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<H1 ALIGN="CENTER">Apache Server Frequently Asked Questions</H1>
<P>
$Revision: 1.63.2.14 $ ($Date: 1997/08/03 08:47:57 $)
</P>
<P>
The latest version of this FAQ is always available from the main
Apache web site, at
&lt;<A
HREF="http://www.apache.org/docs/misc/FAQ"
REL="Help"
><SAMP>http://www.apache.org/docs/misc/FAQ</SAMP></A>&gt;.
</P>
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<P>
If you are reading a text-only version of this FAQ, you may find numbers
enclosed in brackets (such as &quot;[12]&quot;). These refer to the list of
reference URLs to be found at the end of the document. These references
do not appear, and are not needed, for the hypertext version.
</P>
<H2>The Questions</H2>
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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>
<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>
<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">&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="#CGIoutsideScriptAlias">How do I enable CGI execution
in directories other than the ScriptAlias?</A>
</LI>
<LI><A HREF="#premature-script-headers">What does it mean when my
CGIs fail with &quot;<SAMP>Premature end of script
headers</SAMP>&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>
<LI><A HREF="#freebsd-setsize">Can I increase FD_SETSIZE on FreeBSD?</A>
</LI>
<LI><A HREF="#limitGET">Why do I keep getting &quot;access denied&quot; for
form POST requests?</A>
</LI>
<LI><A HREF="#passwdauth">Can I use my <SAMP>/etc/passwd</SAMP> file
for Web page authentication?</A>
</LI>
<LI><A HREF="#errordoc401">Why doesn't my <CODE>ErrorDocument
401</CODE> work?</A>
</LI>
<LI><A HREF="#setgid">Why do I get &quot;<SAMP>setgid: Invalid
argument</SAMP>&quot; at startup?</A>
</LI>
<LI><A HREF="#cookies1">Why does Apache send a cookie on every response?</A>
</LI>
<LI><A HREF="#cookies2">Why don't my cookies work, I even compiled in
<SAMP>mod_cookies</SAMP>?</A>
</LI>
<LI><A HREF="#jdk1-and-http1.1">Why do my Java app[let]s give me plain text
when I request an URL from an Apache server?</A>
</LI>
<LI><A HREF="#putsupport">Why can't I publish to my Apache server
using PUT on Netscape Gold and other programs?</A>
</LI>
<LI><A HREF="#fastcgi">Why isn't FastCGI included with Apache any
more?</A>
</LI>
<LI><A HREF="#nodelay">Why am I getting &quot;<SAMP>httpd: could not
set socket option TCP_NODELAY</SAMP>&quot; in my error log?</A>
</LI>
<LI><A HREF="#peerreset">Why am I getting &quot;<SAMP>connection
reset by peer</SAMP>&quot; in my error log?</A>
</LI>
<LI><A HREF="#nph-scripts">How can I get my script's output without
Apache buffering it?</A>
</LI>
<LI><A HREF="#linuxiovec">Why do I get complaints about redefinition
of &quot;<CODE>struct iovec</CODE>&quot; when compiling under Linux?</A>
</LI>
<LI><A HREF="#wheres-the-dump">The errorlog says Apache dumped core,
but where's the dump file?</A>
</LI>
<LI><A HREF="#dnsauth">Why isn't restricting access by host or domain name
working correctly?</A>
</LI>
<LI><A HREF="#SSL-i">Why doesn't Apache include SSL?</A>
</LI>
<LI><A HREF="#HPUX-core">Why do I get core dumps under HPUX using
HP's ANSI C compiler?</A>
</LI>
<LI><A HREF="#midi">How do I get Apache to send a MIDI file so the
browser can play it?</A>
</LI>
<LI><A HREF="#cantbuild">Why won't Apache compile with my
system's <SAMP>cc</SAMP>?</A>
</LI>
<LI><A HREF="#addlog">How do I add browsers and referrers to my
logs?</A>
</LI>
<LI><A HREF="#bind8.1">Why do I get an error about an undefined
reference to &quot;<SAMP>__inet_ntoa</SAMP>&quot; or other
<SAMP>__inet_*</SAMP> symbols?</A>
</LI>
<LI><A HREF="#set-servername">Why does accessing directories only work
when I include the trailing "/"
(<EM>e.g.</EM>,&nbsp;<SAMP>http://foo.domain.com/~user/</SAMP>) but
not when I omit it
(<EM>e.g.</EM>,&nbsp;<SAMP>http://foo.domain.com/~user</SAMP>)?</A>
</LI>
<LI><A HREF="#user-authentication">How do I set up Apache to require
a username and password to access certain documents?</A>
</LI>
<LI><A HREF="#remote-user-var">Why is the environment variable
<SAMP>REMOTE_USER</SAMP> not set?</A>
</LI>
<LI><A HREF="#remote-auth-only">How do I set up Apache to allow access
to certain documents only if a site is either a local site
<EM>or</EM> the user supplies a password and username?</A>
</LI>
<LI><A HREF="#no-info-directives">Why doesn't mod_info list any
directives?</A>
<LI><A HREF="#linux-shmget">When I run it under Linux I get "shmget:
function not found", what should I do?</A>
</LI>
<LI><A HREF="#authauthoritative">Why does my authentication give
me a server error?</A>
<LI><A HREF="#auth-on-same-machine">Do I have to keep the (mSQL)
authentication information on the same machine?</A>
</LI>
<LI><A HREF="#msql-slow">Why is my mSQL authentication terribly slow?</A>
</LI>
<LI><A HREF="#rewrite-more-config">Where can I find mod_rewrite rulesets
which already solve particular URL-related problems?</A>
</LI>
<LI><A HREF="#rewrite-article">Where can I find any published information about
URL-manipulations and mod_rewrite?</A>
</LI>
<LI><A HREF="#rewrite-complexity">Why is mod_rewrite so difficult to learn
and seems so complicated?</A>
</LI>
<LI><A HREF="#rewrite-dontwork">What can I do if my RewriteRules don't work
as expected?</A>
</LI>
<LI><A HREF="#rewrite-prefixdocroot">Why don't some of my URLs get
prefixed with DocumentRoot when using mod_rewrite?</A>
</LI>
<LI><A HREF="#rewrite-nocase">How can I make all my URLs case-insensitive
with mod_rewrite?</A>
</LI>
<LI><A HREF="#rewrite-virthost">Why are RewriteRules in my VirtualHost
parts ignored?</A>
</LI>
<LI><A HREF="#rewrite-envwhitespace">How can I use strings with whitespaces
in RewriteRule's ENV flag?</A>
</LI>
<LI><A HREF="#cgi-spec">Where can I find the &quot;CGI
specification&quot;?</A>
</LI>
</OL>
</LI>
</UL>
<HR>
<H2>The Answers</H2>
<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.
</P>
<HR>
</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 &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>
<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"
>Web Compare</A>'s
comparison chart.
</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
&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>
<HR>
</LI>
<LI><A NAME="tested">
<STRONG>How thoroughly tested is Apache?</STRONG>
</A>
<P>
Apache is run on over 500,000 Internet servers (as of July 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>
The Apache project's web site includes a page with a partial list of
<A
HREF="http://www.apache.org/info/apache_users"
>sites running Apache</A>.
</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"
>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
<A
HREF="http://www.apache.org/"
>Apache web site</A>.
There is also a regular electronic publication called
<A
HREF="http://www.apacheweek.com/"
REL="Help"
><CITE>Apache Week</CITE></A>
available. Links to relevant <CITE>Apache Week</CITE> articles are
included below where appropriate.
</P>
<HR>
</LI>
<LI><A NAME="where">
<STRONG>Where can I get Apache?</STRONG>
</A>
<P>
You can find out how to download the source for Apache at the
project's
<A
HREF="http://www.apache.org/"
>main web page</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>
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. Sometimes this is enough for you to diagnose
&amp; fix the problem yourself (such as file permissions or the like).
The default location of the error log is
<SAMP>/usr/local/etc/httpd/logs/error_log</SAMP>, but see the
<A
HREF="../mod/core.html#errorlog"
><SAMP>ErrorLog</SAMP></A>
directive in your config files for the location on your server.
</P>
</LI>
<LI><STRONG>Check the
<A
HREF="http://www.apache.org/docs/misc/FAQ.html"
>FAQ</A>!</STRONG>
<P>
The latest version of the Apache Frequently-Asked Questions list can
always be found at the main Apache web site.
</P>
</LI>
<LI><STRONG>Check the Apache bug database</STRONG>
<P>
Most problems that get reported to The Apache Group are recorded in
the
<A
HREF="http://www.apache.org/bugdb.cgi"
>bug database</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 submitter, 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
<A
HREF="http://www.apache.org/bugdb.cgi"
>logging a bug report</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>
<P>
<DL>
<DD><CODE># cd <EM>ServerRoot</EM><BR>
# dbx httpd core<BR>
(dbx) where</CODE>
</DD>
</DL>
</P>
<P>
(Substitute the appropriate locations for your
<SAMP>ServerRoot</SAMP> and your <SAMP>httpd</SAMP> and
<SAMP>core</SAMP> files. You may have to use <CODE>gdb</CODE>
instead of <CODE>dbx</CODE>.)
</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 enhancements stay consistent between the two
servers for the foreseeable future.
</P>
<HR>
</LI>
<LI><A NAME="CGIoutsideScriptAlias">
<STRONG>How do I enable CGI execution in directories other than
the ScriptAlias?</STRONG>
</A>
<P>
Apache recognizes all files in a directory named as a
<A
HREF="../mod/mod_alias.html#scriptalias"
><SAMP>ScriptAlias</SAMP></A>
as being eligible for execution rather than processing as normal
documents. This applies regardless of the file name, so scripts in a
ScriptAlias directory don't need to be named
&quot;<SAMP>*.cgi</SAMP>&quot; or &quot;<SAMP>*.pl</SAMP>&quot; or
whatever. In other words, <EM>all</EM> files in a ScriptAlias
directory are scripts, as far as Apache is concerned.
</P>
<P>
To persuade Apache to execute scripts in other locations, such as in
directories where normal documents may also live, you must tell it how
to recognize them - and also that it's okay to execute them. For
this, you need to use something like the
<A
HREF="../mod/mod_mime.html#addhandler"
><SAMP>AddHandler</SAMP></A>
directive.
</P>
<P>
<OL>
<LI>In an appropriate section of your server configuration files, add
a line such as
<P>
<DL>
<DD><CODE>AddHandler cgi-script .cgi</CODE>
</DD>
</DL>
</P>
<P>
The server will then recognize that all files in that location (and
its logical descendants) that end in &quot;<SAMP>.cgi</SAMP>&quot;
are script files, not documents.
</P>
</LI>
<LI>Make sure that the directory location is covered by an
<A
HREF="../mod/core.html#options"
><SAMP>Options</SAMP></A>
declaration that includes the <SAMP>ExecCGI</SAMP> option.
</LI>
</OL>
</P>
<P>
In some situations it can be not conform to your local policy to actually
allow all files named &quot;<SAMP>*.cgi</SAMP>&quot; to be executable.
Perhaps all you want is to enable a particular file in a normal directory to
be executable. This can be alternatively accomplished
via
<A
HREF="../mod/mod_rewrite.html"
><SAMP>mod_rewrite</SAMP></A>
and the following steps:
</P>
<P>
<OL>
<LI>Locally add to the corresponding <SAMP>.htaccess</SAMP> file a ruleset
similar to this one:
<P>
<DL>
<DD><CODE>RewriteEngine on
<BR>
RewriteBase /~foo/bar/
<BR>
RewriteRule ^quux\.cgi$ - [T=application/x-httpd-cgi]</CODE>
</DD>
</DL>
</P>
</LI>
<LI>Make sure that the directory location is covered by an
<A
HREF="../mod/core.html#options"
><SAMP>Options</SAMP></A>
declaration that includes the <SAMP>ExecCGI</SAMP> and
<SAMP>FollowSymLinks</SAMP> option.
</LI>
</OL>
</P>
<HR>
</LI>
<LI><A NAME="premature-script-headers">
<STRONG>What does it mean when my CGIs fail with
&quot;<SAMP>Premature end of script headers</SAMP>&quot;?</STRONG>
</A>
<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.
</P>
<P>
The most common cause of this problem is the script dying before
sending the complete set of headers, or possibly any at all, to the
server. To see if this is the case, try running the script standalone
from an interactive session, rather than as a script under the server.
If you get error messages, this is almost certainly the cause of the
&quot;premature end of script headers&quot; message.
</P>
<P>
The second most common cause of this (aside from people not
outputting the required headers at all) is a result of an interaction
with Perl's output buffering. To make Perl flush its buffers
after each output statement, insert the following statements around
the <CODE>print</CODE> or <CODE>write</CODE> statements that send your
HTTP headers:
</P>
<P>
<DL>
<DD><CODE>{<BR>
&nbsp;local ($oldbar) = $|;<BR>
&nbsp;$cfh = select (STDOUT);<BR>
&nbsp;$| = 1;<BR>
&nbsp;#<BR>
&nbsp;# print your HTTP headers here<BR>
&nbsp;#<BR>
&nbsp;$| = $oldbar;<BR>
&nbsp;select ($cfh);<BR>
}</CODE>
</DD>
</DL>
</P>
<P>
This is generally only necessary when you are calling external
programs from your script that send output to stdout, or if there will
be a long delay between the time the headers are sent and the actual
content starts being emitted. To maximize performance, you should
turn buffer-flushing back <EM>off</EM> (with <CODE>$| = 0</CODE> or the
equivalent) after the statements that send the headers, as displayed
above.
</P>
<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
<CODE>fflush()</CODE> after writing the headers).
</P>
<HR>
</LI>
<LI><A NAME="ssi-part-i">
<STRONG>How do I enable SSI (parsed HTML)?</STRONG>
</A>
<P>
SSI (an acronym for Server-Side Include) directives allow static HTML
documents to be enhanced at run-time (<EM>e.g.</EM>, when delivered to
a client by Apache). The format of SSI directives is covered
in the <A HREF="../mod/mod_include.html">mod_include manual</A>;
suffice it to say that Apache supports not only SSI but
xSSI (eXtended SSI) directives.
</P>
<P>
Processing a document at run-time is called <EM>parsing</EM> it; hence
the term &quot;parsed HTML&quot; sometimes used for documents that
contain SSI instructions. Parsing tends to be <EM>extremely</EM>
resource-consumptive, and is not enabled by default. It can also
interfere with the cachability of your documents, which can put a
further load on your server. (see the
<A
HREF="#ssi-part-ii"
>next question</A>
for more information about this.)
</P>
<P>
To enable SSI processing, you need to
</P>
<UL>
<LI>Build your server with the
<A
HREF="../mod/mod_include.html"
><SAMP>mod_include</SAMP></A>
module. This is normally compiled in by default.
</LI>
<LI>Make sure your server configuration files have an
<A
HREF="../mod/core.html#options"
><SAMP>Options</SAMP></A>
directive which permits <SAMP>Includes</SAMP>.
</LI>
<LI>Make sure that the directory where you want the SSI documents to
live is covered by the &quot;server-parsed&quot; content handler,
either explicitly or in some ancestral location. That can be done
with the following
<A
HREF="../mod/mod_mime.html#addhandler"
><SAMP>AddHandler</SAMP></A>
directive:
<P>
<DL>
<DD><CODE>AddHandler server-parsed .shtml</CODE>
</DD>
</DL>
</P>
This indicates that all files ending in &quot;.shtml&quot; in that
location (or its descendants) should be parsed. Note that using
&quot;.html&quot; will cause all normal HTML files to be parsed,
which may put an inordinate load on your server.
</LI>
</UL>
<P>
For additional information, see the <CITE>Apache Week</CITE> article
on
<A
HREF="http://www.apacheweek.com/features/ssi"
REL="Help"
><CITE>Using Server Side Includes</CITE></A>.
</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 <SAMP>Content-Length</SAMP> or
<SAMP>Last-Modified</SAMP> headers. Caches commonly work by comparing
the <SAMP>Last-Modified</SAMP> 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
<SAMP>Expires</SAMP> header to be generated. (See the
<A
HREF="../mod/mod_expires.html"
REL="Help"
><SAMP>mod_expires</SAMP></A>
documentation for more details.) Another possibility is to use the
<A
HREF="../mod/mod_include.html#xbithack"
REL="Help"
><SAMP>XBitHack Full</SAMP></A>
mechanism, which tells Apache to send (under certain circumstances
detailed in the XBitHack directive description) a
<SAMP>Last-Modified</SAMP> header based upon the last modification
time of the file being parsed. Note that this may actually be lying
to the client if the parsed file doesn't change but the SSI-inserted
content does; if the included content changes often, this can result
in stale copies being cached.
</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 is potentially
a security liability and, more importantly, it can not be cleanly
implemented under the current server API. The best workaround
is for your script itself to do what the SSIs would be doing.
After all, it's generating the rest of the content.
</P>
<P>
This is a feature The Apache Group hopes to add in the next major
release after 1.2.
</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
<A
HREF="../mod/mod_proxy.html"
>proxy module</A>.
If compiled
in, this will make Apache act as a caching-proxy server.
</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="../content-negotiation.html"
REL="Help"
>content negotiation</A>
description page. In addition, <CITE>Apache Week</CITE> carried an
article on this subject entitled
&quot;<A
HREF="http://www.apacheweek.com/features/negotiation"
REL="Help"
><CITE>Content Negotiation Explained</CITE></A>&quot;.
</P>
<HR>
</LI>
<LI><A NAME="fdlim">
<STRONG>Why can't I run more than &lt;<EM>n</EM>&gt;
virtual hosts?</STRONG>
</A>
<P>
You are probably running into resource limitations in your
operating system. The most common limitation is the
<EM>per</EM>-process limit on <STRONG>file descriptors</STRONG>,
which is almost always the cause of problems seen when adding
virtual hosts. Apache often does not give an intuitive error
message because it is normally some library routine (such as
<CODE>gethostbyname()</CODE>) which needs file descriptors and
doesn't complain intelligibly when it can't get them.
</P>
<P>
Each log file requires a file descriptor, which means that if you are
using separate access and error logs for each virtual host, each
virtual host needs two file descriptors. Each
<A
HREF="../mod/core.html#listen"
><SAMP>Listen</SAMP></A>
directive also needs a file descriptor.
</P>
<P>
Typical values for &lt;<EM>n</EM>&gt; that we've seen are in
the neighborhood of 128 or 250. When the server bumps into the file
descriptor limit, it may dump core with a SIGSEGV, it might just
hang, or it may limp along and you'll see (possibly meaningful) errors
in the error log. One common problem that occurs when you run into
a file descriptor limit is that CGI scripts stop being executed
properly.
</P>
<P>
As to what you can do about this:
</P>
<OL>
<LI>Reduce the number of
<A
HREF="../mod/core.html#listen"
><SAMP>Listen</SAMP></A>
directives. If there are no other servers running on the machine
on the same port then you normally don't
need any Listen directives at all. By default Apache listens to
all addresses on port 80.
</LI>
<LI>Reduce the number of log files. You can use
<A
HREF="../mod/mod_log_config.html"
><SAMP>mod_log_config</SAMP></A>
to log all requests to a single log file while including the name
of the virtual host in the log file. You can then write a
script to split the logfile into separate files later if
necessary.
</LI>
<LI>Increase the number of file descriptors available to the server
(see your system's documentation on the <CODE>limit</CODE> or
<CODE>ulimit</CODE> commands). For some systems, information on
how to do this is available in the
<A
HREF="perf.html"
>performance hints</A>
page. There is a specific note for
<A HREF="#freebsd-setsize">FreeBSD</A> below.
</LI>
<LI>&quot;Don't do that&quot; - try to run with fewer virtual hosts
</LI>
<LI>Spread your operation across multiple server processes (using
<A
HREF="../mod/core.html#listen"
><SAMP>Listen</SAMP></A>
for example, but see the first point) 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>
<P>
As of 1.2.1 we have made attempts to work around various limitations
involving running with many descriptors.
<A HREF="descriptors.html">More information is available.</A>
</P>
<HR>
</LI>
<LI><A NAME="freebsd-setsize">
<STRONG>Can I increase <SAMP>FD_SETSIZE</SAMP> on FreeBSD?</STRONG>
</A>
<P>
On versions of FreeBSD before 3.0, the <SAMP>FD_SETSIZE</SAMP> define
defaults to 256. This means that you will have trouble usefully using
more than 256 file descriptors in Apache. This can be increased, but
doing so can be tricky.
If you are using a version prior to 2.2, you need to recompile your
kernel with a larger FD_SETSIZE. This can be done by adding a
line such as:
</P>
<DL>
<DD><CODE>options FD_SETSIZE <EM>nnn</EM></CODE>
</DD>
</DL>
<P>
To your kernel config file. Starting at version 2.2, this is no
longer necessary.
</P>
<P>
If you are using a version of 2.1-stable from after 1997/03/10 or
2.2 or 3.0-current from before 1997/06/28, there is a limit in
the resolver library that prevents it from using more file descriptors
than what FD_SETSIZE is set to when libc is compiled. To increase
this, you have to recompile libc with a higher FD_SETSIZE.
</P>
<P>
In FreeBSD 3.0, the default FD_SETSIZE has been increased to
1024 and the above limitation in the resolver library
has been removed.
</P>
<P>
After you deal with the appropriate changes above, you can increase
the setting of <SAMP>FD_SETSIZE</SAMP> at Apache compilation time
by adding &quot;<SAMP>-DFD_SETSIZE=<EM>nnn</EM></SAMP>&quot; to the
<SAMP>EXTRA_CFLAGS</SAMP> line in your <SAMP>Configuration</SAMP>
file.
</P>
<HR>
</LI>
<LI><A NAME="limitGET">
<STRONG>Why do I keep getting &quot;access denied&quot; for form POST
requests?</STRONG>
</A>
<P>
The most common cause of this is a <SAMP>&lt;Limit&gt;</SAMP> section
that only names the <SAMP>GET</SAMP> method. Look in your
configuration files for something that resembles the following and
would affect the location where the POST-handling script resides:
</P>
<P>
<DL>
<DD><CODE>&lt;Limit GET&gt;<BR>&nbsp;&nbsp;&nbsp;&nbsp;:</CODE>
</DD>
</DL>
</P>
<P>
Change that to <CODE>&lt;Limit GET POST&gt;</CODE> and the problem
will probably go away.
</P>
<HR>
</LI>
<LI><A NAME="passwdauth">
<STRONG>Can I use my <SAMP>/etc/passwd</SAMP> file
for Web page authentication?</STRONG>
</A>
<P>
Yes, you can - but it's a <STRONG>very bad idea</STRONG>. Here are
some of the reasons:
</P>
<UL>
<LI>The Web technology provides no governors on how often or how
rapidly password (authentication failure) retries can be made. That
means that someone can hammer away at your system's
<SAMP>root</SAMP> password using the Web, using a dictionary or
similar mass attack, just as fast as the wire and your server can
handle the requests. Most operating systems these days include
attack detection (such as <EM>n</EM> failed passwords for the same
account within <EM>m</EM> seconds) and evasion (breaking the
connection, disabling the account under attack, disabling
<EM>all</EM> logins from that source, <EM>et cetera</EM>), but the
Web does not.
</LI>
<LI>An account under attack isn't notified (unless the server is
heavily modified); there's no &quot;You have 19483 login
failures&quot; message when the legitimate owner logs in.
</LI>
<LI>Without an exhaustive and error-prone examination of the server
logs, you can't tell whether an account has been compromised.
Detecting that an attack has occurred, or is in progress, is fairly
obvious, though - <EM>if</EM> you look at the logs.
</LI>
<LI>Web authentication passwords (at least for Basic authentication)
generally fly across the wire, and through intermediate proxy
systems, in what amounts to plain text. &quot;O'er the net we
go/Caching all the way;/O what fun it is to surf/Giving my password
away!&quot;
</LI>
<LI>Since HTTP is stateless, information about the authentication is
transmitted <EM>each and every time</EM> a request is made to the
server. Essentially, the client caches it after the first
successful access, and transmits it without asking for all
subsequent requests to the same server.
</LI>
<LI>It's relatively trivial for someone on your system to put up a
page that will steal the cached password from a client's cache
without them knowing. Can you say &quot;password grabber&quot;?
</LI>
</UL>
<P>
If you still want to do this in light of the above disadvantages, the
method is left as an exercise for the reader. It'll void your Apache
warranty, though, and you'll lose all accumulated UNIX guru points.
</P>
<HR>
</LI>
<LI><A NAME="errordoc401">
<STRONG>Why doesn't my <CODE>ErrorDocument 401</CODE> work?</STRONG>
</A>
<P>
You need to use it with a URL in the form
&quot;<SAMP>/foo/bar</SAMP>&quot; and not one with a method and
hostname such as &quot;<SAMP>http://host/foo/bar</SAMP>&quot;. See the
<A
HREF="../mod/core.html#errordocument"
><SAMP>ErrorDocument</SAMP></A>
documentation for details. This was incorrectly documented in the past.
</P>
<HR>
</LI>
<LI><A NAME="setgid">
<STRONG>Why do I get &quot;<SAMP>setgid: Invalid
argument</SAMP>&quot; at startup?</STRONG>
</A>
<P>
Your
<A
HREF="../mod/core.html#group"
><SAMP>Group</SAMP></A>
directive (probably in <SAMP>conf/httpd.conf</SAMP>) needs to name a
group that actually exists in the <SAMP>/etc/group</SAMP> file (or
your system's equivalent).
</P>
<HR>
</LI>
<LI><A NAME="cookies1">
<STRONG>Why does Apache send a cookie on every response?</STRONG>
</A>
<P>
Apache does <EM>not</EM> send automatically send a cookie on every
response, unless you have re-compiled it with the
<A
HREF="../mod/mod_cookies.html"
><SAMP>mod_cookies</SAMP></A>
module.
This module was distributed with Apache prior to 1.2.
This module may help track users, and uses cookies to do this. If
you are not using the data generated by <SAMP>mod_cookies</SAMP>, do
not compile it into Apache. Note that in 1.2 this module was renamed
to the more correct name
<A
HREF="../mod/mod_usertrack.html"
><SAMP>mod_usertrack</SAMP></A>,
and cookies
have to be specifically enabled with the
<A
HREF="../mod/mod_usertrack.html#cookietracking"
><SAMP>CookieTracking</SAMP></A>
directive.
</P>
<HR>
</LI>
<LI><A NAME="cookies2">
<STRONG>Why don't my cookies work, I even compiled in
<SAMP>mod_cookies</SAMP>?
</STRONG>
</A>
<P>
Firstly, you do <EM>not</EM> need to compile in
<SAMP>mod_cookies</SAMP> in order for your scripts to work (see the
<A
HREF="#cookies1"
>previous question</A>
for more about <SAMP>mod_cookies</SAMP>). Apache passes on your
<SAMP>Set-Cookie</SAMP> header fine, with or without this module. If
cookies do not work it will be because your script does not work
properly or your browser does not use cookies or is not set-up to
accept them.
</P>
<HR>
</LI>
<LI><A NAME="jdk1-and-http1.1">
<STRONG>Why do my Java app[let]s give me plain text when I request
an URL from an Apache server?</STRONG>
</A>
<P>
As of version 1.2, Apache is an HTTP/1.1 (HyperText Transfer Protocol
version 1.1) server. This fact is reflected in the protocol version
that's included in the response headers sent to a client when
processing a request. Unfortunately, low-level Web access classes
included in the Java Development Kit (JDK) version 1.0.2 expect to see
the version string &quot;HTTP/1.0&quot; and do not correctly interpret
the &quot;HTTP/1.1&quot; value Apache is sending (this part of the
response is a declaration of what the server can do rather than a
declaration of the dialect of the response). The result
is that the JDK methods do not correctly parse the headers, and
include them with the document content by mistake.
</P>
<P>
This is definitely a bug in the JDK 1.0.2 foundation classes from Sun,
and it has been fixed in version 1.1. However, the classes in
question are part of the virtual machine environment, which means
they're part of the Web browser (if Java-enabled) or the Java
environment on the client system - so even if you develop
<EM>your</EM> classes with a recent JDK, the eventual users might
encounter the problem.
The classes involved are replaceable by vendors implementing the
Java virtual machine environment, and so even those that are based
upon the 1.0.2 version may not have this problem.
</P>
<P>
In the meantime, a workaround is to tell
Apache to &quot;fake&quot; an HTTP/1.0 response to requests that come
from the JDK methods; this can be done by including a line such as the
following in your server configuration files:
</P>
<P>
<DL>
<DD><CODE>BrowserMatch Java1.0 force-response-1.0
<BR>
BrowserMatch JDK/1.0 force-response-1.0</CODE>
</DD>
</DL>
</P>
<P>
More information about this issue can be found in the
<A
HREF="http://www.apache.org/info/jdk-102"
><CITE>Java and HTTP/1.1</CITE></A>
page at the Apache web site.
</P>
<HR>
</LI>
<LI><A NAME="putsupport">
<STRONG>Why can't I publish to my Apache server using PUT on
Netscape Gold and other programs?</STRONG>
</A>
<P>
Because you need to install and configure a script to handle
the uploaded files. This script is often called a &quot;PUT&quot; handler.
There are several available, but they may have security problems.
Using FTP uploads may be easier and more secure, at least for now.
For more information, see the <CITE>Apache Week</CITE> article
<A
HREF="http://www.apacheweek.com/features/put"
><CITE>Publishing Pages with PUT</CITE></A>.
</P>
<HR>
</LI>
<LI><A NAME="fastcgi">
<STRONG>Why isn't FastCGI included with Apache any more?</STRONG>
</A>
<P>
The simple answer is that it was becoming too difficult to keep the
version being included with Apache synchronized with the master copy
at the
<A
HREF="http://www.fastcgi.com/servers/apache/"
>FastCGI web site</A>. When a new version of Apache was released, the
version of the FastCGI module included with it would soon be out of date.
</P>
<P>
You can still obtain the FastCGI module for Apache from the master
FastCGI web site.
</P>
<HR>
</LI>
<LI><A NAME="nodelay">
<STRONG>Why am I getting &quot;<SAMP>httpd: could not set socket
option TCP_NODELAY</SAMP>&quot; in my error log?</STRONG>
</A>
<P>
This message almost always indicates that the client disconnected
before Apache reached the point of calling <CODE>setsockopt()</CODE>
for the connection. It shouldn't occur for more than about 1% of the
requests your server handles, and it's advisory only in any case.
</P>
<HR>
</LI>
<LI><A NAME="peerreset">
<STRONG>Why am I getting &quot;<SAMP>connection reset by
peer</SAMP>&quot; in my error log?</STRONG>
</A>
<P>
This is a normal message and nothing about which to be alarmed. It simply
means that the client canceled the connection before it had been
completely set up - such as by the end-user pressing the &quot;Stop&quot;
button. People's patience being what it is, sites with response-time
problems or slow network links may experiences this more than
high-capacity ones or those with large pipes to the network.
</P>
<HR>
</LI>
<LI><A NAME="nph-scripts">
<STRONG>How can I get my script's output without Apache buffering
it?</STRONG>
</A>
<P>
In order to improve network performance, Apache buffers script output
into relatively large chunks. If you have a script that sends
information in bursts (such as partial-done messages in a multi-commit
database transaction, perhaps), the client will not necessarily get
the output as the script is generating it.
</P>
<P>
To avoid this, Apache recognizes scripts whose names begin with
&quot;<SAMP>nph-</SAMP>&quot; as <EM>non-parsed-header</EM> scripts.
That is, Apache won't buffer their output, but connect it directly to
the socket going back to the client.
</P>
<P>
While this will probably do what you want, there <EM>are</EM> some
disadvantages to it:
</P>
<UL>
<LI><STRONG>YOU</STRONG> (the script) are responsible for generating
<STRONG>ALL</STRONG> of the HTTP headers, and no longer
<EM>just</EM> the &quot;<SAMP>Content-type</SAMP>&quot; or
&quot;<SAMP>Location</SAMP>&quot; headers
</LI>
<LI>Unless your script generates its output carefully, you will see a
performance penalty as excessive numbers of packets go back and forth
</LI>
</UL>
<P>
As an example how you might handle the former (in a Perl script):
</P>
<P>
<DL>
<DD><CODE>if ($0 =~ m:^(.*/)*nph-[^/]*$:) {
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;
$HTTP_headers&nbsp;=&nbsp;
&quot;HTTP/1.1&nbsp;200&nbsp;OK\015\012&quot;;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;
$HTTP_headers&nbsp;.=&nbsp;
&quot;Connection:&nbsp;close\015\012&quot;;
<BR>
&nbsp;&nbsp;&nbsp;&nbsp;
print&nbsp;$HTTP_headers;
<BR>
}</CODE>
</DD>
</DL>
</P>
<P>
and then follow with your normal non-<SAMP>nph</SAMP> headers.
</P>
<HR>
</LI>
<LI><A NAME="linuxiovec">
<STRONG>Why do I get complaints about redefinition
of &quot;<CODE>struct iovec</CODE>&quot; when
compiling under Linux?</STRONG>
</A>
<P>
This is a conflict between your C library includes and your kernel
includes. You need to make sure that the versions of both are matched
properly. There are two workarounds, either one will solve the problem:
</P>
<P>
<UL>
<LI>Remove the definition of <CODE>struct iovec</CODE> from your C
library includes. It is located in <CODE>/usr/include/sys/uio.h</CODE>.
<STRONG>Or,</STRONG>
</LI>
<LI>Add <CODE>-DNO_WRITEV</CODE> to the <CODE>EXTRA_CFLAGS</CODE>
line in your <SAMP>Configuration</SAMP> and reconfigure/rebuild.
This hurts performance and should only be used as a last resort.
</LI>
</UL>
</P>
<HR>
</LI>
<LI><A NAME="wheres-the-dump">
<STRONG>The errorlog says Apache dumped core, but where's the dump
file?</STRONG>
</A>
<P>
In Apache version 1.2, the error log message
about dumped core includes the directory where the dump file should be
located. However, many Unixes do not allow a process that has
called <CODE>setuid()</CODE> to dump core for security reasons;
the typical Apache setup has the server started as root to bind to
port 80, after which it changes UIDs to a non-privileged user to
serve requests.
</P>
<P>
Dealing with this is extremely operating system-specific, and may
require rebuilding your system kernel. Consult your operating system
documentation or vendor for more information about whether your system
does this and how to bypass it. If there <EM>is</EM> a documented way
of bypassing it, it is recommended that you bypass it only for the
<SAMP>httpd</SAMP> server process if possible.
</P>
<P>
The canonical location for Apache's core-dump files is the
<A
HREF="../mod/core.html#serverroot"
>ServerRoot</A>
directory.
</P>
<HR>
</LI>
<LI><A NAME="dnsauth">
<STRONG>Why isn't restricting access by host or domain name
working correctly?</STRONG>
</A>
<P>
Two of the most common causes of this are:
</P>
<OL>
<LI><STRONG>An error, inconsistency, or unexpected mapping in the DNS
registration</STRONG>
<BR>
This happens frequently: your configuration restricts access to
<SAMP>Host.FooBar.Com</SAMP>, but you can't get in from that host.
The usual reason for this is that <SAMP>Host.FooBar.Com</SAMP> is
actually an alias for another name, and when Apache performs the
address-to-name lookup it's getting the <EM>real</EM> name, not
<SAMP>Host.FooBar.Com</SAMP>. You can verify this by checking the
reverse lookup yourself. The easiest way to work around it is to
specify the correct host name in your configuration.
</LI>
<LI><STRONG>Inadequate checking and verification in your
configuration of Apache</STRONG>
<BR>
If you intend to perform access checking and restriction based upon
the client's host or domain name, you really need to configure
Apache to double-check the origin information it's supplied. You do
this by adding the <SAMP>-DMAXIMUM_DNS</SAMP> clause to the
<SAMP>EXTRA_CFLAGS</SAMP> definition in your
<SAMP>Configuration</SAMP> file. For example:
<P>
<DL>
<DD><CODE>EXTRA_CFLAGS=-DMAXIMUM_DNS</CODE>
</DD>
</DL>
</P>
<P>
This will cause Apache to be very paranoid about making sure a
particular host address is <EM>really</EM> assigned to the name it
claims to be. Note that this <EM>can</EM> incur a significant
performance penalty, however, because of all the name resolution
requests being sent to a nameserver.
</P>
</LI>
</OL>
<HR>
</LI>
<LI><A NAME="SSL-i">
<STRONG>Why doesn't Apache include SSL?</STRONG>
</A>
<P>
SSL (Secure Socket Layer) data transport requires encryption, and many
governments have restrictions upon the import, export, and use of
encryption technology. If Apache included SSL in the base package,
its distribution would involve all sorts of legal and bureaucratic
issues, and it would no longer be freely available. Also, some of
the technology required to talk to current clients using SSL is
patented by <A HREF="http://www.rsa.com/">RSA Data Security</A>,
who restricts its use without a license.
</P>
<P>
Some SSL implementations of Apache are available, however; see the
&quot;<A
HREF="http://www.apache.org/related_projects"
>related projects</A>&quot;
page at the main Apache web site.
</P>
<P>
You can find out more about this topic in the <CITE>Apache Week</CITE>
article about
<A
HREF="http://www.apacheweek.com/features/ssl"
REL="Help"
><CITE>Apache and Secure Transactions</CITE></A>.
</P>
<HR>
</LI>
<LI><A NAME="HPUX-core">
<STRONG>Why do I get core dumps under HPUX using HP's ANSI
C compiler?</STRONG>
</A>
<P>
We have had numerous reports of Apache dumping core when compiled
with HP's ANSI C compiler using optimization. Disabling the compiler
optimization has fixed these problems.
</P>
<HR>
</LI>
<LI><A NAME="midi">
<STRONG>How do I get Apache to send a MIDI file so the browser can
play it?</STRONG>
</A>
<P>
Even though the registered MIME type for MIDI files is
<SAMP>audio/midi</SAMP>, some browsers are not set up to recognize it
as such; instead, they look for <SAMP>audio/x-midi</SAMP>. There are
two things you can do to address this:
</P>
<OL>
<LI>Configure your browser to treat documents of type
<SAMP>audio/midi</SAMP> correctly. This is the type that Apache
sends by default. This may not be workable, however, if you have
many client installations to change, or if some or many of the
clients are not under your control.
</LI>
<LI>Instruct Apache to send a different <SAMP>Content-type</SAMP>
header for these files by adding the following line to your server's
configuration files:
<P>
<DL>
<DD><CODE>AddType audio/x-midi .mid .midi .kar</CODE>
</DD>
</DL>
</P>
<P>
Note that this may break browsers that <EM>do</EM> recognize the
<SAMP>audio/midi</SAMP> MIME type unless they're prepared to also
handle <SAMP>audio/x-midi</SAMP> the same way.
</P>
</LI>
</OL>
<HR>
</LI>
<LI><A NAME="cantbuild">
<STRONG>Why won't Apache compile with my system's
<SAMP>cc</SAMP>?</STRONG>
</A>
<P>
If the server won't compile on your system, it is probably due to one
of the following causes:
</P>
<UL>
<LI><STRONG>The <SAMP>Configure</SAMP> script doesn't recognize your system
environment.</STRONG>
<BR>
This might be either because it's completely unknown or because
the specific environment (include files, OS version, <EM>et
cetera</EM>) isn't explicitly handled. If this happens, you may
need to port the server to your OS yourself.
</LI>
<LI><STRONG>Your system's C compiler is garbage.</STRONG>
<BR>
Some operating systems include a default C compiler that is either
not ANSI C-compliant or suffers from other deficiencies. The usual
recommendation in cases like this is to acquire, install, and use
<SAMP>gcc</SAMP>.
</LI>
<LI><STRONG>Your <SAMP>include</SAMP> files may be confused.</STRONG>
<BR>
In some cases, we have found that a compiler installation or system
upgrade has left the C header files in an inconsistent state. Make
sure that your include directory tree is in sync with the compiler and
the operating system.
</LI>
<LI><STRONG>Your operating system or compiler may be out of
revision.</STRONG>
<BR>
Software vendors (including those that develop operating systems)
issue new releases for a reason; sometimes to add functionality, but
more often to fix bugs that have been discovered. Try upgrading
your compiler and/or your operating system.
</LI>
</UL>
<P>
The Apache Group tests the ability to build the server on many
different platforms. Unfortunately, we can't test all of the OS
platforms there are. If you have verified that none of the above
issues is the cause of your problem, and it hasn't been reported
before, please submit a
<A
HREF="http://www.apache.org/bugdb.cgi"
>problem report</A>.
Be sure to include <EM>complete</EM> details, such as the compiler
&amp; OS versions and exact error messages.
</P>
<HR>
</LI>
<LI><A NAME="addlog">
<STRONG>How do I add browsers and referrers to my logs?</STRONG>
</A>
<P>
Apache provides a couple of different ways of doing this. The
recommended method is to compile the
<A
HREF="../mod/mod_log_config.html"
><SAMP>mod_log_config</SAMP></A>
module into your configuration and use the
<A
HREF="../mod/mod_log_config.html#customlog"
><SAMP>CustomLog</SAMP></A>
directive.
</P>
<P>
You can either log the additional information in files other than your
normal transfer log, or you can add them to the records already being
written. For example:
</P>
<P>
<CODE>
CustomLog&nbsp;logs/access_log&nbsp;"%h&nbsp;%l&nbsp;%u&nbsp;%t&nbsp;\"%r\"&nbsp;%s&nbsp;%b&nbsp;\"%{Referer}i\"&nbsp;\"%{User-Agent}i\""
</CODE>
</P>
<P>
This will add the values of the <SAMP>User-agent:</SAMP> and
<SAMP>Referer:</SAMP> headers, which indicate the client and the
referring page, respectively, to the end of each line in the access
log.
</P>
<P>
You may want to check out the <CITE>Apache Week</CITE> article
entitled:
&quot;<A
HREF="http://www.apacheweek.com/features/logfiles"
REL="Help"
><CITE>Gathering Visitor Information: Customising Your
Logfiles</CITE></A>&quot;.
</P>
<HR>
</LI>
<LI><A NAME="bind8.1">
<STRONG>Why do I get an error about an undefined reference to
&quot;<SAMP>__inet_ntoa</SAMP>&quot; or other
<SAMP>__inet_*</SAMP> symbols?</STRONG>
</A>
<P>
If you have installed <A HREF="http://www.isc.org/bind.html">BIND-8</A>
then this is normally due to a conflict between your include files
and your libraries. BIND-8 installs its include files and libraries
<CODE>/usr/local/include/</CODE> and <CODE>/usr/local/lib/</CODE>, while
the resolver that comes with your system is probably installed in
<CODE>/usr/include/</CODE> and <CODE>/usr/lib/</CODE>. If
your system uses the header files in <CODE>/usr/local/include/</CODE>
before those in <CODE>/usr/include/</CODE> but you do not use the new
resolver library, then the two versions will conflict.
</P>
<P>
To resolve this, you can either make sure you use the include files
and libraries that came with your system or make sure to use the
new include files and libraries. Adding <CODE>-lbind</CODE> to the
<CODE>EXTRA_LDFLAGS</CODE> line in your <SAMP>Configuration</SAMP>
file, then re-running <SAMP>Configure</SAMP>, should resolve the
problem. (Apache versions 1.2.* and earlier use
<CODE>EXTRA_LFLAGS</CODE> instead.)
</P>
<P>
<STRONG>Note:</STRONG>As of BIND 8.1.1, the bind libraries and files are
installed under <SAMP>/usr/local/bind</SAMP> by default, so you
should not run into this problem. Should you want to use the bind
resolvers you'll have to add the following to the respective lines:
</P>
<P>
<DL>
<DD><CODE>EXTRA_CFLAGS=-I/usr/local/bind/include
<BR>
EXTRA_LDFLAGS=-L/usr/local/bind/lib
<BR>
EXTRA_LIBS=-lbind</CODE>
</DD>
</DL>
</P>
<HR>
</LI>
<LI><A NAME="set-servername">
<STRONG>Why does accessing directories only work when I include
the trailing "/"
(<EM>e.g.</EM>,&nbsp;<SAMP>http://foo.domain.com/~user/</SAMP>)
but not when I omit it
(<EM>e.g.</EM>,&nbsp;<SAMP>http://foo.domain.com/~user</SAMP>)?</STRONG>
</A>
<P>
When you access a directory without a trailing "/", Apache needs
to send what is called a redirect to the client to tell it to
add the trailing slash. If it did not do so, relative URLs would
not work properly. When it sends the redirect, it needs to know
the name of the server so that it can include it in the redirect.
There are two ways for Apache to find this out; either it can guess,
or you can tell it. If your DNS is configured correctly, it can
normally guess without any problems. If it is not, however, then
you need to tell it.
</P>
<P>
Add a <A HREF="../mod/core.html#servername">ServerName</A> directive
to the config file to tell it what the domain name of the server is.
</P>
<HR>
</LI>
<LI><A NAME="user-authentication">
<STRONG>How do I set up Apache to require a username and
password to access certain documents?</STRONG>
</A>
<P>
There are several ways to do this; some of the more popular
ones are to use the <A HREF="../mod/mod_auth.html">mod_auth</A>,
<A HREF="../mod/mod_auth_db.html">mod_auth_db</A>, or
<A HREF="../mod/mod_auth_dbm.html">mod_auth_dbm</A> modules.
</P>
<P>
For an explanation on how to implement these restrictions, see
<A
HREF="http://www.apacheweek.com/"
><CITE>Apache Week</CITE></A>'s
articles on
<A
HREF="http://www.apacheweek.com/features/userauth"
><CITE>Using User Authentication</CITE></A>
or
<A
HREF="http://www.apacheweek.com/features/dbmauth"
><CITE>DBM User Authentication</CITE></A>.
</P>
<HR>
</LI>
<LI><A NAME="remote-user-var">
<STRONG>Why is the environment variable
<SAMP>REMOTE_USER</SAMP> not set?</STRONG>
</A>
<P>
This variable is set and thus available in SSI or CGI scripts <STRONG>if and
only if</STRONG> the requested document was protected by access
authentication. For an explanation on how to implement these restrictions,
see
<A
HREF="http://www.apacheweek.com/"
><CITE>Apache Week</CITE></A>'s
articles on
<A
HREF="http://www.apacheweek.com/features/userauth"
><CITE>Using User Authentication</CITE></A>
or
<A
HREF="http://www.apacheweek.com/features/dbmauth"
><CITE>DBM User Authentication</CITE></A>.
</P>
<P>
Hint: When using a CGI script to receive the data of a HTML <SAMP>FORM</SAMP>
notice that protecting the document containing the <SAMP>FORM</SAMP> is not
sufficient to provide <SAMP>REMOTE_USER</SAMP> to the CGI script. You have
to protect the CGI script, too. Or alternatively only the CGI script (then
authentication happens only after filling out the form).
</P>
<HR>
</LI>
<LI><A NAME="remote-auth-only">
<STRONG>How do I set up Apache to allow access to certain
documents only if a site is either a local site <EM>or</EM>
the user supplies a password and username?</STRONG>
</A>
<P>
Use the <A HREF="../mod/core.html#satisfy">Satisfy</A> directive,
in particular the <CODE>Satisfy Any</CODE> directive, to require
that only one of the access restrictions be met. For example,
adding the following configuration to a <SAMP>.htaccess</SAMP>
or server configuration file would restrict access to people who
either are accessing the site from a host under domain.com or
who can supply a valid username and password:
</P>
<P>
<DL>
<DD><CODE>deny from all
<BR>
allow from .domain.com
<BR>
AuthType Basic
<BR>
AuthUserFile /usr/local/etc/httpd/conf/htpasswd.users
<BR>
AuthName special directory
<BR>
require valid-user
<BR>
satisfy any</CODE>
</DD>
</DL>
</P>
<P>
See the <A HREF="#user-authentication">user authentication</A>
question and the <A HREF="../mod/mod_access.html">mod_access</A>
module for details on how the above directives work.
</P>
<HR>
</LI>
<LI><A NAME="no-info-directives">
<STRONG>Why doesn't mod_info list any directives?</STRONG>
</A>
<P>
The
<A
HREF="../mod/mod_info.html"
><SAMP>mod_info</SAMP></A>
module allows you to use a Web browser to see how your server is
configured. Among the information it displays is the list modules and
their configuration directives. The &quot;current&quot; values for
the directives are not necessarily those of the running server; they
are extracted from the configuration files themselves at the time of
the request. If the files have been changed since the server was last
reloaded, the display will will not match the values actively in use.
If the files and the path to the files are not readable by the user as
which the server is running (see the
<A
HREF="../mod/core.html#user"
><SAMP>User</SAMP></A>
directive), then <SAMP>mod_info</SAMP> cannot read them in order to
list their values. An entry <EM>will</EM> be made in the error log in
this event, however.
</P>
<HR>
</LI>
<LI><A NAME="linux-shmget">
<STRONG>When I run it under Linux I get "shmget:
function not found", what should I do?</STRONG>
</A>
<P>
Your kernel has been built without SysV IPC support. You will have to
rebuild the kernel with that support enabled (it's under the
&quot;General Setup&quot; submenu). Documentation for
kernel building is beyond the scope of this FAQ; you should consult
the
<A HREF="http://www.linuxhq.com/HOWTO/Kernel-HOWTO.html"
>Kernel HOWTO</A>,
or the documentation provided with your distribution, or a
<A HREF="http://www.linuxhq.com/HOWTO/META-FAQ.html"
>Linux newsgroup/mailing list</A>.
As a last-resort workaround, you can
comment out the <CODE>#define HAVE_SHMGET</CODE> definition in the
<SAMP>LINUX</SAMP> section of
<SAMP>src/conf.h</SAMP> and rebuild the server. This will produce
a server which is slower and less reliable.
</P>
<HR>
</LI>
<LI><A NAME="authauthoritative">
<STRONG>Why does my authentication give me a server error?</STRONG>
</A>
<P>
Under normal circumstances, the Apache access control modules will
pass unrecognized user IDs on to the next access control module in
line. Only if the user ID is recognized and the password is validated
(or not) will it give the usual success or &quot;authentication
failed&quot; messages.
</P>
<P>
However, if the last access module in line 'declines' the validation
request (because it has never heard of the user ID or because it is not
configured), the <SAMP>http_request</SAMP> handler will give one of
the following, confusing, errors:
</P>
<UL>
<LI><SAMP>check access</SAMP>
</LI>
<LI><SAMP>check user. No user file?</SAMP>
</LI>
<LI><SAMP>check access. No groups file?</SAMP>
</LI>
</UL>
<P>
This does <EM>not</EM> mean that you have to add an
'<SAMP>AuthUserFile&nbsp;/dev/null</SAMP>' line as some magazines suggest!
</P>
<P>
The solution is to ensure that at least the last module is authoritative
and <STRONG>CONFIGURED</STRONG>. By default, <SAMP>mod_auth</SAMP> is
authoritative and will give an OK/Denied, but only if it is configured
with the proper <SAMP>AuthUserFile</SAMP>. Likewise, if a valid group
is required. (Remember that the modules are processed in the reverse
order from that in which they appear in your compile-time
<SAMP>Configuration</SAMP> file.)
</P>
<P>
A typical situation for this error is when you are using the
<SAMP>mod_auth_dbm</SAMP>, <SAMP>mod_auth_msql</SAMP>,
<SAMP>mod_auth_mysql</SAMP>, <SAMP>mod_auth_anon</SAMP> or
<SAMP>mod_auth_cookie</SAMP> modules on their own. These are by
default <STRONG>not</STRONG> authoritative, and this will pass the
buck on to the (non-existent) next authentication module when the
user ID is not in their respective database. Just add the appropriate
'<SAMP><EM>XXX</EM>Authoritative yes</SAMP>' line to the configuration.
</P>
<P>
In general it is a good idea (though not terribly efficient) to have the
file-based <SAMP>mod_auth</SAMP> a module of last resort. This allows
you to access the web server with a few special passwords even if the
databases are down or corrupted. This does cost a
file open/seek/close for each request in a protected area.
</P>
<HR>
</LI>
<LI><A NAME="auth-on-same-machine">
<STRONG>Do I have to keep the (mSQL) authentication information
on the same machine?</STRONG>
</A>
<P>
Some organizations feel very strongly about keeping the authentication
information on a different machine than the webserver. With the
<SAMP>mod_auth_msql</SAMP>, <SAMP>mod_auth_mysql</SAMP>, and other SQL
modules connecting to (R)DBMses this is quite possible. Just configure
an explicit host to contact.
</P>
<P>
Be aware that with mSQL and Oracle, opening and closing these database
connections is very expensive and time consuming. You might want to
look at the code in the <SAMP>auth_*</SAMP> modules and play with the
compile time flags to alleviate this somewhat, if your RDBMS licences
allow for it.
</P>
<HR>
</LI>
<LI><A NAME="msql-slow">
<STRONG>Why is my mSQL authentication terribly slow?</STRONG>
</A>
<P>
You have probably configured the Host by specifying a FQHN,
and thus the libmsql will use a full blown tcp/ip socket to talk to
the database, rather than a fast internal device. The
<SAMP>libmsql</SAMP>, the mSQL FAQ, and the <SAMP>mod_auth_msql</SAMP>
documentation warn you about this. If you have to use different
hosts, check out the <SAMP>mod_auth_msql</SAMP> code for
some compile time flags which might - or might not - suit you.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-more-config">
<STRONG>Where can I find mod_rewrite rulesets which already solve
particular URL-related problems?</STRONG>
</A>
<P>
There is a collection of
<A
HREF="http://www.engelschall.com/sw/mod_rewrite/docs/mod_rewrite/solutions.html#Solutions"
>Practical Solutions for URL-Manipulation</A>
where you can
find all typical solutions the author of
<A
HREF="../mod/mod_rewrite.html"
><SAMP>mod_rewrite</SAMP></A>
currently knows of. If you have more
interesting rulesets which solve particular problems not currently covered in
this document, send it to
<A
HREF="mailto:rse@apache.org"
>Ralf S. Engelschall</A>
for inclusion. The
other webmasters will thank you for avoiding the reinvention of the wheel.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-article">
<STRONG>Where can I find any published information about URL-manipulations and
mod_rewrite?</STRONG>
</A>
<P>
There is an article from
<A
HREF="mailto:rse@apache.org"
>Ralf S. Engelschall</A>
about URL-manipulations based on
<A
HREF="../mod/mod_rewrite.html"
><SAMP>mod_rewrite</SAMP></A>
in the &quot;iX Multiuser Multitasking Magazin&quot; issue #12/96. The
german (original) version
can be read online at
<A
HREF="http://www.heise.de/ix/artikel/9612149/"
>http://www.heise.de/ix/artikel/9612149/</A>,
the English (translated) version can be found at
<A
HREF="http://www.heise.de/ix/artikel/E/9612149/"
>http://www.heise.de/ix/artikel/E/9612149/</A>.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-complexity">
<STRONG>Why is mod_rewrite so difficult to learn and seems so
complicated?</STRONG>
</A>
<P>
Hmmm... there are a lot of reasons. First, mod_rewrite itself is a powerful
module which can help you in really <b>all</b> aspects of URL rewriting, so
it can be no trivial module per definition. To accomplish its hard job it
uses software leverage and makes use of a powerful regular expression
library by Henry Spencer which is an integral part of Apache since its
version 1.2. And regular expressions itself can be difficult to newbies,
while providing the most flexible power to the advanced hacker.
</P>
<P>
On the other hand mod_rewrite has to work inside the Apache API environment
and needs to do some tricks to fit there. For instance the Apache API as of
1.x really was not designed for URL rewriting at the <tt>.htaccess</tt>
level of processing. Or the problem of multiple rewrites in sequence, which
is also not handled by the API per design. To provide this features
mod_rewrite has to do some special (but API compliant!) handling which leads
to difficult processing inside the Apache kernel. While the user usually
doesn't see anything of this processing, it can be difficult to find
problems when some of your RewriteRules seem not to work.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-dontwork">
<STRONG>What can I do if my RewriteRules don't work as expected?
</STRONG>
</A>
<P>
Use &quot;<SAMP>RewriteLog somefile</SAMP>&quot; and
&quot;<SAMP>RewriteLogLevel 9</SAMP>&quot; and have a precise look at the
steps the rewriting engine performs. This is really the only one and best
way to debug your rewriting configuration.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-prefixdocroot"><STRONG>Why don't some of my URLs
get prefixed with DocumentRoot when using mod_rewrite?</STRONG>
</A>
<P>
If the rule starts with <SAMP>/somedir/...</SAMP> make sure that really no
<SAMP>/somedir</SAMP> exists on the filesystem if you don't want to lead the
URL to match this directory, i.e. there must be no root directory named
<SAMP>somedir</SAMP> on the filesystem. Because if there is such a
directory, the URL will not get prefixed with DocumentRoot. This behaviour
looks ugly, but is really important for some other aspects of URL
rewriting.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-nocase">
<STRONG>How can I make all my URLs case-insensitive with mod_rewrite?
</STRONG>
</A>
<P>
You can't! The reason is: First, case translations for arbitrary length URLs
cannot be done via regex patterns and corresponding substitutions. One need
a per-character pattern like sed/Perl <SAMP>tr|..|..|</SAMP> feature. Second, just
making URLs always upper or lower case will not resolve the complete problem
of case-INSENSITIVE URLs, because actually the URLs had to be rewritten to
the correct case-variant residing on the filesystem because in later
processing Apache needs to access the file. And Unix filesystem is always
case-SENSITIVE.
</P>
<P>
But there is a module named <CODE>mod_speling.c</CODE> (yes, it is named
this way!) out there on the net. Try this one.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-virthost">
<STRONG> Why are RewriteRules in my VirtualHost parts ignored?
</STRONG>
</A>
<P>
Because you have to enable the engine for every virtual host explicitly due
to security concerns. Just add a &quot;RewriteEngine on&quot; to your
virtual host configuration parts.
</P>
<HR>
</LI>
<LI><A NAME="rewrite-envwhitespace">
<STRONG> How can I use strings with whitespaces in RewriteRule's ENV
flag?</STRONG>
</A>
<P>
There is only one ugly solution: You have to surround the complete flag
argument by quotation marks (<SAMP>"[E=...]"</SAMP>). Notice: The argument
to quote here is not the argument to the E-flag, it is the argument of the
Apache config file parser, i.e. the third argument of the RewriteRule here.
So you have to write <SAMP>"[E=any text with whitespaces]"</SAMP>.
</P>
<HR>
</LI>
<LI><A NAME="cgi-spec"><STRONG>Where can I find the &quot;CGI
specification&quot;?</STRONG></A>
<P>
The Common Gateway Interface (CGI) specification currently lives in at
least two versions:
</P>
<P>
<OL>
<LI>At the original NCSA site
&lt;<A
HREF="http://hoohoo.ncsa.uiuc.edu/cgi/interface.html"
><SAMP>http://hoohoo.ncsa.uiuc.edu/cgi/interface.html</SAMP></A>&gt;.
This version hasn't been updated since 1995, and there have been
some efforts to update it and replace it with
</LI>
<LI>The most current version, which is struggling to become an
Internet RFC, found at
&lt;<A
HREF="http://www.ast.cam.ac.uk/~drtr/cgi-spec.html"
><SAMP>http://www.ast.cam.ac.uk/~drtr/cgi-spec.html</SAMP></A>&gt;.
</LI>
</OL>
</P>
<HR>
</LI>
<!-- Don't forget to add HR tags at the end of each list item.. -->
</OL>
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