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Date: Fri, 12 Sep 2014 20:53:41 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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Subject: usb printer vs cups
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>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