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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

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


COPYRIGHT

       Copyright 2007-2013 by Apple Inc.



23 April 2012                        CUPS                           backend(7)

Mac OS X 10.9 - Generated Thu Oct 17 05:44:22 CDT 2013
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