So I go over to a stock rh7.1 box, compile my serial port application. Run it, it fails since I don't have privileges to /dev/ttyS0. I'd normally do a: su - chmod u+s /dev/ttyS0 or chmod u+s serial_prog Problem is that this lets everybody have root privileges. I would guess that a better way would be to make me part of the select group that has privileges to /dev/ttyS0. ls -l /dev/ttyS0 crw-rw---- root uucp ....... Say I have a UID of "karl", apparently I default to being my own group named "karl". So how do I make user karl be a part of the uucp group? I assume then I would be able to use the port.