On Mon, Aug 11, 2025 at 11:11 AM Neil Bird <li...@fnxweb.com> wrote:
> I'm struggling to get UEFI working cleanly on an existing system. > The working kernel and the one I have just installed seem to > fundamentally disagree on where things should go, and the new one won't > even start grub. > The EFI partition has specifications independent of linux. < https://en.wikipedia.org/wiki/EFI_system_partition> has: > The EFI system partition is formatted with a file system <https://en.wikipedia.org/wiki/File_system> whose specification is based on the FAT file system <https://en.wikipedia.org/wiki/FAT_file_system> and maintained as part of the UEFI specification; therefore, the file system specification is independent from the original FAT specification. The actual extent of divergence is unknown:[2] <https://en.wikipedia.org/wiki/EFI_System_partition#cite_note-uefi-spec-2.5-2> [3] <https://en.wikipedia.org/wiki/EFI_System_partition#cite_note-efi-fs-spec-0.9-3> Apple maintains a separate tool that should be used on Intel/x86-64 Macs,[4 ] <https://en.wikipedia.org/wiki/EFI_System_partition#cite_note-4> while other systems use FAT utilities just fine.[5] <https://en.wikipedia.org/wiki/EFI_System_partition#cite_note-5> The globally unique identifier <https://en.wikipedia.org/wiki/Globally_unique_identifier> (GUID) for the EFI system partition in the GUID Partition Table <https://en.wikipedia.org/wiki/GUID_Partition_Table> (GPT) scheme is C12A7328-F81F-11D2-BA4B-00A0C93EC93B, while its ID in the master boot record <https://en.wikipedia.org/wiki/Master_boot_record>(MBR) partition-table scheme is 0xEF <https://en.wikipedia.org/wiki/Partition_type#PID_EFh>. Both GPT- and MBR-partitioned disks can contain an EFI system partition, as UEFI firmware is required to support both partitioning schemes. > > Background: > > My old motherboard didn't support it, but I tried to prepare the way > last time I rejigged discs by allocating an EFI partition. Before I > realised my mobo didn't even have the option, I tested mounting it and > setting it up. At least one kernel managed to install, with a bit of > jiggery pokery as I recall. One big issue was the efi partition filled > up, and things haven't been right since (I have changed the partition > sizes since). > > I have since had to get a new motherboard, and while the old boot > does work, I wanted to move to UEFI. That seemed initially to “just > work”, as I was able to select the UEFI partition that one kernel > install had populated and it booted. That is what I am currently using. > > However, the latest kernel generated loads of errors installing. I > believe *most* of that was down to my having tried to mount the EFI > partition using RAID 1 / metadata 1.0. Almost *all* the kernel RPM > scripting doesn't like that, so I've given up fighting it and am using a > single FAT32 EFI partition I'll occasionally rsync to the alternate. > The UEFI software runs before linux is loaded, so can't use linux software RAID, symbolic links, etc. There are some alternatives mentioned in the Wikipedia article. You will do better by consulting <https://uefi.org/specifications> instead of trial and error. -- George N. White III
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