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When installing openSUSE Tumbleweed, I get a red warning before the last confirmation:

 Boot from MBR does not work together with btrfs filesystem and GPT disk label without bios_grub partition. To fix this issue, create bios_grub partition or use any ext filesystem for boot partition or do not install stage 1 to MBR.

The warning is right, installed like that openSUSE can't boot.

As far as I understand my machine is probably in EFI mode, because YaST creates something that looks like GPT to me (at least in the graph visualization of the expert partitioning I can see GPT under both /dev/sda and /dev/sdb).

What may be relevant is that automatic partitioning creates a BIOS boot partition as /dev/sda1. Apparently this is not enough, neither is setting /dev/sda1 as the custom boot partition instead of MBR on at the boot loader settings, so how do I turn this one into a "bios_grub partition" (whatever that is)?

  • "Boot from MBR" means "boot the old BIOS way". If this is the case, your machine is not in EFI mode, but the disk is GPT partitioned, which is why you need a BIOS boot partition. It would be interesting to know why the openSUSE installer failed to create a bootable system, or did you change the firmware mode at some point during or after the installation? I recommend using EFI mode, especially if your disk is already GPT. – Johan Myréen Oct 5 '18 at 11:47
  • The only specialty I see with this system compared to my previous one is that it has two hard drives used as one with LVM, but I achieved even that with guided partitioning. I would not have dared to use the expert mode. – ytg Oct 5 '18 at 12:26
  • If the machine is in EFI mode, you need an EFI System Partition (ESP) to boot from. The ESP must be a FAT-formatted, separate partition that is not part of a LVM logical volume. If the firmware is in legacy BIOS mode, and a GPT partition table is used, the BIOS boot partition is needed because there is no gap between the MBR and the partition table where Grub can store code and data that does not fit in the MBR. – Johan Myréen Oct 5 '18 at 13:32
  • Apparently my mistake was that I trusted the installer that it recognizes EFI mode correctly. The BIOS really was set to boot in legacy mode. Changing that fixed the install process. @JohanMyréen: if you post your suggestions as an answer, then I'd be happy to accept it. – ytg Oct 5 '18 at 14:25

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