Following a recent Ubuntu upgrade to 20.04, our CUPS server was no longer able to print to a USB connected Brother FAX-2820. This started a journey to disentangle packages that had been active on my system through a myriad of upgrades starting when this device was first plugged in way back in 2008.
This particular configuration uses a CUPS server (2.3.1) to deliver via USB 1.0 to a Brother FAX-2820. In fact this had worked successfully for over a million page prints and more toner cartridges then I can count. The first evidence that the printer was not working was that jobs being sent had simply stopped printing.
There was one error visible in the logs:
Use "pdftops-renderer" option (see cups-filters README file) to use Ghostscript or MuPDF for the PDF -> PostScript conversion.
Using lpadmin my first attempt was to follow the advice provided by this error message and convert the printer to Ghostscript:
lpadmin -p "Brother_FAX-2820" -o pdftops-renderer-default=gs
Unfortunately, this produced a new error message:
After tinkering with a few other pdftops-renderer-default options, this left me with the following error:
Grayscale/monochrome printing requested for this job but Poppler is not able to convert to grayscale/monochrome PostScript.
My next step was to review the current state of the installed printer drivers. While the drivers can be downloaded on the Brother FAX-2820 page, these are in fact 32 bit and are not supported on my x86_64 system; however, apt search showed that brfax2820lpr:i386 was somehow still installed!
apt remove brfax2820lpr:i386
Then the existing Ubuntu drivers were re-installed:
apt update apt purge brother-lpr-drivers-laser brother-cups-wrapper-laser && apt autoremove apt upgrade ghostscript apt install brother-lpr-drivers-laser brother-cups-wrapper-laser brother-lpr-drivers-common
Following a final restart of cups the printer test page was successful. While I’m not sure on the exact nature of the conflict, clearly having the brfax2820lpr for i386 would have been a problem for the currently supported brother-lpr-drivers-laser. Once these were resolved, the Ghostscript option was supported and printing has resumed.