A couple of further details: First, I notice that the "No such device" in fact does *not* appear in the log files, but appears in the boot messages in real time -- so I suppose that means that setserial is putting this message out on its stderr rather than stdout. Second, I have confirmed that echo "AT" > /dev/ttyS14 produces /dev/ttyS14: No such device Hope somebody finds this useful! -- Andy Young