Partitioning with Legacy Boot (BIOS) and GPT

Support
1

Hi all,

after using Debian and Ubuntu for some years, I decided to switch over to Manjaro. Today I was fiddling around with a test system (a laptop) before I install it on my main PC.

The laptop boots in Bios (this is also what is shown in the installer on the top) and I wanted to choose GPT as the partioning table. As far as I understood in this combination (=BIOS+GPT) a 8 MB unformatted partition is needed which is marked as bios_grub. This is my first partition. Then I have root (/), home (/home) and a swap partition. I don’t have any boot partition. Manjaro boots fine, but the bios_grub partition is formatted as ext4 after the installation. Does this make sense and how can I make sure that it is even used?

df -h gives me

df -h

Dateisystem Größe Benutzt Verf. Verw% Eingehängt auf
dev 1,8G 0 1,8G 0% /dev
run 1,8G 1,4M 1,8G 1% /run
/dev/sda1 39G 6,4G 30G 18% /
tmpfs 1,8G 0 1,8G 0% /dev/shm
tmpfs 4,0M 0 4,0M 0% /sys/fs/cgroup
tmpfs 1,8G 9,2M 1,8G 1% /tmp
/dev/sda2 411G 227M 390G 1% /home
tmpfs 364M 96K 364M 1% /run/user/1000

Thanks for any help.

2

you only need a 8Mb unformatted partition with flag_bios_grub ,
i think that grub and all modules for grub are inside , so i t can boot on ext4

3

this is what I had before the installation, but after the installation it’s ext4. So, it’s fine as it is?
The 8 mb partition (which is now ext4) is then not used by grub and grub is located on my root partition?

4

If you can boot it is fine.

However, the /boot/grub folder is just a config folder for grub and not program grub that boots.

Please provide

fdisk -l /dev/sda

and maybe also

lsblk /dev/sda
5

Hi,

here it is:

sudo fdisk -l /dev/sda
[sudo] Passwort fĂĽr top: 
Festplatte /dev/sda: 465,76 GiB, 500107862016 Bytes, 976773168 Sektoren
Festplattenmodell: ST500LM000-SSHD-
Einheiten: Sektoren von 1 * 512 = 512 Bytes
Sektorgröße (logisch/physikalisch): 512 Bytes / 4096 Bytes
E/A-Größe (minimal/optimal): 4096 Bytes / 4096 Bytes
Festplattenbezeichnungstyp: gpt
Festplattenbezeichner: 69E31F54-6843-6148-A970-99DF61C62E9A

Gerät         Anfang      Ende  Sektoren Größe Typ
/dev/sda1      18432  81938431  81920000 39,1G Linux-Dateisystem
/dev/sda2   81938432 958482431 876544000  418G Linux-Dateisystem
/dev/sda3  958482432 976768031  18285600  8,7G Linux Swap
/dev/sda4       2048     18431     16384    8M Linux-Dateisystem

Partitionstabelleneinträge sind nicht in Festplatten-Reihenfolge.

lsblk /dev/sda
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 465,8G  0 disk 
├─sda1   8:1    0  39,1G  0 part /
├─sda2   8:2    0   418G  0 part /home
├─sda3   8:3    0   8,7G  0 part [SWAP]
└─sda4   8:4    0     8M  0 part
6

This is not a “BIOS boot” partition. so it can’t be used by grub. Do you have any other drive connected to your system?

7

This is the partition I made, because the installer told me that when using a GPT Partition table with BIOS I should make a 8 MB big partition (unformatted) and mark it with bios_grub.

That’s what I did. After the installation it was formatted to ext4.

8

This is still a little bit weird. But as long as it works.

You could try to mount the partition, maybe there are some files on it.

9

I tried mounting it, but it tells me wrong fs type. I can try installing just with /, /home and swap. Maybe I don’t need that partition at all.

10

Maybe it is just the wrong type. How did you know it is ext4.

If it is a legacy boot system, you will need it.

11

this is shown in gparted, but it also tells me that the content cannot be read and that the partition is not mounted. I can delete it and see if it still boots. :smiley:

12

I deleted the 8 MB partition and it still works.

I only have /, /home and swap now. Filesystem is GPT and system uses BIOS. How is that possible?

13

I would bet your grub’s boot.ing ended up in the MBR and the core.img in sectors #34ff. The BIOS_grub partition won’t be used in that case. It’s a configuration which is not very well known and outworn, but usually it works. I would expect that this also could happen if CSM is not disabled when people try to install in UEFI mode.

Reference:
GNU GRUB - Wikipedia

14

Is it better to use MBR as the partition table then to be on the safe side?
I also tried to choose option “erase disk” in the installation manager. There it automatically chooses MBR as the partition table and I see no possibility to choose GPT. I only have root and home, so basically I don’t need nothing more fancy than just MBR.

Is this a bug in the installer then or did I make a mistake?

15

I don’t think so.

Sorry to say, but with every new post you show more that an installation in BIOS mode on a gpt parted disk is not a way you should go with your current skill level. You can not hope to always find a helping hand to guide you through all little issues your are going to face.

I would recommend you to decide to do an installation either in

UEFI mode on a gpt parted disk (recommended)

or

BIOS mode on a msdos parted disk with MBR (if you cannot boot in UEFI mode)

Use the time to search the web for grub, BIOS, UEFI, MBR, gpt to understand the basics before a new atempt of installation.

16

Ok, i’ll do more reading. As it is just a “test installation” on a PC which is not in use I’ll try to install it with UEFI. Thanks again.

17

Works in UEFI mode. I’ll also choose this on my main PC. Up to now I avoided UEFI.

18

GNU GRUB Manual > 4.4 BIOS installation > GPT

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