GPT boot has less features than legacy MBR-based one (Was: UEFI, loader.efi and /boot.config)

Rebecca Cran bcran at freebsd.org
Sun Jan 20 04:28:06 UTC 2019


On Saturday, 19 January 2019 13:54:25 MST Lev Serebryakov wrote:

>  Yes, I know. But what should I do next? There is no  "Set UEFI Boot Var"
> item in it. You could select different physical drives (but not partitions
> of the drives) and network cards (if PXE is enabled), and, sometimes, "EFI
> Shell" which is not documented anywhere, and it doesn't work always.
> 
>  When I google "ASUS EFI Shell", for example, all results says about
> preparing USB stick with EFI shell and such, not about commands and
> variables of EFI shell.
> 
>  I don't say, that it is impossible, I only could not find good (or any)
> documentation.

Yeah, the documentation is definitely lacking.
If you want to specifically run the EFI Shell, then you'll need to either 
install Shell_Full.efi from https://github.com/tianocore/edk2/tree/UDK2014.SP1/
EdkShellBinPkg/FullShell/X64 as Shellx64.efi on a USB stick formatted as FAT16 
or FAT32 - or, install the shell as EFI/BOOT/BOOTx64.efi on an ESP.

For booting FreeBSD, you might want to consider installing rEFInd (http://
www.rodsbooks.com/refind/), since it can find the loader in EFI/freebsd/
loader.efi and displays the FreeBSD logo - see https://bluestop.org/files/
rEFInd_FreeBSD.jpeg . For comparison, my ASUS UEFI firmware doesn't find FreeBSD 
at all in /EFI/freebsd, and when installed as /EFI/boot/BOOTx64.efi just 
displays a "UEFI OS" entry.

Ultimately, UEFI doesn't care about disks and partitions: it only really knows 
about ESPs -- FAT12/16/32 formatted partitions that contain the EFI directory 
structure. For now, that means /EFI/BOOT/BOOT{x64,i386,aa64,arm}.efi, the 
Microsoft boot loader in /EFI/Microsoft and GRUB/shim in /EFI/fedora, /EFI/
opensuse etc.

-- 
Rebecca Cran
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