Rebuild the user manual with listen-backlog documentation
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21       <tr>
22         <th colspan="3" align="center">Privoxy 3.0.27 User Manual</th>
23       </tr>
24       <tr>
25         <td width="10%" align="left" valign="bottom"><a href=
26         "configuration.html" accesskey="P">Prev</a></td>
27         <td width="80%" align="center" valign="bottom"></td>
28         <td width="10%" align="right" valign="bottom"><a href=
29         "actions-file.html" accesskey="N">Next</a></td>
30       </tr>
31     </table>
32     <hr align="left" width="100%">
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34   <div class="SECT1">
35     <h1 class="SECT1"><a name="CONFIG" id="CONFIG">7. The Main Configuration
36     File</a></h1>
37     <p>By default, the main configuration file is named <tt class=
38     "FILENAME">config</tt>, with the exception of Windows, where it is named
39     <tt class="FILENAME">config.txt</tt>. Configuration lines consist of an
40     initial keyword followed by a list of values, all separated by whitespace
41     (any number of spaces or tabs). For example:</p>
42     <p class="LITERALLAYOUT"><tt class="LITERAL">&nbsp;&nbsp;<span class=
43     "emphasis"><i class="EMPHASIS">confdir /etc/privoxy</i></span></tt></p>
44     <p>Assigns the value <tt class="LITERAL">/etc/privoxy</tt> to the option
45     <tt class="LITERAL">confdir</tt> and thus indicates that the
46     configuration directory is named <span class=
47     "QUOTE">"/etc/privoxy/"</span>.</p>
48     <p>All options in the config file except for <tt class=
49     "LITERAL">confdir</tt> and <tt class="LITERAL">logdir</tt> are optional.
50     Watch out in the below description for what happens if you leave them
51     unset.</p>
52     <p>The main config file controls all aspects of <span class=
53     "APPLICATION">Privoxy</span>'s operation that are not location dependent
54     (i.e. they apply universally, no matter where you may be surfing). Like
55     the filter and action files, the config file is a plain text file and can
56     be modified with a text editor like emacs, vim or notepad.exe.</p>
57     <div class="SECT2">
58       <h2 class="SECT2"><a name="LOCAL-SET-UP" id="LOCAL-SET-UP">7.1. Local
59       Set-up Documentation</a></h2>
60       <p>If you intend to operate <span class="APPLICATION">Privoxy</span>
61       for more users than just yourself, it might be a good idea to let them
62       know how to reach you, what you block and why you do that, your
63       policies, etc.</p>
64       <div class="SECT3">
65         <h4 class="SECT3"><a name="USER-MANUAL" id="USER-MANUAL">7.1.1.
66         user-manual</a></h4>
67         <div class="VARIABLELIST">
68           <dl>
69             <dt>Specifies:</dt>
70             <dd>
71               <p>Location of the <span class="APPLICATION">Privoxy</span>
72               User Manual.</p>
73             </dd>
74             <dt>Type of value:</dt>
75             <dd>
76               <p>A fully qualified URI</p>
77             </dd>
78             <dt>Default value:</dt>
79             <dd>
80               <p><span class="emphasis"><i class=
81               "EMPHASIS">Unset</i></span></p>
82             </dd>
83             <dt>Effect if unset:</dt>
84             <dd>
85               <p><a href="https://www.privoxy.org/user-manual/" target=
86               "_top">https://www.privoxy.org/<tt class=
87               "REPLACEABLE"><i>version</i></tt>/user-manual/</a> will be
88               used, where <tt class="REPLACEABLE"><i>version</i></tt> is the
89               <span class="APPLICATION">Privoxy</span> version.</p>
90             </dd>
91             <dt>Notes:</dt>
92             <dd>
93               <p>The User Manual URI is the single best source of information
94               on <span class="APPLICATION">Privoxy</span>, and is used for
95               help links from some of the internal CGI pages. The manual
96               itself is normally packaged with the binary distributions, so
97               you probably want to set this to a locally installed copy.</p>
98               <p>Examples:</p>
99               <p>The best all purpose solution is simply to put the full
100               local <tt class="LITERAL">PATH</tt> to where the <i class=
101               "CITETITLE">User Manual</i> is located:</p>
102               <table border="0" bgcolor="#E0E0E0" width="90%">
103                 <tr>
104                   <td>
105                     <pre class="SCREEN">
106                     ��user-manual��/usr/share/doc/privoxy/user-manual</pre>
107                   </td>
108                 </tr>
109               </table>
110               <p>The User Manual is then available to anyone with access to
111               <span class="APPLICATION">Privoxy</span>, by following the
112               built-in URL: <tt class=
113               "LITERAL">http://config.privoxy.org/user-manual/</tt> (or the
114               shortcut: <tt class=
115               "LITERAL">http://p.p/user-manual/</tt>).</p>
116               <p>If the documentation is not on the local system, it can be
117               accessed from a remote server, as:</p>
118               <table border="0" bgcolor="#E0E0E0" width="90%">
119                 <tr>
120                   <td>
121                     <pre class="SCREEN">
122                     ��user-manual��http://example.com/privoxy/user-manual/</pre>
123                   </td>
124                 </tr>
125               </table>
126               <div class="WARNING">
127                 <table class="WARNING" border="1" width="90%">
128                   <tr>
129                     <td align="center"><b>Warning</b></td>
130                   </tr>
131                   <tr>
132                     <td align="left">
133                       <p>If set, this option should be <span class=
134                       "emphasis"><i class="EMPHASIS">the first option in the
135                       config file</i></span>, because it is used while the
136                       config file is being read on start-up.</p>
137                     </td>
138                   </tr>
139                 </table>
140               </div>
141             </dd>
142           </dl>
143         </div>
144       </div>
145       <div class="SECT3">
146         <h4 class="SECT3"><a name="TRUST-INFO-URL" id="TRUST-INFO-URL">7.1.2.
147         trust-info-url</a></h4>
148         <div class="VARIABLELIST">
149           <dl>
150             <dt>Specifies:</dt>
151             <dd>
152               <p>A URL to be displayed in the error page that users will see
153               if access to an untrusted page is denied.</p>
154             </dd>
155             <dt>Type of value:</dt>
156             <dd>
157               <p>URL</p>
158             </dd>
159             <dt>Default value:</dt>
160             <dd>
161               <p><span class="emphasis"><i class=
162               "EMPHASIS">Unset</i></span></p>
163             </dd>
164             <dt>Effect if unset:</dt>
165             <dd>
166               <p>No links are displayed on the "untrusted" error page.</p>
167             </dd>
168             <dt>Notes:</dt>
169             <dd>
170               <p>The value of this option only matters if the experimental
171               trust mechanism has been activated. (See <a href=
172               "config.html#TRUSTFILE"><span class="emphasis"><i class=
173               "EMPHASIS">trustfile</i></span></a> below.)</p>
174               <p>If you use the trust mechanism, it is a good idea to write
175               up some on-line documentation about your trust policy and to
176               specify the URL(s) here. Use multiple times for multiple
177               URLs.</p>
178               <p>The URL(s) should be added to the trustfile as well, so
179               users don't end up locked out from the information on why they
180               were locked out in the first place!</p>
181             </dd>
182           </dl>
183         </div>
184       </div>
185       <div class="SECT3">
186         <h4 class="SECT3"><a name="ADMIN-ADDRESS" id="ADMIN-ADDRESS">7.1.3.
187         admin-address</a></h4>
188         <div class="VARIABLELIST">
189           <dl>
190             <dt>Specifies:</dt>
191             <dd>
192               <p>An email address to reach the <span class=
193               "APPLICATION">Privoxy</span> administrator.</p>
194             </dd>
195             <dt>Type of value:</dt>
196             <dd>
197               <p>Email address</p>
198             </dd>
199             <dt>Default value:</dt>
200             <dd>
201               <p><span class="emphasis"><i class=
202               "EMPHASIS">Unset</i></span></p>
203             </dd>
204             <dt>Effect if unset:</dt>
205             <dd>
206               <p>No email address is displayed on error pages and the CGI
207               user interface.</p>
208             </dd>
209             <dt>Notes:</dt>
210             <dd>
211               <p>If both <tt class="LITERAL">admin-address</tt> and
212               <tt class="LITERAL">proxy-info-url</tt> are unset, the whole
213               "Local Privoxy Support" box on all generated pages will not be
214               shown.</p>
215             </dd>
216           </dl>
217         </div>
218       </div>
219       <div class="SECT3">
220         <h4 class="SECT3"><a name="PROXY-INFO-URL" id="PROXY-INFO-URL">7.1.4.
221         proxy-info-url</a></h4>
222         <div class="VARIABLELIST">
223           <dl>
224             <dt>Specifies:</dt>
225             <dd>
226               <p>A URL to documentation about the local <span class=
227               "APPLICATION">Privoxy</span> setup, configuration or
228               policies.</p>
229             </dd>
230             <dt>Type of value:</dt>
231             <dd>
232               <p>URL</p>
233             </dd>
234             <dt>Default value:</dt>
235             <dd>
236               <p><span class="emphasis"><i class=
237               "EMPHASIS">Unset</i></span></p>
238             </dd>
239             <dt>Effect if unset:</dt>
240             <dd>
241               <p>No link to local documentation is displayed on error pages
242               and the CGI user interface.</p>
243             </dd>
244             <dt>Notes:</dt>
245             <dd>
246               <p>If both <tt class="LITERAL">admin-address</tt> and
247               <tt class="LITERAL">proxy-info-url</tt> are unset, the whole
248               "Local Privoxy Support" box on all generated pages will not be
249               shown.</p>
250               <p>This URL shouldn't be blocked ;-)</p>
251             </dd>
252           </dl>
253         </div>
254       </div>
255     </div>
256     <div class="SECT2">
257       <h2 class="SECT2"><a name="CONF-LOG-LOC" id="CONF-LOG-LOC">7.2.
258       Configuration and Log File Locations</a></h2>
259       <p><span class="APPLICATION">Privoxy</span> can (and normally does) use
260       a number of other files for additional configuration, help and logging.
261       This section of the configuration file tells <span class=
262       "APPLICATION">Privoxy</span> where to find those other files.</p>
263       <p>The user running <span class="APPLICATION">Privoxy</span>, must have
264       read permission for all configuration files, and write permission to
265       any files that would be modified, such as log files and actions
266       files.</p>
267       <div class="SECT3">
268         <h4 class="SECT3"><a name="CONFDIR" id="CONFDIR">7.2.1.
269         confdir</a></h4>
270         <div class="VARIABLELIST">
271           <dl>
272             <dt>Specifies:</dt>
273             <dd>
274               <p>The directory where the other configuration files are
275               located.</p>
276             </dd>
277             <dt>Type of value:</dt>
278             <dd>
279               <p>Path name</p>
280             </dd>
281             <dt>Default value:</dt>
282             <dd>
283               <p>/etc/privoxy (Unix) <span class="emphasis"><i class=
284               "EMPHASIS">or</i></span> <span class=
285               "APPLICATION">Privoxy</span> installation dir (Windows)</p>
286             </dd>
287             <dt>Effect if unset:</dt>
288             <dd>
289               <p><span class="emphasis"><i class=
290               "EMPHASIS">Mandatory</i></span></p>
291             </dd>
292             <dt>Notes:</dt>
293             <dd>
294               <p>No trailing <span class="QUOTE">"<tt class=
295               "LITERAL">/</tt>"</span>, please.</p>
296             </dd>
297           </dl>
298         </div>
299       </div>
300       <div class="SECT3">
301         <h4 class="SECT3"><a name="TEMPLDIR" id="TEMPLDIR">7.2.2.
302         templdir</a></h4>
303         <div class="VARIABLELIST">
304           <dl>
305             <dt>Specifies:</dt>
306             <dd>
307               <p>An alternative directory where the templates are loaded
308               from.</p>
309             </dd>
310             <dt>Type of value:</dt>
311             <dd>
312               <p>Path name</p>
313             </dd>
314             <dt>Default value:</dt>
315             <dd>
316               <p>unset</p>
317             </dd>
318             <dt>Effect if unset:</dt>
319             <dd>
320               <p>The templates are assumed to be located in
321               confdir/template.</p>
322             </dd>
323             <dt>Notes:</dt>
324             <dd>
325               <p><span class="APPLICATION">Privoxy's</span> original
326               templates are usually overwritten with each update. Use this
327               option to relocate customized templates that should be kept. As
328               template variables might change between updates, you shouldn't
329               expect templates to work with <span class=
330               "APPLICATION">Privoxy</span> releases other than the one they
331               were part of, though.</p>
332             </dd>
333           </dl>
334         </div>
335       </div>
336       <div class="SECT3">
337         <h4 class="SECT3"><a name="TEMPORARY-DIRECTORY" id=
338         "TEMPORARY-DIRECTORY">7.2.3. temporary-directory</a></h4>
339         <div class="VARIABLELIST">
340           <dl>
341             <dt>Specifies:</dt>
342             <dd>
343               <p>A directory where Privoxy can create temporary files.</p>
344             </dd>
345             <dt>Type of value:</dt>
346             <dd>
347               <p>Path name</p>
348             </dd>
349             <dt>Default value:</dt>
350             <dd>
351               <p>unset</p>
352             </dd>
353             <dt>Effect if unset:</dt>
354             <dd>
355               <p>No temporary files are created, external filters don't
356               work.</p>
357             </dd>
358             <dt>Notes:</dt>
359             <dd>
360               <p>To execute <tt class="LITERAL"><a href=
361               "actions-file.html#EXTERNAL-FILTER" target="_top">external
362               filters</a></tt>, <span class="APPLICATION">Privoxy</span> has
363               to create temporary files. This directive specifies the
364               directory the temporary files should be written to.</p>
365               <p>It should be a directory only <span class=
366               "APPLICATION">Privoxy</span> (and trusted users) can
367               access.</p>
368             </dd>
369           </dl>
370         </div>
371       </div>
372       <div class="SECT3">
373         <h4 class="SECT3"><a name="LOGDIR" id="LOGDIR">7.2.4. logdir</a></h4>
374         <div class="VARIABLELIST">
375           <dl>
376             <dt>Specifies:</dt>
377             <dd>
378               <p>The directory where all logging takes place (i.e. where the
379               <tt class="FILENAME">logfile</tt> is located).</p>
380             </dd>
381             <dt>Type of value:</dt>
382             <dd>
383               <p>Path name</p>
384             </dd>
385             <dt>Default value:</dt>
386             <dd>
387               <p>/var/log/privoxy (Unix) <span class="emphasis"><i class=
388               "EMPHASIS">or</i></span> <span class=
389               "APPLICATION">Privoxy</span> installation dir (Windows)</p>
390             </dd>
391             <dt>Effect if unset:</dt>
392             <dd>
393               <p><span class="emphasis"><i class=
394               "EMPHASIS">Mandatory</i></span></p>
395             </dd>
396             <dt>Notes:</dt>
397             <dd>
398               <p>No trailing <span class="QUOTE">"<tt class=
399               "LITERAL">/</tt>"</span>, please.</p>
400             </dd>
401           </dl>
402         </div>
403       </div>
404       <div class="SECT3">
405         <h4 class="SECT3"><a name="ACTIONSFILE" id="ACTIONSFILE">7.2.5.
406         actionsfile</a></h4><a name="DEFAULT.ACTION" id=
407         "DEFAULT.ACTION"></a><a name="STANDARD.ACTION" id=
408         "STANDARD.ACTION"></a><a name="USER.ACTION" id="USER.ACTION"></a>
409         <div class="VARIABLELIST">
410           <dl>
411             <dt>Specifies:</dt>
412             <dd>
413               <p>The <a href="actions-file.html">actions file(s)</a> to
414               use</p>
415             </dd>
416             <dt>Type of value:</dt>
417             <dd>
418               <p>Complete file name, relative to <tt class=
419               "LITERAL">confdir</tt></p>
420             </dd>
421             <dt>Default values:</dt>
422             <dd>
423               <table border="0">
424                 <tbody>
425                   <tr>
426                     <td>
427                       <p class="LITERALLAYOUT">
428                       &nbsp;&nbsp;match-all.action&nbsp;#&nbsp;Actions&nbsp;that&nbsp;are&nbsp;applied&nbsp;to&nbsp;all&nbsp;sites&nbsp;and&nbsp;maybe&nbsp;overruled&nbsp;later&nbsp;on.</p>
429                     </td>
430                   </tr>
431                   <tr>
432                     <td>
433                       <p class="LITERALLAYOUT">
434                       &nbsp;&nbsp;default.action&nbsp;&nbsp;&nbsp;#&nbsp;Main&nbsp;actions&nbsp;file</p>
435                     </td>
436                   </tr>
437                   <tr>
438                     <td>
439                       <p class="LITERALLAYOUT">
440                       &nbsp;&nbsp;user.action&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;#&nbsp;User&nbsp;customizations</p>
441                     </td>
442                   </tr>
443                 </tbody>
444               </table>
445             </dd>
446             <dt>Effect if unset:</dt>
447             <dd>
448               <p>No actions are taken at all. More or less neutral
449               proxying.</p>
450             </dd>
451             <dt>Notes:</dt>
452             <dd>
453               <p>Multiple <tt class="LITERAL">actionsfile</tt> lines are
454               permitted, and are in fact recommended!</p>
455               <p>The default values are <tt class=
456               "FILENAME">default.action</tt>, which is the <span class=
457               "QUOTE">"main"</span> actions file maintained by the
458               developers, and <tt class="FILENAME">user.action</tt>, where
459               you can make your personal additions.</p>
460               <p>Actions files contain all the per site and per URL
461               configuration for ad blocking, cookie management, privacy
462               considerations, etc.</p>
463             </dd>
464           </dl>
465         </div>
466       </div>
467       <div class="SECT3">
468         <h4 class="SECT3"><a name="FILTERFILE" id="FILTERFILE">7.2.6.
469         filterfile</a></h4><a name="DEFAULT.FILTER" id="DEFAULT.FILTER"></a>
470         <div class="VARIABLELIST">
471           <dl>
472             <dt>Specifies:</dt>
473             <dd>
474               <p>The <a href="filter-file.html">filter file(s)</a> to use</p>
475             </dd>
476             <dt>Type of value:</dt>
477             <dd>
478               <p>File name, relative to <tt class="LITERAL">confdir</tt></p>
479             </dd>
480             <dt>Default value:</dt>
481             <dd>
482               <p>default.filter (Unix) <span class="emphasis"><i class=
483               "EMPHASIS">or</i></span> default.filter.txt (Windows)</p>
484             </dd>
485             <dt>Effect if unset:</dt>
486             <dd>
487               <p>No textual content filtering takes place, i.e. all
488               <tt class="LITERAL">+<a href=
489               "actions-file.html#FILTER">filter</a>{<tt class=
490               "REPLACEABLE"><i>name</i></tt>}</tt> actions in the actions
491               files are turned neutral.</p>
492             </dd>
493             <dt>Notes:</dt>
494             <dd>
495               <p>Multiple <tt class="LITERAL">filterfile</tt> lines are
496               permitted.</p>
497               <p>The <a href="filter-file.html">filter files</a> contain
498               content modification rules that use <a href=
499               "appendix.html#REGEX">regular expressions</a>. These rules
500               permit powerful changes on the content of Web pages, and
501               optionally the headers as well, e.g., you could try to disable
502               your favorite JavaScript annoyances, re-write the actual
503               displayed text, or just have some fun playing buzzword bingo
504               with web pages.</p>
505               <p>The <tt class="LITERAL">+<a href=
506               "actions-file.html#FILTER">filter</a>{<tt class=
507               "REPLACEABLE"><i>name</i></tt>}</tt> actions rely on the
508               relevant filter (<tt class="REPLACEABLE"><i>name</i></tt>) to
509               be defined in a filter file!</p>
510               <p>A pre-defined filter file called <tt class=
511               "FILENAME">default.filter</tt> that contains a number of useful
512               filters for common problems is included in the distribution.
513               See the section on the <tt class="LITERAL"><a href=
514               "actions-file.html#FILTER">filter</a></tt> action for a
515               list.</p>
516               <p>It is recommended to place any locally adapted filters into
517               a separate file, such as <tt class=
518               "FILENAME">user.filter</tt>.</p>
519             </dd>
520           </dl>
521         </div>
522       </div>
523       <div class="SECT3">
524         <h4 class="SECT3"><a name="LOGFILE" id="LOGFILE">7.2.7.
525         logfile</a></h4>
526         <div class="VARIABLELIST">
527           <dl>
528             <dt>Specifies:</dt>
529             <dd>
530               <p>The log file to use</p>
531             </dd>
532             <dt>Type of value:</dt>
533             <dd>
534               <p>File name, relative to <tt class="LITERAL">logdir</tt></p>
535             </dd>
536             <dt>Default value:</dt>
537             <dd>
538               <p><span class="emphasis"><i class="EMPHASIS">Unset (commented
539               out)</i></span>. When activated: logfile (Unix) <span class=
540               "emphasis"><i class="EMPHASIS">or</i></span> privoxy.log
541               (Windows).</p>
542             </dd>
543             <dt>Effect if unset:</dt>
544             <dd>
545               <p>No logfile is written.</p>
546             </dd>
547             <dt>Notes:</dt>
548             <dd>
549               <p>The logfile is where all logging and error messages are
550               written. The level of detail and number of messages are set
551               with the <tt class="LITERAL">debug</tt> option (see below). The
552               logfile can be useful for tracking down a problem with
553               <span class="APPLICATION">Privoxy</span> (e.g., it's not
554               blocking an ad you think it should block) and it can help you
555               to monitor what your browser is doing.</p>
556               <p>Depending on the debug options below, the logfile may be a
557               privacy risk if third parties can get access to it. As most
558               users will never look at it, <span class=
559               "APPLICATION">Privoxy</span> only logs fatal errors by
560               default.</p>
561               <p>For most troubleshooting purposes, you will have to change
562               that, please refer to the debugging section for details.</p>
563               <p>Any log files must be writable by whatever user <span class=
564               "APPLICATION">Privoxy</span> is being run as (on Unix, default
565               user id is <span class="QUOTE">"privoxy"</span>).</p>
566               <p>To prevent the logfile from growing indefinitely, it is
567               recommended to periodically rotate or shorten it. Many
568               operating systems support log rotation out of the box, some
569               require additional software to do it. For details, please refer
570               to the documentation for your operating system.</p>
571             </dd>
572           </dl>
573         </div>
574       </div>
575       <div class="SECT3">
576         <h4 class="SECT3"><a name="TRUSTFILE" id="TRUSTFILE">7.2.8.
577         trustfile</a></h4>
578         <div class="VARIABLELIST">
579           <dl>
580             <dt>Specifies:</dt>
581             <dd>
582               <p>The name of the trust file to use</p>
583             </dd>
584             <dt>Type of value:</dt>
585             <dd>
586               <p>File name, relative to <tt class="LITERAL">confdir</tt></p>
587             </dd>
588             <dt>Default value:</dt>
589             <dd>
590               <p><span class="emphasis"><i class="EMPHASIS">Unset (commented
591               out)</i></span>. When activated: trust (Unix) <span class=
592               "emphasis"><i class="EMPHASIS">or</i></span> trust.txt
593               (Windows)</p>
594             </dd>
595             <dt>Effect if unset:</dt>
596             <dd>
597               <p>The entire trust mechanism is disabled.</p>
598             </dd>
599             <dt>Notes:</dt>
600             <dd>
601               <p>The trust mechanism is an experimental feature for building
602               white-lists and should be used with care. It is <span class=
603               "emphasis"><i class="EMPHASIS">NOT</i></span> recommended for
604               the casual user.</p>
605               <p>If you specify a trust file, <span class=
606               "APPLICATION">Privoxy</span> will only allow access to sites
607               that are specified in the trustfile. Sites can be listed in one
608               of two ways:</p>
609               <p>Prepending a <tt class="LITERAL">~</tt> character limits
610               access to this site only (and any sub-paths within this site),
611               e.g. <tt class="LITERAL">~www.example.com</tt> allows access to
612               <tt class="LITERAL">~www.example.com/features/news.html</tt>,
613               etc.</p>
614               <p>Or, you can designate sites as <span class=
615               "emphasis"><i class="EMPHASIS">trusted referrers</i></span>, by
616               prepending the name with a <tt class="LITERAL">+</tt>
617               character. The effect is that access to untrusted sites will be
618               granted -- but only if a link from this trusted referrer was
619               used to get there. The link target will then be added to the
620               <span class="QUOTE">"trustfile"</span> so that future, direct
621               accesses will be granted. Sites added via this mechanism do not
622               become trusted referrers themselves (i.e. they are added with a
623               <tt class="LITERAL">~</tt> designation). There is a limit of
624               512 such entries, after which new entries will not be made.</p>
625               <p>If you use the <tt class="LITERAL">+</tt> operator in the
626               trust file, it may grow considerably over time.</p>
627               <p>It is recommended that <span class=
628               "APPLICATION">Privoxy</span> be compiled with the <tt class=
629               "LITERAL">--disable-force</tt>, <tt class=
630               "LITERAL">--disable-toggle</tt> and <tt class=
631               "LITERAL">--disable-editor</tt> options, if this feature is to
632               be used.</p>
633               <p>Possible applications include limiting Internet access for
634               children.</p>
635             </dd>
636           </dl>
637         </div>
638       </div>
639     </div>
640     <div class="SECT2">
641       <h2 class="SECT2"><a name="DEBUGGING" id="DEBUGGING">7.3.
642       Debugging</a></h2>
643       <p>These options are mainly useful when tracing a problem. Note that
644       you might also want to invoke <span class="APPLICATION">Privoxy</span>
645       with the <tt class="LITERAL">--no-daemon</tt> command line option when
646       debugging.</p>
647       <div class="SECT3">
648         <h4 class="SECT3"><a name="DEBUG" id="DEBUG">7.3.1. debug</a></h4>
649         <div class="VARIABLELIST">
650           <dl>
651             <dt>Specifies:</dt>
652             <dd>
653               <p>Key values that determine what information gets logged.</p>
654             </dd>
655             <dt>Type of value:</dt>
656             <dd>
657               <p>Integer values</p>
658             </dd>
659             <dt>Default value:</dt>
660             <dd>
661               <p>0 (i.e.: only fatal errors (that cause Privoxy to exit) are
662               logged)</p>
663             </dd>
664             <dt>Effect if unset:</dt>
665             <dd>
666               <p>Default value is used (see above).</p>
667             </dd>
668             <dt>Notes:</dt>
669             <dd>
670               <p>The available debug levels are:</p>
671               <table border="0" bgcolor="#E0E0E0" width="90%">
672                 <tr>
673                   <td>
674                     <pre class="PROGRAMLISTING">
675                     debug     1 # Log the destination for each request <span class="APPLICATION">Privoxy</span> let through. See also debug 1024.
676   debug     2 # show each connection status
677   debug     4 # show I/O status
678   debug     8 # show header parsing
679   debug    16 # log all data written to the network
680   debug    32 # debug force feature
681   debug    64 # debug regular expression filters
682   debug   128 # debug redirects
683   debug   256 # debug GIF de-animation
684   debug   512 # Common Log Format
685   debug  1024 # Log the destination for requests <span class=
686 "APPLICATION">Privoxy</span> didn't let through, and the reason why.
687   debug  2048 # CGI user interface
688   debug  4096 # Startup banner and warnings.
689   debug  8192 # Non-fatal errors
690   debug 32768 # log all data read from the network
691   debug 65536 # Log the applying actions</pre>
692                   </td>
693                 </tr>
694               </table>
695               <p>To select multiple debug levels, you can either add them or
696               use multiple <tt class="LITERAL">debug</tt> lines.</p>
697               <p>A debug level of 1 is informative because it will show you
698               each request as it happens. <span class="emphasis"><i class=
699               "EMPHASIS">1, 1024, 4096 and 8192 are recommended</i></span> so
700               that you will notice when things go wrong. The other levels are
701               probably only of interest if you are hunting down a specific
702               problem. They can produce a hell of an output (especially
703               16).</p>
704               <p>If you are used to the more verbose settings, simply enable
705               the debug lines below again.</p>
706               <p>If you want to use pure CLF (Common Log Format), you should
707               set <span class="QUOTE">"debug 512"</span> <span class=
708               "emphasis"><i class="EMPHASIS">ONLY</i></span> and not enable
709               anything else.</p>
710               <p><span class="APPLICATION">Privoxy</span> has a hard-coded
711               limit for the length of log messages. If it's reached, messages
712               are logged truncated and marked with <span class="QUOTE">"...
713               [too long, truncated]"</span>.</p>
714               <p>Please don't file any support requests without trying to
715               reproduce the problem with increased debug level first. Once
716               you read the log messages, you may even be able to solve the
717               problem on your own.</p>
718             </dd>
719           </dl>
720         </div>
721       </div>
722       <div class="SECT3">
723         <h4 class="SECT3"><a name="SINGLE-THREADED" id=
724         "SINGLE-THREADED">7.3.2. single-threaded</a></h4>
725         <div class="VARIABLELIST">
726           <dl>
727             <dt>Specifies:</dt>
728             <dd>
729               <p>Whether to run only one server thread.</p>
730             </dd>
731             <dt>Type of value:</dt>
732             <dd>
733               <p><span class="emphasis"><i class="EMPHASIS">1 or
734               0</i></span></p>
735             </dd>
736             <dt>Default value:</dt>
737             <dd>
738               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
739             </dd>
740             <dt>Effect if unset:</dt>
741             <dd>
742               <p>Multi-threaded (or, where unavailable: forked) operation,
743               i.e. the ability to serve multiple requests simultaneously.</p>
744             </dd>
745             <dt>Notes:</dt>
746             <dd>
747               <p>This option is only there for debugging purposes.
748               <span class="emphasis"><i class="EMPHASIS">It will drastically
749               reduce performance.</i></span></p>
750             </dd>
751           </dl>
752         </div>
753       </div>
754       <div class="SECT3">
755         <h4 class="SECT3"><a name="HOSTNAME" id="HOSTNAME">7.3.3.
756         hostname</a></h4>
757         <div class="VARIABLELIST">
758           <dl>
759             <dt>Specifies:</dt>
760             <dd>
761               <p>The hostname shown on the CGI pages.</p>
762             </dd>
763             <dt>Type of value:</dt>
764             <dd>
765               <p>Text</p>
766             </dd>
767             <dt>Default value:</dt>
768             <dd>
769               <p><span class="emphasis"><i class=
770               "EMPHASIS">Unset</i></span></p>
771             </dd>
772             <dt>Effect if unset:</dt>
773             <dd>
774               <p>The hostname provided by the operating system is used.</p>
775             </dd>
776             <dt>Notes:</dt>
777             <dd>
778               <p>On some misconfigured systems resolving the hostname fails
779               or takes too much time and slows Privoxy down. Setting a fixed
780               hostname works around the problem.</p>
781               <p>In other circumstances it might be desirable to show a
782               hostname other than the one returned by the operating system.
783               For example if the system has several different hostnames and
784               you don't want to use the first one.</p>
785               <p>Note that Privoxy does not validate the specified hostname
786               value.</p>
787             </dd>
788           </dl>
789         </div>
790       </div>
791     </div>
792     <div class="SECT2">
793       <h2 class="SECT2"><a name="ACCESS-CONTROL" id="ACCESS-CONTROL">7.4.
794       Access Control and Security</a></h2>
795       <p>This section of the config file controls the security-relevant
796       aspects of <span class="APPLICATION">Privoxy</span>'s
797       configuration.</p>
798       <div class="SECT3">
799         <h4 class="SECT3"><a name="LISTEN-ADDRESS" id="LISTEN-ADDRESS">7.4.1.
800         listen-address</a></h4>
801         <div class="VARIABLELIST">
802           <dl>
803             <dt>Specifies:</dt>
804             <dd>
805               <p>The address and TCP port on which <span class=
806               "APPLICATION">Privoxy</span> will listen for client
807               requests.</p>
808             </dd>
809             <dt>Type of value:</dt>
810             <dd>
811               <p>[<tt class="REPLACEABLE"><i>IP-Address</i></tt>]:<tt class=
812               "REPLACEABLE"><i>Port</i></tt></p>
813               <p>[<tt class="REPLACEABLE"><i>Hostname</i></tt>]:<tt class=
814               "REPLACEABLE"><i>Port</i></tt></p>
815             </dd>
816             <dt>Default value:</dt>
817             <dd>
818               <p>127.0.0.1:8118</p>
819             </dd>
820             <dt>Effect if unset:</dt>
821             <dd>
822               <p>Bind to 127.0.0.1 (IPv4 localhost), port 8118. This is
823               suitable and recommended for home users who run <span class=
824               "APPLICATION">Privoxy</span> on the same machine as their
825               browser.</p>
826             </dd>
827             <dt>Notes:</dt>
828             <dd>
829               <p>You will need to configure your browser(s) to this proxy
830               address and port.</p>
831               <p>If you already have another service running on port 8118, or
832               if you want to serve requests from other machines (e.g. on your
833               local network) as well, you will need to override the
834               default.</p>
835               <p>You can use this statement multiple times to make
836               <span class="APPLICATION">Privoxy</span> listen on more ports
837               or more <abbr class="ABBREV">IP</abbr> addresses. Suitable if
838               your operating system does not support sharing <abbr class=
839               "ABBREV">IPv6</abbr> and <abbr class="ABBREV">IPv4</abbr>
840               protocols on the same socket.</p>
841               <p>If a hostname is used instead of an IP address, <span class=
842               "APPLICATION">Privoxy</span> will try to resolve it to an IP
843               address and if there are multiple, use the first one
844               returned.</p>
845               <p>If the address for the hostname isn't already known on the
846               system (for example because it's in /etc/hostname), this may
847               result in DNS traffic.</p>
848               <p>If the specified address isn't available on the system, or
849               if the hostname can't be resolved, <span class=
850               "APPLICATION">Privoxy</span> will fail to start.</p>
851               <p>IPv6 addresses containing colons have to be quoted by
852               brackets. They can only be used if <span class=
853               "APPLICATION">Privoxy</span> has been compiled with IPv6
854               support. If you aren't sure if your version supports it, have a
855               look at <tt class=
856               "LITERAL">http://config.privoxy.org/show-status</tt>.</p>
857               <p>Some operating systems will prefer IPv6 to IPv4 addresses
858               even if the system has no IPv6 connectivity which is usually
859               not expected by the user. Some even rely on DNS to resolve
860               localhost which mean the "localhost" address used may not
861               actually be local.</p>
862               <p>It is therefore recommended to explicitly configure the
863               intended IP address instead of relying on the operating system,
864               unless there's a strong reason not to.</p>
865               <p>If you leave out the address, <span class=
866               "APPLICATION">Privoxy</span> will bind to all IPv4 interfaces
867               (addresses) on your machine and may become reachable from the
868               Internet and/or the local network. Be aware that some GNU/Linux
869               distributions modify that behaviour without updating the
870               documentation. Check for non-standard patches if your
871               <span class="APPLICATION">Privoxy</span> version behaves
872               differently.</p>
873               <p>If you configure <span class="APPLICATION">Privoxy</span> to
874               be reachable from the network, consider using <a href=
875               "config.html#ACLS">access control lists</a> (ACL's, see below),
876               and/or a firewall.</p>
877               <p>If you open <span class="APPLICATION">Privoxy</span> to
878               untrusted users, you will also want to make sure that the
879               following actions are disabled: <tt class="LITERAL"><a href=
880               "config.html#ENABLE-EDIT-ACTIONS">enable-edit-actions</a></tt>
881               and <tt class="LITERAL"><a href=
882               "config.html#ENABLE-REMOTE-TOGGLE">enable-remote-toggle</a></tt></p>
883             </dd>
884             <dt>Example:</dt>
885             <dd>
886               <p>Suppose you are running <span class=
887               "APPLICATION">Privoxy</span> on a machine which has the address
888               192.168.0.1 on your local private network (192.168.0.0) and has
889               another outside connection with a different address. You want
890               it to serve requests from inside only:</p>
891               <table border="0" bgcolor="#E0E0E0" width="90%">
892                 <tr>
893                   <td>
894                     <pre class="PROGRAMLISTING">
895                     listen-address  192.168.0.1:8118</pre>
896                   </td>
897                 </tr>
898               </table>
899               <p>Suppose you are running <span class=
900               "APPLICATION">Privoxy</span> on an IPv6-capable machine and you
901               want it to listen on the IPv6 address of the loopback
902               device:</p>
903               <table border="0" bgcolor="#E0E0E0" width="90%">
904                 <tr>
905                   <td>
906                     <pre class="PROGRAMLISTING">
907                     listen-address [::1]:8118</pre>
908                   </td>
909                 </tr>
910               </table>
911             </dd>
912           </dl>
913         </div>
914       </div>
915       <div class="SECT3">
916         <h4 class="SECT3"><a name="TOGGLE" id="TOGGLE">7.4.2. toggle</a></h4>
917         <div class="VARIABLELIST">
918           <dl>
919             <dt>Specifies:</dt>
920             <dd>
921               <p>Initial state of "toggle" status</p>
922             </dd>
923             <dt>Type of value:</dt>
924             <dd>
925               <p>1 or 0</p>
926             </dd>
927             <dt>Default value:</dt>
928             <dd>
929               <p>1</p>
930             </dd>
931             <dt>Effect if unset:</dt>
932             <dd>
933               <p>Act as if toggled on</p>
934             </dd>
935             <dt>Notes:</dt>
936             <dd>
937               <p>If set to 0, <span class="APPLICATION">Privoxy</span> will
938               start in <span class="QUOTE">"toggled off"</span> mode, i.e.
939               mostly behave like a normal, content-neutral proxy with both ad
940               blocking and content filtering disabled. See <tt class=
941               "LITERAL">enable-remote-toggle</tt> below.</p>
942             </dd>
943           </dl>
944         </div>
945       </div>
946       <div class="SECT3">
947         <h4 class="SECT3"><a name="ENABLE-REMOTE-TOGGLE" id=
948         "ENABLE-REMOTE-TOGGLE">7.4.3. enable-remote-toggle</a></h4>
949         <div class="VARIABLELIST">
950           <dl>
951             <dt>Specifies:</dt>
952             <dd>
953               <p>Whether or not the <a href=
954               "http://config.privoxy.org/toggle" target="_top">web-based
955               toggle feature</a> may be used</p>
956             </dd>
957             <dt>Type of value:</dt>
958             <dd>
959               <p>0 or 1</p>
960             </dd>
961             <dt>Default value:</dt>
962             <dd>
963               <p>0</p>
964             </dd>
965             <dt>Effect if unset:</dt>
966             <dd>
967               <p>The web-based toggle feature is disabled.</p>
968             </dd>
969             <dt>Notes:</dt>
970             <dd>
971               <p>When toggled off, <span class="APPLICATION">Privoxy</span>
972               mostly acts like a normal, content-neutral proxy, i.e. doesn't
973               block ads or filter content.</p>
974               <p>Access to the toggle feature can <span class=
975               "emphasis"><i class="EMPHASIS">not</i></span> be controlled
976               separately by <span class="QUOTE">"ACLs"</span> or HTTP
977               authentication, so that everybody who can access <span class=
978               "APPLICATION">Privoxy</span> (see <span class=
979               "QUOTE">"ACLs"</span> and <tt class=
980               "LITERAL">listen-address</tt> above) can toggle it for all
981               users. So this option is <span class="emphasis"><i class=
982               "EMPHASIS">not recommended</i></span> for multi-user
983               environments with untrusted users.</p>
984               <p>Note that malicious client side code (e.g Java) is also
985               capable of using this option.</p>
986               <p>As a lot of <span class="APPLICATION">Privoxy</span> users
987               don't read documentation, this feature is disabled by
988               default.</p>
989               <p>Note that you must have compiled <span class=
990               "APPLICATION">Privoxy</span> with support for this feature,
991               otherwise this option has no effect.</p>
992             </dd>
993           </dl>
994         </div>
995       </div>
996       <div class="SECT3">
997         <h4 class="SECT3"><a name="ENABLE-REMOTE-HTTP-TOGGLE" id=
998         "ENABLE-REMOTE-HTTP-TOGGLE">7.4.4. enable-remote-http-toggle</a></h4>
999         <div class="VARIABLELIST">
1000           <dl>
1001             <dt>Specifies:</dt>
1002             <dd>
1003               <p>Whether or not Privoxy recognizes special HTTP headers to
1004               change its behaviour.</p>
1005             </dd>
1006             <dt>Type of value:</dt>
1007             <dd>
1008               <p>0 or 1</p>
1009             </dd>
1010             <dt>Default value:</dt>
1011             <dd>
1012               <p>0</p>
1013             </dd>
1014             <dt>Effect if unset:</dt>
1015             <dd>
1016               <p>Privoxy ignores special HTTP headers.</p>
1017             </dd>
1018             <dt>Notes:</dt>
1019             <dd>
1020               <p>When toggled on, the client can change <span class=
1021               "APPLICATION">Privoxy's</span> behaviour by setting special
1022               HTTP headers. Currently the only supported special header is
1023               <span class="QUOTE">"X-Filter: No"</span>, to disable filtering
1024               for the ongoing request, even if it is enabled in one of the
1025               action files.</p>
1026               <p>This feature is disabled by default. If you are using
1027               <span class="APPLICATION">Privoxy</span> in a environment with
1028               trusted clients, you may enable this feature at your
1029               discretion. Note that malicious client side code (e.g Java) is
1030               also capable of using this feature.</p>
1031               <p>This option will be removed in future releases as it has
1032               been obsoleted by the more general header taggers.</p>
1033             </dd>
1034           </dl>
1035         </div>
1036       </div>
1037       <div class="SECT3">
1038         <h4 class="SECT3"><a name="ENABLE-EDIT-ACTIONS" id=
1039         "ENABLE-EDIT-ACTIONS">7.4.5. enable-edit-actions</a></h4>
1040         <div class="VARIABLELIST">
1041           <dl>
1042             <dt>Specifies:</dt>
1043             <dd>
1044               <p>Whether or not the <a href=
1045               "http://config.privoxy.org/show-status" target="_top">web-based
1046               actions file editor</a> may be used</p>
1047             </dd>
1048             <dt>Type of value:</dt>
1049             <dd>
1050               <p>0 or 1</p>
1051             </dd>
1052             <dt>Default value:</dt>
1053             <dd>
1054               <p>0</p>
1055             </dd>
1056             <dt>Effect if unset:</dt>
1057             <dd>
1058               <p>The web-based actions file editor is disabled.</p>
1059             </dd>
1060             <dt>Notes:</dt>
1061             <dd>
1062               <p>Access to the editor can <span class="emphasis"><i class=
1063               "EMPHASIS">not</i></span> be controlled separately by
1064               <span class="QUOTE">"ACLs"</span> or HTTP authentication, so
1065               that everybody who can access <span class=
1066               "APPLICATION">Privoxy</span> (see <span class=
1067               "QUOTE">"ACLs"</span> and <tt class=
1068               "LITERAL">listen-address</tt> above) can modify its
1069               configuration for all users.</p>
1070               <p>This option is <span class="emphasis"><i class=
1071               "EMPHASIS">not recommended</i></span> for environments with
1072               untrusted users and as a lot of <span class=
1073               "APPLICATION">Privoxy</span> users don't read documentation,
1074               this feature is disabled by default.</p>
1075               <p>Note that malicious client side code (e.g Java) is also
1076               capable of using the actions editor and you shouldn't enable
1077               this options unless you understand the consequences and are
1078               sure your browser is configured correctly.</p>
1079               <p>Note that you must have compiled <span class=
1080               "APPLICATION">Privoxy</span> with support for this feature,
1081               otherwise this option has no effect.</p>
1082             </dd>
1083           </dl>
1084         </div>
1085       </div>
1086       <div class="SECT3">
1087         <h4 class="SECT3"><a name="ENFORCE-BLOCKS" id="ENFORCE-BLOCKS">7.4.6.
1088         enforce-blocks</a></h4>
1089         <div class="VARIABLELIST">
1090           <dl>
1091             <dt>Specifies:</dt>
1092             <dd>
1093               <p>Whether the user is allowed to ignore blocks and can
1094               <span class="QUOTE">"go there anyway"</span>.</p>
1095             </dd>
1096             <dt>Type of value:</dt>
1097             <dd>
1098               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
1099             </dd>
1100             <dt>Default value:</dt>
1101             <dd>
1102               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
1103             </dd>
1104             <dt>Effect if unset:</dt>
1105             <dd>
1106               <p>Blocks are not enforced.</p>
1107             </dd>
1108             <dt>Notes:</dt>
1109             <dd>
1110               <p><span class="APPLICATION">Privoxy</span> is mainly used to
1111               block and filter requests as a service to the user, for example
1112               to block ads and other junk that clogs the pipes. <span class=
1113               "APPLICATION">Privoxy's</span> configuration isn't perfect and
1114               sometimes innocent pages are blocked. In this situation it
1115               makes sense to allow the user to enforce the request and have
1116               <span class="APPLICATION">Privoxy</span> ignore the block.</p>
1117               <p>In the default configuration <span class=
1118               "APPLICATION">Privoxy's</span> <span class=
1119               "QUOTE">"Blocked"</span> page contains a <span class=
1120               "QUOTE">"go there anyway"</span> link to adds a special string
1121               (the force prefix) to the request URL. If that link is used,
1122               <span class="APPLICATION">Privoxy</span> will detect the force
1123               prefix, remove it again and let the request pass.</p>
1124               <p>Of course <span class="APPLICATION">Privoxy</span> can also
1125               be used to enforce a network policy. In that case the user
1126               obviously should not be able to bypass any blocks, and that's
1127               what the <span class="QUOTE">"enforce-blocks"</span> option is
1128               for. If it's enabled, <span class="APPLICATION">Privoxy</span>
1129               hides the <span class="QUOTE">"go there anyway"</span> link. If
1130               the user adds the force prefix by hand, it will not be accepted
1131               and the circumvention attempt is logged.</p>
1132             </dd>
1133             <dt>Examples:</dt>
1134             <dd>
1135               <p>enforce-blocks 1</p>
1136             </dd>
1137           </dl>
1138         </div>
1139       </div>
1140       <div class="SECT3">
1141         <h4 class="SECT3"><a name="ACLS" id="ACLS">7.4.7. ACLs: permit-access
1142         and deny-access</a></h4><a name="PERMIT-ACCESS" id=
1143         "PERMIT-ACCESS"></a><a name="DENY-ACCESS" id="DENY-ACCESS"></a>
1144         <div class="VARIABLELIST">
1145           <dl>
1146             <dt>Specifies:</dt>
1147             <dd>
1148               <p>Who can access what.</p>
1149             </dd>
1150             <dt>Type of value:</dt>
1151             <dd>
1152               <p><tt class="REPLACEABLE"><i>src_addr</i></tt>[:<tt class=
1153               "REPLACEABLE"><i>port</i></tt>][/<tt class=
1154               "REPLACEABLE"><i>src_masklen</i></tt>] [<tt class=
1155               "REPLACEABLE"><i>dst_addr</i></tt>[:<tt class=
1156               "REPLACEABLE"><i>port</i></tt>][/<tt class=
1157               "REPLACEABLE"><i>dst_masklen</i></tt>]]</p>
1158               <p>Where <tt class="REPLACEABLE"><i>src_addr</i></tt> and
1159               <tt class="REPLACEABLE"><i>dst_addr</i></tt> are IPv4 addresses
1160               in dotted decimal notation or valid DNS names, <tt class=
1161               "REPLACEABLE"><i>port</i></tt> is a port number, and <tt class=
1162               "REPLACEABLE"><i>src_masklen</i></tt> and <tt class=
1163               "REPLACEABLE"><i>dst_masklen</i></tt> are subnet masks in CIDR
1164               notation, i.e. integer values from 2 to 30 representing the
1165               length (in bits) of the network address. The masks and the
1166               whole destination part are optional.</p>
1167               <p>If your system implements <a href=
1168               "http://tools.ietf.org/html/rfc3493" target="_top">RFC
1169               3493</a>, then <tt class="REPLACEABLE"><i>src_addr</i></tt> and
1170               <tt class="REPLACEABLE"><i>dst_addr</i></tt> can be IPv6
1171               addresses delimeted by brackets, <tt class=
1172               "REPLACEABLE"><i>port</i></tt> can be a number or a service
1173               name, and <tt class="REPLACEABLE"><i>src_masklen</i></tt> and
1174               <tt class="REPLACEABLE"><i>dst_masklen</i></tt> can be a number
1175               from 0 to 128.</p>
1176             </dd>
1177             <dt>Default value:</dt>
1178             <dd>
1179               <p><span class="emphasis"><i class=
1180               "EMPHASIS">Unset</i></span></p>
1181               <p>If no <tt class="REPLACEABLE"><i>port</i></tt> is specified,
1182               any port will match. If no <tt class=
1183               "REPLACEABLE"><i>src_masklen</i></tt> or <tt class=
1184               "REPLACEABLE"><i>src_masklen</i></tt> is given, the complete IP
1185               address has to match (i.e. 32 bits for IPv4 and 128 bits for
1186               IPv6).</p>
1187             </dd>
1188             <dt>Effect if unset:</dt>
1189             <dd>
1190               <p>Don't restrict access further than implied by <tt class=
1191               "LITERAL">listen-address</tt></p>
1192             </dd>
1193             <dt>Notes:</dt>
1194             <dd>
1195               <p>Access controls are included at the request of ISPs and
1196               systems administrators, and <span class="emphasis"><i class=
1197               "EMPHASIS">are not usually needed by individual
1198               users</i></span>. For a typical home user, it will normally
1199               suffice to ensure that <span class="APPLICATION">Privoxy</span>
1200               only listens on the localhost (127.0.0.1) or internal (home)
1201               network address by means of the <a href=
1202               "config.html#LISTEN-ADDRESS"><span class="emphasis"><i class=
1203               "EMPHASIS">listen-address</i></span></a> option.</p>
1204               <p>Please see the warnings in the FAQ that <span class=
1205               "APPLICATION">Privoxy</span> is not intended to be a substitute
1206               for a firewall or to encourage anyone to defer addressing basic
1207               security weaknesses.</p>
1208               <p>Multiple ACL lines are OK. If any ACLs are specified,
1209               <span class="APPLICATION">Privoxy</span> only talks to IP
1210               addresses that match at least one <tt class=
1211               "LITERAL">permit-access</tt> line and don't match any
1212               subsequent <tt class="LITERAL">deny-access</tt> line. In other
1213               words, the last match wins, with the default being <tt class=
1214               "LITERAL">deny-access</tt>.</p>
1215               <p>If <span class="APPLICATION">Privoxy</span> is using a
1216               forwarder (see <tt class="LITERAL">forward</tt> below) for a
1217               particular destination URL, the <tt class=
1218               "REPLACEABLE"><i>dst_addr</i></tt> that is examined is the
1219               address of the forwarder and <span class="emphasis"><i class=
1220               "EMPHASIS">NOT</i></span> the address of the ultimate target.
1221               This is necessary because it may be impossible for the local
1222               <span class="APPLICATION">Privoxy</span> to determine the IP
1223               address of the ultimate target (that's often what gateways are
1224               used for).</p>
1225               <p>You should prefer using IP addresses over DNS names, because
1226               the address lookups take time. All DNS names must resolve! You
1227               can <span class="emphasis"><i class="EMPHASIS">not</i></span>
1228               use domain patterns like <span class="QUOTE">"*.org"</span> or
1229               partial domain names. If a DNS name resolves to multiple IP
1230               addresses, only the first one is used.</p>
1231               <p>Some systems allow IPv4 clients to connect to IPv6 server
1232               sockets. Then the client's IPv4 address will be translated by
1233               the system into IPv6 address space with special prefix
1234               ::ffff:0:0/96 (so called IPv4 mapped IPv6 address).
1235               <span class="APPLICATION">Privoxy</span> can handle it and maps
1236               such ACL addresses automatically.</p>
1237               <p>Denying access to particular sites by ACL may have undesired
1238               side effects if the site in question is hosted on a machine
1239               which also hosts other sites (most sites are).</p>
1240             </dd>
1241             <dt>Examples:</dt>
1242             <dd>
1243               <p>Explicitly define the default behavior if no ACL and
1244               <tt class="LITERAL">listen-address</tt> are set: <span class=
1245               "QUOTE">"localhost"</span> is OK. The absence of a <tt class=
1246               "REPLACEABLE"><i>dst_addr</i></tt> implies that <span class=
1247               "emphasis"><i class="EMPHASIS">all</i></span> destination
1248               addresses are OK:</p>
1249               <table border="0" bgcolor="#E0E0E0" width="90%">
1250                 <tr>
1251                   <td>
1252                     <pre class="SCREEN">  permit-access  localhost</pre>
1253                   </td>
1254                 </tr>
1255               </table>
1256               <p>Allow any host on the same class C subnet as www.privoxy.org
1257               access to nothing but www.example.com (or other domains hosted
1258               on the same system):</p>
1259               <table border="0" bgcolor="#E0E0E0" width="90%">
1260                 <tr>
1261                   <td>
1262                     <pre class="SCREEN">
1263                     permit-access  www.privoxy.org/24 www.example.com/32</pre>
1264                   </td>
1265                 </tr>
1266               </table>
1267               <p>Allow access from any host on the 26-bit subnet
1268               192.168.45.64 to anywhere, with the exception that
1269               192.168.45.73 may not access the IP address behind
1270               www.dirty-stuff.example.com:</p>
1271               <table border="0" bgcolor="#E0E0E0" width="90%">
1272                 <tr>
1273                   <td>
1274                     <pre class="SCREEN">  permit-access  192.168.45.64/26
1275   deny-access    192.168.45.73    www.dirty-stuff.example.com</pre>
1276                   </td>
1277                 </tr>
1278               </table>
1279               <p>Allow access from the IPv4 network 192.0.2.0/24 even if
1280               listening on an IPv6 wild card address (not supported on all
1281               platforms):</p>
1282               <table border="0" bgcolor="#E0E0E0" width="90%">
1283                 <tr>
1284                   <td>
1285                     <pre class="PROGRAMLISTING">
1286                     permit-access  192.0.2.0/24</pre>
1287                   </td>
1288                 </tr>
1289               </table>
1290               <p>This is equivalent to the following line even if listening
1291               on an IPv4 address (not supported on all platforms):</p>
1292               <table border="0" bgcolor="#E0E0E0" width="90%">
1293                 <tr>
1294                   <td>
1295                     <pre class="PROGRAMLISTING">
1296                     permit-access  [::ffff:192.0.2.0]/120</pre>
1297                   </td>
1298                 </tr>
1299               </table>
1300             </dd>
1301           </dl>
1302         </div>
1303       </div>
1304       <div class="SECT3">
1305         <h4 class="SECT3"><a name="BUFFER-LIMIT" id="BUFFER-LIMIT">7.4.8.
1306         buffer-limit</a></h4>
1307         <div class="VARIABLELIST">
1308           <dl>
1309             <dt>Specifies:</dt>
1310             <dd>
1311               <p>Maximum size of the buffer for content filtering.</p>
1312             </dd>
1313             <dt>Type of value:</dt>
1314             <dd>
1315               <p>Size in Kbytes</p>
1316             </dd>
1317             <dt>Default value:</dt>
1318             <dd>
1319               <p>4096</p>
1320             </dd>
1321             <dt>Effect if unset:</dt>
1322             <dd>
1323               <p>Use a 4MB (4096 KB) limit.</p>
1324             </dd>
1325             <dt>Notes:</dt>
1326             <dd>
1327               <p>For content filtering, i.e. the <tt class=
1328               "LITERAL">+filter</tt> and <tt class=
1329               "LITERAL">+deanimate-gif</tt> actions, it is necessary that
1330               <span class="APPLICATION">Privoxy</span> buffers the entire
1331               document body. This can be potentially dangerous, since a
1332               server could just keep sending data indefinitely and wait for
1333               your RAM to exhaust -- with nasty consequences. Hence this
1334               option.</p>
1335               <p>When a document buffer size reaches the <tt class=
1336               "LITERAL">buffer-limit</tt>, it is flushed to the client
1337               unfiltered and no further attempt to filter the rest of the
1338               document is made. Remember that there may be multiple threads
1339               running, which might require up to <tt class=
1340               "LITERAL">buffer-limit</tt> Kbytes <span class=
1341               "emphasis"><i class="EMPHASIS">each</i></span>, unless you have
1342               enabled <span class="QUOTE">"single-threaded"</span> above.</p>
1343             </dd>
1344           </dl>
1345         </div>
1346       </div>
1347       <div class="SECT3">
1348         <h4 class="SECT3"><a name="ENABLE-PROXY-AUTHENTICATION-FORWARDING"
1349         id="ENABLE-PROXY-AUTHENTICATION-FORWARDING">7.4.9.
1350         enable-proxy-authentication-forwarding</a></h4>
1351         <div class="VARIABLELIST">
1352           <dl>
1353             <dt>Specifies:</dt>
1354             <dd>
1355               <p>Whether or not proxy authentication through <span class=
1356               "APPLICATION">Privoxy</span> should work.</p>
1357             </dd>
1358             <dt>Type of value:</dt>
1359             <dd>
1360               <p>0 or 1</p>
1361             </dd>
1362             <dt>Default value:</dt>
1363             <dd>
1364               <p>0</p>
1365             </dd>
1366             <dt>Effect if unset:</dt>
1367             <dd>
1368               <p>Proxy authentication headers are removed.</p>
1369             </dd>
1370             <dt>Notes:</dt>
1371             <dd>
1372               <p>Privoxy itself does not support proxy authentication, but
1373               can allow clients to authenticate against Privoxy's parent
1374               proxy.</p>
1375               <p>By default Privoxy (3.0.21 and later) don't do that and
1376               remove Proxy-Authorization headers in requests and
1377               Proxy-Authenticate headers in responses to make it harder for
1378               malicious sites to trick inexperienced users into providing
1379               login information.</p>
1380               <p>If this option is enabled the headers are forwarded.</p>
1381               <p>Enabling this option is <span class="emphasis"><i class=
1382               "EMPHASIS">not recommended</i></span> if there is no parent
1383               proxy that requires authentication or if the local network
1384               between Privoxy and the parent proxy isn't trustworthy. If
1385               proxy authentication is only required for some requests, it is
1386               recommended to use a client header filter to remove the
1387               authentication headers for requests where they aren't
1388               needed.</p>
1389             </dd>
1390           </dl>
1391         </div>
1392       </div>
1393       <div class="SECT3">
1394         <h4 class="SECT3"><a name="TRUSTED-CGI-REFERER" id=
1395         "TRUSTED-CGI-REFERER">7.4.10. trusted-cgi-referer</a></h4>
1396         <div class="VARIABLELIST">
1397           <dl>
1398             <dt>Specifies:</dt>
1399             <dd>
1400               <p>A trusted website or webpage whose links can be followed to
1401               reach sensitive CGI pages</p>
1402             </dd>
1403             <dt>Type of value:</dt>
1404             <dd>
1405               <p>URL or URL prefix</p>
1406             </dd>
1407             <dt>Default value:</dt>
1408             <dd>
1409               <p>Unset</p>
1410             </dd>
1411             <dt>Effect if unset:</dt>
1412             <dd>
1413               <p>No external pages are considered trusted referers.</p>
1414             </dd>
1415             <dt>Notes:</dt>
1416             <dd>
1417               <p>Before <span class="APPLICATION">Privoxy</span> accepts
1418               configuration changes through CGI pages like <a href=
1419               "config.html#CLIENT-SPECIFIC-TAG">client-tags</a> or the
1420               <a href="config.html#ENABLE-REMOTE-TOGGLE">remote toggle</a>,
1421               it checks the Referer header to see if the request comes from a
1422               trusted source.</p>
1423               <p>By default only the webinterface domains <a href=
1424               "http://config.privoxy.org/" target=
1425               "_top">config.privoxy.org</a> and <a href="http://p.p/" target=
1426               "_top">p.p</a> are considered trustworthy. Requests originating
1427               from other domains are rejected to prevent third-parties from
1428               modifiying Privoxy's state by e.g. embedding images that result
1429               in CGI requests.</p>
1430               <p>In some environments it may be desirable to embed links to
1431               CGI pages on external pages, for example on an Intranet
1432               homepage the Privoxy admin controls.</p>
1433               <p>The <span class="QUOTE">"trusted-cgi-referer"</span> option
1434               can be used to add that page, or the whole domain, as trusted
1435               source so the resulting requests aren't rejected. Requests are
1436               accepted if the specified trusted-cgi-refer is the prefix of
1437               the Referer.</p>
1438               <div class="WARNING">
1439                 <table class="WARNING" border="1" width="90%">
1440                   <tr>
1441                     <td align="center"><b>Warning</b></td>
1442                   </tr>
1443                   <tr>
1444                     <td align="left">
1445                       <p>Declaring pages the admin doesn't control
1446                       trustworthy may allow malicious third parties to modify
1447                       Privoxy's internal state against the user's wishes and
1448                       without the user's knowledge.</p>
1449                     </td>
1450                   </tr>
1451                 </table>
1452               </div>
1453             </dd>
1454           </dl>
1455         </div>
1456       </div>
1457     </div>
1458     <div class="SECT2">
1459       <h2 class="SECT2"><a name="FORWARDING" id="FORWARDING">7.5.
1460       Forwarding</a></h2>
1461       <p>This feature allows routing of HTTP requests through a chain of
1462       multiple proxies.</p>
1463       <p>Forwarding can be used to chain Privoxy with a caching proxy to
1464       speed up browsing. Using a parent proxy may also be necessary if the
1465       machine that <span class="APPLICATION">Privoxy</span> runs on has no
1466       direct Internet access.</p>
1467       <p>Note that parent proxies can severely decrease your privacy level.
1468       For example a parent proxy could add your IP address to the request
1469       headers and if it's a caching proxy it may add the <span class=
1470       "QUOTE">"Etag"</span> header to revalidation requests again, even
1471       though you configured Privoxy to remove it. It may also ignore
1472       Privoxy's header time randomization and use the original values which
1473       could be used by the server as cookie replacement to track your steps
1474       between visits.</p>
1475       <p>Also specified here are SOCKS proxies. <span class=
1476       "APPLICATION">Privoxy</span> supports the SOCKS 4 and SOCKS 4A
1477       protocols.</p>
1478       <div class="SECT3">
1479         <h4 class="SECT3"><a name="FORWARD" id="FORWARD">7.5.1.
1480         forward</a></h4>
1481         <div class="VARIABLELIST">
1482           <dl>
1483             <dt>Specifies:</dt>
1484             <dd>
1485               <p>To which parent HTTP proxy specific requests should be
1486               routed.</p>
1487             </dd>
1488             <dt>Type of value:</dt>
1489             <dd>
1490               <p><tt class="REPLACEABLE"><i>target_pattern</i></tt>
1491               <tt class="REPLACEABLE"><i>http_parent</i></tt>[:<tt class=
1492               "REPLACEABLE"><i>port</i></tt>]</p>
1493               <p>where <tt class="REPLACEABLE"><i>target_pattern</i></tt> is
1494               a <a href="actions-file.html#AF-PATTERNS">URL pattern</a> that
1495               specifies to which requests (i.e. URLs) this forward rule shall
1496               apply. Use <tt class="LITERAL">/</tt> to denote <span class=
1497               "QUOTE">"all URLs"</span>. <tt class=
1498               "REPLACEABLE"><i>http_parent</i></tt>[:<tt class=
1499               "REPLACEABLE"><i>port</i></tt>] is the DNS name or IP address
1500               of the parent HTTP proxy through which the requests should be
1501               forwarded, optionally followed by its listening port (default:
1502               8000). Use a single dot (<tt class="LITERAL">.</tt>) to denote
1503               <span class="QUOTE">"no forwarding"</span>.</p>
1504             </dd>
1505             <dt>Default value:</dt>
1506             <dd>
1507               <p><span class="emphasis"><i class=
1508               "EMPHASIS">Unset</i></span></p>
1509             </dd>
1510             <dt>Effect if unset:</dt>
1511             <dd>
1512               <p>Don't use parent HTTP proxies.</p>
1513             </dd>
1514             <dt>Notes:</dt>
1515             <dd>
1516               <p>If <tt class="REPLACEABLE"><i>http_parent</i></tt> is
1517               <span class="QUOTE">"."</span>, then requests are not forwarded
1518               to another HTTP proxy but are made directly to the web
1519               servers.</p>
1520               <p><tt class="REPLACEABLE"><i>http_parent</i></tt> can be a
1521               numerical IPv6 address (if <a href=
1522               "http://tools.ietf.org/html/rfc3493" target="_top">RFC 3493</a>
1523               is implemented). To prevent clashes with the port delimiter,
1524               the whole IP address has to be put into brackets. On the other
1525               hand a <tt class="REPLACEABLE"><i>target_pattern</i></tt>
1526               containing an IPv6 address has to be put into angle brackets
1527               (normal brackets are reserved for regular expressions
1528               already).</p>
1529               <p>Multiple lines are OK, they are checked in sequence, and the
1530               last match wins.</p>
1531             </dd>
1532             <dt>Examples:</dt>
1533             <dd>
1534               <p>Everything goes to an example parent proxy, except SSL on
1535               port 443 (which it doesn't handle):</p>
1536               <table border="0" bgcolor="#E0E0E0" width="90%">
1537                 <tr>
1538                   <td>
1539                     <pre class="SCREEN">
1540                     forward   /      parent-proxy.example.org:8080
1541   forward   :443   .</pre>
1542                   </td>
1543                 </tr>
1544               </table>
1545               <p>Everything goes to our example ISP's caching proxy, except
1546               for requests to that ISP's sites:</p>
1547               <table border="0" bgcolor="#E0E0E0" width="90%">
1548                 <tr>
1549                   <td>
1550                     <pre class="SCREEN">
1551                     forward   /                  caching-proxy.isp.example.net:8000
1552   forward   .isp.example.net   .</pre>
1553                   </td>
1554                 </tr>
1555               </table>
1556               <p>Parent proxy specified by an IPv6 address:</p>
1557               <table border="0" bgcolor="#E0E0E0" width="90%">
1558                 <tr>
1559                   <td>
1560                     <pre class="PROGRAMLISTING">
1561                     forward   /                   [2001:DB8::1]:8000</pre>
1562                   </td>
1563                 </tr>
1564               </table>
1565               <p>Suppose your parent proxy doesn't support IPv6:</p>
1566               <table border="0" bgcolor="#E0E0E0" width="90%">
1567                 <tr>
1568                   <td>
1569                     <pre class="PROGRAMLISTING">
1570                     forward  /                        parent-proxy.example.org:8000
1571   forward  ipv6-server.example.org  .
1572   forward  &lt;[2-3][0-9a-f][0-9a-f][0-9a-f]:*&gt;   .</pre>
1573                   </td>
1574                 </tr>
1575               </table>
1576             </dd>
1577           </dl>
1578         </div>
1579       </div>
1580       <div class="SECT3">
1581         <h4 class="SECT3"><a name="SOCKS" id="SOCKS">7.5.2. forward-socks4,
1582         forward-socks4a, forward-socks5 and forward-socks5t</a></h4><a name=
1583         "FORWARD-SOCKS4" id="FORWARD-SOCKS4"></a><a name="FORWARD-SOCKS4A"
1584         id="FORWARD-SOCKS4A"></a>
1585         <div class="VARIABLELIST">
1586           <dl>
1587             <dt>Specifies:</dt>
1588             <dd>
1589               <p>Through which SOCKS proxy (and optionally to which parent
1590               HTTP proxy) specific requests should be routed.</p>
1591             </dd>
1592             <dt>Type of value:</dt>
1593             <dd>
1594               <p><tt class="REPLACEABLE"><i>target_pattern</i></tt>
1595               <tt class="REPLACEABLE"><i>socks_proxy</i></tt>[:<tt class=
1596               "REPLACEABLE"><i>port</i></tt>] <tt class=
1597               "REPLACEABLE"><i>http_parent</i></tt>[:<tt class=
1598               "REPLACEABLE"><i>port</i></tt>]</p>
1599               <p>where <tt class="REPLACEABLE"><i>target_pattern</i></tt> is
1600               a <a href="actions-file.html#AF-PATTERNS">URL pattern</a> that
1601               specifies to which requests (i.e. URLs) this forward rule shall
1602               apply. Use <tt class="LITERAL">/</tt> to denote <span class=
1603               "QUOTE">"all URLs"</span>. <tt class=
1604               "REPLACEABLE"><i>http_parent</i></tt> and <tt class=
1605               "REPLACEABLE"><i>socks_proxy</i></tt> are IP addresses in
1606               dotted decimal notation or valid DNS names (<tt class=
1607               "REPLACEABLE"><i>http_parent</i></tt> may be <span class=
1608               "QUOTE">"."</span> to denote <span class="QUOTE">"no HTTP
1609               forwarding"</span>), and the optional <tt class=
1610               "REPLACEABLE"><i>port</i></tt> parameters are TCP ports, i.e.
1611               integer values from 1 to 65535</p>
1612             </dd>
1613             <dt>Default value:</dt>
1614             <dd>
1615               <p><span class="emphasis"><i class=
1616               "EMPHASIS">Unset</i></span></p>
1617             </dd>
1618             <dt>Effect if unset:</dt>
1619             <dd>
1620               <p>Don't use SOCKS proxies.</p>
1621             </dd>
1622             <dt>Notes:</dt>
1623             <dd>
1624               <p>Multiple lines are OK, they are checked in sequence, and the
1625               last match wins.</p>
1626               <p>The difference between <tt class=
1627               "LITERAL">forward-socks4</tt> and <tt class=
1628               "LITERAL">forward-socks4a</tt> is that in the SOCKS 4A
1629               protocol, the DNS resolution of the target hostname happens on
1630               the SOCKS server, while in SOCKS 4 it happens locally.</p>
1631               <p>With <tt class="LITERAL">forward-socks5</tt> the DNS
1632               resolution will happen on the remote server as well.</p>
1633               <p><tt class="LITERAL">forward-socks5t</tt> works like vanilla
1634               <tt class="LITERAL">forward-socks5</tt> but lets <span class=
1635               "APPLICATION">Privoxy</span> additionally use Tor-specific
1636               SOCKS extensions. Currently the only supported SOCKS extension
1637               is optimistic data which can reduce the latency for the first
1638               request made on a newly created connection.</p>
1639               <p><tt class="REPLACEABLE"><i>socks_proxy</i></tt> and
1640               <tt class="REPLACEABLE"><i>http_parent</i></tt> can be a
1641               numerical IPv6 address (if <a href=
1642               "http://tools.ietf.org/html/rfc3493" target="_top">RFC 3493</a>
1643               is implemented). To prevent clashes with the port delimiter,
1644               the whole IP address has to be put into brackets. On the other
1645               hand a <tt class="REPLACEABLE"><i>target_pattern</i></tt>
1646               containing an IPv6 address has to be put into angle brackets
1647               (normal brackets are reserved for regular expressions
1648               already).</p>
1649               <p>If <tt class="REPLACEABLE"><i>http_parent</i></tt> is
1650               <span class="QUOTE">"."</span>, then requests are not forwarded
1651               to another HTTP proxy but are made (HTTP-wise) directly to the
1652               web servers, albeit through a SOCKS proxy.</p>
1653             </dd>
1654             <dt>Examples:</dt>
1655             <dd>
1656               <p>From the company example.com, direct connections are made to
1657               all <span class="QUOTE">"internal"</span> domains, but
1658               everything outbound goes through their ISP's proxy by way of
1659               example.com's corporate SOCKS 4A gateway to the Internet.</p>
1660               <table border="0" bgcolor="#E0E0E0" width="90%">
1661                 <tr>
1662                   <td>
1663                     <pre class="SCREEN">
1664                     forward-socks4a   /              socks-gw.example.com:1080  www-cache.isp.example.net:8080
1665   forward           .example.com   .</pre>
1666                   </td>
1667                 </tr>
1668               </table>
1669               <p>A rule that uses a SOCKS 4 gateway for all destinations but
1670               no HTTP parent looks like this:</p>
1671               <table border="0" bgcolor="#E0E0E0" width="90%">
1672                 <tr>
1673                   <td>
1674                     <pre class="SCREEN">
1675                     forward-socks4   /               socks-gw.example.com:1080  .</pre>
1676                   </td>
1677                 </tr>
1678               </table>
1679               <p>To chain Privoxy and Tor, both running on the same system,
1680               you would use something like:</p>
1681               <table border="0" bgcolor="#E0E0E0" width="90%">
1682                 <tr>
1683                   <td>
1684                     <pre class="SCREEN">
1685                     forward-socks5t   /               127.0.0.1:9050 .</pre>
1686                   </td>
1687                 </tr>
1688               </table>
1689               <p>Note that if you got Tor through one of the bundles, you may
1690               have to change the port from 9050 to 9150 (or even another
1691               one). For details, please check the documentation on the
1692               <a href="https://torproject.org/" target="_top">Tor
1693               website</a>.</p>
1694               <p>The public <span class="APPLICATION">Tor</span> network
1695               can't be used to reach your local network, if you need to
1696               access local servers you therefore might want to make some
1697               exceptions:</p>
1698               <table border="0" bgcolor="#E0E0E0" width="90%">
1699                 <tr>
1700                   <td>
1701                     <pre class="SCREEN">  forward         192.168.*.*/     .
1702   forward            10.*.*.*/     .
1703   forward           127.*.*.*/     .</pre>
1704                   </td>
1705                 </tr>
1706               </table>
1707               <p>Unencrypted connections to systems in these address ranges
1708               will be as (un)secure as the local network is, but the
1709               alternative is that you can't reach the local network through
1710               <span class="APPLICATION">Privoxy</span> at all. Of course this
1711               may actually be desired and there is no reason to make these
1712               exceptions if you aren't sure you need them.</p>
1713               <p>If you also want to be able to reach servers in your local
1714               network by using their names, you will need additional
1715               exceptions that look like this:</p>
1716               <table border="0" bgcolor="#E0E0E0" width="90%">
1717                 <tr>
1718                   <td>
1719                     <pre class="SCREEN">
1720                     forward           localhost/     .</pre>
1721                   </td>
1722                 </tr>
1723               </table>
1724             </dd>
1725           </dl>
1726         </div>
1727       </div>
1728       <div class="SECT3">
1729         <h4 class="SECT3"><a name="ADVANCED-FORWARDING-EXAMPLES" id=
1730         "ADVANCED-FORWARDING-EXAMPLES">7.5.3. Advanced Forwarding
1731         Examples</a></h4>
1732         <p>If you have links to multiple ISPs that provide various special
1733         content only to their subscribers, you can configure multiple
1734         <span class="APPLICATION">Privoxies</span> which have connections to
1735         the respective ISPs to act as forwarders to each other, so that
1736         <span class="emphasis"><i class="EMPHASIS">your</i></span> users can
1737         see the internal content of all ISPs.</p>
1738         <p>Assume that host-a has a PPP connection to isp-a.example.net. And
1739         host-b has a PPP connection to isp-b.example.org. Both run
1740         <span class="APPLICATION">Privoxy</span>. Their forwarding
1741         configuration can look like this:</p>
1742         <p>host-a:</p>
1743         <table border="0" bgcolor="#E0E0E0" width="100%">
1744           <tr>
1745             <td>
1746               <pre class="SCREEN">  forward    /           .
1747   forward    .isp-b.example.net  host-b:8118</pre>
1748             </td>
1749           </tr>
1750         </table>
1751         <p>host-b:</p>
1752         <table border="0" bgcolor="#E0E0E0" width="100%">
1753           <tr>
1754             <td>
1755               <pre class="SCREEN">  forward    /           .
1756   forward    .isp-a.example.org  host-a:8118</pre>
1757             </td>
1758           </tr>
1759         </table>
1760         <p>Now, your users can set their browser's proxy to use either host-a
1761         or host-b and be able to browse the internal content of both isp-a
1762         and isp-b.</p>
1763         <p>If you intend to chain <span class="APPLICATION">Privoxy</span>
1764         and <span class="APPLICATION">squid</span> locally, then chaining as
1765         <tt class="LITERAL">browser -&gt; squid -&gt; privoxy</tt> is the
1766         recommended way.</p>
1767         <p>Assuming that <span class="APPLICATION">Privoxy</span> and
1768         <span class="APPLICATION">squid</span> run on the same box, your
1769         <span class="APPLICATION">squid</span> configuration could then look
1770         like this:</p>
1771         <table border="0" bgcolor="#E0E0E0" width="100%">
1772           <tr>
1773             <td>
1774               <pre class="SCREEN">
1775               # Define Privoxy as parent proxy (without ICP)
1776   cache_peer 127.0.0.1 parent 8118 7 no-query
1777
1778   # Define ACL for protocol FTP
1779   acl ftp proto FTP
1780
1781   # Do not forward FTP requests to Privoxy
1782   always_direct allow ftp
1783
1784   # Forward all the rest to Privoxy
1785   never_direct allow all</pre>
1786             </td>
1787           </tr>
1788         </table>
1789         <p>You would then need to change your browser's proxy settings to
1790         <span class="APPLICATION">squid</span>'s address and port. Squid
1791         normally uses port 3128. If unsure consult <tt class=
1792         "LITERAL">http_port</tt> in <tt class="FILENAME">squid.conf</tt>.</p>
1793         <p>You could just as well decide to only forward requests you suspect
1794         of leading to Windows executables through a virus-scanning parent
1795         proxy, say, on <tt class="LITERAL">antivir.example.com</tt>, port
1796         8010:</p>
1797         <table border="0" bgcolor="#E0E0E0" width="100%">
1798           <tr>
1799             <td>
1800               <pre class="SCREEN">  forward   /                          .
1801   forward   /.*\.(exe|com|dll|zip)$    antivir.example.com:8010</pre>
1802             </td>
1803           </tr>
1804         </table>
1805       </div>
1806       <div class="SECT3">
1807         <h4 class="SECT3"><a name="FORWARDED-CONNECT-RETRIES" id=
1808         "FORWARDED-CONNECT-RETRIES">7.5.4. forwarded-connect-retries</a></h4>
1809         <div class="VARIABLELIST">
1810           <dl>
1811             <dt>Specifies:</dt>
1812             <dd>
1813               <p>How often Privoxy retries if a forwarded connection request
1814               fails.</p>
1815             </dd>
1816             <dt>Type of value:</dt>
1817             <dd>
1818               <p><tt class="REPLACEABLE"><i>Number of retries.</i></tt></p>
1819             </dd>
1820             <dt>Default value:</dt>
1821             <dd>
1822               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
1823             </dd>
1824             <dt>Effect if unset:</dt>
1825             <dd>
1826               <p>Connections forwarded through other proxies are treated like
1827               direct connections and no retry attempts are made.</p>
1828             </dd>
1829             <dt>Notes:</dt>
1830             <dd>
1831               <p><tt class=
1832               "REPLACEABLE"><i>forwarded-connect-retries</i></tt> is mainly
1833               interesting for socks4a connections, where <span class=
1834               "APPLICATION">Privoxy</span> can't detect why the connections
1835               failed. The connection might have failed because of a DNS
1836               timeout in which case a retry makes sense, but it might also
1837               have failed because the server doesn't exist or isn't
1838               reachable. In this case the retry will just delay the
1839               appearance of Privoxy's error message.</p>
1840               <p>Note that in the context of this option, <span class=
1841               "QUOTE">"forwarded connections"</span> includes all connections
1842               that Privoxy forwards through other proxies. This option is not
1843               limited to the HTTP CONNECT method.</p>
1844               <p>Only use this option, if you are getting lots of
1845               forwarding-related error messages that go away when you try
1846               again manually. Start with a small value and check Privoxy's
1847               logfile from time to time, to see how many retries are usually
1848               needed.</p>
1849             </dd>
1850             <dt>Examples:</dt>
1851             <dd>
1852               <p>forwarded-connect-retries 1</p>
1853             </dd>
1854           </dl>
1855         </div>
1856       </div>
1857     </div>
1858     <div class="SECT2">
1859       <h2 class="SECT2"><a name="MISC" id="MISC">7.6. Miscellaneous</a></h2>
1860       <div class="SECT3">
1861         <h4 class="SECT3"><a name="ACCEPT-INTERCEPTED-REQUESTS" id=
1862         "ACCEPT-INTERCEPTED-REQUESTS">7.6.1.
1863         accept-intercepted-requests</a></h4>
1864         <div class="VARIABLELIST">
1865           <dl>
1866             <dt>Specifies:</dt>
1867             <dd>
1868               <p>Whether intercepted requests should be treated as valid.</p>
1869             </dd>
1870             <dt>Type of value:</dt>
1871             <dd>
1872               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
1873             </dd>
1874             <dt>Default value:</dt>
1875             <dd>
1876               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
1877             </dd>
1878             <dt>Effect if unset:</dt>
1879             <dd>
1880               <p>Only proxy requests are accepted, intercepted requests are
1881               treated as invalid.</p>
1882             </dd>
1883             <dt>Notes:</dt>
1884             <dd>
1885               <p>If you don't trust your clients and want to force them to
1886               use <span class="APPLICATION">Privoxy</span>, enable this
1887               option and configure your packet filter to redirect outgoing
1888               HTTP connections into <span class=
1889               "APPLICATION">Privoxy</span>.</p>
1890               <p>Note that intercepting encrypted connections (HTTPS) isn't
1891               supported.</p>
1892               <p>Make sure that <span class="APPLICATION">Privoxy's</span>
1893               own requests aren't redirected as well. Additionally take care
1894               that <span class="APPLICATION">Privoxy</span> can't
1895               intentionally connect to itself, otherwise you could run into
1896               redirection loops if <span class="APPLICATION">Privoxy's</span>
1897               listening port is reachable by the outside or an attacker has
1898               access to the pages you visit.</p>
1899               <p>If you are running Privoxy as intercepting proxy without
1900               being able to intercept all client requests you may want to
1901               adjust the CGI templates to make sure they don't reference
1902               content from config.privoxy.org.</p>
1903             </dd>
1904             <dt>Examples:</dt>
1905             <dd>
1906               <p>accept-intercepted-requests 1</p>
1907             </dd>
1908           </dl>
1909         </div>
1910       </div>
1911       <div class="SECT3">
1912         <h4 class="SECT3"><a name="ALLOW-CGI-REQUEST-CRUNCHING" id=
1913         "ALLOW-CGI-REQUEST-CRUNCHING">7.6.2.
1914         allow-cgi-request-crunching</a></h4>
1915         <div class="VARIABLELIST">
1916           <dl>
1917             <dt>Specifies:</dt>
1918             <dd>
1919               <p>Whether requests to <span class=
1920               "APPLICATION">Privoxy's</span> CGI pages can be blocked or
1921               redirected.</p>
1922             </dd>
1923             <dt>Type of value:</dt>
1924             <dd>
1925               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
1926             </dd>
1927             <dt>Default value:</dt>
1928             <dd>
1929               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
1930             </dd>
1931             <dt>Effect if unset:</dt>
1932             <dd>
1933               <p><span class="APPLICATION">Privoxy</span> ignores block and
1934               redirect actions for its CGI pages.</p>
1935             </dd>
1936             <dt>Notes:</dt>
1937             <dd>
1938               <p>By default <span class="APPLICATION">Privoxy</span> ignores
1939               block or redirect actions for its CGI pages. Intercepting these
1940               requests can be useful in multi-user setups to implement
1941               fine-grained access control, but it can also render the
1942               complete web interface useless and make debugging problems
1943               painful if done without care.</p>
1944               <p>Don't enable this option unless you're sure that you really
1945               need it.</p>
1946             </dd>
1947             <dt>Examples:</dt>
1948             <dd>
1949               <p>allow-cgi-request-crunching 1</p>
1950             </dd>
1951           </dl>
1952         </div>
1953       </div>
1954       <div class="SECT3">
1955         <h4 class="SECT3"><a name="SPLIT-LARGE-FORMS" id=
1956         "SPLIT-LARGE-FORMS">7.6.3. split-large-forms</a></h4>
1957         <div class="VARIABLELIST">
1958           <dl>
1959             <dt>Specifies:</dt>
1960             <dd>
1961               <p>Whether the CGI interface should stay compatible with broken
1962               HTTP clients.</p>
1963             </dd>
1964             <dt>Type of value:</dt>
1965             <dd>
1966               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
1967             </dd>
1968             <dt>Default value:</dt>
1969             <dd>
1970               <p><span class="emphasis"><i class="EMPHASIS">0</i></span></p>
1971             </dd>
1972             <dt>Effect if unset:</dt>
1973             <dd>
1974               <p>The CGI form generate long GET URLs.</p>
1975             </dd>
1976             <dt>Notes:</dt>
1977             <dd>
1978               <p><span class="APPLICATION">Privoxy's</span> CGI forms can
1979               lead to rather long URLs. This isn't a problem as far as the
1980               HTTP standard is concerned, but it can confuse clients with
1981               arbitrary URL length limitations.</p>
1982               <p>Enabling split-large-forms causes <span class=
1983               "APPLICATION">Privoxy</span> to divide big forms into smaller
1984               ones to keep the URL length down. It makes editing a lot less
1985               convenient and you can no longer submit all changes at once,
1986               but at least it works around this browser bug.</p>
1987               <p>If you don't notice any editing problems, there is no reason
1988               to enable this option, but if one of the submit buttons appears
1989               to be broken, you should give it a try.</p>
1990             </dd>
1991             <dt>Examples:</dt>
1992             <dd>
1993               <p>split-large-forms 1</p>
1994             </dd>
1995           </dl>
1996         </div>
1997       </div>
1998       <div class="SECT3">
1999         <h4 class="SECT3"><a name="KEEP-ALIVE-TIMEOUT" id=
2000         "KEEP-ALIVE-TIMEOUT">7.6.4. keep-alive-timeout</a></h4>
2001         <div class="VARIABLELIST">
2002           <dl>
2003             <dt>Specifies:</dt>
2004             <dd>
2005               <p>Number of seconds after which an open connection will no
2006               longer be reused.</p>
2007             </dd>
2008             <dt>Type of value:</dt>
2009             <dd>
2010               <p><tt class="REPLACEABLE"><i>Time in seconds.</i></tt></p>
2011             </dd>
2012             <dt>Default value:</dt>
2013             <dd>
2014               <p>None</p>
2015             </dd>
2016             <dt>Effect if unset:</dt>
2017             <dd>
2018               <p>Connections are not kept alive.</p>
2019             </dd>
2020             <dt>Notes:</dt>
2021             <dd>
2022               <p>This option allows clients to keep the connection to
2023               <span class="APPLICATION">Privoxy</span> alive. If the server
2024               supports it, <span class="APPLICATION">Privoxy</span> will keep
2025               the connection to the server alive as well. Under certain
2026               circumstances this may result in speed-ups.</p>
2027               <p>By default, <span class="APPLICATION">Privoxy</span> will
2028               close the connection to the server if the client connection
2029               gets closed, or if the specified timeout has been reached
2030               without a new request coming in. This behaviour can be changed
2031               with the <a href="#CONNECTION-SHARING" target=
2032               "_top">connection-sharing</a> option.</p>
2033               <p>This option has no effect if <span class=
2034               "APPLICATION">Privoxy</span> has been compiled without
2035               keep-alive support.</p>
2036               <p>Note that a timeout of five seconds as used in the default
2037               configuration file significantly decreases the number of
2038               connections that will be reused. The value is used because some
2039               browsers limit the number of connections they open to a single
2040               host and apply the same limit to proxies. This can result in a
2041               single website <span class="QUOTE">"grabbing"</span> all the
2042               connections the browser allows, which means connections to
2043               other websites can't be opened until the connections currently
2044               in use time out.</p>
2045               <p>Several users have reported this as a Privoxy bug, so the
2046               default value has been reduced. Consider increasing it to 300
2047               seconds or even more if you think your browser can handle it.
2048               If your browser appears to be hanging, it probably can't.</p>
2049             </dd>
2050             <dt>Examples:</dt>
2051             <dd>
2052               <p>keep-alive-timeout 300</p>
2053             </dd>
2054           </dl>
2055         </div>
2056       </div>
2057       <div class="SECT3">
2058         <h4 class="SECT3"><a name="TOLERATE-PIPELINING" id=
2059         "TOLERATE-PIPELINING">7.6.5. tolerate-pipelining</a></h4>
2060         <div class="VARIABLELIST">
2061           <dl>
2062             <dt>Specifies:</dt>
2063             <dd>
2064               <p>Whether or not pipelined requests should be served.</p>
2065             </dd>
2066             <dt>Type of value:</dt>
2067             <dd>
2068               <p><tt class="REPLACEABLE"><i>0 or 1.</i></tt></p>
2069             </dd>
2070             <dt>Default value:</dt>
2071             <dd>
2072               <p>None</p>
2073             </dd>
2074             <dt>Effect if unset:</dt>
2075             <dd>
2076               <p>If Privoxy receives more than one request at once, it
2077               terminates the client connection after serving the first
2078               one.</p>
2079             </dd>
2080             <dt>Notes:</dt>
2081             <dd>
2082               <p><span class="APPLICATION">Privoxy</span> currently doesn't
2083               pipeline outgoing requests, thus allowing pipelining on the
2084               client connection is not guaranteed to improve the
2085               performance.</p>
2086               <p>By default <span class="APPLICATION">Privoxy</span> tries to
2087               discourage clients from pipelining by discarding aggressively
2088               pipelined requests, which forces the client to resend them
2089               through a new connection.</p>
2090               <p>This option lets <span class="APPLICATION">Privoxy</span>
2091               tolerate pipelining. Whether or not that improves performance
2092               mainly depends on the client configuration.</p>
2093               <p>If you are seeing problems with pages not properly loading,
2094               disabling this option could work around the problem.</p>
2095             </dd>
2096             <dt>Examples:</dt>
2097             <dd>
2098               <p>tolerate-pipelining 1</p>
2099             </dd>
2100           </dl>
2101         </div>
2102       </div>
2103       <div class="SECT3">
2104         <h4 class="SECT3"><a name="DEFAULT-SERVER-TIMEOUT" id=
2105         "DEFAULT-SERVER-TIMEOUT">7.6.6. default-server-timeout</a></h4>
2106         <div class="VARIABLELIST">
2107           <dl>
2108             <dt>Specifies:</dt>
2109             <dd>
2110               <p>Assumed server-side keep-alive timeout if not specified by
2111               the server.</p>
2112             </dd>
2113             <dt>Type of value:</dt>
2114             <dd>
2115               <p><tt class="REPLACEABLE"><i>Time in seconds.</i></tt></p>
2116             </dd>
2117             <dt>Default value:</dt>
2118             <dd>
2119               <p>None</p>
2120             </dd>
2121             <dt>Effect if unset:</dt>
2122             <dd>
2123               <p>Connections for which the server didn't specify the
2124               keep-alive timeout are not reused.</p>
2125             </dd>
2126             <dt>Notes:</dt>
2127             <dd>
2128               <p>Enabling this option significantly increases the number of
2129               connections that are reused, provided the <a href=
2130               "#KEEP-ALIVE-TIMEOUT" target="_top">keep-alive-timeout</a>
2131               option is also enabled.</p>
2132               <p>While it also increases the number of connections problems
2133               when <span class="APPLICATION">Privoxy</span> tries to reuse a
2134               connection that already has been closed on the server side, or
2135               is closed while <span class="APPLICATION">Privoxy</span> is
2136               trying to reuse it, this should only be a problem if it happens
2137               for the first request sent by the client. If it happens for
2138               requests on reused client connections, <span class=
2139               "APPLICATION">Privoxy</span> will simply close the connection
2140               and the client is supposed to retry the request without
2141               bothering the user.</p>
2142               <p>Enabling this option is therefore only recommended if the
2143               <a href="#CONNECTION-SHARING" target=
2144               "_top">connection-sharing</a> option is disabled.</p>
2145               <p>It is an error to specify a value larger than the <a href=
2146               "#KEEP-ALIVE-TIMEOUT" target="_top">keep-alive-timeout</a>
2147               value.</p>
2148               <p>This option has no effect if <span class=
2149               "APPLICATION">Privoxy</span> has been compiled without
2150               keep-alive support.</p>
2151             </dd>
2152             <dt>Examples:</dt>
2153             <dd>
2154               <p>default-server-timeout 60</p>
2155             </dd>
2156           </dl>
2157         </div>
2158       </div>
2159       <div class="SECT3">
2160         <h4 class="SECT3"><a name="CONNECTION-SHARING" id=
2161         "CONNECTION-SHARING">7.6.7. connection-sharing</a></h4>
2162         <div class="VARIABLELIST">
2163           <dl>
2164             <dt>Specifies:</dt>
2165             <dd>
2166               <p>Whether or not outgoing connections that have been kept
2167               alive should be shared between different incoming
2168               connections.</p>
2169             </dd>
2170             <dt>Type of value:</dt>
2171             <dd>
2172               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
2173             </dd>
2174             <dt>Default value:</dt>
2175             <dd>
2176               <p>None</p>
2177             </dd>
2178             <dt>Effect if unset:</dt>
2179             <dd>
2180               <p>Connections are not shared.</p>
2181             </dd>
2182             <dt>Notes:</dt>
2183             <dd>
2184               <p>This option has no effect if <span class=
2185               "APPLICATION">Privoxy</span> has been compiled without
2186               keep-alive support, or if it's disabled.</p>
2187             </dd>
2188             <dt>Notes:</dt>
2189             <dd>
2190               <p>Note that reusing connections doesn't necessary cause
2191               speedups. There are also a few privacy implications you should
2192               be aware of.</p>
2193               <p>If this option is effective, outgoing connections are shared
2194               between clients (if there are more than one) and closing the
2195               browser that initiated the outgoing connection does no longer
2196               affect the connection between <span class=
2197               "APPLICATION">Privoxy</span> and the server unless the client's
2198               request hasn't been completed yet.</p>
2199               <p>If the outgoing connection is idle, it will not be closed
2200               until either <span class="APPLICATION">Privoxy's</span> or the
2201               server's timeout is reached. While it's open, the server knows
2202               that the system running <span class=
2203               "APPLICATION">Privoxy</span> is still there.</p>
2204               <p>If there are more than one client (maybe even belonging to
2205               multiple users), they will be able to reuse each others
2206               connections. This is potentially dangerous in case of
2207               authentication schemes like NTLM where only the connection is
2208               authenticated, instead of requiring authentication for each
2209               request.</p>
2210               <p>If there is only a single client, and if said client can
2211               keep connections alive on its own, enabling this option has
2212               next to no effect. If the client doesn't support connection
2213               keep-alive, enabling this option may make sense as it allows
2214               <span class="APPLICATION">Privoxy</span> to keep outgoing
2215               connections alive even if the client itself doesn't support
2216               it.</p>
2217               <p>You should also be aware that enabling this option increases
2218               the likelihood of getting the "No server or forwarder data"
2219               error message, especially if you are using a slow connection to
2220               the Internet.</p>
2221               <p>This option should only be used by experienced users who
2222               understand the risks and can weight them against the
2223               benefits.</p>
2224             </dd>
2225             <dt>Examples:</dt>
2226             <dd>
2227               <p>connection-sharing 1</p>
2228             </dd>
2229           </dl>
2230         </div>
2231       </div>
2232       <div class="SECT3">
2233         <h4 class="SECT3"><a name="SOCKET-TIMEOUT" id="SOCKET-TIMEOUT">7.6.8.
2234         socket-timeout</a></h4>
2235         <div class="VARIABLELIST">
2236           <dl>
2237             <dt>Specifies:</dt>
2238             <dd>
2239               <p>Number of seconds after which a socket times out if no data
2240               is received.</p>
2241             </dd>
2242             <dt>Type of value:</dt>
2243             <dd>
2244               <p><tt class="REPLACEABLE"><i>Time in seconds.</i></tt></p>
2245             </dd>
2246             <dt>Default value:</dt>
2247             <dd>
2248               <p>None</p>
2249             </dd>
2250             <dt>Effect if unset:</dt>
2251             <dd>
2252               <p>A default value of 300 seconds is used.</p>
2253             </dd>
2254             <dt>Notes:</dt>
2255             <dd>
2256               <p>The default is quite high and you probably want to reduce
2257               it. If you aren't using an occasionally slow proxy like Tor,
2258               reducing it to a few seconds should be fine.</p>
2259             </dd>
2260             <dt>Examples:</dt>
2261             <dd>
2262               <p>socket-timeout 300</p>
2263             </dd>
2264           </dl>
2265         </div>
2266       </div>
2267       <div class="SECT3">
2268         <h4 class="SECT3"><a name="MAX-CLIENT-CONNECTIONS" id=
2269         "MAX-CLIENT-CONNECTIONS">7.6.9. max-client-connections</a></h4>
2270         <div class="VARIABLELIST">
2271           <dl>
2272             <dt>Specifies:</dt>
2273             <dd>
2274               <p>Maximum number of client connections that will be
2275               served.</p>
2276             </dd>
2277             <dt>Type of value:</dt>
2278             <dd>
2279               <p><tt class="REPLACEABLE"><i>Positive number.</i></tt></p>
2280             </dd>
2281             <dt>Default value:</dt>
2282             <dd>
2283               <p>128</p>
2284             </dd>
2285             <dt>Effect if unset:</dt>
2286             <dd>
2287               <p>Connections are served until a resource limit is
2288               reached.</p>
2289             </dd>
2290             <dt>Notes:</dt>
2291             <dd>
2292               <p><span class="APPLICATION">Privoxy</span> creates one thread
2293               (or process) for every incoming client connection that isn't
2294               rejected based on the access control settings.</p>
2295               <p>If the system is powerful enough, <span class=
2296               "APPLICATION">Privoxy</span> can theoretically deal with
2297               several hundred (or thousand) connections at the same time, but
2298               some operating systems enforce resource limits by shutting down
2299               offending processes and their default limits may be below the
2300               ones <span class="APPLICATION">Privoxy</span> would require
2301               under heavy load.</p>
2302               <p>Configuring <span class="APPLICATION">Privoxy</span> to
2303               enforce a connection limit below the thread or process limit
2304               used by the operating system makes sure this doesn't happen.
2305               Simply increasing the operating system's limit would work too,
2306               but if <span class="APPLICATION">Privoxy</span> isn't the only
2307               application running on the system, you may actually want to
2308               limit the resources used by <span class=
2309               "APPLICATION">Privoxy</span>.</p>
2310               <p>If <span class="APPLICATION">Privoxy</span> is only used by
2311               a single trusted user, limiting the number of client
2312               connections is probably unnecessary. If there are multiple
2313               possibly untrusted users you probably still want to
2314               additionally use a packet filter to limit the maximal number of
2315               incoming connections per client. Otherwise a malicious user
2316               could intentionally create a high number of connections to
2317               prevent other users from using <span class=
2318               "APPLICATION">Privoxy</span>.</p>
2319               <p>Obviously using this option only makes sense if you choose a
2320               limit below the one enforced by the operating system.</p>
2321               <p>One most POSIX-compliant systems <span class=
2322               "APPLICATION">Privoxy</span> can't properly deal with more than
2323               FD_SETSIZE file descriptors at the same time and has to reject
2324               connections if the limit is reached. This will likely change in
2325               a future version, but currently this limit can't be increased
2326               without recompiling <span class="APPLICATION">Privoxy</span>
2327               with a different FD_SETSIZE limit.</p>
2328             </dd>
2329             <dt>Examples:</dt>
2330             <dd>
2331               <p>max-client-connections 256</p>
2332             </dd>
2333           </dl>
2334         </div>
2335       </div>
2336       <div class="SECT3">
2337         <h4 class="SECT3"><a name="LISTEN-BACKLOG" id=
2338         "LISTEN-BACKLOG">7.6.10. listen-backlog</a></h4>
2339         <div class="VARIABLELIST">
2340           <dl>
2341             <dt>Specifies:</dt>
2342             <dd>
2343               <p>Connection queue length requested from the operating
2344               system.</p>
2345             </dd>
2346             <dt>Type of value:</dt>
2347             <dd>
2348               <p><tt class="REPLACEABLE"><i>Number.</i></tt></p>
2349             </dd>
2350             <dt>Default value:</dt>
2351             <dd>
2352               <p>128</p>
2353             </dd>
2354             <dt>Effect if unset:</dt>
2355             <dd>
2356               <p>A connection queue length of 128 is requested from the
2357               operating system.</p>
2358             </dd>
2359             <dt>Notes:</dt>
2360             <dd>
2361               <p>Under high load incoming connection may queue up before
2362               Privoxy gets around to serve them. The queue length is limitted
2363               by the operating system. Once the queue is full, additional
2364               connections are dropped before Privoxy can accept and serve
2365               them.</p>
2366               <p>Increasing the queue length allows Privoxy to accept more
2367               incomming connections that arrive roughly at the same time.</p>
2368               <p>Note that Privoxy can only request a certain queue length,
2369               whether or not the requested length is actually used depends on
2370               the operating system which may use a different length
2371               instead.</p>
2372               <p>On many operating systems a limit of -1 can be specified to
2373               instruct the operating system to use the maximum queue length
2374               allowed. Check the listen man page to see if your platform
2375               allows this.</p>
2376               <p>On some platforms you can use "netstat -Lan -p tcp" to see
2377               the effective queue length.</p>
2378               <p>Effectively using a value above 128 usually requires
2379               changing the system configuration as well. On FreeBSD-based
2380               system the limit is controlled by the kern.ipc.soacceptqueue
2381               sysctl.</p>
2382             </dd>
2383             <dt>Examples:</dt>
2384             <dd>
2385               <p>listen-backlog 4096</p>
2386             </dd>
2387           </dl>
2388         </div>
2389       </div>
2390       <div class="SECT3">
2391         <h4 class="SECT3"><a name="HANDLE-AS-EMPTY-DOC-RETURNS-OK" id=
2392         "HANDLE-AS-EMPTY-DOC-RETURNS-OK">7.6.11.
2393         handle-as-empty-doc-returns-ok</a></h4>
2394         <div class="VARIABLELIST">
2395           <dl>
2396             <dt>Specifies:</dt>
2397             <dd>
2398               <p>The status code Privoxy returns for pages blocked with
2399               <tt class="LITERAL"><a href=
2400               "actions-file.html#HANDLE-AS-EMPTY-DOCUMENT" target=
2401               "_top">+handle-as-empty-document</a></tt>.</p>
2402             </dd>
2403             <dt>Type of value:</dt>
2404             <dd>
2405               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
2406             </dd>
2407             <dt>Default value:</dt>
2408             <dd>
2409               <p>0</p>
2410             </dd>
2411             <dt>Effect if unset:</dt>
2412             <dd>
2413               <p>Privoxy returns a status 403(forbidden) for all blocked
2414               pages.</p>
2415             </dd>
2416             <dt>Effect if set:</dt>
2417             <dd>
2418               <p>Privoxy returns a status 200(OK) for pages blocked with
2419               +handle-as-empty-document and a status 403(Forbidden) for all
2420               other blocked pages.</p>
2421             </dd>
2422             <dt>Notes:</dt>
2423             <dd>
2424               <p>This directive was added as a work-around for Firefox bug
2425               492459: <span class="QUOTE">"Websites are no longer rendered if
2426               SSL requests for JavaScripts are blocked by a proxy."</span>
2427               (<a href="https://bugzilla.mozilla.org/show_bug.cgi?id=492459"
2428               target=
2429               "_top">https://bugzilla.mozilla.org/show_bug.cgi?id=492459</a>),
2430               the bug has been fixed for quite some time, but this directive
2431               is also useful to make it harder for websites to detect whether
2432               or not resources are being blocked.</p>
2433             </dd>
2434           </dl>
2435         </div>
2436       </div>
2437       <div class="SECT3">
2438         <h4 class="SECT3"><a name="ENABLE-COMPRESSION" id=
2439         "ENABLE-COMPRESSION">7.6.12. enable-compression</a></h4>
2440         <div class="VARIABLELIST">
2441           <dl>
2442             <dt>Specifies:</dt>
2443             <dd>
2444               <p>Whether or not buffered content is compressed before
2445               delivery.</p>
2446             </dd>
2447             <dt>Type of value:</dt>
2448             <dd>
2449               <p><tt class="REPLACEABLE"><i>0 or 1</i></tt></p>
2450             </dd>
2451             <dt>Default value:</dt>
2452             <dd>
2453               <p>0</p>
2454             </dd>
2455             <dt>Effect if unset:</dt>
2456             <dd>
2457               <p>Privoxy does not compress buffered content.</p>
2458             </dd>
2459             <dt>Effect if set:</dt>
2460             <dd>
2461               <p>Privoxy compresses buffered content before delivering it to
2462               the client, provided the client supports it.</p>
2463             </dd>
2464             <dt>Notes:</dt>
2465             <dd>
2466               <p>This directive is only supported if Privoxy has been
2467               compiled with FEATURE_COMPRESSION, which should not to be
2468               confused with FEATURE_ZLIB.</p>
2469               <p>Compressing buffered content is mainly useful if Privoxy and
2470               the client are running on different systems. If they are
2471               running on the same system, enabling compression is likely to
2472               slow things down. If you didn't measure otherwise, you should
2473               assume that it does and keep this option disabled.</p>
2474               <p>Privoxy will not compress buffered content below a certain
2475               length.</p>
2476             </dd>
2477           </dl>
2478         </div>
2479       </div>
2480       <div class="SECT3">
2481         <h4 class="SECT3"><a name="COMPRESSION-LEVEL" id=
2482         "COMPRESSION-LEVEL">7.6.13. compression-level</a></h4>
2483         <div class="VARIABLELIST">
2484           <dl>
2485             <dt>Specifies:</dt>
2486             <dd>
2487               <p>The compression level that is passed to the zlib library
2488               when compressing buffered content.</p>
2489             </dd>
2490             <dt>Type of value:</dt>
2491             <dd>
2492               <p><tt class="REPLACEABLE"><i>Positive number ranging from 0 to
2493               9.</i></tt></p>
2494             </dd>
2495             <dt>Default value:</dt>
2496             <dd>
2497               <p>1</p>
2498             </dd>
2499             <dt>Notes:</dt>
2500             <dd>
2501               <p>Compressing the data more takes usually longer than
2502               compressing it less or not compressing it at all. Which level
2503               is best depends on the connection between Privoxy and the
2504               client. If you can't be bothered to benchmark it for yourself,
2505               you should stick with the default and keep compression
2506               disabled.</p>
2507               <p>If compression is disabled, the compression level is
2508               irrelevant.</p>
2509             </dd>
2510             <dt>Examples:</dt>
2511             <dd>
2512               <table border="0" bgcolor="#E0E0E0" width="90%">
2513                 <tr>
2514                   <td>
2515                     <pre class="SCREEN">
2516                     # Best speed (compared to the other levels)
2517     compression-level 1
2518     # Best compression
2519     compression-level 9
2520     # No compression. Only useful for testing as the added header
2521     # slightly increases the amount of data that has to be sent.
2522     # If your benchmark shows that using this compression level
2523     # is superior to using no compression at all, the benchmark
2524     # is likely to be flawed.
2525     compression-level 0
2526     </pre>
2527                   </td>
2528                 </tr>
2529               </table>
2530             </dd>
2531           </dl>
2532         </div>
2533       </div>
2534       <div class="SECT3">
2535         <h4 class="SECT3"><a name="CLIENT-HEADER-ORDER" id=
2536         "CLIENT-HEADER-ORDER">7.6.14. client-header-order</a></h4>
2537         <div class="VARIABLELIST">
2538           <dl>
2539             <dt>Specifies:</dt>
2540             <dd>
2541               <p>The order in which client headers are sorted before
2542               forwarding them.</p>
2543             </dd>
2544             <dt>Type of value:</dt>
2545             <dd>
2546               <p><tt class="REPLACEABLE"><i>Client header names delimited by
2547               spaces or tabs</i></tt></p>
2548             </dd>
2549             <dt>Default value:</dt>
2550             <dd>
2551               <p>None</p>
2552             </dd>
2553             <dt>Notes:</dt>
2554             <dd>
2555               <p>By default <span class="APPLICATION">Privoxy</span> leaves
2556               the client headers in the order they were sent by the client.
2557               Headers are modified in-place, new headers are added at the end
2558               of the already existing headers.</p>
2559               <p>The header order can be used to fingerprint client requests
2560               independently of other headers like the User-Agent.</p>
2561               <p>This directive allows to sort the headers differently to
2562               better mimic a different User-Agent. Client headers will be
2563               emitted in the order given, headers whose name isn't explicitly
2564               specified are added at the end.</p>
2565               <p>Note that sorting headers in an uncommon way will make
2566               fingerprinting actually easier. Encrypted headers are not
2567               affected by this directive.</p>
2568             </dd>
2569           </dl>
2570         </div>
2571       </div>
2572       <div class="SECT3">
2573         <h4 class="SECT3"><a name="CLIENT-SPECIFIC-TAG" id=
2574         "CLIENT-SPECIFIC-TAG">7.6.15. client-specific-tag</a></h4>
2575         <div class="VARIABLELIST">
2576           <dl>
2577             <dt>Specifies:</dt>
2578             <dd>
2579               <p>The name of a tag that will always be set for clients that
2580               requested it through the webinterface.</p>
2581             </dd>
2582             <dt>Type of value:</dt>
2583             <dd>
2584               <p><tt class="REPLACEABLE"><i>Tag name followed by a
2585               description that will be shown in the webinterface</i></tt></p>
2586             </dd>
2587             <dt>Default value:</dt>
2588             <dd>
2589               <p>None</p>
2590             </dd>
2591             <dt>Notes:</dt>
2592             <dd>
2593               <div class="WARNING">
2594                 <table class="WARNING" border="1" width="90%">
2595                   <tr>
2596                     <td align="center"><b>Warning</b></td>
2597                   </tr>
2598                   <tr>
2599                     <td align="left">
2600                       <p>This is an experimental feature. The syntax is
2601                       likely to change in future versions.</p>
2602                     </td>
2603                   </tr>
2604                 </table>
2605               </div>
2606               <p>Client-specific tags allow Privoxy admins to create
2607               different profiles and let the users chose which one they want
2608               without impacting other users.</p>
2609               <p>One use case is allowing users to circumvent certain blocks
2610               without having to allow them to circumvent all blocks. This is
2611               not possible with the <a href=
2612               "config.html#ENABLE-REMOTE-TOGGLE">enable-remote-toggle
2613               feature</a> because it would bluntly disable all blocks for all
2614               users and also affect other actions like filters. It also is
2615               set globally which renders it useless in most multi-user
2616               setups.</p>
2617               <p>After a client-specific tag has been defined with the
2618               client-specific-tag directive, action sections can be activated
2619               based on the tag by using a <a href=
2620               "actions-file.html#CLIENT-TAG-PATTERN" target=
2621               "_top">CLIENT-TAG</a> pattern. The CLIENT-TAG pattern is
2622               evaluated at the same priority as URL patterns, as a result the
2623               last matching pattern wins. Tags that are created based on
2624               client or server headers are evaluated later on and can
2625               overrule CLIENT-TAG and URL patterns!</p>
2626               <p>The tag is set for all requests that come from clients that
2627               requested it to be set. Note that "clients" are differentiated
2628               by IP address, if the IP address changes the tag has to be
2629               requested again.</p>
2630               <p>Clients can request tags to be set by using the CGI
2631               interface <a href="http://config.privoxy.org/client-tags"
2632               target="_top">http://config.privoxy.org/client-tags</a>. The
2633               specific tag description is only used on the web page and
2634               should be phrased in away that the user understand the effect
2635               of the tag.</p>
2636             </dd>
2637             <dt>Examples:</dt>
2638             <dd>
2639               <table border="0" bgcolor="#E0E0E0" width="90%">
2640                 <tr>
2641                   <td>
2642                     <pre class="SCREEN">
2643                     # Define a couple of tags, the described effect requires action sections
2644     # that are enabled based on CLIENT-TAG patterns.
2645     client-specific-tag circumvent-blocks Overrule blocks but do not affect other actions
2646     disable-content-filters Disable content-filters but do not affect other actions
2647     </pre>
2648                   </td>
2649                 </tr>
2650               </table>
2651             </dd>
2652           </dl>
2653         </div>
2654       </div>
2655       <div class="SECT3">
2656         <h4 class="SECT3"><a name="CLIENT-TAG-LIFETIME" id=
2657         "CLIENT-TAG-LIFETIME">7.6.16. client-tag-lifetime</a></h4>
2658         <div class="VARIABLELIST">
2659           <dl>
2660             <dt>Specifies:</dt>
2661             <dd>
2662               <p>How long a temporarily enabled tag remains enabled.</p>
2663             </dd>
2664             <dt>Type of value:</dt>
2665             <dd>
2666               <p><tt class="REPLACEABLE"><i>Time in seconds.</i></tt></p>
2667             </dd>
2668             <dt>Default value:</dt>
2669             <dd>
2670               <p>60</p>
2671             </dd>
2672             <dt>Notes:</dt>
2673             <dd>
2674               <div class="WARNING">
2675                 <table class="WARNING" border="1" width="90%">
2676                   <tr>
2677                     <td align="center"><b>Warning</b></td>
2678                   </tr>
2679                   <tr>
2680                     <td align="left">
2681                       <p>This is an experimental feature. The syntax is
2682                       likely to change in future versions.</p>
2683                     </td>
2684                   </tr>
2685                 </table>
2686               </div>
2687               <p>In case of some tags users may not want to enable them
2688               permanently, but only for a short amount of time, for example
2689               to circumvent a block that is the result of an overly-broad URL
2690               pattern.</p>
2691               <p>The CGI interface <a href=
2692               "http://config.privoxy.org/client-tags" target=
2693               "_top">http://config.privoxy.org/client-tags</a> therefore
2694               provides a "enable this tag temporarily" option. If it is used,
2695               the tag will be set until the client-tag-lifetime is over.</p>
2696             </dd>
2697             <dt>Examples:</dt>
2698             <dd>
2699               <table border="0" bgcolor="#E0E0E0" width="90%">
2700                 <tr>
2701                   <td>
2702                     <pre class="SCREEN">
2703                     # Increase the time to life for temporarily enabled tags to 3 minutes
2704       client-tag-lifetime 180
2705     </pre>
2706                   </td>
2707                 </tr>
2708               </table>
2709             </dd>
2710           </dl>
2711         </div>
2712       </div>
2713       <div class="SECT3">
2714         <h4 class="SECT3"><a name="TRUST-X-FORWARDED-FOR" id=
2715         "TRUST-X-FORWARDED-FOR">7.6.17. trust-x-forwarded-for</a></h4>
2716         <div class="VARIABLELIST">
2717           <dl>
2718             <dt>Specifies:</dt>
2719             <dd>
2720               <p>Whether or not Privoxy should use IP addresses specified
2721               with the X-Forwarded-For header</p>
2722             </dd>
2723             <dt>Type of value:</dt>
2724             <dd>
2725               <p><tt class="REPLACEABLE"><i>0 or one</i></tt></p>
2726             </dd>
2727             <dt>Default value:</dt>
2728             <dd>
2729               <p>0</p>
2730             </dd>
2731             <dt>Notes:</dt>
2732             <dd>
2733               <div class="WARNING">
2734                 <table class="WARNING" border="1" width="90%">
2735                   <tr>
2736                     <td align="center"><b>Warning</b></td>
2737                   </tr>
2738                   <tr>
2739                     <td align="left">
2740                       <p>This is an experimental feature. The syntax is
2741                       likely to change in future versions.</p>
2742                     </td>
2743                   </tr>
2744                 </table>
2745               </div>
2746               <p>If clients reach Privoxy through another proxy, for example
2747               a load balancer, Privoxy can't tell the client's IP address
2748               from the connection. If multiple clients use the same proxy,
2749               they will share the same client tag settings which is usually
2750               not desired.</p>
2751               <p>This option lets Privoxy use the X-Forwarded-For header
2752               value as client IP address. If the proxy sets the header,
2753               multiple clients using the same proxy do not share the same
2754               client tag settings.</p>
2755               <p>This option should only be enabled if Privoxy can only be
2756               reached through a proxy and if the proxy can be trusted to set
2757               the header correctly. It is recommended that ACL are used to
2758               make sure only trusted systems can reach Privoxy.</p>
2759               <p>If access to Privoxy isn't limited to trusted systems, this
2760               option would allow malicious clients to change the client tags
2761               for other clients or increase Privoxy's memory requirements by
2762               registering lots of client tag settings for clients that don't
2763               exist.</p>
2764             </dd>
2765             <dt>Examples:</dt>
2766             <dd>
2767               <table border="0" bgcolor="#E0E0E0" width="90%">
2768                 <tr>
2769                   <td>
2770                     <pre class="SCREEN">
2771                     # Allow systems that can reach Privoxy to provide the client
2772       # IP address with a X-Forwarded-For header.
2773       trust-x-forwarded-for 1
2774     </pre>
2775                   </td>
2776                 </tr>
2777               </table>
2778             </dd>
2779           </dl>
2780         </div>
2781       </div>
2782       <div class="SECT3">
2783         <h4 class="SECT3"><a name="RECEIVE-BUFFER-SIZE" id=
2784         "RECEIVE-BUFFER-SIZE">7.6.18. receive-buffer-size</a></h4>
2785         <div class="VARIABLELIST">
2786           <dl>
2787             <dt>Specifies:</dt>
2788             <dd>
2789               <p>The size of the buffer Privoxy uses to receive data from the
2790               server.</p>
2791             </dd>
2792             <dt>Type of value:</dt>
2793             <dd>
2794               <p><tt class="REPLACEABLE"><i>Size in bytes</i></tt></p>
2795             </dd>
2796             <dt>Default value:</dt>
2797             <dd>
2798               <p>5000</p>
2799             </dd>
2800             <dt>Notes:</dt>
2801             <dd>
2802               <p>Increasing the receive-buffer-size increases Privoxy's
2803               memory usage but can lower the number of context switches and
2804               thereby reduce the cpu usage and potentially increase the
2805               throughput.</p>
2806               <p>This is mostly relevant for fast network connections and
2807               large downloads that don't require filtering.</p>
2808               <p>Reducing the buffer size reduces the amount of memory
2809               Privoxy needs to handle the request but increases the number of
2810               systemcalls and may reduce the throughput.</p>
2811               <p>A dtrace command like: <span class="QUOTE">"sudo dtrace -n
2812               'syscall::read:return /execname == "privoxy"/ { @[execname] =
2813               llquantize(arg0, 10, 0, 5, 20); @m = max(arg0)}'"</span> can be
2814               used to properly tune the receive-buffer-size. On systems
2815               without dtrace, strace or truss may be used as less convenient
2816               alternatives.</p>
2817               <p>If the buffer is too large it will increase Privoxy's memory
2818               footprint without any benefit. As the memory is (currently)
2819               cleared before using it, a buffer that is too large can
2820               actually reduce the throughput.</p>
2821             </dd>
2822             <dt>Examples:</dt>
2823             <dd>
2824               <table border="0" bgcolor="#E0E0E0" width="90%">
2825                 <tr>
2826                   <td>
2827                     <pre class="SCREEN">
2828                     # Increase the receive buffer size
2829       receive-buffer-size 32768
2830     </pre>
2831                   </td>
2832                 </tr>
2833               </table>
2834             </dd>
2835           </dl>
2836         </div>
2837       </div>
2838     </div>
2839     <div class="SECT2">
2840       <h2 class="SECT2"><a name="WINDOWS-GUI" id="WINDOWS-GUI">7.7. Windows
2841       GUI Options</a></h2>
2842       <p><span class="APPLICATION">Privoxy</span> has a number of options
2843       specific to the Windows GUI interface:</p><a name="ACTIVITY-ANIMATION"
2844       id="ACTIVITY-ANIMATION"></a>
2845       <p>If <span class="QUOTE">"activity-animation"</span> is set to 1, the
2846       <span class="APPLICATION">Privoxy</span> icon will animate when
2847       <span class="QUOTE">"Privoxy"</span> is active. To turn off, set to
2848       0.</p>
2849       <p class="LITERALLAYOUT"><tt class="LITERAL">&nbsp;&nbsp;<span class=
2850       "emphasis"><i class="EMPHASIS">activity-animation 1</i></span><br>
2851       &nbsp;&nbsp;&nbsp;</tt></p><a name="LOG-MESSAGES" id=
2852       "LOG-MESSAGES"></a>
2853       <p>If <span class="QUOTE">"log-messages"</span> is set to 1,
2854       <span class="APPLICATION">Privoxy</span> copies log messages to the
2855       console window. The log detail depends on the <a href=
2856       "config.html#DEBUG">debug</a> directive.</p>
2857       <p class="LITERALLAYOUT"><tt class="LITERAL">&nbsp;&nbsp;<span class=
2858       "emphasis"><i class="EMPHASIS">log-messages 1</i></span><br>
2859       &nbsp;&nbsp;&nbsp;</tt></p><a name="LOG-BUFFER-SIZE" id=
2860       "LOG-BUFFER-SIZE"></a>
2861       <p>If <span class="QUOTE">"log-buffer-size"</span> is set to 1, the
2862       size of the log buffer, i.e. the amount of memory used for the log
2863       messages displayed in the console window, will be limited to
2864       <span class="QUOTE">"log-max-lines"</span> (see below).</p>
2865       <p>Warning: Setting this to 0 will result in the buffer to grow
2866       infinitely and eat up all your memory!</p>
2867       <p class="LITERALLAYOUT"><tt class="LITERAL">&nbsp;&nbsp;<span class=
2868       "emphasis"><i class="EMPHASIS">log-buffer-size 1</i></span><br>
2869       &nbsp;&nbsp;&nbsp;</tt></p><a name="LOG-MAX-LINES" id=
2870       "LOG-MAX-LINES"></a>
2871       <p><span class="APPLICATION">log-max-lines</span> is the maximum number
2872       of lines held in the log buffer. See above.</p>
2873       <p class="LITERALLAYOUT"><tt class="LITERAL">&nbsp;&nbsp;<span class=
2874       "emphasis"><i class="EMPHASIS">log-max-lines 200</i></span><br>