backend(7)

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 authen-
     tication information  in  argv[0]  is  removed,  so  backend
     developers are urged to use the DEVICE_URI environment vari-
     able 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 dev-
     ices  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  dev-
          ice  with  no options, such as a parallel, USB, or SCSI

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backend(7)                 Apple Inc.                  backend(7)

          device.

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

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

     serial
          The device-uri refers to a serial device with configur-
          able  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.

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:

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backend(7)                 Apple Inc.                  backend(7)

     0 (CUPS_BACKEND_OK)
          The print file was successfully transmitted to the dev-
          ice 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  stop-
          ping  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.

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