doc/help/overview.html

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   4         <TITLE>Overview of CUPS</TITLE>
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   7
   8 <P>Printing within UNIX has historically been done using one of
   9 two printing systems - the Berkeley Line Printer Daemon (LPD)
  10 [RFC1179] and the AT&amp;T Line Printer system. These printing
  11 systems were designed in the 70's for printing text to line
  12 printers; vendors have since added varying levels of support for
  13 other types of printers.</P>
  14
  15 <P>Replacements for these printing systems have emerged [LPRng,
  16 Palladin, PLP], however none of the replacements change the
  17 fundamental capabilities of these systems.</P>
  18
  19 <P>Over the years several attempts at developing a standard
  20 printing interface have been made, including the draft POSIX
  21 Printing standard developed by the Institute of Electrical and
  22 Electronics Engineers, Inc. (IEEE) [IEEE-1387.4] and Internet
  23 Printing Protocol (IPP) developed by the Internet Engineering
  24 Task Force (IETF) through the Printer Working Group (PWG)
  25 [IETF-IPP]. The POSIX printing standard defines a common set of
  26 command-line tools as well as a C interface for printer
  27 administration and print jobs, but has been shelved by the
  28 IEEE.</P>
  29
  30 <P>The Internet Printing Protocol defines extensions to the
  31 HyperText Transport Protocol 1.1 [RFC2616] to provide support
  32 for remote printing services. IPP/1.1 was accepted by the IETF
  33 as a proposed standard in ??? of ???. Unlike POSIX Printing, IPP
  34 enjoys widespread industry support and has become the standard
  35 network printing solution for all operating systems.</P>
  36
  37 <P>CUPS uses IPP/1.1 to provide a complete, modern printing
  38 system for UNIX that can be extended to support new printers,
  39 devices, and protocols while providing compatibility with
  40 existing UNIX applications. CUPS is free software provided under
  41 the terms of the GNU General Public License and GNU Library
  42 General Public License.</P>
  43
  44 <H2 CLASS="title">History</H2>
  45
  46 <P>The first production release of CUPS (based on IPP/1.0) was
  47 released in October of 1999. Version 1.1 of CUPS was released in
  48 August of 2002 ???? and added support for IPP/1.1.</P>
  49
  50 <P>CUPS 1.2 is based on IPP/1.1 and adds many of the functional
  51 enhancements that have been requested by our users. As with CUPS
  52 1.1, CUPS 1.2 will be followed by patch releases that address
  53 any problems found with the software. New features will be put
  54 in the 1.3 release to follow.</P>
  55
  56 <H2 CLASS="title">Design Overview</H2>
  57
  58 <P>Like most printing systems, CUPS is designed around a central
  59 print scheduling process that dispatches print jobs, processes
  60 administrative commands, provides printer status information to
  61 local and remote programs, and informs users as needed. Figure 1
  62 shows the basic organization of CUPS.</P>
  63
  64 <P ALIGN="CENTER"><IMG SRC="../images/cups-block-diagram.gif"
  65 WIDTH="470" HEIGHT="170" ALT="CUPS Block Diagram"/><BR>
  66 <I>Figure 1 - CUPS Block Diagram</I></P>
  67
  68 <H3>Scheduler</H3>
  69
  70 <P>The scheduler is a HTTP/1.1 server application that handles
  71 HTTP requests. Besides handling printer requests via IPP POST
  72 requests, the scheduler also acts as a full-featured web server
  73 for documentation, status monitoring, and administration.</P>
  74
  75 <P>The scheduler also manages a list of available printers on
  76 the LAN and dispatches print jobs as needed using the
  77 appropriate filters and backends.</P>
  78
  79 <H3>Configuration Files</H3>
  80
  81 <P>The configuration files consist of:</P>
  82
  83 <ul>
  84
  85         <LI>The HTTP server configuration file.</LI>
  86
  87         <LI>Printer and class definition files.</LI>
  88
  89         <LI>MIME type and conversion rule files.</LI>
  90
  91         <LI>PostScript Printer Description (PPD) files.</LI>
  92
  93 </ul>
  94
  95 <P>The HTTP server configuration file is purposely similar to
  96 the Apache server configuration file and defines all of the
  97 access control properties for the server.</P>
  98
  99 <P>The printer and class definition files list the available
 100 printer queues and classes. Printer classes are collections of
 101 printers. Jobs sent to a class are forwarded to the first
 102 available printer in the class, round-robin fashion.</P>
 103
 104 <P>The MIME type files list the supported MIME types
 105 (text/plain, application/postscript, etc.) and "magic' rules for
 106 automatically detecting the format of a file.  These are used by
 107 the HTTP server to determine the <tt>Content-Type</tt> field for
 108 <tt>GET</tt> and <tt>HEAD</tt> requests and by the IPP request
 109 handler to determine the file type when a <tt>Print-Job</tt> or
 110 <tt>Send-File</tt> request is received with a
 111 <tt>document-format</tt> of
 112 <tt>application/octet-stream</tt>.</P>
 113
 114 <P>The MIME conversion rule files list the available filters.
 115 The filters are used when a job is dispatched so that an
 116 application can send a convenient file format to the printing
 117 system which then converts the document into a printable format
 118 as needed. Each filter has a relative cost associated with it,
 119 and the filtering algorithm chooses the set of filters that will
 120 convert the file to the needed format with the lowest total
 121 "cost".</P>
 122
 123 <P>The PPD files describe the capabilities of all printers, not
 124 just PostScript printers. There is one PPD file for each
 125 printer. PPD files for non-PostScript printers define additional
 126 filters through <tt>cupsFilter</tt> attributes to support
 127 printer drivers.</P>
 128
 129 <H3>CUPS API</H3>
 130
 131 <P>The CUPS API contains CUPS-specific convenience functions for
 132 queuing print jobs, getting printer information, accessing
 133 resources via HTTP and IPP, and manipulating PPD files. Unlike
 134 the rest of CUPS, the CUPS API is provided under the terms of
 135 the GNU LGPL so it may be used by non-GPL applications.</P>
 136
 137 <H3>Berkeley and System V Commands</H3>
 138
 139 <P>CUPS provides the System V and Berkeley command-line
 140 interfaces for submitting jobs and checking the printer status.
 141 The <tt>lpstat</tt> and <tt>lpc status</tt> commands
 142 also show network printers ("printer@server") when printer
 143 browsing is enabled.</P>
 144
 145 <P>The System V administation commands are supplied for managing
 146 printers and classes. The Berkeley printer administration tool
 147 (<tt>lpc</tt>) is only supported in a "read-only' mode to
 148 check the current status of the printer queues and
 149 scheduler.</P>
 150
 151 <H3>Filters</H3>
 152
 153 <P>A filter program reads from the standard input or from a file
 154 if a filename is supplied. All filters must support a common set
 155 of options including printer name, job ID, username, job title,
 156 number of copies, and job options. All output is sent to the
 157 standard output.</P>
 158
 159 <P>Filters are provided for many file formats and include image
 160 file and PostScript raster filters that support non-PostScript
 161 printers. Multiple filters are run in parallel to produce the
 162 required output format.</P>
 163
 164 <P>The PostScript raster filter is based on the ESP Ghostscript
 165 core. Instead of using the Ghostscript printer drivers, the CUPS
 166 filter uses a generic CUPS raster printer driver and
 167 CUPS-compliant front-end to support any kind of raster printer.
 168 This allows the same printer driver filter to be used for
 169 printing raster data from any filter.</P>
 170
 171 <pre>Talk about Apple's use of CUPS...</pre>
 172
 173 <H3>CUPS Imaging</H3>
 174
 175 <P>The CUPS Imaging library provides functions for managing
 176 large images, doing colorspace conversion and color management,
 177 scaling images for printing, and managing raster page streams.
 178 It is used by the CUPS image file filters, the PostScript RIP,
 179 and all raster printers drivers.</P>
 180
 181 <H3>Backends</H3>
 182
 183 <P>A backend program is a special filter that sends print data
 184 to a device or network connection. Backends for parallel,
 185 serial, USB, LPD, IPP, and AppSocket (JetDirect) connections are
 186 provided in CUPS 1.2.</P>
 187
 188 <P>SAMBA version 2.0.6 and higher includes a SMB backend
 189 (<tt>smbspool(1)</tt>) that can be used for printing to
 190 Windows.</P>
 191
 192 <H2 CLASS="title">Network Printing</H2>
 193
 194 <P>Traditionally, network printing has been one of the hardest
 195 things to get working under UNIX. One reason is because each
 196 vendor added their own extensions to the LPD protocol (the
 197 previous standard for network printing), making cross-platform
 198 printing difficult if not impossible.</P>
 199
 200 <P>Another reason is that you have to administer every network
 201 printer on every client machine. In some cases you can "clone'
 202 the printer configuration from a "master' client to each of the
 203 others, but even that can be time-consuming and error-prone.
 204 Something better is needed.</P>
 205
 206 <P>CUPS provides "printer browsing", which allows clients to
 207 automatically see and use printers from any server on a LAN.
 208 This means that you only need to configure the server and the
 209 clients will automatically see the printers and classes on
 210 it.</P>
 211
 212 <P>In addition, CUPS can automatically merge multiple identical
 213 network printers into "implicit classes". This allows clients to
 214 send jobs to the implicit class and have them print on the first
 215 available printer or server. In addition, failsafe and
 216 load-balancing functions are enabled simply by defining the same
 217 printer on multiple servers!</P>
 218
 219 <H2 CLASS="title">New Features in CUPS 1.2</H2>
 220
 221 <P>CUPS 1.2 includes many new features and capabilities:
 222
 223 <ol>
 224
 225         <LI><A HREF="#BACKENDS">Backends</A>
 226
 227         <LI><A HREF="#BANNERS">Banner Page Support</A>
 228
 229         <LI><A HREF="#DIGEST">Digest Authentication</A>
 230
 231         <LI><A HREF="#DIRSVC">Directory Services</A>
 232
 233         <LI><A HREF="#FHS2">Directory Structure Changes</A>
 234
 235         <LI><A HREF="#DOCOS">Documentation</A>
 236
 237         <LI><A HREF="#DRIVERS">Drivers</A>
 238
 239         <LI><A HREF="#FILTERS">Filters</A>
 240
 241         <LI><A HREF="#IPP">IPP Support</A>
 242
 243         <LI><A HREF="#PERSISTENCE">Job Persistence</A>
 244
 245         <LI><A HREF="#LPD">LPD Client Support</A>
 246
 247         <LI><A HREF="#USEROPTS">User-Defined Printers and Options</A>
 248
 249         <LI><A HREF="#WEB">Web Administration Interface</A>
 250
 251 </ol>
 252
 253 <H3><A NAME="BACKENDS">1. Backends</A></H3>
 254
 255 <P>CUPS 1.2 implements a new backend interface for retrieving a
 256 list of available devices for CUPS clients. This allows
 257 administration interfaces to query the CUPS scheduler for a list
 258 of available devices, automatically configure printers if the
 259 device identification information is available, and present the
 260 user with a list of available devices rather than relying on the
 261 user to know what devices are configured on the system.</P>
 262
 263 <P>The new release also includes a backend for USB printers
 264 under *BSD and Linux. Support for USB under Solaris 8 will be
 265 provided in a subsequent patch release.</P>
 266
 267 <H3><A NAME="BANNERS">2. Banner Page Support</A></H3>
 268
 269 <P>CUPS 1.2 includes support for banner pages at the beginning
 270 and end of a job. Banner pages may be of any file format and
 271 support variable substitution for job titles, usernames, etc.
 272 Default banner pages are associated with each printer and can be
 273 overridden with command-line options by the user.</P>
 274
 275 <H3><A NAME="DIGEST">3. Digest Authentication</A></H3>
 276
 277 <P>Digest authentication provides a more secure method of
 278 authenticating access to the printing system. Unlike Basic
 279 authentication, Digest authentication does not send passwords
 280 "in the clear' so it is more difficult to gain unauthorized
 281 access to your system.</P>
 282
 283 <P>CUPS 1.2 implements Digest authentication using a special MD5
 284 password file instead of the UNIX password file. This file is
 285 managed using the new <tt>lppasswd</tt> command.</P>
 286
 287 <H3><A NAME="DIRSVC">4. Directory Services</A></H3>
 288
 289 <P>CUPS 1.2 adds new directory service ("printer browsing")
 290 features to make using CUPS on large LANs and WANs easier. You
 291 can now poll a remote server for printer information and relay
 292 it to the LAN as well as restrict what printer information is
 293 processed (e.g. to "hide" servers, domains, or networks that you
 294 don't want to see.)</P>
 295
 296 <H3><A NAME="FHS2">5. Directory Structure Changes</A></H3>
 297
 298 <P>CUPS 1.2 now uses a directory structure that complies with
 299 the Filesystem Hierarchy Standard (FHS), version 2.0. This
 300 should make integration into existing Linux and *BSD
 301 distributions a lot easier.</P>
 302
 303 <H3><A NAME="DOCOS">6. Documentation</A></H3>
 304
 305 <P>The CUPS 1.2 documentation has gone through many revisions,
 306 including a completely rewritten administrators manual, a new
 307 programmers manual, and an IPP implementation reference
 308 manual.</P>
 309
 310 <H3><A NAME="DRIVERS">7. Drivers</A></H3>
 311
 312 <P>CUPS 1.2 includes drivers for EPSON dot-matrix and inkjet
 313 printers. As with the HP PCL drivers, the EPSON drivers don't
 314 necessarily provide the best possible output for each printer
 315 but should provide adequate printing quality for general
 316 day-to-day printing.</P>
 317
 318 <H3><A NAME="FILTERS">8. Filters</A></H3>
 319
 320 <P>CUPS 1.2 includes new image, PostScript, PDF, and text
 321 filters. The image filters have been upgraded to support Windows
 322 BMP and Alias PIX files.</P>
 323
 324 <P>The PostScript filter is now based off ESP Ghostscript. The
 325 new filter provides much better performance with
 326 higher-resolution printers and supports all Level 3 PostScript
 327 language features.</P>
 328
 329 <P>The new PDF filter is based off the excellent Xpdf software
 330 from Derek Noonburg and supports automatic page scaling. The new
 331 filter is a faster, smaller, more reliable replacement for the
 332 GNU Ghostscript PDF filtering that was used in CUPS 1.0.</P>
 333
 334 <P>The new text filter now supports bidirectional text and can
 335 embed fonts as needed.</P>
 336
 337 <H3><A NAME="IPP">9. IPP Support</A></H3>
 338
 339 <P>Probably the least visible portion of CUPS is the IPP
 340 support. CUPS 1.1 implements all of the required IPP/1.1
 341 operations and attributes and most of the optional ones. The
 342 optional Create-Job and Send-File operations are now
 343 implemented, allowing for better System V printing system
 344 compatibility (one job ID per <tt>lp</tt> command) and support
 345 for banner pages.</P>
 346
 347 <H3><A NAME="PERSISTENCE">10. Job Persistence</A></H3>
 348
 349 <P>CUPS 1.2 supports job persistence. This means that jobs are
 350 preserved even after a reboot, a feature that was sorely missing
 351 from CUPS 1.0.</P>
 352
 353 <P>In addition, CUPS 1.2 allows you to keep job information
 354 after the job has printed. The basic post-job persistence mode
 355 provides a job history (number of pages printed, time job was
 356 printed, etc.) but does not preserve the actual job files. This
 357 can be changed to discard all information after a job is printed
 358 or keep the job files after printing so you can reprint a job at
 359 some later time.</P>
 360
 361 <H3><A NAME="LPD">11. LPD Client Support</A></H3>
 362
 363 <P>By popular request, CUPS 1.2 supports LPD-based clients using
 364 a new mini-daemon that handles LPD requests and passes them on
 365 to the main server.</P>
 366
 367 <H3><A NAME="USEROPTS">12. User-Defined Printers and Options</A></H3>
 368
 369 <P>CUPS 1.2 includes support for user-defined printers and
 370 options via a new <tt>lpoptions</tt> command. User-defined
 371 printers are special instances of the available printers (e.g.
 372 "printer/instance" or "printer@server/instance") that can have
 373 their own default options such as media size, resolution, and so
 374 forth. The <tt>lpoptions</tt> command can also be used to set a
 375 different default printer queue.</P>
 376
 377 <H3><A NAME="WEB">13. Web Administration Interface</A></H3>
 378
 379 <P>CUPS 1.0 provided a simple class, job, and printer monitoring
 380 interface for web browsers. CUPS 1.2 replaces this interface
 381 with an enhanced administration interface that allows you to
 382 add, modify, delete, configure, and control classes, jobs, and
 383 printers.</P>
 384
 385 <H2 CLASS="title">Software Using CUPS</H2>
 386
 387 <P>A lot has happened since CUPS 1.0 came out, and many software
 388 packages are supporting CUPS. We have contributed code to the
 389 SAMBA team to support CUPS, and parts of that are already
 390 available in SAMBA 2.0.6 and 2.0.7. With any luck the final
 391 pieces that provide a complete integration with SAMBA will be
 392 available in the next release of SAMBA.</P>
 393
 394 <P>Two graphical interfaces have appeared on the scene that use
 395 CUPS as well. The KUPS project provides a KDE-based interface
 396 for CUPS and can be found at:</P>
 397
 398 <pre>
 399     <A HREF="http://kups.sourceforge.net">http://kups.sourceforge.net</A>
 400 </pre>
 401
 402 <P>The X Printing Panel (XPP) project provides a graphical
 403 printing panel for CUPS and can be found at:</P>
 404
 405 <pre>
 406     <A HREF="http://www.phy.uni-bayreuth.de/till/xpp">http://www.phy.uni-bayreuth.de/till/xpp/</A>
 407 </pre>
 408
 409 <P>Numerous other filters, drivers, tutorials, etc. have been
 410 made available on the CUPS Links web page, available at:</P>
 411
 412 <pre>
 413     <A HREF="http://www.cups.org/links.php">http://www.cups.org/links.php</A>
 414 </pre>
 415
 416 <P>Finally, our own ESP Print Pro software uses CUPS to provide
 417 drivers for thousands of printers and can be found at:</P>
 418
 419 <pre>
 420     <A HREF="http://www.easysw.com/printpro">http://www.easysw.com/printpro</A>
 421 </pre>
 422
 423 <H2 CLASS="title">Operating Systems Using CUPS</H2>
 424
 425 <P>One of our goals has always been to get as many UNIX/Linux
 426 distributions using CUPS as possible. Debian is currently
 427 providing CUPS as part of its stable distribution, and many
 428 other distributions are considering it in their next
 429 releases.</P>
 430
 431 <H2 CLASS="title">Summary</H2>
 432
 433 <P>The Common UNIX Printing System provides a modern printing
 434 interface for UNIX applications that is both flexible and
 435 user-friendly. The software provides System V and Berkeley
 436 compatible command-line interfaces to ensure compatibility with
 437 existing applications. CUPS 1.2 adds many new features that make
 438 it an even better choice for printing under UNIX.</P>
 439
 440 <H2 CLASS="title">Who to Contact</H2>
 441
 442 <P>For more information on CUPS please contact us at:
 443
 444 <pre>
 445     Attn: CUPS Information
 446     Easy Software Products
 447     44141 Airport View Drive Suite 204
 448     Hollywood, Maryland 20636-3142 USA
 449
 450     +1.301.373.9600
 451
 452     <A HREF="mailto:cups-info@cups.org">cups-info@cups.org</A>
 453 </pre>
 454
 455 <H2 CLASS="title">References</H2>
 456
 457 <DL>
 458
 459         <DT>IEEE-1387.4</DT>
 460
 461         <DD>System Administration - Part 4: Printing Interfaces
 462         (draft)</DD>
 463
 464         <DT><A HREF="http://www.pwg.org/ipp/index.html">IETF-IPP</A></DT>
 465
 466         <DD>Internet Printing Protocol/1.1</DD>
 467
 468         <DT><A HREF="http://www.astart.com/lprng.html">LPRng</A></DT>
 469
 470         <DD>An enhanced, extended, and portable implementation
 471         of the Berkeley LPR print spooler functionality</DD>
 472
 473         <DT>Palladin</DT>
 474
 475         <DD>A printing system developed at the Massachussetts
 476         Institute of Technology</DD>
 477
 478         <DT><A HREF="http://www-usa.iona.com//hyplan/jmason/plp.html">PLP</A></DT>
 479
 480         <DD>The Portable Line Printer spooler system</DD>
 481
 482         <DT><A HREF="http://www.ietf.org/rfc/rfc1179.txt">RFC1179</A></DT>
 483
 484         <DD>Line Printer Daemon Protocol</DD>
 485
 486         <DT><A HREF="http://www.ietf.org/rfc/rfc2046.txt">RFC2046</A></DT>
 487
 488         <DD>Multipurpose Internet Mail Extensions (MIME) Part
 489         Two: Media Types</DD>
 490
 491         <DT><A HREF="http://www.ietf.org/rfc/rfc2616.txt">RFC2616</A></DT>
 492
 493         <DD>Hypertext Transfer Protocol -- HTTP/1.1</DD>
 494
 495 </DL>
 496
 497 <H2 CLASS="title">Trademarks</H2>
 498
 499 <P>The Common UNIX Printing System, CUPS, and the CUPS logo are
 500 the trademark property of Easy Software Products. All other
 501 trademarks are the property of their respective owners.</P>
 502
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 504 </HTML>