[cups] How does CUPS find a driver?

[Brian Potkin]

On Sun 12 Jun 2016 at 09:27:12 +0100, Timothy Murphy wrote:

> Brian Potkin wrote:
> 
> >> I'm trying to get a Canon MG5550 printer working with Fedora/KDE.
> >> (It works perfectly under Windows 10.)
> >> I've downloaded and installed Canon's Linux driver (in rpm format),
> >> and told CUPS to use the .ppd file that comes with the Canon software.
> >> Unfortunately this does not work.
> >> 
> >> But what puzzles me is that I see nothing in the .ppd file
> >> directing the printer to the Canon driver.
> >> So how does CUPS know which driver to use?
> 
> > Please post the output of
> > 
> >   grep -i cupsFilter <Canon_ppd>
> 
> [tim at william ~]$ grep -i cupsFilter 
>   /usr/local/src/cnijfilter-source-4.00-1/ppd/canonmg5500.ppd
> *cupsFilter: "application/vnd.cups-postscript 0 pstocanonij"

This line is for printing a job. CUPS now knows the final filter in the
filter chain is pstocanonij. The line also causes cups-filters to
produce PostScript as the output of its filtering process.

> *cupsFilter: "application/vnd.cups-command 0 cmdtocanonij"

This line is for processing printer maintenance commands sent to the
printer.

On a Debian system I installed the i386 .deb and set up a queue with

  lpadmin -p mg5500 -v file:/home/brian/mg5500.data -E -P /usr/share/ppd/canonmg5500.ppd

and printed:

  lp -d mg5500 /etc/nsswitch

If I had such a Canon printer I would expect

  lp -d mg5500 -o raw /home/brian/mg5500.data

to print successfully.

With debug logging ('cupsctl --debug-logging'). I see texttopdf,
pdftopdf, pdftops and pstocanonij all running and exiting correctly.

Regards,

Brian.