[cups] Debugging "Unable to send data to printer."

[Johannes Meixner]

Hello,

On Sep 28 11:12 Nicolas Schmidt wrote (excerpt):
>>> USB printer on an OpenBSD server
...
> After recompiling the kernel with the ulpt driver disabled,
> cups was able to print without any problems. Apparently
> libusb and ulpt should not be used both at the same time

In general one same piece of hardware cannot be used
by two different drivers in the kernel.

That "echo ... >/dev/ulpt0" had worked shows that the ulpt driver
is active for that piece of hardware so that libusb cannot
work at the same time for the same piece of hardware.

I am not at all a kernel expert but I think I remember that
with Linux one can somehow disable/enable whether or not
the traditional usblp Linux kernel driver should be used
for a USB printer or libusb - but (if I remember correctly)
both usblp and libusb at the same time are not possible
for the same USB printer.


> (although I?ve read that some people got cups to work
> with ulpt enabled, by adjusting file permissions, see here
> http://farid.hajji.name/blog/2010/02/02/printing-woes-on-freebsd-8-with-cups/

This was "Posted ... on 2 February 2010".

In 2010 there was CUPS 1.4 where the 'usb' backend
used the traditional usblp Linux kernel driver.

Since CUPS 1.6 that was released in 2012 the 'usb' backend
was changed to use by default libusb but there is a
configure option:
---------------------------------------------------------------
cups-2.1.0 $ ./configure --help | grep usb
   --enable-libusb         use libusb for USB printing
---------------------------------------------------------------

When you compile CUPS on your own you could perhaps use
a --disable-libusb configure option so that the 'usb' backend
still uses the traditional way to send data to a USB printer.

This is only a guess because I don't know about OpenBSD.


Kind Regards
Johannes Meixner
-- 
SUSE LINUX GmbH - GF: Felix Imendoerffer, Jane Smithard,
Graham Norton - HRB 21284 (AG Nuernberg)