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
       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)
