in which way it is not recognized?
Under Ubuntu the Arduino UNO will be found under /dev/ttyACM0 (in my case), to get access via the IDE you need to change the rights of that port to 666 or better you must make your current user member of the dailout group using:
sudo usermod -aG dailout
BTW: a Mega Board will be listed under /dev/ttyUSB0
(The number of the ports can be different from 0)
//E You have to relog after you modified your groups in order to get it work.