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I'm having a problem here, I have a modem that worked on a linux machine perfectly. Suddenly, it doesn't work any more. Linux no longer can see a modem on /dev/ttyS0

Linux doesn't see it using the wvdialconf command.

The dialup modem is hooked up through the serial port (/dev/ttyS0). I use wvdialconf to have it work correctly.

What could be the problem, is there a special lock file I need to manually remove? How can I debug this problem?

By the way, its not a modem problem because the modem works when connected to a different linux machine.

Here is the output of the wvdial.conf command:

[root@localhost ~]# wvdialconf wvdial.conf Scanning your serial ports for a modem.

Port Scan<*1>: Scanning ttyS0 first, /dev/modem is a link to it.

ttyS0<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud

ttyS0<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 115200 baud

ttyS0<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up.

ttyS1<*1>: ATQ0 V1 E1 -- failed with 2400 baud, next try: 9600 baud

ttyS1<*1>: ATQ0 V1 E1 -- failed with 9600 baud, next try: 115200 baud

ttyS1<*1>: ATQ0 V1 E1 -- and failed too at 115200, giving up.

Port Scan<*1>: S2 S3

Sorry, no modem was detected! Is it in use by another program?

Did you configure it properly with setserial?

Please read the FAQ at http://open.nit.ca/wvdial/

If you still have problems, send mail to [email protected].
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I'm a little confused about the testing procedure in use.

I presume that the modem in question is being powered down and powered back up between the connecting it to different computers. Is the same cable being used on both systems?

If the port on the machine worked and just failed, and does not work now, did you power down and then restart the system with the problem persisting? Unfortunately, sometimes hardware gets into a funny state and needs this step.

Have you tried using a terminal emulator program and directly try to talk with the modem using the serial port?

Have you tried using the other TTY port on the machine? On most hardware that I have recently been exposed to there are usually two serial ports.

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It worked now. Although I restarted the machine before, the magic step that I didn't do and mdpc helped me out with is to "power down the machine". This fixed the problem.

Weird problem, I don't know if there is a way to reset the serial port without having to power down then restart the server.

Anyway, thanks mdpc.

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  • As a matter of fact: No, you technically cannot reset the serial port without power-cycling. While most hardware supports it, AFAIK serial (and parallel) ports were never officially "hot-plug" (hotplugging could even electrically damage the ports), so the only safe option is to only touch the plugs when the computer is off.
    – sleske
    Oct 16, 2009 at 10:58

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