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GNU/Linux supports reading from disks with a wide variety of partition tables. Even GNU fdisk supports SGI/IRIX, Sun, and BSD partition tables in addition to the standard DOS and GPT partition tables. There is also a special Apple fdisk for PowerPC based Macs.

My question is, how many of these partition tables could be used on a boot drive for a Linux system? All that is needed is for a portion of the first sector on the drive to be available for boot code, and a boot loader that is aware of the partition table.

Some BIOSes also look for a DOS partition table with an active partition on it or else the drive is ignored. So most of the first sector would need to be available in this case, but this isn't standard.

Part of the reason why I ask this is that support for hybrid MBR & GPT partitions is poor, but needed on disks larger than 2TiB (or 4TiB in some cases), so that partitions in the first 2TiB can be accessible on non GPT aware systems. Many of the GPT partition utilities have no support for the parallel MBR partition map, and some operating systems won't boot or properly recognize the disk if it detects one. Some will ignore the GPT partition system and use the MBR partitions only. A trick to make it work on one OS breaks it on another. Some of these other partitioning systems have no 2TiB limit.

Related topic with a list of Linux supported partitions: What are the differences between the various partition tables?

Alex Cannon
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  • If you're booting using BIOS, the partitioning scheme doesn't matter, BIOS will execute the first (technically the zeroth) sector anyways. For EFI, you must have GPT and System EFI partition. Nothing else is supported. – Artem S. Tashkinov Jan 14 '23 at 17:22
  • Sure it does. If a Sun partition map were to put some important data in the first sector, then boot code can't be put there! – Alex Cannon Jan 14 '23 at 17:25
  • An x86 PC with BIOS will execute the first sector on a drive selected as bootable, period. As to whether some partitioning scheme is compatible with it or not, I've no idea, I can't know all the partitioning schemes. What problem are you trying to solve? – Artem S. Tashkinov Jan 14 '23 at 17:30
  • That's for https://superuser.com/questions anyways. This question is not related to UNIX/Linux. – Artem S. Tashkinov Jan 14 '23 at 18:11
  • @Artem not necessarily, I have a couple of pre-UEFI PCs whose BIOS tries to be too clever and won’t boot on a drive with something other than an MBR-style partitioning scheme. – Stephen Kitt Jan 14 '23 at 18:20
  • That's too clever. :-) Never dealt with such systems before, prolly I'm lucky :-) – Artem S. Tashkinov Jan 14 '23 at 18:52
  • My 2006 laptop & 2009 desktop that were BIOS only worked fine when I converted them to gpt. I had to add the bios_grub partition to have them work in BIOS mode. A few motherboards (Intel?) wanted a boot flag on gpt, even though grub does not use boot flag. But it could be added to any partition to make it work. – oldfred Jan 14 '23 at 20:59

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