when a arduino is plugged in the device /dev/ttyUSB0 will be created by the operating system, and it will be removed when the arduino is unplugged.
Unplug your arduino
Open a console window and list the current devices with
ls -all /dev/ttyUSB*plug your arduino into your machine and list the devices again
ls -all /dev/ttyUSB*You should now see the device created for the Ardunio.
If not, please check the system log with
dmesgIt should contain some kind of error report.