Grub2 problem - can only boot to 2 of 3 OS's

[Liam Proven]

On Fri, 29 May 2020 at 04:48, jim <jf_byrnes at comcast.net> wrote:
>
> I had a system with Mint18.3 and Ubuntu18 installed. I had 100GB of free
> space at the end of the disk. I decided I wanted to install mint19.3 in
> the free space. I booted from the Mint19.3 install dvd. I used gparted
> to shrink the Ubuntu partition so I ended up with about 195GB of free
> space. I then had gparted create a new partition in the free space and
> installed Mint19.3.
>
> This is my configuration:
>
> Partition 1 = sda1 - Ubuntu18
>
> Partition 2 (extended) = sda6 - Mint18.3
>                           sda5 - swap
>
> Partition 3 = sda3 - Mint19.3

2 questions.

[1] Presumably you have an MBR-format disk, if you have an extended partition.

So, if it's there, why not just make another logical partition for
Mint 19.3? It would be easier and cleaner.

[2] When you installed the new distro, where did you tell it to
install its bootloader, do you know?

I think you may now have 2 or 3 copies of GRUB. 1 for Ubuntu, one for
Mint 18.3, one for Mint 19.3.

If you pick one to be the "master" -- i.e. the main one, for the OS
you use the most -- you can move the others by telling them to install
GRUB into their root partition(s), not into the MBR.

Boot the relevant non-master OS, say off /dev/sda5, and run

$ sudo grub-install /dev/sda5

or if off /dev/sda3:

$ sudo grub-install /dev/sda3

This means that they won't fight over the MBR.

On the main OS, boot it up as normal, _check you have mounted the root
drives of *all* OSes_ then run

$ sudo update-grub

It _should_ detect the others and add them to its menu.

You need to do this every time you update any of the OSes.

So if you boot Mint 19, update Mint 19, then to use the new kernel, you need to

#1 Reboot into Ubuntu
#2 Mount all partitions
#3 Update Ubuntu's copy of Grub
#4 Reboot _again_
#5 Now you can reboot into updated Mint

Yes it is a minor PITA but it's easier than switching to a whole new
boot manager, IMHO.

rEFInd won't work on a BIOS machine, AFAIK. I have only tried it on
Macs and although it worked, I found it a pain to deal with.

-- 
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