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Different uses of term "EFI partition"

rated 0 times [ 2] [ 0] / answers: 1 / hits: 1767 / 2 Years ago, mon, may 23, 2022, 6:36:03

I installed Kubuntu on a Macbook Pro 8,2 and am trying to get it from legacy to EFI boot.

Kubuntu forced me to create an "efiboot partition of at least 1 MiB" (fs id 'ee').

Thats just the successor of the MBR in disguise, isn't it?

In the tutorials for grub-efi-amd64, there's always references to the "EFI partition", a FAT16 of at least 200 MiB.

This is independent of the first one and has to be created, right? I could shrink my home-partition and append this as sda5, or is it critical, where the partition is located?

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throecember

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4 Years ago

answered 2 Years ago calcur · Accepted Answer

I suspect that you're seeing, and confusing, three different things:

The GUID Partition Table (GPT) scheme includes a "protective MBR," which is a Master Boot Record (MBR) partition table that contains a single partition, of type 0xEE, that spans (more-or-less) the entire disk, from sector 1 to either the end of the disk or the 2GiB point (assuming 512-byte sectors), whichever is less. The 0xEE partition is often called the "protective partition." This has nothing to do with an "EFI partition," "BIOS boot partition," or any other GPT partition, except to the extent that the protective MBR is a necessary component of a complete GPT configuration. The protective partition isn't really a partition, either; it exists just to keep GPT-unaware utilities from messing with the disk.

On a computer that boots in EFI mode, an EFI System Partition (ESP) is required. This partition uses a FAT32 filesystem (FAT16 can usually work in practice, but the spec requires FAT32) and holds EFI boot loaders and related files. When the computer boots, the EFI reads boot loaders from the ESP. Its size is not defined by the spec, but in practice it's usually around 100-200MiB. I recommend creating a bigger ESP, in the range of 550MiB, because some EFIs seem to have buggy FAT drivers that cause problems with smaller ESPs.

If you install GRUB in BIOS mode to a GPT disk, it will be happiest if the disk contains a BIOS Boot Partition. This partition is typically 1MiB or 2MiB in size, and it holds the second stage of GRUB's boot code (the first stage goes in the MBR's code area). This partition is not required when booting a computer in EFI mode.

The ESP and BIOS Boot Partition can both go just about anywhere, at least in theory, although on an over-2GiB disk, it's best to keep the BIOS Boot Partition under the 2GiB mark.