-<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
+<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 3.2//EN">
<HTML>
<HEAD>
-<TITLE>Apache server Frequently Asked Questions</TITLE>
+<TITLE>Apache Server Frequently Asked Questions</TITLE>
</HEAD>
<BODY>
<!--#include virtual="header.html" -->
-<H1>Apache server Frequently Asked Questions</H1>
+<H1>Apache Server Frequently Asked Questions</H1>
<H2>The Questions</H2>
-<OL>
-<LI><A HREF="#what">What is Apache ?</A>
-<LI><A HREF="#why">Why was Apache created ?</A>
-<LI><A HREF="#relate">How does the Apache group relate to other servers ?</A>
-<LI><A HREF="#name">Why the name "Apache" ?</A>
-<LI><A HREF="#compatible">How compatible is Apache with my existing NCSA 1.3 setup ?</A>
-<LI><A HREF="#compare">OK, so how does Apache compare to other servers ?</A>
-<LI><A HREF="#tested">How thoroughly tested is Apache?</A>
-<LI><A HREF="#proxy">Does or will Apache act as a Proxy server?</A>
-<LI><A HREF="#future">What are the future plans for Apache ?</A>
-<LI><A HREF="#support">Who do I contact for support ?</A>
-<LI><A HREF="#more">Is there any more information on Apache ?</A>
-<LI><A HREF="#where">Where can I get Apache ?</A>
-</OL>
-
-<HR>
-
-<H2>The Answers</H2>
-<OL>
-<LI><A name="what">What is Apache ?</A>
-<P>
- Apache was originally based on code and ideas found in the most
-popular HTTP server of the time.. NCSA httpd 1.3 (early 1995). It has
-since evolved into a far superior system which can rival (and probably
-surpass) almost any other UNIX based HTTP server in terms of functionality,
-efficiency and speed.
-<p>Since it began, it has been completely rewritten, and includes many new
-features. Apache is, as of November 1996, the most popular WWW server on
-the Internet, according to the <a
-href="http://www.netcraft.com/Survey/">Netcraft Survey</a>.
-
-</P>
-<HR>
-<LI><A name="relate">How does the Apache group relate to other
-server efforts, such as NCSA's?</A>
-<P>
-We, of course, owe a great debt to NCSA and their programmers for
-making the server Apache was based on. We now, however, have our own
-server, and our project is mostly our own. The Apache Project is an
-entirely independent venture.
-</P>
-<HR>
-
-<LI><A name="why">Why was Apache created ?</A>
-<P>to address concerns of a group of www providers and part time httpd
-programmers, that httpd didn't behave as they wanted it
-to. Apache is an entirely volunteer effort, completely funded by its
-members, not by commercial sales.
-</P>
-
-<HR>
-
-<LI><A name="name">Why the name "Apache" ?</A>
-<P>A cute name which stuck. Apache is "<B>A PA</B>t<B>CH</B>y server". It was
- based on some existing code and a series of "patch files".
-</P>
-<HR>
-
-
-<LI><A name="compatible">How compatible is Apache with my existing NCSA 1.3
-setup ?</A><P>
-
-Apache attempts to offer all the features and configuration options
-of NCSA httpd 1.3, as well as many of the additional features found in
-NCSA httpd 1.4 and NCSA httpd 1.5.<P>
-
-NCSA httpd appears to be moving toward adding experimental features
-which are not generally required at the moment. Some of the experiments
-will succeed while others will inevitably be dropped. The Apache philosophy is
-to add what's needed as and when it is needed.<p>
-
-Friendly interaction between Apache and NCSA developers should ensure
-that fundamental feature enhancments stay consistent between the two
-servers for the foreseeable future.<p>
-
-<HR>
-
-<LI><A name="compare">OK, so how does Apache compare to other servers ?</A>
-<P>
-For an independent assessment, see <A HREF="http://webcompare.iworld.com/compare/chart.html">http://webcompare.iworld.com/compare/chart.html</A>
-</P>
-
-<P>Apache has been shown to be substantially faster than many other
-free servers. Although certain commercial servers have claimed to
-surpass Apache's speed (it has not been demonstrated that any of these
-"benchmarks" are a good way of measuring WWW server speed at any
-rate), we feel that it is better to have a mostly-fast free server
-than an extremely-fast server that costs thousands of dollars. Apache
-is run on sites that get millions of hits per day, and they have
-experienced no performance difficulties.</p>
-
-<HR>
-<LI><A name="tested">How thoroughly tested is Apache?</A>
-
-<p>Apache is run on over 200,000 Internet servers (as of November 1996). It has
-been tested thoroughly by both developers and users. The Apache Group
-maintains rigorous standards before releasing new versions of their
-server, and our server runs without a hitch on over one third of all
-WWW servers. When bugs do show up, we release patches and new
-versions, as soon as they are available.</a>
-
-<P>See <A HREF="http://www.apache.org/info/apache_users.html">http://www.apache.org/info/apache_users.html</A> for an incomplete list of sites running Apache.</P>
-
-<hr>
-
-<LI><A name="proxy">Does or will Apache act as a Proxy server?
-<p>Apache version 1.1
-and above comes with a proxy module. If compiled in, this will make
-Apache act as a caching-proxy server
-<p>
-<HR>
-
-<LI><A name="future">What are the future plans for Apache ?</A>
-<P><UL>
-<LI>to continue as a public domain HTTP server,
-<LI>to keep up with advances in HTTP protocol and web developments in general
-<LI>to collect suggestions for fixes/improvements from its users,
-<LI>to respond to needs of large volume providers as well as occasional users.
+<!-- Stuff to Add: -->
+<!-- - bad mod_rewrite included in 1.2b6 -->
+<!-- - how-to PUT (publish, Netscape Gold) -->
+<!-- - can't bind to port 80 -->
+<!-- - permission denied -->
+<!-- - address already in use -->
+<!-- - "httpd: could not set socket option TCP_NODELAY" -->
+<!-- not a problem if occasional; client disc before server -->
+<!-- setsockopt -->
+<!-- - disable Apache buffering of script output by using nph- -->
+<!-- - access control based on DNS name really needs MAXIMUM_DNS -->
+<!-- and double-check that rDNS resolves to name expected -->
+<!-- - "I wanna use my /etc/passwd file for auth" -->
+<UL>
+ <LI><STRONG>Background</STRONG>
+ <OL START=1>
+ <LI><A HREF="#what">What is Apache?</A>
+ </LI>
+ <LI><A HREF="#why">Why was Apache created?</A>
+ </LI>
+ <LI><A HREF="#relate">How does The Apache Group's work relate to
+ other servers?</A>
+ </LI>
+ <LI><A HREF="#name">Why the name "Apache"?</A>
+ </LI>
+ <LI><A HREF="#compare">OK, so how does Apache compare to other servers?</A>
+ </LI>
+ <LI><A HREF="#tested">How thoroughly tested is Apache?</A>
+ </LI>
+ <LI><A HREF="#future">What are the future plans for Apache?</A>
+ </LI>
+ <LI><A HREF="#support">Whom do I contact for support?</A>
+ </LI>
+ <LI><A HREF="#more">Is there any more information on Apache?</A>
+ </LI>
+ <LI><A HREF="#where">Where can I get Apache?</A>
+ </LI>
+ </OL>
+ </LI>
+ <LI><STRONG>Technical Questions</STRONG>
+ <OL START=11>
+ <LI><A HREF="#what2do">"Why can't I ...? Why won't ...
+ work?" What to do in case of problems</A>
+ </LI>
+ <LI><A HREF="#compatible">How compatible is Apache with my existing
+ NCSA 1.3 setup?</A>
+ </LI>
+ <LI><A HREF="#premature-script-headers">What does it mean when my
+ CGIs fail with "Premature end of script headers"?</A>
+ </LI>
+ <LI><A HREF="#ssi-part-i">How do I enable SSI (parsed HTML)?</A>
+ </LI>
+ <LI><A HREF="#ssi-part-ii">Why don't my parsed files get cached?</A>
+ </LI>
+ <LI><A HREF="#ssi-part-iii">How can I have my script output parsed?</A>
+ </LI>
+ <LI><A HREF="#proxy">Does or will Apache act as a Proxy server?</A>
+ </LI>
+ <LI><A HREF="#multiviews">What are "multiviews"?</A>
+ </LI>
+ <LI><A HREF="#fdlim">Why can't I run more than <<EM>n</EM>>
+ virtual hosts?</A>
+ </LI>
+ </OL>
+ </LI>
</UL>
-</P><HR>
-<LI><A name="support">Who do I contact for support ?</A>
-<P>There is no official support for Apache. None of the developers want to
-be swamped by a flood of trivial questions that can be resolved elsewhere.
-Bug reports and suggestions should be sent via <A HREF="http://www.apache.org/bug_report.html">the bug report page.</A>
-Other questions should be directed to
-<A HREF="news:comp.infosystems.www.servers.unix">comp.infosystems.www.servers.unix</A>, where some of the Apache team lurk,
-in the company of many other httpd gurus who should be able
-to help.
-<p>
-Commercial support for Apache is, however, available from a number
-third parties.
-</p>
<HR>
-<LI><A name="more">Is there any more information on Apache ?</A>
-<P>Indeed there is. See <A HREF="http://www.apache.org/">http://www.apache.org/</A>.
-</P>
-<HR>
-
-<LI><A name="where">Where can I get Apache ?</A>
+<H2>The Answers</H2>
<P>
-You can find the source for Apache at <A HREF="http://www.apache.org/">http://www.apache.org/</A>.
</P>
+<H3>
+ Background
+</H3>
+<OL START=1>
+ <LI><A
+ NAME="what"
+ ><STRONG>What is Apache?</STRONG></A>
+ <P>
+ Apache was originally based on code and ideas found in the most
+ popular HTTP server of the time.. NCSA httpd 1.3 (early 1995). It has
+ since evolved into a far superior system which can rival (and probably
+ surpass) almost any other UNIX based HTTP server in terms of functionality,
+ efficiency and speed.
+ </P>
+ <P>
+ Since it began, it has been completely rewritten, and includes many new
+ features. Apache is, as of January 1997, the most popular WWW server on
+ the Internet, according to the
+ <A
+ HREF="http://www.netcraft.com/Survey/"
+ >Netcraft Survey</A>.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="why"
+ ><STRONG>Why was Apache created?</STRONG></A>
+ <P>
+ To address the concerns of a group of WWW providers and part-time httpd
+ programmers that httpd didn't behave as they wanted it to behave.
+ Apache is an entirely volunteer effort, completely funded by its
+ members, not by commercial sales.
+ <HR>
+ </P>
+ </LI>
+ <LI><A
+ NAME="relate"
+ ><STRONG>How does The Apache Group's work relate to other
+ server efforts, such as NCSA's?</STRONG></A>
+ <P>
+ We, of course, owe a great debt to NCSA and their programmers for
+ making the server Apache was based on. We now, however, have our own
+ server, and our project is mostly our own. The Apache Project is an
+ entirely independent venture.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="name"
+ ><STRONG>Why the name "Apache"?</STRONG></A>
+ <P>
+ A cute name which stuck. Apache is "<STRONG>A
+ PA</STRONG>t<STRONG>CH</STRONG>y server". It was
+ based on some existing code and a series of "patch files".
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="compare"
+ ><STRONG>OK, so how does Apache compare to other servers?</STRONG></A>
+ <P>
+ For an independent assessment, see
+ <A
+ HREF="http://webcompare.iworld.com/compare/chart.html"
+ ><SAMP>http://webcompare.iworld.com/compare/chart.html</SAMP></A>.
+ </P>
+ <P>
+ Apache has been shown to be substantially faster than many other
+ free servers. Although certain commercial servers have claimed to
+ surpass Apache's speed (it has not been demonstrated that any of these
+ "benchmarks" are a good way of measuring WWW server speed at any
+ rate), we feel that it is better to have a mostly-fast free server
+ than an extremely-fast server that costs thousands of dollars. Apache
+ is run on sites that get millions of hits per day, and they have
+ experienced no performance difficulties.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="tested"
+ ><STRONG>How thoroughly tested is Apache?</STRONG></A>
+ <P>
+ Apache is run on over 400,000 Internet servers (as of April 1997). It has
+ been tested thoroughly by both developers and users. The Apache Group
+ maintains rigorous standards before releasing new versions of their
+ server, and our server runs without a hitch on over one third of all
+ WWW servers available on the Internet. When bugs do show up, we
+ release patches and new versions as soon as they are available.
+ </P>
+ <P>
+ See
+ <A
+ HREF="http://www.apache.org/info/apache_users.html"
+ ><SAMP>http://www.apache.org/info/apache_users.html</SAMP></A>
+ for a partial list of sites running Apache.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="future"
+ ><STRONG>What are the future plans for Apache?</STRONG></A>
+ <P>
+ <UL>
+ <LI>to continue as a public domain HTTP server,
+ </LI>
+ <LI>to keep up with advances in HTTP protocol and web developments in
+ general
+ </LI>
+ <LI>to collect suggestions for fixes/improvements from its users,
+ </LI>
+ <LI>to respond to needs of large volume providers as well as
+ occasional users.
+ </LI>
+ </UL>
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="support"
+ ><STRONG>Whom do I contact for support?</STRONG></A>
+ <P>
+ There is no official support for Apache. None of the developers want to
+ be swamped by a flood of trivial questions that can be resolved elsewhere.
+ Bug reports and suggestions should be sent <EM>via</EM>
+ <A
+ HREF="http://www.apache.org/bug_report.html"
+ >the bug report page</A> .
+ Other questions should be directed to the
+ <A
+ HREF="news:comp.infosystems.www.servers.unix"
+ ><SAMP>comp.infosystems.www.servers.unix</SAMP></A>
+ newsgroup, where some of the Apache team lurk,
+ in the company of many other httpd gurus who should be able
+ to help.
+ </P>
+ <P>
+ Commercial support for Apache is, however, available from a number
+ of third parties.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="more"
+ ><STRONG>Is there any more information available on Apache?</STRONG></A>
+ <P>
+ Indeed there is. See the main Apache Web site at
+ <A
+ HREF="http://www.apache.org/"
+ ><SAMP>http://www.apache.org/</SAMP></A>.
+ There is also a regular electronic publication called <EM>Apache
+ Week</EM> available; you can find out more about this at
+ <A
+ HREF="http://www.apacheweek.com"
+ REL="Help"
+ ><SAMP>http://www.apacheweek.com/</SAMP></A>.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="where"
+ ><STRONG>Where can I get Apache?</STRONG></A>
+ <P>
+ You can find the source for Apache at the main web page,
+ <A
+ HREF="http://www.apache.org/"
+ ><SAMP>http://www.apache.org/</SAMP></A>.
+ </P>
+ <HR>
+ </LI>
+</OL>
+<H3>
+ Technical Questions
+</H3>
+<OL START=11>
+ <LI><A
+ NAME="what2do"
+ ><STRONG>"Why can't I ...? Why won't ... work?" What to
+ do in case of problems</STRONG></A>
+ <P>
+ If you are having trouble with your Apache server software, you should
+ take the following steps:
+ </P>
+ <OL>
+ <LI><STRONG>Check the errorlog!</STRONG>
+ <P>
+ Apache tries to be helpful when it encounters a problem. In many
+ cases, it will provide some details by writing one or messages to
+ the server error log (see the
+ <A
+ HREF="http:../mod/core.html#errorlog"
+ >ErrorLog</A>
+ directive). Somethimes this is enough for you to diagnose &
+ fix the problem yourself (such as file permissions or the like).
+ </P>
+ </LI>
+ <LI><STRONG>Check the Apache bug database</STRONG>
+ <P>
+ Most problems that get reported to The Apache Group are recorded in
+ the bug database (available at
+ <A
+ HREF="http://www.apache.org/bugdb.cgi"
+ ><SAMP>http://www.apache.org/bugdb.cgi</SAMP></A>).
+ <EM><STRONG>Please</STRONG> check the existing reports, open
+ <STRONG>and</STRONG> closed, before adding one.</EM> If you find
+ that your issue has already been reported, please <EM>don't</EM> add
+ a "me, too" report. If the original report isn't closed
+ yet, we suggest that you check it periodically. You might also
+ consider contacting the original submittor, because there may be an
+ email exchange going on about the issue that isn't getting recorded
+ in the database.
+ </P>
+ </LI>
+ <LI><STRONG>Ask in the <SAMP>comp.infosystems.www.servers.unix</SAMP>
+ USENET newsgroup</STRONG>
+ <P>
+ A lot of common problems never make it to the bug database because
+ there's already high Q&A traffic about them in the
+ <A
+ HREF="news:comp.infosystems.www.servers.unix"
+ ><SAMP>comp.infosystems.www.servers.unix</SAMP></A>
+ newsgroup. Many Apache users, and some of the developers, can be
+ found roaming its virtual halls, so it is suggested that you seek
+ wisdom there. The chances are good that you'll get a faster answer
+ there than from the bug database, even if you <EM>don't</EM> see
+ your question already posted.
+ </P>
+ </LI>
+ <LI><STRONG>If all else fails, report the problem in the bug
+ database</STRONG>
+ <P>
+ If you've gone through those steps above that are appropriate and
+ have obtained no relief, then please <EM>do</EM> let The Apache
+ Group know about the problem by logging a bug report (see
+ <A
+ HREF="http://www.apache.org/bugdb.cgi"
+ ><SAMP>http://www.apache.org/bugdb.cgi</SAMP></A>).
+ </P>
+ <P>
+ If your problem involves the server crashing and generating a core
+ dump, please include a backtrace (if possible). As an example,
+ </P>
+ <PRE>
+ # cd <EM>ServerRoot</EM>
+ # dbx httpd core
+ (dbx) where
+ </PRE>
+ <P>
+ (Substitute the appropiate locations for your
+ <SAMP>ServerRoot</SAMP> and your <SAMP>httpd</SAMP> and
+ <SAMP>core</SAMP> files.)
+ </P>
+ </LI>
+ </OL>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="compatible"
+ ><STRONG>How compatible is Apache with my existing NCSA 1.3
+ setup?</STRONG></A>
+ <P>
+ Apache attempts to offer all the features and configuration options
+ of NCSA httpd 1.3, as well as many of the additional features found in
+ NCSA httpd 1.4 and NCSA httpd 1.5.
+ </P>
+ <P>
+ NCSA httpd appears to be moving toward adding experimental features
+ which are not generally required at the moment. Some of the experiments
+ will succeed while others will inevitably be dropped. The Apache
+ philosophy is to add what's needed as and when it is needed.
+ </P>
+ <P>
+ Friendly interaction between Apache and NCSA developers should ensure
+ that fundamental feature enhancments stay consistent between the two
+ servers for the foreseeable future.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="premature-script-headers"
+ ><STRONG>What does it mean when my CGIs fail with "Premature
+ end of script headers"?</STRONG></A>
+ <P>
+ </P>
+ <P>
+ It means just what it says: the server was expecting a complete set of
+ HTTP headers (one or more followed by a blank line), and didn't get
+ them. The most common cause of this is Perl scripts which haven't
+ disabled buffering; if you insert the following statements before your
+ first <SAMP>print</SAMP> statement, this will probably go away.
+ </P>
+ <PRE>
+ $cfh = select (STDOUT);
+ $| = 1;
+ select ($cfh);
+ </PRE>
+ <P>
+ If your script isn't written in Perl, do the equivalent thing for
+ whatever language you <EM>are</EM> using (<EM>e.g.</EM>, for C, call
+ <SAMP>fflush()</SAMP> after writing the headers).
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="ssi-part-i"
+ ><STRONG>How do I enable SSI (parsed HTML)?</STRONG></A>
+ <P>
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="ssi-part-ii"
+ ><STRONG>Why don't my parsed files get cached?</STRONG></A>
+ <P>
+ Since the server is performing run-time processing of your SSI
+ directives, which may change the content shipped to the client, it
+ can't know at the time it starts parsing what the final size of the
+ result will be, or whether the parsed result will always be the same.
+ This means that it can't generate <CODE>Content-Length</CODE> or
+ <CODE>Last-Modified</CODE> headers. Caches commonly work by comparing
+ the <CODE>Last-Modified</CODE> of what's in the cache with that being
+ delivered by the server. Since the server isn't sending that header
+ for a parsed document, whatever's doing the caching can't tell whether
+ the document has changed or not - and so fetches it again to be on the
+ safe side.
+ </P>
+ <P>
+ You can work around this in some cases by causing an
+ <CODE>Expires</CODE> header to be generated. (See the
+ <A
+ HREF="../mod/mod_expires.html"
+ REL="Help"
+ ><CODE>mod_expires</CODE></A>
+ documentation for more details.)
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="ssi-part-iii"
+ ><STRONG>How can I have my script output parsed?</STRONG></A>
+ <P>
+ So you want to include SSI directives in the output from your CGI
+ script, but can't figure out how to do it?
+ The short answer is "you can't." This has been regarded as a
+ security liability, and the basic solution is for your script itself to do
+ what the SSIs would be doing. After all, it's generating the
+ rest of the content.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="proxy"
+ ><STRONG>Does or will Apache act as a Proxy server?</STRONG></A>
+ <P>
+ Apache version 1.1 and above comes with a proxy module. If compiled
+ in, this will make Apache act as a caching-proxy server. This module
+ is still considered experimental, however.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="multiviews"
+ ><STRONG>What are "multiviews"?</STRONG></A>
+ <P>
+ "Multiviews" is the general name given to the Apache
+ server's ability to provide language-specific document variants in
+ response to a request. This is documented quite thoroughly in the
+ <A
+ HREF="http:../content-negotiation.html"
+ REL="Help"
+ >content negotiation</A>
+ description page.
+ </P>
+ <HR>
+ </LI>
+ <LI><A
+ NAME="multiviews"
+ ><STRONG>Why can't I run more than <<EM>n</EM>>
+ virtual hosts?</STRONG></A>
+ <P>
+ The Apache server can behave unpredictably when it encounters some
+ resource limitations. One of these is the <EM>per</EM>-process limit
+ on <STRONG>file descriptors</STRONG>, and that's almost always the
+ cause of problems seen when adding virtual hosts. In this
+ case, it is not actually Apache that's encountering the problem, but
+ typically some library routine (such as <SAMP>gethostbyname()</SAMP>)
+ which needs file descriptors and doesn't complain intelligibly when it
+ can't get them.
+ </P>
+ <P>
+ Each virtual host requires several file descriptors for housekeeping
+ functions, in addition to those actually used to serve files to
+ clients.
+ </P>
+ <P>
+ Typical values for <<EM>n</EM>> that we've seen are in
+ the neighbourhoods of 128 or 250. When the server bumps into the file
+ descriptor limit, it may dump core with a SIGSEGV, or it might just
+ hang, or it may limp along and you'll see (possibly meaningful) errors
+ in the error log.
+ </P>
+ <P>
+ As to what you can do about this:
+ </P>
+ <OL>
+ <LI>Increase the number of file descriptors available to the server
+ (see your system's documentation on the <SAMP>limit</SAMP> or
+ <SAMP>ulimit</SAMP> commands)
+ </LI>
+ <LI>"Don't do that" - try to run with fewer virtual hosts
+ </LI>
+ <LI>Spread your operation across multiple server processes and/or ports
+ </LI>
+ </OL>
+ <P>
+ Since this is an operating-system limitation, there's not much else
+ available in the way of solutions.
+ </P>
+ <HR>
</OL>
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