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    SubjectRe: Console on USB
    On Tue, Aug 19, 2003 at 10:20:51PM -0500, Thomas Molina wrote:
    > I have just spent a very frustrating evening trying to get console on USB
    > working. My laptop does not have regular DB-9 serial connectors, only
    > USB. So I ordered a USB to serial converter,

    Which usb to serial converter? Not all of them work with Linux. Does
    this device work with Linux _not_ as a serial console device?

    > configured a 2.6.0-test3
    > kernel, added a console=/dev/ttyUSB0 to the kernel command line and
    > connected this to my desktop with a null modem adapter. However, I am
    > unable to get output from this setup on the desktop. On another setup I
    > can get a normal serial console output, so I am fairly confident I can set
    > things up correctly.

    Which "serial console" are you trying to get working? The kernel log
    console, or a login console?

    > Googling around and doing a search on lkml archives gave some minimal
    > help, but I can find very little info past early to mid 2.5 kernels. The
    > configuration doesn't quite seem to work the way I read documentation.
    > For instance, the web pages I can find indicate I should be able to build
    > this modular; however the configuration makes the setting of console on
    > usb depend on USB being y and EXPERIMENTAL being defined.

    What web page says you can build this modular? You have to build it
    into the kernel.

    > In /var/log/messages I can see the USB-to-serial converter being recogized
    > and the driver being loaded, just before the synaptics touchpad is probed.

    Can you show us the relevant part of the kernel logs?

    > It looks like things are correct, but, as I said, I am unable to get
    > output. Am I headed for frustration, or is there some advice to get good
    > results?

    You are headed for frustration. USB serial console was a neat hack, but
    pretty pointless. It has the following problems:
    - can't see oopses before USB starts up, and USB starts up
    almost last in the system boot process.
    - really can not capture oopses very well as USB is interrupt
    - most usb-serial converters have a very small buffer, so you
    constantly get over-runs in printing out console messages
    (meaning that only a few of the devices will even work
    properly, you usually have to buy one of the expensive ones to
    see all messages.)

    > Is there any advice I might be able to use to get this going? I really
    > want to be able to catch some oops output.

    Buy a machine with a serial port. That's my recommendation :)

    Good luck,

    greg k-h
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