Re: How does one add a second Ubuntu installation to an existing one?

[Pascal Hambourg]

Le 16/05/2021 à 19:09, Chris Green a écrit :
> I want to add a second version of Ubuntu to my existing xubuntu 20.10
> desktop machine, I want it to be a dual boot system.
>
> I just want to end up with a boot menu that defaults to the existing
> xubuntu 20.10 installation but will allow me to choose Ubuntu (server)
> 20.04 at boot time if I need to.
>
> To add a slight complication my 20.10 installation has a separate
> /boot partition and drive because the main NVME SSD isn't visible to
> the BIOS.

I do not see any complication here. A separate /boot is common practice.

> So I have the following drives:-
>
> /dev/nvme0n1p2 ext4     48174  15748  29912  35% /
> /dev/nvme0n1p3 ext4    896193 295874 554727  35% /home
> /dev/sdb1      ext4     10016    183   9306   2% /boot
> /dev/sdb2      ext4    109596  33138  70850  32% /scratch
> /dev/sda1      ext4    938772 222399 668664  25% /bak
> /dev/sdc1      ext4    937872     77 890087   1% /mnt
>
> The new Ubuntu Server installation can go on /dev/sdc1 as that's empty.
>
> What's the easiest (and least error prone) procedure for doing this?

Install Ubuntu Server in /dev/sdc.
Install its GRUB in /dev/sdc (I assume Xubuntu's GRUB is in /dev/sdb).
Boot Ubuntu Server from the BIOS boot menu, add 
"GRUB_DISABLE_OS_PROBER=true" in /etc/default/grub and run update-grub 
to remove Xubuntu from /boot/grub/grub.cfg. [1]
Boot Xubuntu and run update-grub to add Ubuntu Server to 
/boot/grub/grub.cfg.

[1] This step is not needed if Xubuntu and Ubuntu server use different 
kernels.