/dev/ttyS, "Input/output error"

This means that communication with the serial port isn't working right.

1. It could mean that there isn't any serial port at the IO address that setserial thinks your port is at.

2. It could also be an interrupt conflict (or an IO address conflict).

3. It also may mean that the serial port is in use (busy or opened) and thus the attempt to get/set parameters by setserial or stty failed.

4. It will also happen if you make a typo in the serial port name such as typing "ttys" instead of "ttyS".