>
> 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.
>

sharing /boot actually can work *if* the 2 grubs are in separate
subdirectories, and if the kernels are different enough that updates from
one don't affect the other.  still tho it may work, it will likely lead to
significant confusion.
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