The Yun is more like a Leonardo than an UNO, so you should use Serial1 for the sending object (given you connected the Due to pins 0 and 1, by some level converters, I hope).
The Yun is more like a Leonardo than an UNO, so you should use Serial1 for the sending object (given you connected the Due to pins 0 and 1, by some level converters, I hope).