in Linux? All too often, installing GNU+X+Linux (any distro), everything works but the serial ports. Recently I've been seeing known good PC-Card (aka "16-bit PCMCIA") hardware modems go unrecognized by Hotplug in certain laptops. I also see these modems work correctly (V.90 full speed) with hand-configured "pon" but only run at 9600 under KPPP's automatic configuration.Kernel messages aren't much help. (I know what the LSR is, but why does it have a "safety check"? The old Serial-HOWTO's answer to that question is wrong.) Historically, we could use cu(1) (from Taylor UUCP) to connect (or not) to an external modem, and even though its error messages are vague and misleading they'd tell you about broken handshake lines, wrong "baud" rates, etc.So what tools do you use to discover and configure serial ports, when the driver and setserial get it wrong? How do you tell what's really going on when cu -l/dev/ttyS? gives its infamous "device busy, line in use" message?