There are a couple of similar issues currently.  The other one that comes to 
mind is that every X11 application that needs to use OpenGL (or similar) must 
open /dev/dri/{something}, but the default permissions only permit root.

The correct solution is probably to ship a devfs.conf that puts these devices 
in the a sensible group.  For USB printers, we should probably have a printers 
group and make cupsd run with that group (or set the GUI of cups and printers 
to the same number if that's too difficult).  


On 17 Sep 2014, at 07:00, Andriy Gapon <> wrote:

> Soliciting help.
> -------- Forwarded Message --------
> From my experience I think that cupsd executes backend tools with all uids and
> gids set to cups and no supplementary groups.  In the case of USB printers the
> backends need to access /dev/usbctl and /dev/usb/foobar that corresponds to a
> printer.  That means that the access to those devices must be somehow granted 
> to
> cups:cups.
> How do people solve this?  What kind of permissions / configuration do you 
> use?
> P.S.
> Maybe I over-generalized the issue to all USB printers.  My personal 
> experience
> is with an HP printer handled by hplip / hplip-plugin.
> -- 
> Andriy Gapon
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