In two recent Linux installations I have struggled with biosboot and efi boot partitions. At first I didn’t know why they were needed, I have never seen them before, perhaps because I generally use old hardware for my Linux boxes.
The rule is apparently fairly simple. If the system booted in efi mode, the disks must use gpt and an efi boot partition is required. If on the other hand the system booted in legacy mode there are two options. If the disk is larger than 2T then gpt is required and a biosboot partition is needed. For smaller disks it is possible to use msdos without a biosboot or efi boot partition, using only the mbr for the boot loader.
You can tell if the system booted in efi by checking for
/sys/firmware/efi. If it exists the system booted in efi, otherwise it booted in legacy mode. The…
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