Hi Peter,
> how can I find all the files owned by some user or group (in
> preparation to delete the user/group)?
find(1).
See https://wiki.archlinux.org/index.php/Find#Essentials
sudo find /start1 /start2 \( -user foo -o -group bar \) -ls
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Cheers, Ralph.
https://plus.google.com/+RalphCorderoy