New Intel NUC BIOS update fixes SteamOS, other Linux booting problems
To recap briefly, UEFI-based systems all have a small partition on their hard drives where bootloader files are stored. These bootloaders, which usually have an .EFI file extension, direct the computer to begin loading the operating system from the drive's main OS partition. The problem with older NUC BIOSes is that they didn't always know where to look for Linux bootloader files. Linux distributions would install to the computer just fine, but by default the computer wouldn't be able to tell that the internal hard drive could boot the system, and you would have to manually move the bootloader file where the computer could find it. The NUC team tells us that further improvements to the boot process are coming, but this update appears to at least fix the problems that we had—Ubuntu, Mint, and SteamOS all install and boot just fine with the latest BIOS update installed.