Re: [gentoo-user] Re: How to set up drive with many Linux distros?

[Michael <confabulate@kintzios.com>]

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On Friday, 8 March 2024 23:24:02 GMT Grant Edwards wrote:
> On 2024-02-22, Grant Edwards <grant.b.edwards@gmail.com> wrote:
> > For many years, I've used a hard drive on which I have 8-10 Linux
> > distros installed -- each in a separate (single) partition.
> > 
> > [...]
> > 
> > Is there an easier way to do this?
> 
> After some additional studying of UEFI and boot managers like rEFInd,
> I decided that my current approach was still the easiest method. I did
> switch from DOS to GPT disklabel (I bricked my old drive tring to
> update the firmware, so I had to start over anyway).
> 
> In case anybody is interested in the gory details, I documented my
> scheme and the helper shell scripts at
> 
>   https://github.com/GrantEdwards/Linux-Multiboot


Thank you Grant for taking time to share your clear and well structured write 
up, what with helpful scripts and all!  Its easy to follow and should help 
others, hopefully before they discover belatedly many distro installers can 
mess up a multiboot scheme, if they don't step in to keep things in check.

Perhaps I'm picking up on semantics, but shouldn't this sentence:

"... The gap between the DOS disklabel and the first partition"

read:

"The gap between the MBR and the first partition"?

I'm saying this because the MBR in sector 0 contains the bootstrap code (446 
bytes), the partition table (a.k.a. DOS disklabel 4x16 bytes) and the boot 
sector signature (2 bytes).  On MBR partitioned disks the core.img is stored 
after the MBR, in sector 1 onward.

Your next paragraph pointed out something which I hadn't considered at any 
length.  Namely, the installation of GRUB's boot.img in a MBR or VBR also 
hardcodes in a block list format the location of the first sector where the 
core.img is stored and more importantly, the physical position of this sector 
can be altered both by COW fs (and by the wear levelling firmware of flash 
storage devices).

I had assumed both the COW fs and/or the flash controller will in both cases 
translate any physical data position to the logical layer and presented this 
to inquiring software.  Have you actually tried using btrfs as a distro's root 
fs to see if the VBR installed GRUB boot.img will ever lose access to the 
core.img?

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