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   4         <title>An Overview of the Common UNIX Printing System</title>
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  11         <td><img src='images/cups-large.gif' width='103'
  12         height='120' alt='CUPS Logo'/></td>
  13         <td><h1 align='right'>An Overview of the<br />
  14         Common UNIX Printing System,<br />
  15         Version 1.2</h1>
  16
  17         <p align='right'>July 3, 2004<br />
  18         Michael Sweet, Easy Software Products<br />
  19         Copyright 1998-2004, All Rights Reserved.</p>
  20         </td>
  21 </tr>
  22 </table>
  23
  24 <pre>
  25 New Outline:
  26
  27 New Features:
  28
  29 1. Networking
  30    a. IPv6
  31         i. Next-generation Internet support
  32        ii. ????
  33    b. Domain sockets
  34         i. Enhanced performance under load for local clients.
  35        ii. Authentication without passwords on platforms that support it.
  36    c. CUPS browsing updates
  37         i. "Delete" bit for printers
  38        ii. "lease-time" for printers so that clients and servers don't need
  39           the same browse timeout/interval settings
  40       iii. Additional attributes/default options for network-wide defaults
  41        iv. Network default printer
  42         v. Ability to control send and receive protocols independently
  43    d. Rendevous support
  44    e. LDAP support
  45    f. Per-printer sharing
  46
  47 2. IPP Support
  48    a. Notifications
  49    b. Document object
  50    c. Send-URI, Print-URI
  51    d. Other stuff?
  52    e. Add/delete device operations
  53
  54 3. Scheduler
  55    a. Backchannel support
  56    b. Port monitor support
  57    c. Device monitor
  58       i. Dynamic device discovery/management
  59    d. All errors include a localized message.
  60    e. Fine-grain policies, server default + per-printer
  61    f. UTF-8 throughout
  62
  63 4. Web Interface
  64    a. cupsd.conf interface
  65    b. Move-Job
  66    c. Export printers to windows
  67    d. Per-printer sharing controls
  68    e. Per-printer access control lists
  69    f. Policy stuff
  70
  71 5. I18N
  72    a. Support for ... character sets
  73    b. All commands and messages are localized
  74    c. Character set transcoding
  75    d. ... , and Japanese localizations
  76
  77 6. Drivers
  78    a. New HP-RTL driver.
  79
  80 </pre>
  81
  82 <p>This whitepaper describes the Common UNIX Printing
  83 System<sup>TM</sup> (CUPS<sup>TM</sup>), a portable and
  84 extensible printing system for Linux<sup>&reg;</sup>,
  85 MacOS<sup>&reg;</sup> X, UNIX<sup>&reg;</sup>. CUPS is developed
  86 by <a href='http://www.easysw.com'>Easy Software Products</a>, a
  87 software firm located in Hollywood, Maryland that has been
  88 selling commercial software for UNIX since 1993 through more
  89 than 40 distributors serving over 80 countries worldwide.</p>
  90
  91 <p>CUPS is used by Apple to provide printing on MacOS X and is
  92 the defacto-standard for Linux. Additional information on CUPS
  93 is available on the World Wide Web at the following URL:</p>
  94
  95 <pre>
  96     <a href='http://www.cups.org/'>http://www.cups.org/</a>
  97 </pre>
  98
  99
 100 <h2>Background</h2>
 101
 102 <p>Printing within UNIX has historically been done using one of
 103 two printing systems - the Berkeley Line Printer Daemon (LPD)
 104 [RFC1179] and the AT&amp;T Line Printer system. These printing
 105 systems were designed in the 70's for printing text to line
 106 printers; vendors have since added varying levels of support for
 107 other types of printers.</p>
 108
 109 <p>Replacements for these printing systems have emerged [LPRng,
 110 Palladin, PLP], however none of the replacements change the
 111 fundamental capabilities of these systems.</p>
 112
 113 <p>Over the years several attempts at developing a standard
 114 printing interface have been made, including the draft POSIX
 115 Printing standard developed by the Institute of Electrical and
 116 Electronics Engineers, Inc. (IEEE) [IEEE-1387.4] and Internet
 117 Printing Protocol (IPP) developed by the Internet Engineering
 118 Task Force (IETF) through the Printer Working Group (PWG)
 119 [IETF-IPP]. The POSIX printing standard defines a common set of
 120 command-line tools as well as a C interface for printer
 121 administration and print jobs, but has been shelved by the
 122 IEEE.</p>
 123
 124 <p>The Internet Printing Protocol defines extensions to the
 125 HyperText Transport Protocol 1.1 [RFC2616] to provide support
 126 for remote printing services. IPP/1.1 was accepted by the IETF
 127 as a proposed standard in ??? of ???. Unlike POSIX Printing, IPP
 128 enjoys widespread industry support and has become the standard
 129 network printing solution for all operating systems.</p>
 130
 131 <p>CUPS uses IPP/1.1 to provide a complete, modern printing
 132 system for UNIX that can be extended to support new printers,
 133 devices, and protocols while providing compatibility with
 134 existing UNIX applications. CUPS is free software provided under
 135 the terms of the GNU General Public License and GNU Library
 136 General Public License.</p>
 137
 138 <h2>History</h2>
 139
 140 <p>The first production release of CUPS (based on IPP/1.0) was
 141 released in October of 1999. Version 1.1 of CUPS was released in
 142 August of 2002 ???? and added support for IPP/1.1.</p>
 143
 144 <p>CUPS 1.2 is based on IPP/1.1 and adds many of the functional
 145 enhancements that have been requested by our users. As with CUPS
 146 1.1, CUPS 1.2 will be followed by patch releases that address
 147 any problems found with the software. New features will be put
 148 in the 1.3 release to follow.</p>
 149
 150 <h2>Design Overview</h2>
 151
 152 <p>Like most printing systems, CUPS is designed around a central
 153 print scheduling process that dispatches print jobs, processes
 154 administrative commands, provides printer status information to
 155 local and remote programs, and informs users as needed. Figure 1
 156 shows the basic organization of CUPS.</p>
 157
 158 <p align='center'><img src='images/cups-block-diagram.gif'
 159 width='470' height='170' alt='CUPS Block Diagram'/><br />
 160 <i>Figure 1 - CUPS Block Diagram</i></p>
 161
 162 <h3>Scheduler</h3>
 163
 164 <p>The scheduler is a HTTP/1.1 server application that handles
 165 HTTP requests. Besides handling printer requests via IPP POST
 166 requests, the scheduler also acts as a full-featured web server
 167 for documentation, status monitoring, and administration.</p>
 168
 169 <p>The scheduler also manages a list of available printers on
 170 the LAN and dispatches print jobs as needed using the
 171 appropriate filters and backends.</p>
 172
 173 <h3>Configuration Files</h3>
 174
 175 <p>The configuration files consist of:</p>
 176
 177 <ul>
 178
 179         <li>The HTTP server configuration file.</li>
 180
 181         <li>Printer and class definition files.</li>
 182
 183         <li>MIME type and conversion rule files.</li>
 184
 185         <li>PostScript Printer Description (PPD) files.</li>
 186
 187 </ul>
 188
 189 <p>The HTTP server configuration file is purposely similar to
 190 the Apache server configuration file and defines all of the
 191 access control properties for the server.</p>
 192
 193 <p>The printer and class definition files list the available
 194 printer queues and classes. Printer classes are collections of
 195 printers. Jobs sent to a class are forwarded to the first
 196 available printer in the class, round-robin fashion.</p>
 197
 198 <p>The MIME type files list the supported MIME types
 199 (text/plain, application/postscript, etc.) and "magic' rules for
 200 automatically detecting the format of a file.  These are used by
 201 the HTTP server to determine the <tt>Content-Type</tt> field for
 202 <tt>GET</tt> and <tt>HEAD</tt> requests and by the IPP request
 203 handler to determine the file type when a <tt>Print-Job</tt> or
 204 <tt>Send-File</tt> request is received with a
 205 <tt>document-format</tt> of
 206 <tt>application/octet-stream</tt>.</p>
 207
 208 <p>The MIME conversion rule files list the available filters.
 209 The filters are used when a job is dispatched so that an
 210 application can send a convenient file format to the printing
 211 system which then converts the document into a printable format
 212 as needed. Each filter has a relative cost associated with it,
 213 and the filtering algorithm chooses the set of filters that will
 214 convert the file to the needed format with the lowest total
 215 "cost".</p>
 216
 217 <p>The PPD files describe the capabilities of all printers, not
 218 just PostScript printers. There is one PPD file for each
 219 printer. PPD files for non-PostScript printers define additional
 220 filters through <tt>cupsFilter</tt> attributes to support
 221 printer drivers.</p>
 222
 223 <h3>CUPS API</h3>
 224
 225 <p>The CUPS API contains CUPS-specific convenience functions for
 226 queuing print jobs, getting printer information, accessing
 227 resources via HTTP and IPP, and manipulating PPD files. Unlike
 228 the rest of CUPS, the CUPS API is provided under the terms of
 229 the GNU LGPL so it may be used by non-GPL applications.</p>
 230
 231 <h3>Berkeley and System V Commands</h3>
 232
 233 <p>CUPS provides the System V and Berkeley command-line
 234 interfaces for submitting jobs and checking the printer status.
 235 The <tt>lpstat</tt> and <tt>lpc status</tt> commands
 236 also show network printers ("printer@server") when printer
 237 browsing is enabled.</p>
 238
 239 <p>The System V administation commands are supplied for managing
 240 printers and classes. The Berkeley printer administration tool
 241 (<tt>lpc</tt>) is only supported in a "read-only' mode to
 242 check the current status of the printer queues and
 243 scheduler.</p>
 244
 245 <h3>Filters</h3>
 246
 247 <p>A filter program reads from the standard input or from a file
 248 if a filename is supplied. All filters must support a common set
 249 of options including printer name, job ID, username, job title,
 250 number of copies, and job options. All output is sent to the
 251 standard output.</p>
 252
 253 <p>Filters are provided for many file formats and include image
 254 file and PostScript raster filters that support non-PostScript
 255 printers. Multiple filters are run in parallel to produce the
 256 required output format.</p>
 257
 258 <p>The PostScript raster filter is based on the ESP Ghostscript
 259 core. Instead of using the Ghostscript printer drivers, the CUPS
 260 filter uses a generic CUPS raster printer driver and
 261 CUPS-compliant front-end to support any kind of raster printer.
 262 This allows the same printer driver filter to be used for
 263 printing raster data from any filter.</p>
 264
 265 <pre>Talk about Apple's use of CUPS...</pre>
 266
 267 <h3>CUPS Imaging</h3>
 268
 269 <p>The CUPS Imaging library provides functions for managing
 270 large images, doing colorspace conversion and color management,
 271 scaling images for printing, and managing raster page streams.
 272 It is used by the CUPS image file filters, the PostScript RIP,
 273 and all raster printers drivers.</p>
 274
 275 <h3>Backends</h3>
 276
 277 <p>A backend program is a special filter that sends print data
 278 to a device or network connection. Backends for parallel,
 279 serial, USB, LPD, IPP, and AppSocket (JetDirect) connections are
 280 provided in CUPS 1.2.</p>
 281
 282 <p>SAMBA version 2.0.6 and higher includes a SMB backend
 283 (<tt>smbspool(1)</tt>) that can be used for printing to
 284 Windows.</p>
 285
 286 <h2>Network Printing</h2>
 287
 288 <p>Traditionally, network printing has been one of the hardest
 289 things to get working under UNIX. One reason is because each
 290 vendor added their own extensions to the LPD protocol (the
 291 previous standard for network printing), making cross-platform
 292 printing difficult if not impossible.</p>
 293
 294 <p>Another reason is that you have to administer every network
 295 printer on every client machine. In some cases you can "clone'
 296 the printer configuration from a "master' client to each of the
 297 others, but even that can be time-consuming and error-prone.
 298 Something better is needed.</p>
 299
 300 <p>CUPS provides "printer browsing", which allows clients to
 301 automatically see and use printers from any server on a LAN.
 302 This means that you only need to configure the server and the
 303 clients will automatically see the printers and classes on
 304 it.</p>
 305
 306 <p>In addition, CUPS can automatically merge multiple identical
 307 network printers into "implicit classes". This allows clients to
 308 send jobs to the implicit class and have them print on the first
 309 available printer or server. In addition, failsafe and
 310 load-balancing functions are enabled simply by defining the same
 311 printer on multiple servers!</p>
 312
 313 <h2>New Features in CUPS 1.2</h2>
 314
 315 <p>CUPS 1.2 includes many new features and capabilities:
 316
 317 <ol>
 318
 319         <li><a href='#BACKENDS'>Backends</a>
 320
 321         <li><a href='#BANNERS'>Banner Page Support</a>
 322
 323         <li><a href='#DIGEST'>Digest Authentication</a>
 324
 325         <li><a href='#DIRSVC'>Directory Services</a>
 326
 327         <li><a href='#FHS2'>Directory Structure Changes</a>
 328
 329         <li><a href='#DOCOS'>Documentation</a>
 330
 331         <li><a href='#DRIVERS'>Drivers</a>
 332
 333         <li><a href='#FILTERS'>Filters</a>
 334
 335         <li><a href='#IPP'>IPP Support</a>
 336
 337         <li><a href='#PERSISTENCE'>Job Persistence</a>
 338
 339         <li><a href='#LPD'>LPD Client Support</a>
 340
 341         <li><a href='#USEROPTS'>User-Defined Printers and Options</a>
 342
 343         <li><a href='#WEB'>Web Administration Interface</a>
 344
 345 </ol>
 346
 347 <h3><a name='BACKENDS'>1. Backends</a></h3>
 348
 349 <p>CUPS 1.2 implements a new backend interface for retrieving a
 350 list of available devices for CUPS clients. This allows
 351 administration interfaces to query the CUPS scheduler for a list
 352 of available devices, automatically configure printers if the
 353 device identification information is available, and present the
 354 user with a list of available devices rather than relying on the
 355 user to know what devices are configured on the system.</p>
 356
 357 <p>The new release also includes a backend for USB printers
 358 under *BSD and Linux. Support for USB under Solaris 8 will be
 359 provided in a subsequent patch release.</p>
 360
 361 <h3><a name='BANNERS'>2. Banner Page Support</a></h3>
 362
 363 <p>CUPS 1.2 includes support for banner pages at the beginning
 364 and end of a job. Banner pages may be of any file format and
 365 support variable substitution for job titles, usernames, etc.
 366 Default banner pages are associated with each printer and can be
 367 overridden with command-line options by the user.</p>
 368
 369 <h3><a name='DIGEST'>3. Digest Authentication</a></h3>
 370
 371 <p>Digest authentication provides a more secure method of
 372 authenticating access to the printing system. Unlike Basic
 373 authentication, Digest authentication does not send passwords
 374 "in the clear' so it is more difficult to gain unauthorized
 375 access to your system.</p>
 376
 377 <p>CUPS 1.2 implements Digest authentication using a special MD5
 378 password file instead of the UNIX password file. This file is
 379 managed using the new <tt>lppasswd</tt> command.</p>
 380
 381 <h3><a name='DIRSVC'>4. Directory Services</a></h3>
 382
 383 <p>CUPS 1.2 adds new directory service ("printer browsing")
 384 features to make using CUPS on large LANs and WANs easier. You
 385 can now poll a remote server for printer information and relay
 386 it to the LAN as well as restrict what printer information is
 387 processed (e.g. to "hide" servers, domains, or networks that you
 388 don't want to see.)</p>
 389
 390 <h3><a name='FHS2'>5. Directory Structure Changes</a></h3>
 391
 392 <p>CUPS 1.2 now uses a directory structure that complies with
 393 the Filesystem Hierarchy Standard (FHS), version 2.0. This
 394 should make integration into existing Linux and *BSD
 395 distributions a lot easier.</p>
 396
 397 <h3><a name='DOCOS'>6. Documentation</a></h3>
 398
 399 <p>The CUPS 1.2 documentation has gone through many revisions,
 400 including a completely rewritten administrators manual, a new
 401 programmers manual, and an IPP implementation reference
 402 manual.</p>
 403
 404 <h3><a name='DRIVERS'>7. Drivers</a></h3>
 405
 406 <p>CUPS 1.2 includes drivers for EPSON dot-matrix and inkjet
 407 printers. As with the HP PCL drivers, the EPSON drivers don't
 408 necessarily provide the best possible output for each printer
 409 but should provide adequate printing quality for general
 410 day-to-day printing.</p>
 411
 412 <h3><a name='FILTERS'>8. Filters</a></h3>
 413
 414 <p>CUPS 1.2 includes new image, PostScript, PDF, and text
 415 filters. The image filters have been upgraded to support Windows
 416 BMP and Alias PIX files.</p>
 417
 418 <p>The PostScript filter is now based off ESP Ghostscript. The
 419 new filter provides much better performance with
 420 higher-resolution printers and supports all Level 3 PostScript
 421 language features.</p>
 422
 423 <p>The new PDF filter is based off the excellent Xpdf software
 424 from Derek Noonburg and supports automatic page scaling. The new
 425 filter is a faster, smaller, more reliable replacement for the
 426 GNU Ghostscript PDF filtering that was used in CUPS 1.0.</p>
 427
 428 <p>The new text filter now supports bidirectional text and can
 429 embed fonts as needed.</p>
 430
 431 <h3><a name='IPP'>9. IPP Support</a></h3>
 432
 433 <p>Probably the least visible portion of CUPS is the IPP
 434 support. CUPS 1.1 implements all of the required IPP/1.1
 435 operations and attributes and most of the optional ones. The
 436 optional Create-Job and Send-File operations are now
 437 implemented, allowing for better System V printing system
 438 compatibility (one job ID per <tt>lp</tt> command) and support
 439 for banner pages.</p>
 440
 441 <h3><a name='PERSISTENCE'>10. Job Persistence</a></h3>
 442
 443 <p>CUPS 1.2 supports job persistence. This means that jobs are
 444 preserved even after a reboot, a feature that was sorely missing
 445 from CUPS 1.0.</p>
 446
 447 <p>In addition, CUPS 1.2 allows you to keep job information
 448 after the job has printed. The basic post-job persistence mode
 449 provides a job history (number of pages printed, time job was
 450 printed, etc.) but does not preserve the actual job files. This
 451 can be changed to discard all information after a job is printed
 452 or keep the job files after printing so you can reprint a job at
 453 some later time.</p>
 454
 455 <h3><a name='LPD'>11. LPD Client Support</a></h3>
 456
 457 <p>By popular request, CUPS 1.2 supports LPD-based clients using
 458 a new mini-daemon that handles LPD requests and passes them on
 459 to the main server.</p>
 460
 461 <h3><a name='USEROPTS'>12. User-Defined Printers and Options</a></h3>
 462
 463 <p>CUPS 1.2 includes support for user-defined printers and
 464 options via a new <tt>lpoptions</tt> command. User-defined
 465 printers are special instances of the available printers (e.g.
 466 "printer/instance" or "printer@server/instance") that can have
 467 their own default options such as media size, resolution, and so
 468 forth. The <tt>lpoptions</tt> command can also be used to set a
 469 different default printer queue.</p>
 470
 471 <h3><a name='WEB'>13. Web Administration Interface</a></h3>
 472
 473 <p>CUPS 1.0 provided a simple class, job, and printer monitoring
 474 interface for web browsers. CUPS 1.2 replaces this interface
 475 with an enhanced administration interface that allows you to
 476 add, modify, delete, configure, and control classes, jobs, and
 477 printers.</p>
 478
 479 <h2>Software Using CUPS</h2>
 480
 481 <p>A lot has happened since CUPS 1.0 came out, and many software
 482 packages are supporting CUPS. We have contributed code to the
 483 SAMBA team to support CUPS, and parts of that are already
 484 available in SAMBA 2.0.6 and 2.0.7. With any luck the final
 485 pieces that provide a complete integration with SAMBA will be
 486 available in the next release of SAMBA.</p>
 487
 488 <p>Two graphical interfaces have appeared on the scene that use
 489 CUPS as well. The KUPS project provides a KDE-based interface
 490 for CUPS and can be found at:</p>
 491
 492 <pre>
 493     <a href='http://kups.sourceforge.net'>http://kups.sourceforge.net</a>
 494 </pre>
 495
 496 <p>The X Printing Panel (XPP) project provides a graphical
 497 printing panel for CUPS and can be found at:</p>
 498
 499 <pre>
 500     <a href='http://www.phy.uni-bayreuth.de/till/xpp'>http://www.phy.uni-bayreuth.de/till/xpp/</a>
 501 </pre>
 502
 503 <p>Numerous other filters, drivers, tutorials, etc. have been
 504 made available on the CUPS Links web page, available at:</p>
 505
 506 <pre>
 507     <a href='http://www.cups.org/links.php'>http://www.cups.org/links.php</a>
 508 </pre>
 509
 510 <p>Finally, our own ESP Print Pro software uses CUPS to provide
 511 drivers for thousands of printers and can be found at:</p>
 512
 513 <pre>
 514     <a href='http://www.easysw.com/printpro'>http://www.easysw.com/printpro</a>
 515 </pre>
 516
 517 <h2>Operating Systems Using CUPS</h2>
 518
 519 <p>One of our goals has always been to get as many UNIX/Linux
 520 distributions using CUPS as possible. Debian is currently
 521 providing CUPS as part of its stable distribution, and many
 522 other distributions are considering it in their next
 523 releases.</p>
 524
 525 <h2>Summary</h2>
 526
 527 <p>The Common UNIX Printing System provides a modern printing
 528 interface for UNIX applications that is both flexible and
 529 user-friendly. The software provides System V and Berkeley
 530 compatible command-line interfaces to ensure compatibility with
 531 existing applications. CUPS 1.2 adds many new features that make
 532 it an even better choice for printing under UNIX.</p>
 533
 534 <h2>Who to Contact</h2>
 535
 536 <p>For more information on CUPS please contact us at:
 537
 538 <pre>
 539     Attn: CUPS Information
 540     Easy Software Products
 541     44141 Airport View Drive Suite 204
 542     Hollywood, Maryland 20636-3142 USA
 543
 544     +1.301.373.9600
 545
 546     <a href='mailto:cups-info@cups.org'>cups-info@cups.org</a>
 547 </pre>
 548
 549 <h2>References</h2>
 550
 551 <dl>
 552
 553         <dt>IEEE-1387.4</dt>
 554
 555         <dd>System Administration - Part 4: Printing Interfaces
 556         (draft)</dd>
 557
 558         <dt><a href='http://www.pwg.org/ipp/index.html'>IETF-IPP</a></dt>
 559
 560         <dd>Internet Printing Protocol/1.1</dd>
 561
 562         <dt><a href='http://www.astart.com/lprng.html'>LPRng</a></dt>
 563
 564         <dd>An enhanced, extended, and portable implementation
 565         of the Berkeley LPR print spooler functionality</dd>
 566
 567         <dt>Palladin</dt>
 568
 569         <dd>A printing system developed at the Massachussetts
 570         Institute of Technology</dd>
 571
 572         <dt><a href='http://www-usa.iona.com//hyplan/jmason/plp.html'>PLP</a></dt>
 573
 574         <dd>The Portable Line Printer spooler system</dd>
 575
 576         <dt><a href='http://www.ietf.org/rfc/rfc1179.txt'>RFC1179</a></dt>
 577
 578         <dd>Line Printer Daemon Protocol</dd>
 579
 580         <dt><a href='http://www.ietf.org/rfc/rfc2046.txt'>RFC2046</a></dt>
 581
 582         <dd>Multipurpose Internet Mail Extensions (MIME) Part
 583         Two: Media Types</dd>
 584
 585         <dt><a href='http://www.ietf.org/rfc/rfc2616.txt'>RFC2616</a></dt>
 586
 587         <dd>Hypertext Transfer Protocol -- HTTP/1.1</dd>
 588
 589 </dl>
 590
 591 <h2>Trademarks</h2>
 592
 593 <p>The Common UNIX Printing System, CUPS, and the CUPS logo are
 594 the trademark property of Easy Software Products. All other
 595 trademarks are the property of their respective owners.</p>
 596
 597 </body>
 598 </html>