Yrurtj

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.

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