Arduino not connected to serial port, under Linux

If you cannot see your arduino device listed under "Tools->serial port" of your arduino IDE, maybe you don't have the right drivers or ... more realistically you just have to chmod your device to your user :)

Example:

dmesg  
[13459.071825] ftdi_sio 2-1.2:1.0: FTDI USB Serial Device converter detected   

ls /dev/tty
...
ttyS6
ttyUSB <- that is our arduino

chmod 0666 /dev/ttyUSB

And you're done! :)