doc/help/man-backend.html

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   9 <h1 class="title">backend(7)</h1>
  10
  11 <h2 class="title"><a name="NAME">Name</a></h2>
  12 backend - cups backend transmission interfaces
  13 <h2 class="title"><a name="SYNOPSIS">Synopsis</a></h2>
  14 <b>backend
  15 </b><br>
  16 <b>backend
  17 </b>job user title num-copies options [
  18 <i>filename
  19 </i>]
  20 <h2 class="title"><a name="DESCRIPTION">Description</a></h2>
  21 Backends are a special type of <a href='man-filter.html?TOPIC=Man+Pages'>filter(7)</a> which is used to send print data
  22 to and discover different devices on the system.
  23 <p>Like filters, backends must be capable of reading from a filename on the
  24 command-line or from the standard input, copying the standard input to a
  25 temporary file as required by the physical interface.
  26 <p>The command name (argv[0]) is set to the device URI of the destination printer.
  27 Starting with CUPS 1.1.22, any authentication information in argv[0] is removed,
  28 so backend developers are urged to use the DEVICE_URI environment variable
  29 whenever authentication information is required. The CUPS API includes a
  30 <i>cupsBackendDeviceURI</i> function for retrieving the correct device URI.
  31 <p>Back-channel data from the device should be relayed to the job
  32 filters by writing to file descriptor 3. The CUPS API includes
  33 the <i>cupsBackChannelWrite</i> function for this purpose.
  34 <h2 class="title"><a name="WARNING">Warning</a></h2>
  35 CUPS backends are not generally design to be run directly by the user. Aside
  36 from the device URI issue (argv[0] and DEVICE_URI environment variable contain
  37 the device URI), CUPS backends also expect specific environment variables and
  38 file descriptors, and typically run in a user session that (on OS X) has
  39 additional restrictions that affect how it runs. Backends can also be installed
  40 with restricted permissions (0500 or 0700) that tell the scheduler to run them
  41 as the "root" user instead of an unprivileged user (typically "lp") on the
  42 system.
  43 <p>Unless you are a developer and know what you are doing, please do not run
  44 backends directly. Instead, use the <a href='man-lp.html?TOPIC=Man+Pages'>lp(1)</a> or <a href='man-lpr.html?TOPIC=Man+Pages'>lpr(1)</a> programs to send
  45 a print job or <a href='man-lpinfo.html?TOPIC=Man+Pages'>lpinfo(8)</a> program to query for available printers using the
  46 backend. The one exception is the SNMP backend - see <i>snmpbackend(8)</i> for
  47 more information.
  48 <h2 class="title"><a name="DEVICE_DISCOVERY">Device Discovery</a></h2>
  49 When run with no arguments, the backend should list the devices and schemes it
  50 supports or is advertising to stdout. The output consists of zero or more lines
  51 consisting of any of the following forms:
  52
  53 <pre>
  54     device-class scheme "Unknown" "device-info"
  55     device-class device-uri "device-make-and-model" "device-info"
  56     device-class device-uri "device-make-and-model" "device-info" "device-id"
  57     device-class device-uri "device-make-and-model" "device-info" "device-id" "device-location"
  58 </pre>
  59 <p>The <i>device-class</i> field is one of the following values:
  60 <dl>
  61 <dt>direct
  62 </dt>
  63 <dd></dd>
  64 <dd>The device-uri refers to a specific direct-access device with no options, such
  65 as a parallel, USB, or SCSI device.
  66 </dd>
  67 <dt>file
  68 </dt>
  69 <dd></dd>
  70 <dd>The device-uri refers to a file on disk.
  71 </dd>
  72 <dt>network
  73 </dt>
  74 <dd></dd>
  75 <dd>The device-uri refers to a networked device and conforms to the general form for
  76 network URIs.
  77 </dd>
  78 <dt>serial
  79 </dt>
  80 <dd></dd>
  81 <dd>The device-uri refers to a serial device with configurable baud rate and other
  82 options. If the device-uri contains a baud value, it represents the maximum baud
  83 rate supported by the device.
  84 </dd>
  85 </dl>
  86 <p>The <i>scheme</i> field provides the URI scheme that is supported by the backend.
  87 Backends should use this form only when the backend supports any URI using that
  88 scheme. The <i>device-uri</i> field specifies the full URI to use when
  89 communicating with the device.
  90 <p>The <i>device-make-and-model</i> field specifies the make and model of the
  91 device, e.g. "Example Foojet 2000". If the make and model is not known, you must
  92 report "Unknown".
  93 <p>The <i>device-info</i> field specifies additional information about the device.
  94 Typically this includes the make and model along with the port number or network
  95 address, e.g. "Example Foojet 2000 USB #1".
  96 <p>The optional <i>device-id</i> field specifies the IEEE-1284 device ID string for
  97 the device, which is used to select a matching driver.
  98 <p>The optional <i>device-location</i> field specifies the physical location of
  99 the device, which is often used to pre-populate the printer-location attribute
 100 when adding a printer.
 101 <h2 class="title"><a name="PERMISSIONS">Permissions</a></h2>
 102 Backends without world execute permissions are run as the root user. Otherwise,
 103 the backend is run using an unprivileged user account, typically "lp".
 104 <h2 class="title"><a name="EXIT_CODES">Exit Codes</a></h2>
 105 The following exit codes are defined for backends; C API constants defined in
 106 the &lt;cups/backend.h> header file are defined in parenthesis:
 107 <dl>
 108 <dt>0 (CUPS_BACKEND_OK)
 109 </dt>
 110 <dd></dd>
 111 <dd>The print file was successfully transmitted to the device or remote server.
 112 </dd>
 113 <dt>1 (CUPS_BACKEND_FAILED)
 114 </dt>
 115 <dd></dd>
 116 <dd>The print file was not successfully transmitted to the device or remote server.
 117 The scheduler will respond to this by canceling the job, retrying the job, or
 118 stopping the queue depending on the state of the error-policy attribute.
 119 </dd>
 120 <dt>2 (CUPS_BACKEND_AUTH_REQUIRED)
 121 </dt>
 122 <dd></dd>
 123 <dd>The print file was not successfully transmitted because valid authentication
 124 information is required. The scheduler will respond to this by holding the job
 125 and adding the "cups-held-for-authentication" keyword to the "job-reasons"
 126 attribute.
 127 </dd>
 128 <dt>3 (CUPS_BACKEND_HOLD)
 129 </dt>
 130 <dd></dd>
 131 <dd>The print file was not successfully transmitted because it cannot be printed at
 132 this time. The scheduler will respond to this by holding the job.
 133 </dd>
 134 <dt>4 (CUPS_BACKEND_STOP)
 135 </dt>
 136 <dd></dd>
 137 <dd>The print file was not successfully transmitted because it cannot be printed at
 138 this time. The scheduler will respond to this by stopping the queue.
 139 </dd>
 140 <dt>5 (CUPS_BACKEND_CANCEL)
 141 </dt>
 142 <dd></dd>
 143 <dd>The print file was not successfully transmitted because one or more attributes
 144 are not supported or the job was canceled at the printer. The scheduler will
 145 respond to this by canceling the job.
 146 </dd>
 147 <dt>6 (CUPS_BACKEND_RETRY)
 148 </dt>
 149 <dd></dd>
 150 <dd>The print file was not successfully transmitted because of a temporary issue.
 151 The scheduler will retry the job at a future time - other jobs may print before
 152 this one.
 153 </dd>
 154 <dt>7 (CUPS_BACKEND_RETRY_CURRENT)
 155 </dt>
 156 <dd></dd>
 157 <dd>The print file was not successfully transmitted because of a temporary issue.
 158 The scheduler will retry the job immediately without allowing intervening jobs.
 159 </dd>
 160 </dl>
 161 <p>All other exit code values are reserved.
 162 <h2 class="title"><a name="SEE_ALSO">See Also</a></h2>
 163 <a href='man-cups-snmp.html?TOPIC=Man+Pages'>cups-snmp(8)</a>, <a href='man-cupsd.html?TOPIC=Man+Pages'>cupsd(8)</a>, <a href='man-cupsd.conf.html?TOPIC=Man+Pages'>cupsd.conf(5)</a>, <a href='man-filter.html?TOPIC=Man+Pages'>filter(7)</a>,
 164 <a href='man-lpinfo.html?TOPIC=Man+Pages'>lpinfo(8)</a>,
 165 <br>
 166 <a href='http://localhost:631/help'>http://localhost:631/help</a>
 167 <h2 class="title"><a name="COPYRIGHT">Copyright</a></h2>
 168 Copyright 2007-2013 by Apple Inc.
 169
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