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I followed the very detailed guide for making hybrid MBR record (GPT/MBR) taken from here

Now, gdisk says I have hybrid mbr. But I can only boot in UEFI and cannot do that in BIOS (I use external hard drive). Seems that simple execution of grub-install installs only uefi part. I saw the discussion about requirement for protective entry to be the first on the disk, so I made it the first and that is not the root cause.

So the question is how to install GRUB so it would boot OS both being started from BIOS/MBR and UEFI/GPT?

$ sudo gdisk /dev/sdd

GPT fdisk (gdisk) version 1.0.1

Partition table scan:
  MBR: hybrid
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with hybrid MBR; using GPT.

Command (? for help): r

Recovery/transformation command (? for help): o

Disk size is 468862128 sectors (223.6 GiB)
MBR disk identifier: 0x7213C4A0
MBR partitions:

Number  Boot  Start Sector   End Sector   Status      Code
   1                     1       208895   primary     0xEE
   2      *         208896      1196031   primary     0x83
   3               1196032    135413759   primary     0x83
   4             200425472    468860927   primary     0x83

Recovery/transformation command (? for help): p
Disk /dev/sdd: 468862128 sectors, 223.6 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 21773ad9-3d43-4832-85b7-6c841d20ce75
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 468862094
Partitions will be aligned on 1-sector boundaries
Total free space is 62183 sectors (30.4 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              63           80324   39.2 MiB    EF00  Basic data partition
   2          208896         1196031   482.0 MiB   8300  Basic data partition
   3         1196032       135413759   64.0 GiB    8300
   4       135413760       168968191   16.0 GiB    0700  Basic data partition
   5       168968192       200425471   15.0 GiB    0700  Basic data partition
   6       200425472       468860927   128.0 GiB   8300
   7           81920          149503   33.0 MiB    EF02

$ sudo parted /dev/sdd

GNU Parted 3.2
Using /dev/sdd
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Model: ATA OCZ-VECTOR150 (scsi)
Disk /dev/sdd: 240GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:

Number  Start   End     Size    File system     Name                  Flags
 1      32.3kB  41.1MB  41.1MB  fat32           Basic data partition  boot, esp
 7      41.9MB  76.5MB  34.6MB                                        bios_grub
 2      107MB   612MB   505MB   ext4            Basic data partition
 3      612MB   69.3GB  68.7GB  ext4
 4      69.3GB  86.5GB  17.2GB  linux-swap(v1)  Basic data partition  msftdata
 5      86.5GB  103GB   16.1GB  ntfs            Basic data partition  msftdata
 6      103GB   240GB   137GB   ext4

$ sudo grub-install

Installing for x86_64-efi platform.
Installation finished. No error reported.
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  • 1
    Oh, this question fixed my pentium 4. It wouldn't boot with a 3TB disk, and sparkylinux fixed it with that link on gdisk. :) I know the bios is old, but since I had a blank hard drive, I just put a new OS onto it, and worked around the non-support for GPT.
    – marinara
    Commented Feb 9, 2019 at 16:26

1 Answer 1

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How to install GRUB so it would boot OS both being started from BIOS/MBR and UEFI/GPT?

You should create a bios boot partition labled bios_grub. This partition need to be created before GRUB installation .

For GRUB to boot from a GPT-partitioned disk on a BIOS-based system, a BIOS boot partition is required. Please note that this partition is unrelated to the /boot mountpoint, and will be used by GRUB directly. Do not create a filesystem on it, and do not mount it.

How to create the bios boot partition? What is the minimum size?

When creating a BIOS Boot Partition on a GPT system, you should make sure that it is at least 31 KiB in size. (GPT-formatted disks are not usually particularly small, so we recommend that you make it larger than the bare minimum, such as 1 MiB, to allow plenty of room for growth.) You must also make sure that it has the proper partition type. Using GNU Parted, you can set this using a command such as the following:

parted /dev/disk set partition-number bios_grub on

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  • I've created this partition, but that didn't the trick. Same result - system is booting with UEFI but not with BIOS. I've updated the question with some output, maybe it would be helpful
    – Grief
    Commented Nov 4, 2016 at 0:08
  • From your Bios settings switch to Legacy boot
    – GAD3R
    Commented Nov 4, 2016 at 7:30
  • Doesn't help either.
    – Grief
    Commented Nov 4, 2016 at 17:02
  • This answer seems to be written backwards: so after creating partition, it says you should run grub (I think).
    – ctrl-alt-delor
    Commented Aug 11, 2019 at 12:16
  • 1
    In other words, you'll need to install two versions of GRUB: one for BIOS/MBR (grub-install --target=i386-pc ...) and another for UEFI/GPT (with the default --target if the system is currently booted using UEFI). And since the gap between the MBR and the beginning of the first partition (where the core image of BIOS/MBR GRUB would usually go) is occupied by the GPT partition table, you'll need to have a bios boot partition to hold the core image of the BIOS/MBR GRUB.
    – telcoM
    Commented Nov 24, 2021 at 7:19

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