[SOLVED] Grub issues with GUID partition table warnings in dual boot setup

Sorry, your disk sdc is msdos.
You need to reinstall.

It may work presently, but it will not last.
Make you sdc gpt and prepare partitions ready before installing.

ps: read here for why we shouldn’t install uefi to msdos.

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Yes, reinstalling looks like the good choice. However,

My sda is msdos with legacy windows too. If I install Manjaro the msdos/Legacy BIOS way, then I’ll have everything msdos (sdb is just an extra gpt storage drive. windows/sda can access it so itll be fine). Doesn’t that sound like a better option?

I.e. instead of upgrading to gpt/uefi. Isn’t it better to downgrade to msdos/bios?

Best, if possible, use the same disk as windows.
If you use another disk, remember to ‘set grub’ to the windows disk (usually sda). That’s a common failing for most multiple msdos disk setup.

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Oh I see. Surely I can ask windows to shrink and offer me a small 4th partition 5mb on which i can mount grub (/boot/, boot flag only). I can format sdc, and mount manjaro’s root (no flag, mountpoint /) and some swap(mountpoint linuxswap, flag swap) on all the space there.

I won’t do the reinstall right away; i have some things for 2 hours. Hence, probably tomorrow.

In msdos/bios-legacy, there’s no need for /boot partition.
You can if you want to, but there is no advantage, in fact, more hassles and more things to go wrong and more difficulties to fix if things go wrong. {But I guess many people are bored :laughing:}

However many disks we have, there need to have only one swap partition, in a fixed internal disk, preferably. If swap is in an external disk and is not there when booted, there will be errors and boot will fail. swap is optional and newer computers with much ram don’t really need ram - okay, caveats apply, not worth to discuss, leave it to the experts who uses VM, etc…

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Hmm…what do you mean by that?
I use CSM/Legacy exclusively with zero problems on a dual-boot machine. The installed Manjaro even uses GPT.
The reason for that is a rather bad EFI implementation of the motherboard.

Or do you mean that changing from one to the other is a bad thing? That is definitely true.

You don’t “need” to do that. In fact, I suggest you

  • install Manjaro at sdc (where it was already), leaving the drive partition scheme as “msdos” (not GPT),
  • delete all partitions (actually, you don’t need /boot/efi in an MSDOS/MBR installation)
  • use the installer to create / (root) and swap and possibly /home for your local/personal data.
  • Install GRUB on the same (Manjaro) drive, currently /dev/sdc
  • Set your BIOS disk boot priority to the Manjaro drive.

This way you can even use your BIOS Quick Boot menu to boot to either Windows drive/bootloader or Manjaro drive/bootloader. IMHO this is core clear and lets you more options.

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Not if the Manjaro drive is not sda (it is sdc).
Yes, he can bring it up at bios level if he wants sdc to boot but he has to do that everytime when he boots. He doesn’t need to do that if he ‘sets mbr’ to sda, which is not the manjaro drive.
Have you forgotten how msdos/bios-legacy works? :laughing:
I still have a msdos/bios-legacy system.

ps: maybe if he has a msi… :rofl:


Not in my experience. I only have MSDOS/BIOS Legacy drives.

Right back to you!! :mask:

Fact 1
In a msdos/bios-legacy system, without touching bios setup or boot setup, system will boot the bootloader from the mbr of the primary drive, commonly called ‘sda’.

We don’t need Fact 2 or Fact 3… :grin:

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In my msdos/bios-legacy system … of the primary drive, commonly called ‘sda’

In all msdos/bios-legacy systems I have worked with (several from other users), there is a BIOS setting to choose Boot drive priority. This setting is permanent for subsequent boots and can be overridden from a Quick Boot selector with a shortcut (different than normal BIOS Setup shortcut).

Please continue to your embarrassment… :laughing::rofl:

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Not in the bios-legacy I have/had, and I had I think more than 4.
What system do you have? A msi? :laughing: Please tell us using your favourite ‘inxi’ and what is this “BIOS setting to choose Boot drive priority”? Not bios setup (like F2), you say. Not boot key like F11 (or F8 ~ F12).

You have something within bios-setup (F2) and in ‘Boot’ you select the drive priority?
You must mean that. I’ll reboot to F2 and recheck that. Please do it too yourself to confirm.

ps: you only have msdos/bios-legacy?
I’m impressed. You’ve answered several posts on uefi/gpt.

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It seems they are not enough. I guess you are stuck in the minority… :stuck_out_tongue_winking_eye:

Asus (three) and Acer laptop

Untill I make a special inxi command for that, can you accept an image?


Thank you! This shows my extended understanding and learning capabilities!!

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Okay, I’ve rebooted and at bios-setup (F2), I changed Boot drive Priority to the other disk.
It still uses the ‘normal’ disk bootloader to boot.
But, the ‘other disk’ does not have any bootloader
Do you have the bootloaders in 2 or more disks ‘set to their mbr’s’?

Perhaps it should disqualify you to answer topics on gpt/uefi! :rofl:
But yes, I am impressed.
How about answering posts on systemd-boot and rEFInd (that you do not use)? LOL!!

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RTFMing, of course.

It’s too late now. I have been trained from the best gurus!! :wink:

IIRC we had talked about this method in the past. That’s why I am very much surprised you had this impression…
I have my SSD installed Manjaro grub on my SSD MBR and my HDD installed Manjaro (or whatever) grub on my HDD MBR. While I have them updated, I can boot from both to any, so a failure on one bootloader does not break the other.


Now I’ve learned another thing from you.
That makes you a guru.
Cheers and thanks.


I installed a BIOS version of Manjaro. I went for Guru-petsam’s words of wisdom:

And eveything works great, when I boot override into Manjaros. Both the windows and manjaro can be booted from grub (and everything looks… faster?). I hit grub consistently and the image resolution looks neat! The last step:

Was a bit trickier. Only one option for booting was shown in the list of booting priorities: boot into sda, windows. However, another option, “Hard drive BBS priorities”, allowed me to choose which drive gets looked into first to derive a boot order priority list from. Now "P2: WDC - ". Everything boots naturally into Grub, everything looks good. Onwards to my Wifi drivers!

I hope with all the knowledge I gained I’ll be able to give first aid on the forums while the calvary arrives (gohlip, petsam, fhdk and cscs). I guess near-bricking your computer is sort of an initiation ritual to new users (^^).


Well done! You are now in the list of Grub assistants!

Now mark the post that is your solution (tricky puzzle…) as “Solved”.

OH snap! I only edited the title to say so x.x

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