backend(7)			  Apple Inc.			    backend(7)



NAME
       backend - cups backend transmission interfaces


SYNOPSIS
       backend
       backend job user title num-copies options [ filename ]


DESCRIPTION
       Backends	 are  a	 special type of filter(7) which is used to send print
       data to and discover different devices on the system.


       Like filters, backends must be capable of reading from  a  filename  on
       the command-line or from the standard input, copying the standard input
       to a temporary file as required by the physical interface.


       The command name (argv[0]) is set to the device URI of the  destination
       printer.	  Starting with CUPS 1.1.22, any authentication information in
       argv[0] is  removed,  so	 backend  developers  are  urged  to  use  the
       DEVICE_URI  environment variable whenever authentication information is
       required. The CUPS API includes	a  cupsBackendDeviceURI	 function  for
       retrieving the correct device URI.


       Back-channel  data from the device should be relayed to the job filters
       by writing to file descriptor  3.  The  CUPS  API  includes  the	 cups-
       BackChannelWrite function for this purpose.


DEVICE DISCOVERY
       When  run  with	no  arguments, the backend should list the devices and
       schemes it supports or is advertising to stdout. The output consists of
       zero or more lines consisting of any of the following forms:

	   device-class scheme "Unknown" "device-info"
	   device-class device-uri "device-make-and-model" "device-info"
	   device-class device-uri "device-make-and-model" "device-info" "device-id"
	   device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"


       The device-class field is one of the following values:


       direct
	    The	 device-uri  refers to a specific direct-access device with no
	    options, such as a parallel, USB, or SCSI device.


       file
	    The device-uri refers to a file on disk.


       network
	    The device-uri refers to a networked device and  conforms  to  the
	    general form for network URIs.


       serial
	    The	 device-uri  refers  to a serial device with configurable baud
	    rate and other options. If the device-uri contains a  baud	value,
	    it represents the maximum baud rate supported by the device.


       The scheme field provides the URI scheme that is supported by the back-
       end. Backends should use this form only when the backend	 supports  any
       URI  using  that scheme. The device-uri field specifies the full URI to
       use when communicating with the device.


       The device-make-and-model field specifies the make  and	model  of  the
       device,	e.g.  "Acme  Foojet 2000". If the make and model is not known,
       you must report "Unknown".


       The  device-info	 field	specifies  additional  information  about  the
       device.	Typically this includes the make and model along with the port
       number or network address, e.g. "Acme Foojet 2000 USB #1".


       The optional device-id field specifies the IEEE-1284 device  ID	string
       for the device, which is used to select a matching driver.


       The  optional  device-location field specifies the physical location of
       the device, which is often used to  pre-populate	 the  printer-location
       attribute when adding a printer.


PERMISSIONS
       Backends	 without  world	 execute permissions are run as the root user.
       Otherwise, the backend is run using the unprivileged user account, typ-
       ically "lp".


EXIT CODES
       The  following  exit  codes  are	 defined for backends; C API constants
       defined in the <cups/backend.h> header file are defined in parenthesis:


       0 (CUPS_BACKEND_OK)
	    The print file was	successfully  transmitted  to  the  device  or
	    remote server.


       1 (CUPS_BACKEND_FAILED)
	    The	 print	file was not successfully transmitted to the device or
	    remote server. The scheduler will respond to this by canceling the
	    job,  retrying  the	 job,  or  stopping the queue depending on the
	    state of the error-policy attribute.


       2 (CUPS_BACKEND_AUTH_REQUIRED)
	    The print file was	not  successfully  transmitted	because	 valid
	    authentication information is required. The scheduler will respond
	    to this by holding the job and adding the  authentication-required
	    job-reasons keyword.


       3 (CUPS_BACKEND_HOLD)
	    The	 print file was not successfully transmitted because it cannot
	    be printed at this time. The scheduler will	 respond  to  this  by
	    holding the job.


       4 (CUPS_BACKEND_STOP)
	    The	 print file was not successfully transmitted because it cannot
	    be printed at this time. The scheduler will	 respond  to  this  by
	    stopping the queue.


       5 (CUPS_BACKEND_CANCEL)
	    The	 print	file  was  not successfully transmitted because one or
	    more attributes are not supported. The scheduler will  respond  to
	    this by canceling the job.


       All other exit code values are reserved.


SEE ALSO
       cupsd(8), cupsd.conf(5), filter(7),
       http://localhost:631/help


COPYRIGHT
       Copyright 2007-2009 by Apple Inc.



12 May 2009			     CUPS			    backend(7)