Re: Console on USB

[Greg KH]

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
	  driven
	- 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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