Had to get access to serial port with new 64-bit Ubuntu 18.04 OS

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Your user account probably doesn't have permission to use the serial port.
Two ways to address this:

• Easiest, but not advised: Run the Arduino IDE as root (eg launch from the command line using sudo).
• The second, more advisable way to do it is to add your user to the dialout group, which has permission to use the serial port. Use the command sudo adduser $USER dialout. You will need to log out then log back in for it to take effect though (or try this). To list groups of current user use groups or id -Gn.

Once this is done, when you select the correct serial port (as others have mentioned maybe /dev/ttyUSB0) you should be able to write, allowing you to program the Arduino.