Comment # 4 on bug 963840 from Michael Chang

(In reply to Matthias Sch�nemann from comment #3)
> (In reply to Michael Chang from comment #2)
> > You need to edit your /boot/grub2/grub.cfg in your new /dev/sda5 for the new
> > fs uuid, 
> 
> Just to make sure, I did it (running grub2-mkconfig, I mean. I had edited
> the grub.cfg long since, I need the system).
> 
> Doesn't work. As far as I understand grub, it _can't_ work. grub2-mkconfig
> doesn't read it's own output from the last run, now, does it?

Sorry, but I didn't follow your question well, so my answer would not be for it
(but I'll try still..). 

It's os-prober issue and we are not talking grub2-mkconfig. The os-prober is
called to probe foreign partition and will delegate parsing grub.cfg of that
partition by linux-boot-prober to get kernel command line options. 

In your case please check grub.cfg in /dev/sda5 (Linux Mint) did really contain
the correct root=UUID=..., otherwise linux-boot-prober will just pass anything
in it to your master grub.cfg (your Leap 42.1).

Or you could just attach it here then we could have a look.

> 
> > ... Then os-prober should find correct uuid from it.
> 
> Regrettably no.

Please also attach output of 

   ts=`date "+%Y-%m-%d %H:%M:%S"`; grub2-mkconfig; journalctl --since="$ts"
--no-pager

Thanks.