5

On a BIOS-GPT system (i.e. no UEFI): I partition my disk this way:

1) 2MiB with the bios_grub flag
2) 1GiB ext2 for /boot
3) 30Gib ext4 for / for Gentoo.
4) the rest divided for other distros and for /home.

My question is concerning the second partition, the ext2 for /boot/.
In gparted, do I need to set the 'boot' flag?
I read conflicting information about it:

"Some buggy BIOSes or EFIs configured to boot in BIOS/CSM/legacy mode might also have problems with booting from GPT labeled disks. If that is the case, it might be possible to work around the problem by adding the boot/active flag on the protective MBR partition which has to be done through fdisk with the -t dos option to force it to read the partition table using the MBR format."
...
"When using the UEFI interface to boot the system (instead of BIOS), mark the boot partition as the EFI System Partition. Parted does this automatically when the boot option is set on the partition:"
...
"Type a to toggle the bootable flag on a partition and select 2. After pressing p again, notice that an * is placed in the "Boot" column."

elsewhere I read that the 'boot' flag on an uefi system was for a partition of type fat32 (vsfat).

Basically, I am confused: the 'boot' flag is to be used for BIOS or for EUFI or both?
Should I set it for my ext2 /boot/, or I shouldn't, or it doesn't matter either way?

GAD3R
  • 63,407
  • 31
  • 131
  • 192
augustin
  • 433
  • 2
  • 5
  • 12

1 Answers1

13
  • grub itself does not care about boot flags.
  • An EFI System partition is distinguished by its GUID type C12A7328-F81F-11D2-BA4B-00A0C93EC93B, not by a boot flag. Yes, this partition needs to be formatted FAT32. Not all FAT32 partitions are EFI System partitions, only one of them, and that one, if present, is small and has a special purpose. On a computer which boots through BIOS or BIOS emulation you don't need it. You may want to create an EFI System partition (about 300 MB, in parted say mkpart fat32 and set boot on), for the case that some day the disk will be moved to a computer with UEFI.
  • Your /boot partition does not need a boot flag and should not have one.
  • However, the sole partition in the protective MBR may need a (legacy) boot flag if the firmware of your computer wants it. (Some BIOSes won't boot a hard disk unless it has a primary MBR partition with the active flag set.)
  • Not all computers support booting from GPT disks under BIOS or BIOS emulation. In fact, this is explicitly unsupported. It usually works, though.
AlexP
  • 10,217
  • 32
  • 41