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281 lines
11 KiB
281 lines
11 KiB
<chapter id="technical-overview">
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<title>Technical Overview</title>
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<para>This chapter aims to give a technical overview of &kdeprint; which
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non-programmers can comprehend.</para>
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<para>&kdeprint; is a new and revolutionary tool to give easy access to
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printing services for both &kde; users and &kde; developers.</para>
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<sect1 id="brief-description">
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<title>A Brief Description of &kdeprint;</title>
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<para>You can access the functions of &kdeprint; in different ways:
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through the Printing Manger in the &kcontrol;, through the
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<command>kprinter</command> command or through the dialog that pops up
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if you want to print.</para>
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<sect2 id="what-kdeprint-is-not">
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<title>What it is <emphasis>not</emphasis></title>
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<para>&kdeprint; is <emphasis>not</emphasis> a replacement for the
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printing subsystem itself. &kdeprint; does <emphasis>not</emphasis>
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therefore give provision for spooling, and it does
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<emphasis>not</emphasis> do the basic processing of &PostScript; or
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other print data.</para>
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</sect2>
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<sect2 id="what-kde-print-is">
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<title>What it <emphasis>is</emphasis></title>
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<para>&kdeprint; is an intermediate layer between the spooling and the
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data processing print subsystem (as installed), and the application that
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seeks to print. &kdeprint; provides a common interface for &kde;
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developers and &kde; users, to various supported print subsystems. At
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the same time, it is customizable, and highly configurable.</para>
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<para>&kdeprint; is easy to use for both &kde; developers and end-users.
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Developers can port their applications, with minimal changes, to use
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&kdeprint; instead of the old &Qt; print <quote>system</quote>. Users
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can easily choose and configure their print subsystem.</para>
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<para>For a reference to new &kde; users: &Qt; is the basic library and
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graphical toolkit, which is used by all &kde; applications; &Qt; is
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developed by TrollTech, a Norwegian software company.</para>
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</sect2>
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</sect1>
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<sect1 id="different-users">
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<title>&kdeprint; -- Different Usage for Different People</title>
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<para>&kdeprint; has different faces for different people.</para>
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<sect2 id="what-users-can-do">
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<title>What users and administrators can do with &kdeprint;</title>
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<para>&kdeprint; allows users and/or administrators, depending on their
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rights, access to printing subsystems (&CUPS;, <acronym>LPD</acronym>,
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<acronym>RLPR</acronym>, <application>LPRng</application>,
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<application>PDQ</application> &etc;) through a &kde; graphical user
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interface (&GUI;). Using &kdeprint;, they can print, administer jobs,
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printers and the printing daemon, all in a comfortable manner.</para>
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<para>Experienced users will like the capability to plug any working
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filter for the print data between the output of their application and
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the input, into the chosen print subsystem. Some examples for this
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already ship with <quote>plain vanilla</quote> &kdeprint;. Read
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on.</para>
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</sect2>
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<sect2 id="what-developers-can-do">
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<title>What &kde; developers can do with it...</title>
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<para>If a &kde; developer needs printing access for his application, he
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does not code the printing functions from scratch. Before &kde; 2.2 this
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service was provided by the <classname>QPrinter</classname> class, a
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library function of the &Qt; Toolkit. The
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<classname>QPrinter</classname> class relied on the out-moded
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<quote>Line Printer Daemon</quote> (<acronym>LPD</acronym>). The
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&kdeprint; library bases itself firmly on the more modern Common &UNIX;
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Printing System (&CUPS;), while at the same time keeping backward
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compatibility with <acronym>LPD</acronym> and other legacy, or less
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elaborate, print systems. It also <quote>leaves the door open</quote>
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for any new development that might occur.</para>
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<para>For &kde; developers to use the new &kdeprint; class in their
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applications, they require only minimal changes to their code: for every
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call of <classname>QPrinter</classname>, they just need to change this to
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<classname>KPrinter</classname>. Replacing one (!) letter in a few
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spots, and automatically they are done; their application can then use
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all of the features of the new &kdeprint; library.</para>
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<para>More ambitious developers, or ones with special requirements, can
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do more: despite &kdeprint;'s feature-rich framework, they are still able
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to customize the print dialog of their application
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by creating an additional <quote>Tab</quote>, where their
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extensions to the standard &kdeprint; will feel right at home.</para>
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<para>This last mentioned feature has not been used widely inside
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&kde; so far, as developers are not yet fully aware of &kdeprint;'s
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power. Expect more of this in the near future. One example I
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discovered is the &kcron; application. It lets you edit the crontab
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through a &GUI;. The developers have implemented a printing feature
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that lets you (or <systemitem class="username">root</systemitem>)
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choose if you want to print the whole of crontab (for all users) or
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just the part that is marked. You can see the effects on &kdeprint;
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in the following screenshots.</para>
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<para>This shot shows a sample from the &kcron; utility.
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<screenshot>
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<screeninfo>&kcron; utility: a small sample of a system's cronjobs as
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shown through the &kde; <acronym>GUI</acronym>&GUI;.</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="kcron_to_be_printed.png"
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format="PNG"/></imageobject>
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<textobject>
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<phrase>The &kcron; developers let you choose to print the whole of the
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cron table or just the marked part of it.</phrase></textobject>
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</mediaobject>
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</screenshot>
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</para>
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<para>The dialog to configure &kcron;'s printing options: the
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additional tab titled <guilabel>Cron Options</guilabel> is from inside
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&kcron;, not &kdeprint;; it is a special extension added by the
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&kcron; developers for printing purposes, not originating from, but
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executed by &kdeprint;. Developers of other applications are free
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to implement their own goodies, if they feel need for it.</para>
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<screenshot>
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<screeninfo>&kcron;'s addition to the &kdeprint; dialog.</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="kprinter_with_kcron_developer_special.png"
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format="PNG"/></imageobject>
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<textobject>
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<phrase>&kcron;'s addition to the &kdeprint; dialog.</phrase></textobject>
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<caption>
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<para>&kcron;'s addition to the &kdeprint; dialog.</para>
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</caption>
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</mediaobject>
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</screenshot>
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</sect2>
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<sect2>
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<title>What &kdeprint; offers to everybody...</title>
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<para>&kdeprint;'s easy-to-use interface for all supported print subsystems
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of course does not eliminate basic traditional weaknesses of some of
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those systems. But it smooths some rough edges. Different users may use
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different printing systems on the same box. A user is free to even
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switch <quote>on the fly</quote>, from the print dialog, the print
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subsystem to be used for the next job. (This is possible if different
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systems are installed in a way that they don't <quote>get in each
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other's way</quote>.)</para>
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<para>Most &UNIX; users are used to
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<acronym>LPD</acronym> printing. <acronym>LPD</acronym> provides only
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basic printing functions, is very inflexible and does not utilize the
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many options of more modern print systems like &CUPS;. While also
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working remotely over any distance (like every TCP/IP based protocol),
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<acronym>LPD</acronym> lacks bi-directional communication,
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authentication, access control and encryption support.</para>
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<para>&kdeprint; can use &CUPS; to support:</para>
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<itemizedlist>
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<listitem>
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<para>Querying the <acronym>LAN</acronym> for available printers,</para>
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</listitem>
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<listitem>
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<para>Basic, Digest, and Certificate Authentication,</para>
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</listitem>
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<listitem>
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<para>Access Control based on <acronym>IP</acronym> addresses, net
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addresses, netmasks, host- and domain names,</para>
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</listitem>
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<listitem>
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<para>and 128-Bit TLS or SSL3 encryption of print data, to prevent
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eavesdropping, or at least make it much more difficult.</para>
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</listitem>
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</itemizedlist>
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<para>This makes &kdeprint; a much more robust and reliable solution
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than using the venerable <acronym>LPD</acronym>.</para>
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</sect2>
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<sect2>
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<title>How to access &kdeprint; </title>
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<para>You get access to &kdeprint;, or parts of it, in four different
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ways:</para>
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<itemizedlist>
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<listitem><para>through your applications: if you call the printing
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dialog (either <menuchoice><guilabel>File</guilabel>
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<guilabel>Print...</guilabel></menuchoice>) or the button with the
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little printer icon on it; this opens the printing
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dialog.</para></listitem>
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<listitem><para>through the typed command <command>kprinter</command>
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in a <application>terminal</application> or a &konsole; window or from
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the <guilabel>Run Command...</guilabel> mini-<acronym>CLI</acronym>
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window: this also opens the printing dialog.</para></listitem>
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<listitem><para>from the <inlinemediaobject><imageobject> <imagedata
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fileref="kcontrol-icon.png" format="PNG"/></imageobject>
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</inlinemediaobject> button, starting &kcontrol;, and then go to
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<menuchoice><guilabel>System</guilabel><guilabel>Printing
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Manager</guilabel></menuchoice>. This opens the &kdeprint;
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administration which is part of the &kcontrolcenter; and also lets
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you switch to other parts of the &kcontrol;</para></listitem>
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<listitem><para>from a command line (&konsole; or
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mini-<acronym>CLI</acronym>) type <userinput>
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<command>kcmshell</command> <option>printers</option></userinput>.
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This opens just the &kdeprint; part of &kcontrol; to change your settings
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</para></listitem>
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</itemizedlist>
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<screenshot>
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<screeninfo>&kprinter; dialog to be started from <guilabel>Run Command...</guilabel> window</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="kprinter_called_from_run_command.png"
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format="PNG"/></imageobject>
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<textobject>
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<phrase>Starting the &kprinter; dialog from
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a <guilabel>Run Command...</guilabel> window.</phrase></textobject>
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<caption><para>Starting the &kprinter; dialog from a <guilabel>Run
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Command...</guilabel> window.</para></caption>
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</mediaobject>
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</screenshot>
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<!-- TODO: This one ought to be a screenshot LW. --> <para>Here is a
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&kivio; drawing of the &kprinter; dialog as it pops up after being
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started... You can always add a new printer by clicking on the small
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<guiicon>Wizard</guiicon> button (marked red/yellow in this
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drawing).</para>
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<screenshot>
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<screeninfo>&kprinter; dialog started (&kivio; draft drawing)
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</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="kprinter-kivio.png"
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format="PNG"/></imageobject>
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<textobject>
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<phrase>&kprinter; dialog started (&kivio; draft drawing)</phrase></textobject>
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<caption><para>&kprinter; dialog started (&kivio; draft
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drawing)</para></caption>
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</mediaobject>
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</screenshot>
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</sect2>
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</sect1>
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</chapter>
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