commands don't do anything. It is pretty simple to make changes after accessing the BIOS though.