Commit d650b994 authored by Ken Coar's avatar Ken Coar
Browse files

Latest version of the Apache FAQ. Not the ultimate, but enough for 

now, and somewhat improved over what's there.  More to come soon.
Reviewed by:	Roy Fielding, Paul Sutton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@77815 13f79535-47bb-0310-9956-ffa450edef68
parent ea3a3ba8

docs/manual/misc/FAQ.html

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<!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>

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<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><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>

   <LI><A HREF="#relate">How does The Apache Group's work relate to

    other servers?</A> 

   </LI>

   <LI><A HREF="#name">Why the name &quot;Apache&quot;?</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><A HREF="#proxy">Does or will Apache act as a Proxy server?</A>

   </LI>

   <LI><A HREF="#future">What are the future plans for Apache?</A>

<LI><A HREF="#support">Who do I contact for support ?</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">&quot;Why can't I ...?  Why won't ...

        work?&quot;  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 &quot;Premature end of script headers&quot;?</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 &quot;multiviews&quot;?</A>

   </LI>

   <LI><A HREF="#fdlim">Why can't I run more than &lt;<EM>n</EM>&gt;

    virtual hosts?</A>

   </LI>

  </OL>

 </LI>

</UL>



<HR>



<H2>The Answers</H2>

<OL>

<LI><A name="what">What is Apache ?</A>

<P>

</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>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>

  <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>

<LI><A name="relate">How does the Apache group relate to other

server efforts, such as NCSA's?</A>

  </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
@@ -51,108 +127,378 @@ 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".

 </LI>

 <LI><A

      NAME="name"

     ><STRONG>Why the name &quot;Apache&quot;?</STRONG></A>

  <P>

  A cute name which stuck. Apache is &quot;<STRONG>A

  PA</STRONG>t<STRONG>CH</STRONG>y server&quot;.  It was

  based on some existing code and a series of &quot;patch files&quot;.

  </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>

 </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">http://webcompare.iworld.com/compare/chart.html</A>

  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

  <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

  &quot;benchmarks&quot; 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>



  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

 </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. 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>

  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><A name="future">What are the future plans for Apache ?</A>

<P><UL>

 </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>to keep up with advances in HTTP protocol and web developments in general

   </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>to respond to needs of large volume providers as well as occasional users.

   </LI>

   <LI>to respond to needs of large volume providers as well as

    occasional users.

   </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

  </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 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,

  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>

  <P>

  Commercial support for Apache is, however, available from a number

third parties.

</p>

  of 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>.

 </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><A name="where">Where can I get Apache ?</A>

 </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>&quot;Why can't I ...?  Why won't ... work?&quot;  What to

     do in case of problems</STRONG></A>

  <P>

You can find the source for Apache at <A HREF="http://www.apache.org/">http://www.apache.org/</A>.

  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 &amp;

    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 &quot;me, too&quot; 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&amp;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 &quot;Premature

     end of script headers&quot;?</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 &quot;you can't.&quot;  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 &quot;multiviews&quot;?</STRONG></A>

  <P>

  &quot;Multiviews&quot; 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 &lt;<EM>n</EM>&gt;

      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 &lt;<EM>n</EM>&gt; 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>&quot;Don't do that&quot; - 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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