Problem - The Arduino IDE 1.6.x will not see the your Arduino board or USB to TTL converster OR worse, the port option is greyed out! I post this here in the hope to help anyone who has found this horrible problem, as solving this may otherwise become a major waste of hours; it's a problem that is easily solved.
Sometimes the Linux distribution installs brltty (braille device) which will conflict with the Arduino. You must uninstall brltty! (Ubuntu 14.04 and later versions now does this by default)
You can use synaptic package manger to uninstall brltty OR do it from the command line:
Open a terminal window.
Type: sudo apt-get remove brltty
enter your password and wait for it to finish the process.
You should restart the Arduino IDE to see the result. You should now be able to see your board or other device such as a USB to TTL converter.