[cups] Print stuck in cue / becomes unstuck when opening GUI print cue / OSX.

[Tim Mooney]

In regard to: [cups] Print stuck in cue / becomes unstuck when opening GUI...:

> we've encountering a rather strange error with the print cue in OSX,
> running a printer in a photo booth setup.
>
> We use 'lp' to print a jpeg on DNP RX1 HS printer from the command line. It
> works great, and can run for days, printing 10-50 prints a day.
>
> But for some reason / once in a blue moon / the print becomes stuck in the
> print cue. BUT - when we open the Printer Cue GUI in OSX, it immediately
> prints / becomes unstuck again.

I don't have an easy way to test this, but my guess is that

1) some minor or intermittent issue causes CUPS to treat the printer as
    having an error.

2) You're using the default setting for ErrorPolicy, which is
    'stop-printer'

   See: https://www.cups.org/doc/man-cupsd.conf.html for more info.

3) still guessing, but it's possible that the Print Queue GUI, whenever
   it's opened, automatically causes CUPS to re-enable any stopped
   printers.

Here's how you test to see if these guesses are accurate:

1) The next time the print queue becomes stuck, do this:
 	a) open the "Terminal" app
 	b) type

 		sudo lpadmin -p your_exact_queue_name_here -E

 	(note: the -E must be at the end of the command line, don't put it
 	before the -p, it means something different there)

2) if that causes the stuck print job(s) to print, then the queue had
almost certainly been in the "accepting" but not "enabled" state.

3) you can verify the ErrorPolicy that's set for a queue by doing a

 	sudo less /etc/cups/printers.conf

and finding the <Printer your_exact_queue_name_here> entry and the
ErrorPolicy statement after it.

4) if you want the queue to just retry the print job, instead of going
into an error state, you can try changing the ErrorPolicy for the queue:

 	sudo lpadmin -p your_exact_queue_name_here -o printer-error-policy=retry-job

You can look at /etc/cups/printers.conf again to verify that ErrorPolicy
for your printer has changed after running that command.

These are all guesses, but based on what you've described, it would
be the first thing I would look at.

Tim
-- 
Tim Mooney                                             Tim.Mooney at ndsu.edu
Enterprise Computing & Infrastructure                  701-231-1076 (Voice)
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