Great article Alison! I am always interested in the inner workings of how the Linux boot process works and your article cleared up a few things for me.
But the one thing that I didn't see, (unless I missed it), and that I have been trying to resolve and understand for sometime now, is...on a uefi boot system, how does the grubx64.efi that is in the firmware, (efibootmgr -c -d /dev/sda -p 1 -l \\EFI\\ubuntu\\grubx64.efi -L Ubuntu), find the files to the grub boot menu or the kernel to continue the boot process?
Rod Smith has a great blog for uefi boot loaders and how to install, but he only mentions that the grubx64.efi is called and then the boot process proceeds, with no mention of exactly how it occurs.
Can you enlighten me or point me in the right direction to understand this process?