9 thoughts on - UEFI Booting

• There’s this document:

  https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Installation_Guide/ch-Boot-x86.html

  The important thing is that you need to install the OS with the firmware that you want to run the system with, so you’ll need to re-install the system using the UEFI boot mode to boot your installation media in order to get the system going with UEFI.

  Erik

• Hi Jerry,

  As UEFI and LEGACY mode installations are hardware features, you need to go through the systems BIOS settings where you can find installation method settings, then flip the method from LEGACY to UEFI . You need to reinstall the OS after making this change.

  Thanks,

• I installed my first UEFI disk yesterday. Seemed to go fine. CentOS 7.6
  x86_64
  I then took that disk “out” of that machine and put it another machine – it seems to not even boot. I put the original disk back in that machine and it boots fine.

  I put the UEFI disk back in the machine I built it on and it works fine. They are similar machines either and i3 and i7.

  Shouldn’t that work? Build a UEFI disk on machine A – move it to machine B?

  Thanks

  Jerry

• Perhaps a silly question but
  1- Does your new machine has EFI mode enabled on BIOS and not CSM?
  2- is it at the same port/bay as the original one?
  3- When do you say “not even boot” what do you mean? any messages on screen? past POST/BIOS/EFI does it gets to the linux bootloader?

• I think the issue is that the UEFI firmware doesn’t know which UEFI boot loader to load. I think this should help:

  https://noobient.com/2017/09/27/fixing-the-efi-bootloader-on-CentOS-7/

  Boot into rescue mode, and run:

  efibootmgr –create –label CentOS –disk /dev/sda1 –loader “\EFI\CentOS\shim.efi”

  I think you then should end up in a happy place. You can probably add that entry by hand within the UEFI config itself.

  HTH,

  jh

• Just wondering, will it still boot if he then puts the disk back to the other machine?

  Regards, Simon

• My understanding is yes, as this is just updating the EFI Boot Manager, which is stored in non-volatile storage on the motherboard.

  If anyone knows better, feel free to poke holes in my limited understanding.

  jh

• My experience with UEFI is that it is a black art. Fought with it until a deadline forced me to non-UEFI. In my case a drive-based UEFI partition (FAT32) was required. See if efibootmgr is available and would help you. I should note that, in the process. I discovered that the UEFI standard makes no provision for RAID if it is disk-based. I would love to hear someone contradict me on that and point me to documentation on how to do it without resorting to exotic maneuvers.

• UEFI isn’t really a *disk* but a hardware firmware setting on the computer’s motherboard. Instead of looking for a boot configuration in the Master Boot Record of the disk, the UEFI firmware looks for it on a specially labelled FAT32 partition with an EFI directory on it.

  If your motherboard’s firmware can boot UEFI, then it can boot off the UEFI executables on that disk. If the motherboard is too old and only supports MBR (legacy) boot mode, it’ll look for the MBR on the disk. If you’ve got a newer motherboard, but it’s set to boot in legacy mode (which is just a specialized UEFI boot service that emulates the old boot method) it’ll only look for the legacy boot bits.

  I would not be surprised that your other system would not immediately detect a UEFI disk if it was set to look for the legacy boot method.

  —
  Jonathan Billings