tmux and the arrow keys

If the arrow keys do not work, try setting the environment variable TERM to "xterm-256color".

This should solve the issue!

USB serial devices and Arduino Yun

How to use USB serial devices on an Arduino Yun

You have a device send serial data via USB like an Arduino UNO, Leonardo or similar?
You need to run:

opkg update
opkg install kmod-usb-serial
opkg install kmod-usb-acm

After that you should find  that device as "/dev/ttyACM0".