backend man page on MacOSX

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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.

WARNING
       CUPS  backends are not generally design to be run directly by the user.
       Aside from the device URI issue	(argv[0]  and  DEVICE_URI  environment
       variable	 contain  the  device URI), CUPS backends also expect specific
       environment variables and file descriptors, and typically run in a user
       session	that  (on OS X) has additional restrictions that affect how it
       runs. Backends can also be installed with restricted permissions	 (0500
       or 0700) that tell the scheduler to run them as the "root" user instead
       of an unprivileged user (typically "lp") on the system.

       Unless you are a developer and know what you are doing, please  do  not
       run  backends  directly.	 Instead,  use the lp(1) or lpr(1) programs to
       send a print job or lpinfo(8) program to query for  available  printers
       using  the  backend.  The one exception is the SNMP backend - see snmp‐
       backend(8) for more information.

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. "Example 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. "Example 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 an unprivileged user account, typi‐
       cally "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 "cups-held-for-authenti‐
	    cation" keyword to the "job-reasons" attribute.

       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 or the job was canceled at the
	    printer. The scheduler will respond to this by canceling the job.

       6 (CUPS_BACKEND_RETRY)
	    The print file was not successfully transmitted because of a  tem‐
	    porary issue.  The scheduler will retry the job at a future time -
	    other jobs may print before this one.

       7 (CUPS_BACKEND_RETRY_CURRENT)
	    The print file was not successfully transmitted because of a  tem‐
	    porary  issue.  The scheduler will retry the job immediately with‐
	    out allowing intervening jobs.

       All other exit code values are reserved.

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

COPYRIGHT
       Copyright 2007-2013 by Apple Inc.

23 April 2012			     CUPS			    backend(7)
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