First time set up- permission denied to usb port- ubuntu 14.04
From the documentation:


  Open Terminal and type:

ls -l /dev/ttyACM*

  
  you will get something like:

crw-rw---- 1 root dialout 188, 0 5 apr 23.01 ttyACM0

  
  The "0" at the end of ACM might be a different number, or multiple entries might be returned. The data we need is "dialout" (is the group owner of the file).
  
  Now we just need to add our user to the group:

sudo usermod -a -G dialout $USER

  
  then:

sudo chmod a+rw /dev/ttyACM0

  
  You will need to log out and log in again for this change to take effect.


Note that the preceding is old Ubuntu instructions. On modern distros that use ConsoleKit create the file /etc/udev/rules.d/01-ttyusb.rules containing the following and then reload the udev rules and replug the Arduino device:

SUBSYSTEMS=="usb-serial", TAG+="uaccess"