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

[Pascal Hambourg]

Le 19/05/2021 à 14:02, Chris Green a écrit :
> I've realised the easiest thing to do will be to simply duplicate my
> existing xubuntu 20.10 installation on another partition.  As before
> partitions are:-
>
> /dev/nvme0n1p2 ext4     48174  15782  29877  35% /
> /dev/nvme0n1p3 ext4    896193 295877 554724  35% /home
> /dev/sdb1      ext4     10016    183   9306   2% /boot
> /dev/sdb2      ext4    109596  33138  70850  32% /scratch
> /dev/sda1      ext4    938772 222397 668666  25% /bak
> /dev/sdc1      ext4    937872     77 890087   1% /mnt
>
> If I simply copy / to /mnt and also copy /boot to / how do I get grub
> to add the new partition to the boot menu?  (/dev/sdc is a SATA disk
> so is visible to the BIOS so /boot can be on there with the OS)
>
> Then if, when I ugrade my 'main' xubuntu 20.10 to 21.04, it falls in a
> heap I can simply boot the xubuntu 20.10 on /dev/sdc1 and everything
> will still work as before (if a little more slowly).

Duplicate an installed system requires a few more steps because the copy 
uses different partitions. You need to adjust /etc/fstab and 
/boot/grub/grub.cfg with the new / UUID and no separate /boot.

I would also install GRUB on /dev/sdc from the copy to be able to boot 
if the original installation is so broken that even GRUB does not work 
any more.