on my Laptop=Dell latitude E6510, RAM=8Gb, GPU=GT218 NVS 3100M, CPU=i7 Q 720 @ 1.60GHz running opensuse leap 42.2, plasma 5.9.1, KDE frameworks 5.30.0, KDE applications 16.12.1, Kernel 4.4.36-8-default, nvidia drivers:
if I login with user “pla” then switch to user “nipoti” and in “nipoti” I insert an usb key it result not accessible and in the “pla” session the root password is asked, if I insert the usb key in the “pla” session the root password isn’t asked.
so, how can I avoid to be asked for root password when inserting an usb key in user “nipoti” ???
manythanks, ciao, pier 
How exactly do you switch between the users? Do you log out as “pia” and log in as “nipoti” or do you just “switch users” (suspending the session)?
Passwordless mounting of USB thumbdrives is done via per-user policies. Therefore, if you log in as “pia” it might be that the access to USB devices is assigned to “pia” on log-in and remains that way after logging in with “nipoti” afterwards. However, this is strange regardless and might be worth further investigation to see whether the situation is reproducible.
uh, I didn’t logout from “pla”, I switched the user by the user switcher widget choosing new session, so I suppose suspending the session.
yes, tried now, twice, it seems reproducible, I was logged in as “pla”, switched to “nipoti” by the user switcher widget choosing new session, when I was in “nipoti” inserted an usb key and nothing happen in nipoti, the usb key is recognized but not accessible, I switch back ti “pla” by ctrl+alt+F7, and in “pla” desktop there was the window of request of root password.
manythanks, ciao :-), pier