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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"


       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.


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 by Apple Inc.



20 March 2006             Common UNIX Printing System               backend(7)