Arduino IDE error - avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied

If you run Arduino IDE on Ubuntu (Arduino 1.5.7 and Ubuntu 14.04 in my case), most possibly you cannot upload to Arduino board, caused by the error of:

avrdude: ser_open(): can't open device "/dev/ttyACM0": Permission denied
ioctl("TIOCMGET"): Inappropriate ioctl for device

To fix it, enter the command:
$ sudo usermod -a -G dialout <username>
$ sudo chmod a+rw /dev/ttyACM0

Where <username> is your user name in Ubuntu, /dev/ttyACM0 is the detected device of your Arduino board.

ref:
http://arduino-er.blogspot.ca/2014/08/arduino-ide-error-avrdude-seropen-cant.html