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43 >Privoxy Frequently Asked Questions</TH
51 HREF="configuration.html"
88 >4.1. How much does Privoxy slow my browsing down? This
89 has to add extra time to browsing.</A
92 > How much of an impact depends on many things, including the CPU of the host
93 system, how aggressive the configuration is, which specific actions are being triggered,
94 the size of the page, the bandwidth of the connection, etc.</P
96 > Overall, it should not slow you down any in real terms, and may actually help
97 speed things up since ads, banners and other junk are not typically being
98 retrieved and displayed. The actual processing time required by
102 > itself for each page, is relatively small
103 in the overall scheme of things, and happens very quickly. This is typically
104 more than offset by time saved not downloading and rendering ad images and
105 other junk content (if ad blocking is being used).</P
110 > content via the <TT
113 HREF="../user-manual/actions-file.html#FILTER"
121 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
126 actions may cause a perceived slowdown, since the entire document
127 needs to be buffered before displaying. And on very large documents,
128 filtering may have some measurable impact. How much depends on the page size,
129 the actual definition of the filter(s), etc. See below. Most other actions
130 have little to no impact on speed.</P
132 > Also, when filtering is enabled but zlib support isn't available, compression
133 is often disabled (see <A
134 HREF="../user-manual/actions-file.html#PREVENT-COMPRESSION"
136 >prevent-compression</A
138 This can have an impact on speed as well, although it's probably smaller than
139 you might think. Again, the page size, etc. will determine how much of an impact.</P
147 >4.2. I notice considerable
148 delays in page requests. What's wrong?</A
154 HREF="../user-manual/actions-file.html#FILTER"
159 such as filtering banners by size, web-bugs etc, or the <TT
162 HREF="../user-manual/actions-file.html#DEANIMATE-GIFS"
167 action, the entire document must be loaded into memory in order for the filtering
168 mechanism to work, and nothing is sent to the browser during this time.</P
170 > The loading time typically does not really change much in real numbers, but
171 the feeling is different, because most browsers are able to start rendering
172 incomplete content, giving the user a feeling of "it works". This effect is
173 more noticeable on slower dialup connections. Extremely large documents
174 may have some impact on the time to load the page where there is filtering
175 being done. But overall, the difference should be very minimal. If there is a
176 big impact, then probably some other situation is contributing (like
177 anti-virus software).
180 > Filtering is automatically disabled for inappropriate MIME types. But note
181 that if the web server mis-reports the MIME type, then content that should
182 not be filtered, could be. <SPAN
186 to differentiate filterable content because of the MIME type as reported by
187 the server, or because of some configuration setting that enables/disables
196 >4.3. What are "http://config.privoxy.org/" and
201 HREF="http://config.privoxy.org/"
203 >http://config.privoxy.org/</A
208 >'s built-in user interface, and
213 > is a shortcut for it.</P
218 > sits between your web browser and the Internet,
219 it can simply intercept requests for these addresses and answer them with its built-in
225 > This also makes for a good test for your browser configuration: If entering the
227 HREF="http://config.privoxy.org/"
229 >http://config.privoxy.org/</A
231 takes you to a page saying <SPAN
233 >"This is Privoxy ..."</SPAN
235 If you get a page saying <SPAN
237 >"Privoxy is not working"</SPAN
239 your browser didn't use <SPAN
243 hence it could not be intercepted, and you have accessed the <SPAN
250 web site at config.privoxy.org.</P
252 > Note that config.privoxy.org resolves to a public IP address.
253 If you use config.privoxy.org as ping or traceroute target you will
254 reach the system on the Internet (Privoxy can't intercept ICMP requests).
255 If you want to ping the system Privoxy runs on,
256 you should use its IP address or local DNS name (if it has got one).</P
264 >4.4. How can I submit new ads, or report
272 various ways to interact with the developers.</P
280 >4.5. If I do submit missed ads, will
281 they be included in future updates?</A
284 > Whether such submissions are eventually included in the
288 > configuration file depends on how
289 significant the issue is. We of course want to address any potential
290 problem with major, high-profile sites such as <I
297 >, etc. Any site with global or regional reach,
298 has a good chance of being a candidate. But at the other end of the spectrum
299 are any number of smaller, low-profile sites such as for local clubs or
300 schools. Since their reach and impact are much less, they are best handled by
301 inclusion in the user's <TT
305 unlikely to be included.</P
313 >4.6. Why doesn't anyone answer my support
317 >Rest assured that it has been read and considered. Why it is not answered,
318 could be for various reasons, including no one has a good answer for it, no
319 one has had time to yet investigate it thoroughly, it has been reported
320 numerous times already, or because not enough information was provided to help
321 us help you. Your efforts are not wasted, and we do appreciate them.</P
329 >4.7. How can I hide my IP address?</A
332 > If you run both the browser and <SPAN
335 > locally, you cannot hide your IP
339 > or ultimately any other
340 software alone. The server needs to know your IP address so that it knows
341 where to send the responses back.</P
343 > There are many publicly usable "anonymous" proxies out there, which
344 provide a further level of indirection between you and the web server.</P
346 > However, these proxies are called "anonymous" because you don't need
347 to authenticate, not because they would offer any real anonymity.
348 Most of them will log your IP address and make it available to the
349 authorities in case you violate the law of the country they run in. In fact
350 you can't even rule out that some of them only exist to *collect* information
351 on (those suspicious) people with a more than average preference for privacy.</P
353 > If you want to hide your IP address from most adversaries,
354 you should consider chaining <SPAN
359 HREF="https://www.torproject.org/"
363 The configuration details can be found in
384 >4.8. Can Privoxy guarantee I am anonymous?</A
387 > No. Your chances of remaining anonymous are improved, but unless you
399 or a similar proxy and know what you're doing when it comes to configuring
400 the rest of your system, you should assume that everything you do
401 on the Web can be traced back to you.</P
406 > can remove various information about you,
413 > more freedom to decide which sites
414 you can trust, and what details you want to reveal. But it neither
415 hides your IP address, nor can it guarantee that the rest of the system
416 behaves correctly. There are several possibilities how a web sites can find
417 out who you are, even if you are using a strict <SPAN
421 configuration and chained it with <SPAN
429 > privacy-enhancing features can be easily subverted
430 by an insecure browser configuration, therefore you should use a browser that can
431 be configured to only execute code from trusted sites, and be careful which sites you trust.
432 For example there is no point in having <SPAN
436 modify the User-Agent header, if websites can get all the information they want
437 through JavaScript, ActiveX, Flash, Java etc.</P
439 > A few browsers disclose the user's email address in certain situations, such
440 as when transferring a file by FTP. <SPAN
444 does not filter FTP. If you need this feature, or are concerned about the
445 mail handler of your browser disclosing your email address, you might
446 consider products such as <SPAN
451 > Browsers available only as binaries could use non-standard headers to give
452 out any information they can have access to: see the manufacturer's license
453 agreement. It's impossible to anticipate and prevent every breach of privacy
454 that might occur. The professionally paranoid prefer browsers available as
455 source code, because anticipating their behavior is easier. Trust the source,
464 >4.9. A test site says I am not using a Proxy.</A
467 > Good! Actually, they are probably testing for some other kinds of proxies.
468 Hiding yourself completely would require additional steps.</P
476 >4.10. How do I use Privoxy
477 together with Tor?</A
480 > Before you configure <SPAN
485 HREF="https://www.torproject.org/"
494 HREF="../user-manual/installation.html"
499 HREF="../user-manual/startup.html"
506 > itself is setup correctly.</P
508 > If it is, refer to <A
509 HREF="https://www.torproject.org/documentation.html"
512 extensive documentation</A
513 > to learn how to install <SPAN
520 >'s logfile says that
523 >"Tor has successfully opened a circuit"</SPAN
527 >"looks like client functionality is working"</SPAN
537 isn't working, their combination most likely will neither. Testing them on their
538 own will also help you to direct problem reports to the right audience.
542 > isn't working, don't bother the
546 > developers. If <SPAN
550 isn't working, don't send bug reports to the <SPAN
555 > If you verified that <SPAN
562 are working, it is time to connect them. As far as <SPAN
569 > is just another proxy that can be reached
570 by socks4, socks4a and socks5. Most likely you are interested in <SPAN
574 to increase your anonymity level, therefore you should use socks5, to make sure DNS
575 requests are done through <SPAN
578 > and thus invisible to your
579 local network. Using socks4a would work too, but with socks5 you get more precise error
587 HREF="../user-manual/config.html"
589 >main configuration file</A
591 is already prepared for <SPAN
594 >, if you are using a
598 > configuration and run it on the same
602 >, you just have to edit the
604 HREF="../user-manual/config.html#FORWARDING"
606 >forwarding section</A
608 and uncomment the line:</P
617 ># forward-socks5t / 127.0.0.1:9050 .
623 > Note that if you got Tor through one of the bundles, you may
624 have to change the port from 9050 to 9150 (or even another one).
625 For details, please check the documentation on the
627 HREF="https://torproject.org/"
632 > This is enough to reach the Internet, but additionally you might want to
633 uncomment the following forward rules, to make sure your local network is still
634 reachable through Privoxy:</P
643 ># forward 192.168.*.*/ .
644 # forward 10.*.*.*/ .
645 # forward 127.*.*.*/ .
651 > Unencrypted connections to systems in these address ranges will
652 be as (un)secure as the local network is, but the alternative is
653 that your browser can't reach the network at all. Then again,
654 that may actually be desired and if you don't know for sure
655 that your browser has to be able to reach the local network,
656 there's no reason to allow it.</P
658 > If you want your browser to be able to reach servers in your local
659 network by using their names, you will need additional exceptions
660 that look like this:</P
669 ># forward localhost/ .
675 > Save the modified configuration file and open
677 HREF="http://config.privoxy.org/show-status"
679 >http://config.privoxy.org/show-status</A
681 in your browser, confirm that <SPAN
684 > has reloaded its configuration
685 and that there are no other forward lines, unless you know that you need them. If everything looks good,
688 HREF="https://wiki.torproject.org/noreply/TheOnionRouter/TorFAQ#IsMyConnectionPrivate"
692 > to learn how to verify that you are really using <SPAN
697 > Afterward, please take the time to at least skim through the rest
701 > documentation. Make sure you understand
705 > does, why it is no replacement for
706 application level security, and why you probably don't want to
707 use it for unencrypted logins.</P
715 >4.11. Might some things break because header information or
716 content is being altered?</A
719 > Definitely. It is common for sites to use browser type, browser version,
720 HTTP header content, and various other techniques in order to dynamically
721 decide what to display and how to display it. What you see, and what I see,
722 might be very different. There are many, many ways that this can be handled,
723 so having hard and fast rules, is tricky.</P
728 > is sometimes used in this way to identify
729 the browser, and adjust content accordingly.</P
731 > Also, different browsers use different encodings of non-English
732 characters, certain web servers convert pages on-the-fly according to the
733 User Agent header. Giving a <SPAN
737 operating system or browser manufacturer causes some sites in these languages
738 to be garbled; Surfers to Eastern European sites should change it to
739 something closer. And then some page access counters work by looking at the
743 > header; they may fail or break if unavailable. The
744 weather maps of Intellicast have been blocked by their server when no
748 > or cookie is provided, is another example. (But you
749 can forge both headers without giving information away). There are
750 many other ways things can go wrong when trying to fool a web server. The
751 results of which could inadvertently cause pages to load incorrectly,
752 partially, or even not at all. And there may be no obvious clues as to just
753 what went wrong, or why. Nowhere will there be a message that says
769 > Similar thoughts apply to modifying JavaScript, and, to a lesser degree,
772 > If you have problems with a site, you will have to adjust your configuration
773 accordingly. Cookies are probably the most likely adjustment that may
774 be required, but by no means the only one.</P
782 >4.12. Can Privoxy act as a <SPAN
786 speed up web browsing?</A
789 > No, it does not have this ability at all. You want something like
791 HREF="http://www.squid-cache.org/"
796 HREF="http://www.pps.jussieu.fr/~jch/software/polipo/"
800 And, yes, before you ask, <SPAN
804 with other kinds of proxies like <SPAN
809 HREF="../user-manual/config.html#FORWARDING"
814 HREF="../user-manual/index.html"
826 >4.13. What about as a firewall? Can Privoxy protect me?</A
829 > Not in the way you mean, or in the way some firewall vendors claim they can.
833 > can help protect your privacy, but can't
834 protect your system from intrusion attempts. It is, of course, perfectly possible
849 >4.14. I have large empty spaces / a checkerboard pattern now where
850 ads used to be. Why?</A
853 > It is technically possible to eliminate banners and ads in a way that frees
854 their allocated page space. This could easily be done by blocking with
859 and eliminating the <SPAN
865 > image references from the
868 > But, this would consume considerably more CPU resources (IOW, slow things
869 down), would likely destroy the layout of some web pages which rely on the
870 banners utilizing a certain amount of page space, and might fail in other
871 cases, where the screen space is reserved (e.g. by HTML tables for instance).
872 Also, making ads and banners disappear without any trace complicates
873 troubleshooting, and would sooner or later be problematic.</P
875 > The better alternative is to instead let them stay, and block the resulting
876 requests for the banners themselves as is now the case. This leaves either
877 empty space, or the familiar checkerboard pattern.</P
879 > So the developers won't support this in the default configuration, but you
880 can of course define appropriate filters yourself to achieve this.</P
888 >4.15. How can Privoxy filter Secure (HTTPS) URLs?</A
891 > Since secure HTTP connections are encrypted SSL sessions between your browser
892 and the secure site, and are meant to be reliably <SPAN
899 there is little that <SPAN
902 > can do but hand the raw
903 gibberish data though from one end to the other unprocessed.</P
905 > The only exception to this is blocking by host patterns, as the client needs
909 > the name of the remote server,
913 > can establish the connection.
914 If that name matches a host-only pattern, the connection will be blocked.</P
916 > As far as ad blocking is concerned, this is less of a restriction than it may
917 seem, since ad sources are often identifiable by the host name, and often
918 the banners to be placed in an encrypted page come unencrypted nonetheless
919 for efficiency reasons, which exposes them to the full power of
927 >"Content cookies"</SPAN
928 > (those that are embedded in the actual HTML or
929 JS page content, see <TT
932 HREF="../user-manual/actions-file.html#FILTER-CONTENT-COOKIES"
934 >filter{content-cookies}</A
937 in an SSL transaction will be impossible to block under these conditions.
938 Fortunately, this does not seem to be a very common scenario since most
939 cookies come by traditional means.</P
947 >4.16. Does Privoxy support HTTP/2?</A
950 > Privoxy currently doesn't parse HTTP/2 but applications
951 can tunnel HTTP/2 through Privoxy if Privoxy is configured
952 to allow CONNECT requests (default) which are also used
955 > Adding HTTP/2 support is on the TODO list but currently
956 nobody is known to work on it.</P
964 >4.17. Privoxy runs as a <SPAN
968 secure is it? Do I need to take any special precautions?</A
971 > On Unix-like systems, <SPAN
974 > can run as a non-privileged
975 user, which is how we recommend it be run. Also, by default
979 > listens to requests from <SPAN
985 > The server aspect of <SPAN
988 > is not itself directly
989 exposed to the Internet in this configuration. If you want to have
993 > serve as a LAN proxy, this will have to
994 be opened up to allow for LAN requests. In this case, we'd recommend
995 you specify only the LAN gateway address, e.g. 192.168.1.1, in the main
999 > configuration file and check all <A
1000 HREF="../user-manual/config.html#ACCESS-CONTROL"
1002 >access control and security
1004 >. All LAN hosts can then use this as their proxy address
1005 in the browser proxy configuration, but <SPAN
1009 will not listen on any external interfaces. ACLs can be defined in addition,
1010 and using a firewall is always good too. Better safe than sorry.</P
1018 >4.18. Can I temporarily disable Privoxy?</A
1024 > doesn't have a transparent proxy mode,
1025 but you can toggle off blocking and content filtering.</P
1027 > The easiest way to do that is to point your browser
1028 to the remote toggle URL: <A
1029 HREF="http://config.privoxy.org/toggle"
1031 >http://config.privoxy.org/toggle</A
1035 HREF="../user-manual/appendix.html#BOOKMARKLETS"
1037 >Bookmarklets section</A
1042 > for an easy way to access this
1043 feature. Note that this is a feature that may need to be enabled in the main
1058 > is Privoxy totally
1059 out of the picture?</A
1062 > No, this just means all optional filtering and actions are disabled.
1066 > is still acting as a proxy, but just
1067 doing less of the things that <SPAN
1071 normally be expected to do. It is still a <SPAN
1075 the interaction between your browser and web sites. See below to bypass
1084 >4.20. How can I tell Privoxy to totally ignore certain sites?</A
1087 > Bypassing a proxy, or proxying based on arbitrary criteria, is purely a browser
1088 configuration issue, not a <SPAN
1091 > issue. Modern browsers typically do have
1092 settings for not proxying certain sites. Check your browser's help files.</P
1100 >4.21. My logs show Privoxy <SPAN
1104 ads, but also its own internal CGI pages. What is a <SPAN
1123 >, nothing more. Often this is indeed ads or
1127 > uses the same mechanism for
1128 trapping requests for its own internal pages. For instance, a request for
1132 > configuration page at: <A
1133 HREF="http://config.privoxy.org"
1135 >http://config.privoxy.org</A
1137 intercepted (i.e. it does not go out to the 'net), and the familiar CGI
1138 configuration is returned to the browser, and the log consequently will show
1144 > Since version 3.0.7, Privoxy will also log the crunch reason.
1145 If you are using an older version you might want to upgrade.</P
1153 >4.22. Can Privoxy affect files that I download
1154 from a webserver? FTP server?</A
1157 > From the webserver's perspective, there is no difference between
1158 viewing a document (i.e. a page), and downloading a file. The same is true of
1162 >. If there is a match for a <TT
1165 HREF="../user-manual/actions-file.html#BLOCK"
1170 it will still be blocked, and of course this is obvious.
1173 > Filtering is potentially more of a concern since the results are not always
1174 so obvious, and the effects of filtering are there whether the file is simply
1175 viewed, or downloaded. And potentially whether the content is some obnoxious
1176 advertisement, or Mr. Jimmy's latest/greatest source code jewel. Of course,
1177 one of these presumably is <SPAN
1180 > content that we don't want, and
1184 > content that we do want.
1188 > is blind to the differences, and can only
1191 >"good from bad"</SPAN
1192 > by the configuration parameters
1204 > knows the differences in files according
1207 >"Content Type"</SPAN
1208 > as reported by the webserver. If this is
1209 reported accurately (e.g. <SPAN
1211 >"application/zip"</SPAN
1212 > for a zip archive),
1216 > knows to ignore these where
1220 > potentially can filter HTML
1221 as well as plain text documents, subject to configuration parameters of
1222 course. Also, documents that are of an unknown type (generally assumed to be
1226 >) can be filtered, as will those that might be
1227 incorrectly reported by the webserver. If such a file is a downloaded file
1228 that is intended to be saved to disk, then any content that might have been
1229 altered by filtering, will be saved too, for these (probably rare) cases.</P
1231 > Note that versions later than 3.0.2 do NOT filter document types reported as
1235 >. Prior to this, <SPAN
1239 did filter this document type.</P
1241 > In short, filtering is <SPAN
1244 > if a) the content type as reported
1245 by the webserver is appropriate <SPAN
1251 > b) the configuration
1252 allows it (or at least does not disallow it). That's it. There is no magic
1253 cookie anywhere to say this is <SPAN
1260 >. It's the configuration that lets it all happen or not.</P
1262 > If you download text files, you probably do not want these to be filtered,
1263 particularly if the content is source code, or other critical content. Source
1264 code sometimes might be mistaken for Javascript (i.e. the kind that might
1265 open a pop-up window). It is recommended to turn off filtering for download
1266 sites (particularly if the content may be plain text files and you are using
1267 version 3.0.2 or earlier) in your <TT
1271 also, for any site or page where making <SPAN
1278 all to the content is to be avoided.</P
1283 > does not do FTP at all, only HTTP
1284 and HTTPS (SSL) protocols.</P
1292 >4.23. I just downloaded a Perl script, and Privoxy
1293 altered it! Yikes, what is wrong!</A
1296 > Please read above.</P
1304 >4.24. Should I continue to use a <SPAN
1307 > file for ad-blocking?</A
1310 > One time-tested technique to defeat common ads is to trick the local DNS
1311 system by giving a phony IP address for the ad generator in the local
1315 > file, typically using <TT
1322 >. This effectively blocks the ad.</P
1324 > There is no reason to use this technique in conjunction with
1332 does essentially the same thing, much more elegantly and with much more
1333 flexibility. A large <TT
1336 > file, in fact, not only
1337 duplicates effort, but may get in the way and seriously slow down your system.
1338 It is recommended to remove such entries from your <TT
1341 > file. If you think
1342 your hosts list is neglected by <SPAN
1346 configuration, consider adding your list to your <TT
1361 ads.galore.example.com
1362 etc.example.com</PRE
1373 >4.25. Where can I find more information about Privoxy
1374 and related issues?</A
1377 > Other references and sites of interest to <SPAN
1390 HREF="https://www.privoxy.org/"
1392 >https://www.privoxy.org/</A
1412 HREF="https://www.privoxy.org/faq/"
1414 >https://www.privoxy.org/faq/</A
1434 HREF="https://www.privoxy.org/developer-manual/"
1436 >https://www.privoxy.org/developer-manual/</A
1456 HREF="https://sourceforge.net/projects/ijbswa/"
1458 >https://sourceforge.net/projects/ijbswa/</A
1460 the Project Page for <SPAN
1465 HREF="http://sourceforge.net"
1483 HREF="http://config.privoxy.org/"
1485 >http://config.privoxy.org/</A
1487 the web-based user interface. <SPAN
1491 running for this to work. Shortcut: <A
1510 HREF="https://sourceforge.net/tracker/?group_id=11118&atid=460288"
1512 >https://sourceforge.net/tracker/?group_id=11118&atid=460288</A
1517 configuration related suggestions to the developers.
1532 HREF="http://www.squid-cache.org/"
1534 >http://www.squid-cache.org/</A
1536 caching proxy, which is often used together with <SPAN
1554 HREF="http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/"
1556 >http://www.pps.univ-paris-diderot.fr/~jch/software/polipo/</A
1561 > is a caching proxy with advanced features
1562 like pipelining, multiplexing and caching of partial instances. In many setups
1563 it can be used as <SPAN
1581 HREF="https://www.torproject.org/"
1583 >https://www.torproject.org/</A
1588 > can help anonymize web browsing,
1589 web publishing, instant messaging, IRC, SSH, and other applications.
1603 >4.26. I've noticed that Privoxy changes <SPAN
1610 >! Why are you manipulating my browsing?</A
1613 > We're not. The text substitutions that you are seeing are disabled
1614 in the default configuration as shipped. You have either manually
1622 is clearly labeled <SPAN
1624 >"Text replacements for subversive browsing
1626 > or you are using an older Privoxy version and have implicitly
1627 activated it by choosing the <SPAN
1631 web-based editor. Please upgrade.</P
1639 >4.27. Does Privoxy produce <SPAN
1642 > HTML (or XHTML)?</A
1645 > Privoxy generates HTML in both its own <SPAN
1649 whenever there are text substitutions via a <SPAN
1652 > filter. While this
1653 should always conform to the HTML 4.01 specifications, it has not been
1654 validated against this or any other standard.</P
1661 NAME="SURPRISE-PRIVOXY"
1662 >4.28. How did you manage to get Privoxy on my computer without my consent?</A
1665 > We didn't. We make Privoxy available for download, but we don't go
1666 around installing it on other people's systems behind their back.
1667 If you discover Privoxy running on your system and are sure you didn't
1668 install it yourself, somebody else did. You may not even be running
1669 the real Privoxy, but maybe something else that only pretends to be
1670 Privoxy, or maybe something that is based on the real Privoxy,
1671 but has been modified.</P
1673 > Lately there have been reports of problems with some kind of
1674 "parental control" software based on Privoxy that came preinstalled on
1676 HREF="https://sourceforge.net/p/ijbswa/bugs/813/"
1680 The problems described are inconsistent with the behaviour of official
1681 Privoxy versions, which suggests that the preinstalled software may
1682 contain vendor modifications that we don't know about and thus can't debug.</P
1685 HREF="copyright.html"
1688 modifications, but the vendor has to comply with the license,
1689 which involves informing the user about the changes and to make
1690 the changes available under the same license as Privoxy itself.</P
1692 > If you are having trouble with a modified Privoxy version,
1693 please try to talk to whoever made the modifications before
1694 reporting the problem to us. Please also try to convince
1695 whoever made the modifications to talk to us. If you think
1696 somebody gave you a modified Privoxy version without complying
1697 to the license, please let us know.</P
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1754 >Troubleshooting</TD