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 <H1>CUPS Software Design Description</H1></A><BR>
 CUPS-SDD-1.2<BR>
 Easy Software Products<BR>
 Copyright 1997-2003, All Rights Reserved<BR>
 </CENTER>
 <HR>
 <H1 ALIGN="CENTER"><A NAME="CONTENTS">Table of Contents</A></H1>
 <BR>
 <BR><B><A HREF="#1">1 Scope</A></B>
 <UL>
 <LI><A HREF="#1_1">1.1 Identification</A></LI>
 <LI><A HREF="#1_2">1.2 System Overview</A></LI>
 <LI><A HREF="#1_3">1.3 Document Overview</A></LI>
 </UL>
 <B><A HREF="#2">2 References</A></B>
 <UL>
 <LI><A HREF="#2_1">2.1 CUPS Documentation</A></LI>
 <LI><A HREF="#2_2">2.2 Other Documents</A></LI>
 </UL>
 <B><A HREF="#3">3 Design Overview</A></B>
 <UL>
 <LI><A HREF="#3_1">3.1 Backends</A></LI>
 <UL>
 <LI><A HREF="#3_1_1">3.1.1 ipp</A></LI>
 <LI><A HREF="#3_1_2">3.1.2 lpd</A></LI>
 <LI><A HREF="#3_1_3">3.1.3 parallel</A></LI>
 <LI><A HREF="#3_1_4">3.1.4 serial</A></LI>
 <LI><A HREF="#3_1_5">3.1.5 socket</A></LI>
 <LI><A HREF="#3_1_6">3.1.6 usb</A></LI>
 </UL>
 <LI><A HREF="#3_2">3.2 Berkeley Commands</A></LI>
 <UL>
 <LI><A HREF="#3_2_1">3.2.1 lpc</A></LI>
 <LI><A HREF="#3_2_2">3.2.2 lpq</A></LI>
 <LI><A HREF="#3_2_3">3.2.3 lpr</A></LI>
 <LI><A HREF="#3_2_4">3.2.4 lprm</A></LI>
 </UL>
 <LI><A HREF="#3_3">3.3 CGI</A></LI>
 <UL>
 <LI><A HREF="#3_3_1">3.3.1 admin.cgi</A></LI>
 <LI><A HREF="#3_3_2">3.3.2 classes.cgi</A></LI>
 <LI><A HREF="#3_3_3">3.3.3 jobs.cgi</A></LI>
 <LI><A HREF="#3_3_4">3.3.4 printers.cgi</A></LI>
 </UL>
 <LI><A HREF="#3_4">3.4 CUPS Application Programmers Interface</A></LI>
 <UL>
 <LI><A HREF="#3_4_1">3.4.1 Convenience Functions</A></LI>
 <LI><A HREF="#3_4_2">3.4.2 HTTP Functions</A></LI>
 <LI><A HREF="#3_4_3">3.4.3 IPP Functions</A></LI>
 <LI><A HREF="#3_4_4">3.4.4 Language Functions</A></LI>
 <LI><A HREF="#3_4_5">3.4.5 PPD Functions</A></LI>
 </UL>
 <LI><A HREF="#3_5">3.5 CUPS Imaging Library</A></LI>
 <UL>
 <LI><A HREF="#3_5_1">3.5.1 Colorspace Conversion Functions</A></LI>
 <LI><A HREF="#3_5_2">3.5.2 Color Management Functions</A></LI>
 <LI><A HREF="#3_5_3">3.5.3 Image Management Functions</A></LI>
 <LI><A HREF="#3_5_4">3.5.4 Scaling Functions</A></LI>
 <LI><A HREF="#3_5_5">3.5.5 Image File Functions</A></LI>
 <LI><A HREF="#3_5_6">3.5.6 Raster Functions</A></LI>
 </UL>
 <LI><A HREF="#3_6">3.6 Daemons</A></LI>
 <UL>
 <LI><A HREF="#3_6_1">3.6.1 Line Printer Daemon</A></LI>
 <LI><A HREF="#3_6_2">3.6.2 Polling Daemon</A></LI>
 </UL>
 <LI><A HREF="#3_7">3.7 Filters</A></LI>
 <UL>
 <LI><A HREF="#3_7_1">3.7.1 hpgltops</A></LI>
 <LI><A HREF="#3_7_2">3.7.2 imagetops</A></LI>
 <LI><A HREF="#3_7_3">3.7.3 imagetoraster</A></LI>
 <LI><A HREF="#3_7_4">3.7.4 pdftops</A></LI>
 <LI><A HREF="#3_7_5">3.7.5 pstops</A></LI>
 <LI><A HREF="#3_7_6">3.7.6 pstoraster</A></LI>
 <LI><A HREF="#3_7_7">3.7.7 rastertoepson</A></LI>
 <LI><A HREF="#3_7_8">3.7.8 rastertohp</A></LI>
 <LI><A HREF="#3_7_9">3.7.9 texttops</A></LI>
 </UL>
 <LI><A HREF="#3_8">3.8 Scheduler</A></LI>
 <UL>
 <LI><A HREF="#3_8_1">3.8.1 Authorization</A></LI>
 <LI><A HREF="#3_8_2">3.8.2 Classes</A></LI>
 <LI><A HREF="#3_8_3">3.8.3 Client</A></LI>
 <LI><A HREF="#3_8_4">3.8.4 Configuration</A></LI>
 <LI><A HREF="#3_8_5">3.8.5 Devices</A></LI>
 <LI><A HREF="#3_8_6">3.8.6 Directory Services</A></LI>
 <LI><A HREF="#3_8_7">3.8.7 IPP</A></LI>
 <LI><A HREF="#3_8_8">3.8.8 Jobs</A></LI>
 <LI><A HREF="#3_8_9">3.8.9 Logging</A></LI>
 <LI><A HREF="#3_8_10">3.8.10 Main</A></LI>
 <LI><A HREF="#3_8_11">3.8.11 MIME</A></LI>
 <LI><A HREF="#3_8_12">3.8.12 PPDs</A></LI>
 <LI><A HREF="#3_8_13">3.8.13 Printers</A></LI>
 </UL>
 <LI><A HREF="#3_9">3.9 System V Commands</A></LI>
 <UL>
 <LI><A HREF="#3_9_1">3.9.1 accept</A></LI>
 <LI><A HREF="#3_9_2">3.9.2 cancel</A></LI>
 <LI><A HREF="#3_9_3">3.9.3 disable</A></LI>
 <LI><A HREF="#3_9_4">3.9.4 enable</A></LI>
 <LI><A HREF="#3_9_5">3.9.5 lp</A></LI>
 <LI><A HREF="#3_9_6">3.9.6 lpadmin</A></LI>
 <LI><A HREF="#3_9_7">3.9.7 lpinfo</A></LI>
 <LI><A HREF="#3_9_8">3.9.8 lpmove</A></LI>
 <LI><A HREF="#3_9_9">3.9.9 lpoptions</A></LI>
 <LI><A HREF="#3_9_10">3.9.10 lpstat</A></LI>
 <LI><A HREF="#3_9_11">3.9.11 reject</A></LI>
 </UL>
 </UL>
 <B><A HREF="#4">A Glossary</A></B>
 <UL>
 <LI><A HREF="#4_1">A.1 Terms</A></LI>
 <LI><A HREF="#4_2">A.2 Acronyms</A></LI>
 </UL>
 <HR>
 <H1><A NAME="1">1 Scope</A></H1>
 <H2><A NAME="1_1">1.1 Identification</A></H2>
  This software design description document provides general information
  on the architecture and coding of the Common UNIX Printing System
  (&quot;CUPS&quot;) Version 1.2.
 <H2><A NAME="1_2">1.2 System Overview</A></H2>
 <P>CUPS provides a portable printing layer for UNIX&reg;-based operating
  systems. It has been developed by<A HREF="http://www.easysw.com"> Easy
  Software Products</A> to promote a standard printing solution for all
  UNIX vendors and users. CUPS provides the System V and Berkeley
  command-line interfaces.</P>
 <P>CUPS uses the Internet Printing Protocol (&quot;IPP&quot;) as the basis for
  managing print jobs and queues. The Line Printer Daemon (&quot;LPD&quot;) Server
  Message Block (&quot;SMB&quot;), and AppSocket (a.k.a. JetDirect) protocols are
  also supported with reduced functionality. CUPS adds network printer
  browsing and PostScript Printer Description (&quot;PPD&quot;) based printing
  options to support real-world printing under UNIX.</P>
 <P>CUPS also includes a customized version of GNU Ghostscript (currently
  based off GNU Ghostscript 5.50) and an image file RIP that are used to
  support non-PostScript printers. Sample drivers for HP and EPSON
  printers are included that use these filters.</P>
 <H2><A NAME="1_3">1.3 Document Overview</A></H2>
  This software design description document is organized into the
  following sections:
 <UL>
 <LI>1 - Scope</LI>
 <LI>2 - References</LI>
 <LI>3 - Design Overview</LI>
 <LI>A - Glossary</LI>
 </UL>
 <H1><A NAME="2">2 References</A></H1>
 <H2><A NAME="2_1">2.1 CUPS Documentation</A></H2>
 <P>The following CUPS documentation is referenced by this document:</P>
 <UL>
 <LI>CUPS-CMP-1.2: CUPS Configuration Management Plan</LI>
 <LI>CUPS-IDD-1.2: CUPS System Interface Design Description</LI>
 <LI>CUPS-IPP-1.2: CUPS Implementation of IPP</LI>
 <LI>CUPS-SAM-1.2.x: CUPS Software Administrators Manual</LI>
 <LI>CUPS-SDD-1.2: CUPS Software Design Description</LI>
 <LI>CUPS-SPM-1.2.x: CUPS Software Programming Manual</LI>
 <LI>CUPS-SSR-1.2: CUPS Software Security Report</LI>
 <LI>CUPS-STP-1.2: CUPS Software Test Plan</LI>
 <LI>CUPS-SUM-1.2.x: CUPS Software Users Manual</LI>
 <LI>CUPS-SVD-1.2: CUPS Software Version Description</LI>
 </UL>
 <H2><A NAME="2_2">2.2 Other Documents</A></H2>
 <P>The following non-CUPS documents are referenced by this document:</P>
 <UL>
 <LI><A HREF="http://partners.adobe.com/asn/developer/PDFS/TN/5003.PPD_Spec_v4.3.pdf">
 Adobe PostScript Printer Description File Format Specification, Version
  4.3.</A></LI>
 <LI><A HREF="http://partners.adobe.com/asn/developer/PDFS/TN/PLRM.pdf">
 Adobe PostScript Language Reference, Third Edition.</A></LI>
 <LI>IPP: Job and Printer Set Operations</LI>
 <LI>IPP/1.1: Encoding and Transport</LI>
 <LI>IPP/1.1: Implementers Guide</LI>
 <LI>IPP/1.1: Model and Semantics</LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc1179.txt">RFC 1179, Line Printer
  Daemon Protocol</A></LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc2567.txt">RFC 2567, Design Goals
  for an Internet Printing Protocol</A></LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc2568.txt">RFC 2568, Rationale
  for the Structure of the Model and Protocol for the Internet Printing
  Protocol</A></LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc2569.txt">RFC 2569, Mapping
  between LPD and IPP Protocols</A></LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616, Hypertext
  Transfer Protocol -- HTTP/1.1</A></LI>
 <LI><A HREF="http://www.ietf.org/rfc/rfc2617.txt">RFC 2617, HTTP
  Authentication: Basic and Digest Access</A> Authentication</LI>
 </UL>
 <H1><A NAME="3">3 Design Overview</A></H1>
  CUPS is composed of 9 software sub-systems that operate together to
  perform common printing tasks:
 <UL>
 <LI>Backends</LI>
 <LI>Berkeley Commands</LI>
 <LI>CGI</LI>
 <LI>CUPS Application Programmers Interface</LI>
 <LI>CUPS Imaging Library</LI>
 <LI>Daemons</LI>
 <LI>Filters</LI>
 <LI>Scheduler</LI>
 <LI>System V Commands</LI>
 </UL>
 <H2><A NAME="3_1">3.1 Backends</A></H2>
  The backends implement communications over a number of different
  interfaces. All backends are called with a common set of arguments:
 <UL>
 <LI>Device URI - the Uniform Resource Identifier for the output device
  (e.g. <CODE>parallel:/dev/plp</CODE>, <CODE>ipp://hostname/resource</CODE>
 ).</LI>
 <LI>Job Identifier - the job identifier for this job (integer).</LI>
 <LI>User Name - the user associated with this job (name string).</LI>
 <LI>Title - the title/job-name associated with this job (name string).</LI>
 <LI>Copies - the number of copies required (integer).</LI>
 <LI>Options - the options associated with this job (space separated
  option strings).</LI>
 <LI>Filename (optional) - the file to print; if this option is not
  specified, the backend must read the print file from the standard
  input.</LI>
 </UL>
 <P>Backends are named using the scheme of the URI, so a URI of
  &quot;ipp://hostname/resource&quot; would be processed by the &quot;ipp&quot; backend.</P>
 <H3><A NAME="3_1_1">3.1.1 ipp</A></H3>
 <P>The ipp backend sends the specified job to a network printer or host
  using the Internet Printing Protocol. The URI is as specified by the <CODE>
 printer-uri-supported</CODE> attribute from the printer or host.</P>
 <H3><A NAME="3_1_2">3.1.2 lpd</A></H3>
 <P>The lpd backend sends the specified job to a network printer or host
  using the Line Printer Daemon protocol. The URI is of the form:</P>
 <UL>
 <PRE>lpd://hostname/queue
 </PRE>
 </UL>
 <H3><A NAME="3_1_3">3.1.3 parallel</A></H3>
 <P>The parallel backend sends the specified job to a local printer
  connected via the specified parallel port device. The URI is of the
  form:</P>
 <UL>
 <PRE>parallel:/dev/file
 </PRE>
 </UL>
 <H3><A NAME="3_1_4">3.1.4 serial</A></H3>
 <P>The serial backend sends the specified job to a local printer
  connected via the specified serial port device. The URI is of the form:</P>
 <UL>
 <PRE>serial:/dev/file?option[+option+...]
 </PRE>
 </UL>
  The options can be any combination of the following:
 <UL>
 <LI><CODE>baud=<I>rate</I></CODE> - Sets the baud rate for the device.</LI>
 <LI><CODE>bits=<I>7 or 8</I></CODE> - Sets the number of data bits.</LI>
 <LI><CODE>parity=<I>even</I></CODE> - Sets even parity checking.</LI>
 <LI><CODE>parity=<I>odd</I></CODE> - Sets odd parity checking.</LI>
 <LI><CODE>parity=<I>none</I></CODE> - Turns parity checking off.</LI>
 <LI><CODE>flow=dtrdsr<I></I></CODE> - Turns DTR/DSR (hardware) flow
  control on.</LI>
 <LI><CODE>flow=hard<I></I></CODE> - Turns RTS/CTS (hardware) flow
  control on.</LI>
 <LI><CODE>flow=none<I></I></CODE> - Turns flow control off.</LI>
 <LI><CODE>flow=rtscts<I></I></CODE> - Turns RTS/CTS (hardware) flow
  control on.</LI>
 <LI><CODE>flow=xonxoff<I></I></CODE> - Turns XON/XOFF (software) flow
  control on.</LI>
 </UL>
 <H3><A NAME="3_1_5">3.1.5 socket</A></H3>
 <P>The socket backend sends the specified job to a network host using
  the AppSocket protocol commonly used by Hewlett-Packard and Tektronix
  printers. The URI is of the form:</P>
 <UL>
 <PRE>socket://hostname[:port]
 </PRE>
 </UL>
  The default port number is 9100.
 <H3><A NAME="3_1_6">3.1.6 usb</A></H3>
 <P>The usb backend sends the specified job to a local printer connected
  via the specified usb port device. The URI is of the form:</P>
 <UL>
 <PRE>usb:/dev/file
 </PRE>
 </UL>
 <H2><A NAME="3_2">3.2 Berkeley Commands</A></H2>
 <P>The Berkeley commands provide a simple command-line interface to CUPS
  to submit and control print jobs. It is provided for compatibility with
  existing software that is hardcoded to use the Berkeley commands.</P>
 <H3><A NAME="3_2_1">3.2.1 lpc</A></H3>
  The lpc command allows users and administrators to check the status and
  control print queues. The version provided with CUPS supports the
  following commands:
 <UL>
 <LI>quit - Quits the lpc command.</LI>
 <LI>status - Shows the status of printers and jobs in the queue.</LI>
 </UL>
 <H3><A NAME="3_2_2">3.2.2 lpq</A></H3>
 <P>The lpq command shows the current queue status.</P>
 <H3><A NAME="3_2_3">3.2.3 lpr</A></H3>
 <P>The lpr command submits a job for printing. The CUPS version of lpr
  silently ignores the &quot;i&quot;, &quot;t&quot;, &quot;m&quot;, &quot;h&quot;, and &quot;s&quot; options.</P>
 <H3><A NAME="3_2_4">3.2.4 lprm</A></H3>
 <P>The lprm removes one or more print jobs.</P>
 <H2><A NAME="3_3">3.3 CGI</A></H2>
 <P>The Common Gateway Interface (CGI) programs provide a web-based
  status interface to monitor the status of printers, classes, and jobs.
  Each of the CGIs utilize HTML template files that can be customized to
  provide alternate appearances.</P>
 <H3><A NAME="3_3_1">3.3.1 admin.cgi</A></H3>
 <P>The admin CGI provides administration interfaces for printers and
  classes. The user can add, modify, delete, start, stop, and configure
  printers and classes using &quot;wizard&quot; interfaces.</P>
 <H3><A NAME="3_3_2">3.3.2 classes.cgi</A></H3>
 <P>The classes CGI lists the available printer classes and any pending
  jobs for the class. The user can click on individual classes to limit
  the display and click on jobs to see the job status.</P>
 <H3><A NAME="3_3_3">3.3.3 jobs.cgi</A></H3>
 <P>The jobs CGI lists the queued print jobs in order of priority. The
  list can be limited by printer or job.</P>
 <H3><A NAME="3_3_4">3.3.4 printers.cgi</A></H3>
 <P>The printers CGI lists the available printer queues and any pending
  jobs for the printer. The user can click on individual printers to
  limit the display and click on jobs to see the job status.</P>
 <H2><A NAME="3_4">3.4 CUPS Application Programmers Interface</A></H2>
 <P>The CUPS Application Programmers Interface (&quot;API&quot;) provides common
  convenience, HTTP, IPP, language, and PPD functions used by the CUPS
  software.</P>
 <H3><A NAME="3_4_1">3.4.1 Convenience Functions</A></H3>
 <P>Convenience functions are provided to submit an IPP request, send a
  print file, cancel a job, get a list of available printers, get a list
  of available classes, get the default printer or class, get the default
  server name, get the local username, and get a password string.</P>
 <H3><A NAME="3_4_2">3.4.2 HTTP Functions</A></H3>
 <P>The HTTP functions provide functions to connect to HTTP servers,
  issue requests, read data from a server, and write data to a server.</P>
 <H3><A NAME="3_4_3">3.4.3 IPP Functions</A></H3>
 <P>The IPP function provide functions to manage IPP request data and
  attributes, read IPP responses from a server, and write IPP requests to
  a server.</P>
 <H3><A NAME="3_4_4">3.4.4 Language Functions</A></H3>
 <P>The language functions provide a standard interface for retrieving
  common textual messages for a particular locale and determining the
  correct encoding (e.g. US ASCII, UTF-8, ISO-8859-1, etc.)</P>
 <H3><A NAME="3_4_5">3.4.5 PPD Functions</A></H3>
 <P>The PostScript Printer Description functions manage PPD files, select
  options, check for option conflicts, and emit selected options in the
  correct order.</P>
 <H2><A NAME="3_5">3.5 CUPS Imaging Library</A></H2>
 <P>The CUPS imaging library provides colorspace conversion, color
  management, image management, scaling, image file, and raster functions
  used by the CUPS raster filters.</P>
 <H3><A NAME="3_5_1">3.5.1 Colorspace Conversion Functions</A></H3>
 <P>The colorspace conversion functions handle conversion of grayscale
  and RGB colors to grayscale, RGB, K, CMY, CMYK, and CMYKcm colorspaces.</P>
 <H3><A NAME="3_5_2">3.5.2 Color Management Functions</A></H3>
 <P>The color management functions handle gamut mapping and density
  correction. These are integrated with the colorspace conversion
  functions so that colorspace conversion and color management are
  processed in a single step.</P>
 <H3><A NAME="3_5_3">3.5.3 Image Management Functions</A></H3>
 <P>The image management functions manage a tiled image database that is
  swapped to/from disk as needed.</P>
 <H3><A NAME="3_5_4">3.5.4 Scaling Functions</A></H3>
 <P>The scaling functions provide image scaling services using
  nearest-neighbor sampling and bilinear interpolation as appropriate.</P>
 <H3><A NAME="3_5_5">3.5.5 Image File Functions</A></H3>
 <P>The image file functions handle loading of all image file formats.</P>
 <H3><A NAME="3_5_6">3.5.6 Raster Functions</A></H3>
 <P>The raster functions manage streams of CUPS raster data (described in
  the Interface Design Document) used by non-PostScript printer drivers
  and raster filters.</P>
 <H2><A NAME="3_6">3.6 Daemons</A></H2>
 <P>The daemons provide additional network functions for the scheduler.
  Currently only two daemons are provided with CUPS.</P>
 <H3><A NAME="3_6_1">3.6.1 Line Printer Daemon</A></H3>
 <P>The line printer daemon provides remote LPD client support and is run
  by the <CODE>inetd(8)</CODE> daemon as needed.</P>
 <H3><A NAME="3_6_2">3.6.2 Polling Daemon</A></H3>
 <P>The polling daemon is used to poll a remote server for a list of
  available printers and provide it to the scheduler for addition. A
  separate polling daemon is run by the scheduler for every remote system
  listed for polling in the scheduler configuration file.</P>
 <H2><A NAME="3_7">3.7 Filters</A></H2>
 <P>The filters implement file conversion services for CUPS. All filters
  are called with a common set of arguments:</P>
 <UL>
 <LI>Printer name - the name of the destination printer (name string).</LI>
 <LI>Job Identifier - the job identifier for this job (integer).</LI>
 <LI>User Name - the user associated with this job (name string).</LI>
 <LI>Title - the title/job-name associated with this job (name string).</LI>
 <LI>Copies - the number of copies required (integer).</LI>
 <LI>Options - the options associated with this job (space separated
  option strings).</LI>
 <LI>Filename (optional) - the file to print; if this option is not
  specified, the filter must read the input file from the standard input.</LI>
 </UL>
 <P>Filters are added to the MIME conversion data file and implement all
  necessary conversions from one file type to another.</P>
 <H3><A NAME="3_7_1">3.7.1 hpgltops</A></H3>
 <P>The hpgltops filter converts HP-GL/2 files into PostScript.</P>
 <H3><A NAME="3_7_2">3.7.2 imagetops</A></H3>
 <P>The imagetops filter converts image files into PostScript.</P>
 <H3><A NAME="3_7_3">3.7.3 imagetoraster</A></H3>
 <P>The imagetoraster filter converts image files into CUPS raster data.</P>
 <H3><A NAME="3_7_4">3.7.4 pdftops</A></H3>
 <P>The pdftops filter converts PDF files into PostScript.</P>
 <H3><A NAME="3_7_5">3.7.5 pstops</A></H3>
 <P>The pstops filter inserts printer-specific commands from PPD files
  and performs page filtering as requested by the user.</P>
 <H3><A NAME="3_7_6">3.7.6 pstoraster</A></H3>
 <P>The pstoraster filter converts PostScript program data into CUPS
  raster data.</P>
 <H3><A NAME="3_7_7">3.7.7 rastertoepson</A></H3>
 <P>The rastertoepson filter handles converting CUPS raster data to ESC/P
  and supports both color and black-and-white printers.</P>
 <H3><A NAME="3_7_8">3.7.8 rastertohp</A></H3>
 <P>The rastertohp filter handles converting CUPS raster data to HP-PCL
  and supports both color and black-and-white printers.</P>
 <H3><A NAME="3_7_9">3.7.9 texttops</A></H3>
 <P>The texttops filter converts text files into PostScript.</P>
 <H2><A NAME="3_8">3.8 Scheduler</A></H2>
 <P>The scheduler is a fully-functional HTTP/1.1 and IPP/1.1 server that
  manages the printers, classes, and jobs in the system. It also handles
  a simple broadcast-based directory service so that remote print queues
  and classes can be accessed transparently from the local system.</P>
 <H3><A NAME="3_8_1">3.8.1 Authorization</A></H3>
 <P>The authorization module is responsible for performing access control
  and authentication for all HTTP and IPP requests entering the system.</P>
 <H3><A NAME="3_8_2">3.8.2 Classes</A></H3>
 <P>The classes module is responsible for managing printer classes in the
  system. Each class is a collection of local and/or remote printers. The
  classes module also reads and writes the classes configuration file.</P>
 <H3><A NAME="3_8_3">3.8.3 Client</A></H3>
 <P>The client module is responsible for all HTTP client communications.
  It handles listening on selected interfaces, accepting connections from
  prospective clients, processing incoming HTTP requests, and sending
  HTTP responses to those requests. The client module also is responsible
  for executing the external CGI programs as needed to support web-based
  printer, class, and job status monitoring and administration.</P>
 <P>Once authorized, all IPP requests are sent to the IPP module.</P>
 <H3><A NAME="3_8_4">3.8.4 Configuration</A></H3>
 <P>The configuration module is responsible for reading the CUPS
  configuration file and initializing the appropriate data structures and
  values. The configuration module also stops CUPS services before
  reading the configuration file and restarts them after the
  configuration file has been read.</P>
 <H3><A NAME="3_8_5">3.8.5 Devices</A></H3>
 <P>The devices module is responsible for managing the list of available
  devices for the CUPS-Get-Devices operation.</P>
 <H3><A NAME="3_8_6">3.8.6 Directory Services</A></H3>
 <P>The directory services module sends and recieves printer state
  information over a broadcast socket. Remote printers and classes are
  automatically added to or removed from the local printer and class
  lists as needed.</P>
 <P>The directory services module can only recieve printer state
  information over a single UDP port, however it can broadcast to
  multiple addresses and ports as needed.</P>
 <H3><A NAME="3_8_7">3.8.7 IPP</A></H3>
 <P>The IPP module handles IPP requests and acts accordingly. URI
  validation is also performed here, as a client can post IPP data to any
  URI on the server which might sidestep the access control or
  authentication of the HTTP server.</P>
 <H3><A NAME="3_8_8">3.8.8 Jobs</A></H3>
 <P>The jobs module manages print jobs, starts filter and backend
  processes for jobs to be printed, and monitors status messages from
  those filters and backends.</P>
 <H3><A NAME="3_8_9">3.8.9 Logging</A></H3>
 <P>The logging module manages the access, error, and page log files that
  are generated by the scheduler.</P>
 <H3><A NAME="3_8_10">3.8.10 Main</A></H3>
 <P>The main module is responsible for timing out and dispatching input
  and output for client connections. It also watches for incoming <CODE>
 SIGHUP</CODE> and <CODE>SIGCHLD</CODE> signals, reloads the server
  configuration files as needed, and handles child process errors and
  exits.</P>
 <H3><A NAME="3_8_11">3.8.11 MIME</A></H3>
 <P>The Multimedia Internet Mail Exchange module manages a MIME type and
  conversion database that supports file typing by extension and content
  and least-cost file filtering from a source to a destination file type.</P>
 <H3><A NAME="3_8_12">3.8.12 PPDs</A></H3>
 <P>The PPDs module is responsible for managing the list of available PPD
  files for the CUPS-Get-PPDs operation.</P>
 <H3><A NAME="3_8_13">3.8.13 Printers</A></H3>
 <P>The printers module is responsible for managing printers and PPD
  files in the system. The printers module also reads and writes the
  printers configuration file.</P>
 <H2><A NAME="3_9">3.9 System V Commands</A></H2>
 <P>The System V commands provide a robust command-line interface to CUPS
  to submit and control printers and jobs.</P>
 <H3><A NAME="3_9_1">3.9.1 accept</A></H3>
 <P>The accept command tells the scheduler to accept new jobs for
  specific printers.</P>
 <H3><A NAME="3_9_2">3.9.2 cancel</A></H3>
 <P>The cancel command tells the scheduler to cancel one or more jobs
  that are queued for printing.</P>
 <H3><A NAME="3_9_3">3.9.3 disable</A></H3>
 <P>The disable command tells the scheduler to stop printing jobs on the
  specified printers.</P>
 <H3><A NAME="3_9_4">3.9.4 enable</A></H3>
 <P>The enable command tells the scheduler to start printing jobs on the
  specified printers.</P>
 <H3><A NAME="3_9_5">3.9.5 lp</A></H3>
 <P>The lp command submits submits files for printing. Unlike the
  standard System V lp command, a single CUPS lp command will generate a
  separate job ID for each file that is printed. Also, the Solaris &quot;f&quot;,
  &quot;H&quot;, &quot;P&quot;, &quot;S&quot;, and &quot;y&quot; options are silently ignored.</P>
 <H3><A NAME="3_9_6">3.9.6 lpadmin</A></H3>
 <P>The lpadmin command manages printer queues and classes. The Solaris
  &quot;A&quot;, &quot;F&quot;, &quot;I&quot;, &quot;M&quot;, &quot;P&quot;, &quot;Q&quot;, &quot;S&quot;, &quot;T&quot;, &quot;U&quot;, &quot;W&quot;, &quot;f&quot;, &quot;l&quot;, &quot;m&quot;, &quot;o&quot;,
  &quot;s&quot;, &quot;t&quot;, and &quot;u&quot; options are not supported, and new options &quot;P&quot; (PPD
  file) and &quot;E&quot; (enable and accept) are provided to configure
  CUPS-specific features.</P>
 <H3><A NAME="3_9_7">3.9.7 lpinfo</A></H3>
 <P>The lpinfo command lists the available PPD files or devices as
  selected by the user.</P>
 <H3><A NAME="3_9_8">3.9.8 lpmove</A></H3>
 <P>The lpmove command moves a print job to a new destination.</P>
 <H3><A NAME="3_9_9">3.9.9 lpoptions</A></H3>
 <P>The lpoptions command manages user-defined printers and options.</P>
 <H3><A NAME="3_9_10">3.9.10 lpstat</A></H3>
 <P>The lpstat command lists printers, classes, and jobs as requested by
  the user.</P>
 <H3><A NAME="3_9_11">3.9.11 reject</A></H3>
 <P>The reject command tells the scheduler not to accept new jobs for
  specific printers.</P>
 <H1 TYPE="A" VALUE="1"><A NAME="4">A Glossary</A></H1>
 <H2><A NAME="4_1">A.1 Terms</A></H2>
 <DL>
 <DT>C</DT>
 <DD>A computer language.</DD>
 <DT>parallel</DT>
 <DD>Sending or receiving data more than 1 bit at a time.</DD>
 <DT>pipe</DT>
 <DD>A one-way communications channel between two programs.</DD>
 <DT>serial</DT>
 <DD>Sending or receiving data 1 bit at a time.</DD>
 <DT>socket</DT>
 <DD>A two-way network communications channel.</DD>
 </DL>
 <H2><A NAME="4_2">A.2 Acronyms</A></H2>
 <DL>
 <DT>ASCII</DT>
 <DD>American Standard Code for Information Interchange</DD>
 <DT>CUPS</DT>
 <DD>Common UNIX Printing System</DD>
 <DT>ESC/P</DT>
 <DD>EPSON Standard Code for Printers</DD>
 <DT>FTP</DT>
 <DD>File Transfer Protocol</DD>
 <DT>HP-GL</DT>
 <DD>Hewlett-Packard Graphics Language</DD>
 <DT>HP-PCL</DT>
 <DD>Hewlett-Packard Page Control Language</DD>
 <DT>HP-PJL</DT>
 <DD>Hewlett-Packard Printer Job Language</DD>
 <DT>IETF</DT>
 <DD>Internet Engineering Task Force</DD>
 <DT>IPP</DT>
 <DD>Internet Printing Protocol</DD>
 <DT>ISO</DT>
 <DD>International Standards Organization</DD>
 <DT>LPD</DT>
 <DD>Line Printer Daemon</DD>
 <DT>MIME</DT>
 <DD>Multimedia Internet Mail Exchange</DD>
 <DT>PPD</DT>
 <DD>PostScript Printer Description</DD>
 <DT>SMB</DT>
 <DD>Server Message Block</DD>
 <DT>TFTP</DT>
 <DD>Trivial File Transfer Protocol</DD>
 </DL>
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