Re: Using udev as-is and device URI

[José Alburquerque <jaalburquerque@cox.net>]

T wrote:

> Hi
>
> I know that udev has the advantage that allowing people to write their own
> rules for mounting the devices. But can I just use the udev as-is? Does
> udev fully backward compatible with traditional /dev directory?
>
> I have a Epson Stylus CX1500, which has been working fine. I used to check
> the ink level with the command:
>
>  $ escputil --ink-level --new --raw-device /dev/usb/lp0
>
> But now, having upgraded from Sarge to Etch, the command does not work any
> more. Is it because of udev or the escputil itself? Now when the command is
> issued, the printer reacted with some noise then tried to print something,
> then stopped. The escputil just hangs there.
>  
Hi. :-) I have an Epson Stylus C82 (also connected via USB).  On my etch 
system, the escputil command above works exactly as you have it without 
any problems:

jose@sweety:~$ escputil --ink-level --new --raw-device /dev/usb/lp0
Escputil version 5.0.0-rc3, Copyright (C) 2000-2006 Robert Krawitz
Escputil comes with ABSOLUTELY NO WARRANTY; for details type 'escputil -l'
This is free software, and you are welcome to redistribute it
under certain conditions; type 'escputil -l' for details.

        Ink color       Percent remaining
            Black                      82
             Cyan                       6
          Magenta                      10
           Yellow                      26
jose@sweety:~$

> Moreover, how does the device URI work?
>
> To be specific, after upgrading from Sarge to Etch, I configured my CUPS the
> Sarge way, and it works great. Then I found that there is an auto-detected
> printer, so I give it a try too. However, no matter how I tweak it, it just
> refuses to work. The following list is the 2 CUPS printer in my system. The
> 1st works, the 2nd doesn't. The only difference that I can tell now is the 
> device URI. 
>  
I also used the auto-detection function when configuring my printer.  
Here's what CUPS (http://localhost:631) says:

*
Description:* Stylus-C82---CUPS+Gutenprint-v5.0.0-rc3
*Location:*
*Make and Model:* Epson Stylus C82 - CUPS+Gutenprint v5.0.0-rc3
*Printer State:* idle, accepting jobs, published.
*Device URI:* usb://EPSON/Stylus%20C82

What's really interesting is that though the printer has a device URI, 
it can also be accessed via /dev/usb/lp0.

> Please help
>
> thanks
>
> epson_cx1500:
>
> Description: Epson Stylus CX1500
> Location: USB Printer #1
> Make and Model: Epson Stylus CX1500 - CUPS+Gutenprint v5.0.0-rc3
> Printer State: idle, accepting jobs, published.
> Device URI: usb://EPSON/Stylus%20CX1500
>
> USB_Printer_1:
>
> Description: EPSON
> Location: Local Printer
> Make and Model: Epson Stylus CX1500 - CUPS+Gutenprint v5.0.0-rc3
> Printer State: idle, accepting jobs, published.
> Device URI: epson:/dev/usb/lp0
>  
A couple of things that I've noticed on my system that may be helpful to 
you (I'm sure you probably know some of them, but anyways!): :)

1) The device files (I found one at /dev/usb/lp0 and another at 
/dev/bus/usb/001/002) disappear when the printer is turned off (They 
reappear when the printer is turned on, however, the one at 
/dev/bus/usb/001/ reappears as a different name eg. /dev/bus/usb/001/003)

2) I've found that if a user is not in the lp group, he/she cannot 
access the printer (directly through escputil or otherwise)

3) If the printer is off, the device files are not present (at least on 
my system).

I'm no expert on device URI's but I've found that the hal-device-manager 
command (found in the similar named package) is quite useful.

I'm sure I haven't answered your questions, but I hope some of this info 
helps.

Take care.

Sincerely
Jose