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As far as I remember the user (= you) that runs a software which should communicate with usb-ports must belong to the group "dialout" to use the ports.
Give it a try, just open a terminal an type in
sudo adduser xxx dialout
where "xxx" is your username.
A little late, but I can confirm that
"sudo usermod -a -G dialout [your_username]"
did the trick for me. Actually I neater found nor did the trick, it came to me by "accident" as I installed Arduino IDE (for playing with Marlin FW), and it did it all for me.. It was never Cura, just a stupid permission, however there is a way for software to ensure the needed permissions to work, so here we are.. (BTW RepetierHost and Repsnapper now works for me as well)
[Ubuntu] Cura 3.2.1 can't find USB connected printer
in UltiMaker Cura
Posted
A little late, but I can confirm that
"sudo usermod -a -G dialout [your_username]"
did the trick for me.
Actually I neater found nor did the trick, it came to me by "accident" as I installed Arduino IDE (for playing with Marlin FW), and it did it all for me.. It was never Cura, just a stupid permission, however there is a way for software to ensure the needed permissions to work, so here we are.. 
(BTW RepetierHost and Repsnapper now works for me as well)