On Sat, Sep 20, 2025 at 5:47 PM Steve Litt <[email protected]> wrote: > UEFI is a booting scheme that goes along with GPT partitioned disks but > can't be used with MBR partitioned disks. UEFI uses hardware on the > motherboard, blended with files in /boot/efi and UEFI settings available > via the bios. UEFI is a very complicated specification, so many > motherboard manufacturers get it wrong, to the extent that on some > computers if you delete files from /boot/efi or delete /boot/efi > itself, you can permanently brick the computer. I dislike UEFI.
Not exactly... UEFI can also boot from MBR-partitioned disks if they have an EFI System Partition (code 0xEF). I believe the OpenBSD install images use this setup, as a hybrid image that boots on both BIOS and UEFI. In some ways UEFI is easier to boot from, as you can format a FAT partition, give it the ESP ID, and place a bootloader in EFI\BOOT\BOOTX64.EFI (or the appropriate filename for your architecture, e.g. BOOTAA64.EFI), and the system will boot from that, even if the file is replaced. For BIOS you have to install a sector of bootloader code at the beginning of the partition, which will load the rest of itself from a hardcoded location. Which means if that file changes, you have to rerun installboot. (And also the MBR needs to chainload that partition, which is usually done by marking it active.) The only "permanent bricking" I've heard of was Linux setting EFI system variables (which are stored in NVRAM, not files on the ESP) and a bug in certain devices' firmware not properly handling that. That only affected a few hardware models and the Linux code now has workarounds, so it's not something worth worrying about. -Andrew
