man/backend.man

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   4 .\"   Backend man page for CUPS.
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  15 .TH backend 7 "CUPS" "23 April 2012" "Apple Inc."
  16
  17 .SH NAME
  18 backend \- cups backend transmission interfaces
  19 .SH SYNOPSIS
  20 .B backend
  21 .br
  22 .B backend
  23 job user title num-copies options [
  24 .I filename
  25 ]
  26 .SH DESCRIPTION
  27 Backends are a special type of \fIfilter(7)\fR which is used to send print data
  28 to and discover different devices on the system.
  29 .LP
  30 Like filters, backends must be capable of reading from a filename on the
  31 command-line or from the standard input, copying the standard input to a
  32 temporary file as required by the physical interface.
  33 .LP
  34 The command name (argv[0]) is set to the device URI of the destination printer.
  35 Starting with CUPS 1.1.22, any authentication information in argv[0] is removed,
  36 so backend developers are urged to use the DEVICE_URI environment variable
  37 whenever authentication information is required. The CUPS API includes a
  38 \fIcupsBackendDeviceURI\fR function for retrieving the correct device URI.
  39 .LP
  40 Back-channel data from the device should be relayed to the job
  41 filters by writing to file descriptor 3. The CUPS API includes
  42 the \fIcupsBackChannelWrite\fR function for this purpose.
  43 .SH WARNING
  44 CUPS backends are not generally design to be run directly by the user. Aside
  45 from the device URI issue (argv[0] and DEVICE_URI environment variable contain
  46 the device URI), CUPS backends also expect specific environment variables and
  47 file descriptors, and typically run in a user session that (on OS X) has
  48 additional restrictions that affect how it runs. Backends can also be installed
  49 with restricted permissions (0500 or 0700) that tell the scheduler to run them
  50 as the "root" user instead of an unprivileged user (typically "lp") on the
  51 system.
  52 .LP
  53 Unless you are a developer and know what you are doing, please do not run
  54 backends directly. Instead, use the \fIlp(1)\fR or \fIlpr(1)\fR programs to send
  55 a print job or \fIlpinfo(8)\fR program to query for available printers using the
  56 backend. The one exception is the SNMP backend - see \fIsnmpbackend(8)\fR for
  57 more information.
  58 .SH DEVICE DISCOVERY
  59 When run with no arguments, the backend should list the devices and schemes it
  60 supports or is advertising to stdout. The output consists of zero or more lines
  61 consisting of any of the following forms:
  62
  63 .nf
  64     device-class scheme "Unknown" "device-info"
  65     device-class device-uri "device-make-and-model" "device-info"
  66     device-class device-uri "device-make-and-model" "device-info" "device-id"
  67     device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"
  68 .fi
  69 .LP
  70 The \fIdevice-class\fR field is one of the following values:
  71 .TP 5
  72 direct
  73 .br
  74 The device-uri refers to a specific direct-access device with no options, such
  75 as a parallel, USB, or SCSI device.
  76 .TP 5
  77 file
  78 .br
  79 The device-uri refers to a file on disk.
  80 .TP 5
  81 network
  82 .br
  83 The device-uri refers to a networked device and conforms to the general form for
  84 network URIs.
  85 .TP 5
  86 serial
  87 .br
  88 The device-uri refers to a serial device with configurable baud rate and other
  89 options. If the device-uri contains a baud value, it represents the maximum baud
  90 rate supported by the device.
  91 .LP
  92 The \fIscheme\fR field provides the URI scheme that is supported by the backend.
  93 Backends should use this form only when the backend supports any URI using that
  94 scheme. The \fIdevice-uri\fR field specifies the full URI to use when
  95 communicating with the device.
  96 .LP
  97 The \fIdevice-make-and-model\fR field specifies the make and model of the
  98 device, e.g. "Example Foojet 2000". If the make and model is not known, you must
  99 report "Unknown".
 100 .LP
 101 The \fIdevice-info\fR field specifies additional information about the device.
 102 Typically this includes the make and model along with the port number or network
 103 address, e.g. "Example Foojet 2000 USB #1".
 104 .LP
 105 The optional \fIdevice-id\fR field specifies the IEEE-1284 device ID string for
 106 the device, which is used to select a matching driver.
 107 .LP
 108 The optional \fIdevice-location\fR field specifies the physical location of
 109 the device, which is often used to pre-populate the printer-location attribute
 110 when adding a printer.
 111 .SH PERMISSIONS
 112 Backends without world execute permissions are run as the root user. Otherwise,
 113 the backend is run using an unprivileged user account, typically "lp".
 114 .SH EXIT CODES
 115 The following exit codes are defined for backends; C API constants defined in
 116 the <cups/backend.h> header file are defined in parenthesis:
 117 .TP 5
 118 0 (CUPS_BACKEND_OK)
 119 .br
 120 The print file was successfully transmitted to the device or remote server.
 121 .TP 5
 122 1 (CUPS_BACKEND_FAILED)
 123 .br
 124 The print file was not successfully transmitted to the device or remote server.
 125 The scheduler will respond to this by canceling the job, retrying the job, or
 126 stopping the queue depending on the state of the error-policy attribute.
 127 .TP 5
 128 2 (CUPS_BACKEND_AUTH_REQUIRED)
 129 .br
 130 The print file was not successfully transmitted because valid authentication
 131 information is required. The scheduler will respond to this by holding the job
 132 and adding the "cups-held-for-authentication" keyword to the "job-reasons"
 133 attribute.
 134 .TP 5
 135 3 (CUPS_BACKEND_HOLD)
 136 .br
 137 The print file was not successfully transmitted because it cannot be printed at
 138 this time. The scheduler will respond to this by holding the job.
 139 .TP 5
 140 4 (CUPS_BACKEND_STOP)
 141 .br
 142 The print file was not successfully transmitted because it cannot be printed at
 143 this time. The scheduler will respond to this by stopping the queue.
 144 .TP 5
 145 5 (CUPS_BACKEND_CANCEL)
 146 .br
 147 The print file was not successfully transmitted because one or more attributes
 148 are not supported or the job was canceled at the printer. The scheduler will
 149 respond to this by canceling the job.
 150 .TP 5
 151 6 (CUPS_BACKEND_RETRY)
 152 .br
 153 The print file was not successfully transmitted because of a temporary issue.
 154 The scheduler will retry the job at a future time - other jobs may print before
 155 this one.
 156 .TP 5
 157 7 (CUPS_BACKEND_RETRY_CURRENT)
 158 .br
 159 The print file was not successfully transmitted because of a temporary issue.
 160 The scheduler will retry the job immediately without allowing intervening jobs.
 161 .PP
 162 All other exit code values are reserved.
 163 .SH SEE ALSO
 164 \fIcups-snmp(8)\fR, \fIcupsd(8)\fR, \fIcupsd.conf(5)\fR, \fIfilter(7)\fR,
 165 \fIlpinfo(8)\fR,
 166 .br
 167 http://localhost:631/help
 168 .SH COPYRIGHT
 169 Copyright 2007-2013 by Apple Inc.
 170 .\"
 171 .\" End of "$Id$".
 172 .\"