title: Permission denied for ttyACM0 Port in nexus 5
body: <p>I am trying to connect external GSM modem with nexus 5 and send AT command using android RIL layer.I am using android 5.0 AOSP for nexus 5 downloaded from Google source.</p>
  
  <p>Error: Permission denied with trying to open ttyACM0 port.
  i have checked this by changing permissions but still permission denied error.</p>
  
  <p>Does there any other permissions do i have to change to open port?</p>