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Understanding EFI, GRUB and all that jazz

Posted: Tue Sep 15, 2020 10:27 am
by GS3
In the good old days before EFI the BIOS would have a look around and tell you what devices you could boot from and would have a default boot order you could set. You could connect or disconnect devices and it would not affect the rest. One bootable device knew nothing about any other bootable devices. Simple, easy and it worked.

Enter the EFI which was done to solve some problem of which I am not aware (except maybe helping MS prevent other OS from booting).

Now we have EFI and, I for one, all the problems which come with it. Which are many and frequent. I see EFI entries for things which I have no idea what they are or may be or may have been.

Every time I add some device it seems the EFI list gets more mangled.

GRUB was updated and that mangled things even further.

So I am trying to understand how this thing works and see if I can make any sense of it.

It seems to me the EFI boot list or table is kept on NVRAM on the mobo and this list can be modified by the BIOS itself or by any of the OS installed which is a problem when they all decide to mess with entries for other OS. Which I think is what is happening to me.

Somehow entries keep being added which I think just are duplicates of existing entries. Once one entry was deleted but I think it was overwritten by another entry.

So, if I focus only on three of the entries It seems to me the first one "Ubuntu" points to a GRUB on the HDD where LM18 resides but that GRUB menu also gives me the option of starting LM19 which resides on a different SSD

If in EFI I choose the second choice, "Ubuntu" it sends me to GRUB on the SSD and it only gives me the choice of booting LM19 from that very SSD.

If in the EFI menu I choose the third choice, "Mint" (this entry was created manually to replace one which was deleted) it send me to the same GRUB menu as the first choice, with the same options.

I am not going to list all the entries because there are too many.

Is my understanding so far correct?

It seems to me it would be better to have each drive be self-contained and not have GRUB pointing at an OS on another drive.

Not only that, entries are added to the EFI list which I think are duplicates of existing entries. Why?
Does the BIOS not recognise the drives already have entries?

It seems to me since GRUB was updated all these problems have cropped up.

And I have the HDD containing Windows 7 physically disconnected and I am afraid to connect it. If the EFI/BIOS has problems with two versions of LM I hate to think how trying to have Windows and Mint get along would work out. Probably each one deleting the other's entries.

Come to think about it, does "Secureboot" lock the EFI in place as it is? Because I guess I could try to get the EFI in a reasonably usable state and then lock it so no one could mess with it.

I have half dozen EFI entries named "Ubuntu" and I don't need any more.

Should I be afraid to physically connect the Windows HDD? Will it kill the EFI entries for LM so I can no longer boot?

Re: Understanding EFI, GRUB and all that jazz

Posted: Tue Sep 15, 2020 4:42 pm
by Portreve
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Re: Understanding EFI, GRUB and all that jazz

Posted: Thu Sep 17, 2020 4:37 pm
by lexon
I got around that by buying a Dell laptop with W10 about three years ago when my Two Acer's all failed with Linux. Could not figure out dual boot anymore even following instructions here. Details not the same.
I bought another with Lenovo from Amazon with Linux Mint on it. USB mouse not recognized. Must need a driver but no CD machine in it.
Problem solved anyway.

L

Re: Understanding EFI, GRUB and all that jazz

Posted: Thu Sep 17, 2020 4:38 pm
by lexon
I will not mess up a good W10 PC.

L