Samba Administration Guide

The last part of any CUPS filtering chain is a backend. Backends are special programs that send the print-ready file to the final device. There is a separate backend program for any transfer protocol for sending print jobs over the network, and one for every local interface. Every CUPS print queue needs to have a CUPS “device-URI” associated with it. The device URI is the way to encode the backend used to send the job to its destination. Network device-URIs use two slashes in their syntax, local device URIs only one, as you can see from the following list. Keep in mind that local interface names may vary greatly from my examples, if your OS is not Linux:

usb

This backend sends print files to USB-connected printers. An example for the CUPS device-URI to use is usb:/dev/usb/lp0.

serial

This backend sends print files to serially connected printers. An example for the CUPS device-URI to use is serial:/dev/ttyS0?baud=11500.

parallel

This backend sends print files to printers connected to the parallel port. An example for the CUPS device-URI to use is parallel:/dev/lp0.

SCSI

This backend sends print files to printers attached to the SCSI interface. An example for the CUPS device-URI to use is scsi:/dev/sr1.

lpd

This backend sends print files to LPR/LPD-connected network printers. An example for the CUPS device-URI to use is lpd://remote_host_name/remote_queue_name.

AppSocket/HP JetDirect

This backend sends print files to AppSocket (a.k.a., HP JetDirect) connected network printers. An example for the CUPS device-URI to use is socket://10.11.12.13:9100.

ipp

This backend sends print files to IPP-connected network printers (or to other CUPS servers). Examples for CUPS device-URIs to use are ipp:://192.193.194.195/ipp (for many HP printers) and ipp://remote_cups_server/printers/remote_printer_name.

http

This backend sends print files to HTTP-connected printers. (The https:// CUPS backend is only a symlink to the ipp:// backend.) Examples for the CUPS device-URIs to use are https:://192.193.194.195:631/ipp (for many HP printers) and https://remote_cups_server:631/printers/remote_printer_name.

smb

This backend sends print files to printers shared by a Windows host. Examples of CUPS device-URIs that may be used includes:

smb://workgroup/server/printersharename

smb://server/printersharename

smb://username:password@workgroup/server/printersharename

smb://username:password@server/printersharename

The smb:// backend is a symlink to the Samba utility smbspool (does not ship with CUPS). If the symlink is not present in your CUPS backend directory, have your root user create it: ln -s `which smbspool' /usr/lib/cups/backend/smb .

It is easy to write your own backends as shell or Perl scripts if you need any modification or extension to the CUPS print system. One reason could be that you want to create “special” printers that send the print jobs as email (through a “mailto:/” backend), convert them to PDF (through a “pdfgen:/” backend) or dump them to “/dev/null”. (In fact, I have the systemwide default printer set up to be connected to a devnull:/ backend: there are just too many people sending jobs without specifying a printer, and scripts and programs that do not name a printer. The systemwide default deletes the job and sends a polite email back to the $USER asking him or her to always specify the correct printer name.)

Not all of the mentioned backends may be present on your system or usable (depending on your hardware configuration). One test for all available CUPS backends is provided by the lpinfo utility. Used with the -v parameter, it lists all available backends:

CUPS Backends