I've determined the source of this bug, which should only affect USB
printers

$ ls -l /dev/usblp0 /dev/lp0
crw-rw---- 1 root lp        6, 0 2007-01-20 12:34 /dev/lp0
crw-rw---- 1 root plugdev 180, 0 2007-01-20 12:34 /dev/usblp0

The problem is this: udev makes ALL usb devices owned by group
"plugdev", but it makes built-in parallel ports owned by group "lp".

Now, when attempting to detect printers or print, CUPS runs with the
permissions of the user "cupsys".  This user belongs to the "lp" group,
but NOT to the "plugdev" group:

$ groups cupsys
cupsys : lpadmin lp dialout scanner ssl-cert

There are two possible solutions (both of which I have confirmed to work):
(a) make "cupsys" a member of the "plugdev" group
(b) make /dev/usblp0 owned by the group "lp" rather than by "plugdev"

I'm not sure which solution is better.  Anyone?

-- 
[Feisty]At this moment can't detected printers
https://launchpad.net/bugs/80468

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