[cups] Unable to add a printer

[Johannes Meixner]

Hello,

On Apr 29 17:34 Znoteer wrote (excerpt):
> On Mon, Apr 29, 2019 at 07:51:19PM +0100, Brian Potkin wrote:
>>> I've just reinstalled Debian 9.9 and cups to a computer.  I have an HP
>>> LaserJet 6P attached via USB cable.  I am unable to add the printer to cups.
...
>> /usr/sbin/lpinfo -v
>
> $ sudo lpinfo -v
...
> direct usb://Unknown/Printer

your printer is physically connected via USB cable
but it is not recognized by the CUPS 'usb' backend
so that your printer is invisible for CUPS and as a
result you cannot configure your printer with CUPS.

See "What is a CUPS backend and how does it work" in
https://en.opensuse.org/SDB:CUPS_in_a_Nutshell
and see "Connection" in
https://en.opensuse.org/YaST_Printer#Connection

When the CUPS 'usb' backend cannot detect a printer
that is physically connected via USB cable the usual
reason is lower-level USB issues (USB hardware, kernel,
libusb, whatever... ).

You can run the CUPS 'usb' backend directly as root
by calling its program file directly e.g. like

/usr/lib/cups/backend/usb

so that you can directly see all its output messages
including its DEBUG messages. The CUPS 'usb' backend may be
installed under a different path in your Linux distribution.

See "The printer must be accessible" in
https://en.opensuse.org/SDB:Installing_a_Printer
which is somewhat outdated because nowadays USB printer access
does usually no longer happen via the usblp kernel module
but more directly via libusb.

In general regarding USB you may also have a look at "USB" in
https://en.opensuse.org/SDB:Configuring_Scanners
which is more up to date.

For example if a USB printer is not accessible, you
can get usb-related kernel messages via the command:

dmesg | grep -i usb >/tmp/dmesg.usb

Then you can inspect /tmp/dmesg.usb and extract only those
messages which seem to be of particular interest regarding
the USB printer issue.

In general you may also have a look at
https://en.opensuse.org/SDB:How_to_Report_a_Printing_Issue


Kind Regards
Johannes Meixner
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