I can only guess that what you're referring to here is that they could then have full access on your server. There are the root_squash options to get around that. I can never remember which way is which though, no_root_squash vs root_squash, thank you man page ;).
and what prevents root to change to the required uid? nowthing ;-) -- To unsubscribe from this list go to the following URL and read the instructions: https://lists.samba.org/mailman/listinfo/samba
