Re: [gentoo-user] Grub, gpt partitions and BIOS, not uefi thing.

[Dale <rdalek1967@gmail.com>]

Michael wrote:
> On Saturday, 27 April 2024 17:53:25 BST Dale wrote:
>> Howdy,
>>
>> I'm installing Gentoo on another old box.  To be consistent I like to
>> use cgdisk, GPT I think it is called, to partition all my drives,
>> regardless of size.
> GPT is the partition table structure, which is more advanced than the old DOS 
> partition table structure.
>

I just wasn't 100% sure what it was called. 

>> Thing is, Grub works differently with GPT than it
>> does with the old DOS or whatever it is called, like fdisk does in the
>> old days.
> GRUB works the same, but the disk/partition table structure is different.
>
>
>> I did some research but still find myself in some muddy
>> waters.  My take on some things I've read, I need a boot partition, not
>> to be confused with the /boot for kernels, init thingys and such.  Where
>> I get lost, most use gdisk.  I like cgdisk.  Before that I liked
>> cfdisk.  Anyway, how do I set up that partition with cgdisk?  Any
>> minimum size requirements or tiny is enough?
> 1MB

OK.  You know that "alignment" thing that is always on the beginning of
a drive, could it use it?  I think it is like 2MBs or something. 

>> Does it have to be a
>> specific type?
> Yes, it has to be set up as a "BIOS Boot Partition", with the "ef02", or GUID 
> 21686148-6449-6E6F-744E-656564454649.
>

Light bulb moment.  I've seen 8300 and friends, 8200 etc but never seen
EF02 before.  Now I see what that type means.  That cleared up some
muddy water.  That lead me to finding this, it has a nice table of
common codes. 

https://wiki.archlinux.org/title/GPT_fdisk



>> Does it need to be in a specific place?  
> Not necessarily, but since you're not booting this disk on a UEFI MoBo and 
> consequently won't be using an EFI System Partition (ESP), the very first 
> partition is fine and will be out of the way of the remaining disk.
>
>
>> Formatted with a file system?
> Do not format it.  The raw 1MB partition will be used by GRUB to install its 
> core.img file.
>
>
>> Also, when I do grub-install, do I still point to
>> /dev/sda or to /dev/sda1, if sda1 is the special boot partition?
> Sector 0 of your disk /dev/sda is where GRUB will drop its boot loader image 
> 'boot.img'.  This is the Master Boot Record region.
>
> Normally, with a DOS partition table, GRUB's core.img would be dropped in the 
> empty space of sector 1, following sector 0.  However, in the GPT structure 
> sector 1 is where the GPT partition array data is stored.  You don't want GRUB 
> making a mess by dropping it's core.img on top of it!
>
> So, from what I recall you'd install GRUB like so:
>
> grub-install --boot-directory=/mnt/gentoo/boot --force /dev/sda
>
> If this won't do it, I'll have to boot an old system of mine to check the disk 
> layout in more detail.
>
>

I may look on youtube and see if I can find someone setting up a disk. 
It may have a video, old one for sure.  Maybe that will help me make
sense of it even more.  I think I got figured out how to use cgdisk now
but installing grub may require some more details. 

What I find odd, most of the howtos I found don't show example outputs. 
Then again, it could just work.  O_o

Thanks to all. 

Dale

:-)  :-)