Problem: Can Not Change Printer Driver ("unable to open")


When trying to assign a different printer driver you will see error messages in /var/log/cups/error.log

E [18/Sep/2018:08:54:16 +0200] [cups-driverd] **Unable to open \"/usr/share/cups/model/foomatic-rip/Generic-PostScript_Printer-Postscript.ppd\" - No such file or directory**
E [18/Sep/2018:08:54:16 +0200] [cups-driverd] Unable to open \"/usr/share/cups/model/foomatic-rip/Generic-PostScript_Printer-Postscript.ppd\" - No such file or directory
E [18/Sep/2018:08:54:16 +0200] copy_model: empty PPD file
E [18/Sep/2018:08:54:16 +0200] [Client 30] Returning IPP server-error-internal-error for CUPS-Add-Modify-Printer (ipp://localhost:631/printers/ms_csmc-Kyo) from localhost


The directory is an outdated place for cups and it might be still in place due to long-term upgrade procedures from ancient versions.
You could try to re-install all cups related files or create symlinks for the missing files. Ie:

root@ucs:~# cd /usr/share/cups/model/
root@ucs:~#  ln -s ppd/foomatic-rip foomatic-rip