> There are 20+ partitions on the hard disk so both systems have everything
> separate except /boot and /efi (whatever that partition is called).

so boot is shared?  if so, eek.  apt-get update on one will throw out
kernels still expected by the other.  and similar ugly contention for
maintaining grub.  this would explain why grub couldn't find the other OS.

advises that users do not directly edit grub.conf, and use their own
> "discovery" and mangement
> of GRUB scripts.
> But I always tweak the grub.conf myself.

grub.conf is regenerated, and your mods lost, whenever a new kernel is
installed.  i know, i hated it when i first started learning grub2.  your
mods belong in /etc/default/grub and /etc/grub.d/40_custom.  copy 40_custom
to 07_custom and stuff in there will precede, and thus be what boots by
default.  put in there entries which boot via the kernel and initrd in /,
those softlinks are updated whenever a new kernel is installed.  then
either regenerate grub.conf, or i confess i then edit the same mods into
grub.conf as well, it's just plain far quicker.

also if you're interested in how to boot multiple installs all from the
same partition, just ask.

this concludes test 42 of big bang inflation dynamics.  in the advent of an
actual universe, further instructions will be provided.
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