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 sys-
       tem.


       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 authenti-
       cation 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 cupsBackChannelWrite 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 backend. 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, typically "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)