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Apache / Apache Server Frequently Asked Questions

Apache Server Frequently Asked Questions

Apache HTTP Server Version 1.3

Apache Server Frequently Asked Questions

The latest version of this FAQ is always available from the main Apache web site, at <http://httpd.apache.org/docs/misc/FAQ.html>.

If you are reading a text-only version of this FAQ, you may find numbers enclosed in brackets (such as "[12]"). 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.

The Questions

Background
General Technical Questions
Building Apache
Error Log Messages and Problems Starting Apache
Configuration Questions
Dynamic Content (CGI and SSI)
Authentication and Access Restrictions
URL Rewriting
Features

The Answers

A. Background

What is Apache?
The Apache httpd server
- is a powerful, flexible, HTTP/1.1 compliant web server
- implements the latest protocols, including HTTP/1.1 (RFC2616)
- is highly configurable and extensible with third-party modules
- can be customised by writing 'modules' using the Apache module API
- provides full source code and comes with an unrestrictive license
- runs on Windows NT/9x, Netware 5.x and above, OS/2, and most versions of Unix, as well as several other operating systems
- is actively being developed
- encourages user feedback through new ideas, bug reports and patches
- implements many frequently requested features, including:
  
  DBM databases for authentication
  
  allows you to easily set up password-protected pages with enormous numbers of authorized users, without bogging down the server.
  
  Customized responses to errors and problems
  
  Allows you to set up files, or even CGI scripts, which are returned by the server in response to errors and problems, e.g. setup a script to intercept 500 Server Errors and perform on-the-fly diagnostics for both users and yourself.
  
  Multiple DirectoryIndex directives
  
  Allows you to say DirectoryIndex index.html index.cgi, which instructs the server to either send back index.html or run index.cgi when a directory URL is requested, whichever it finds in the directory.
  
  Unlimited flexible URL rewriting and aliasing
  
  Apache has no fixed limit on the numbers of Aliases and Redirects which may be declared in the config files. In addition, a powerful rewriting engine can be used to solve most URL manipulation problems.
  
  Content negotiation
  
  i.e. the ability to automatically serve clients of varying sophistication and HTML level compliance, with documents which offer the best representation of information that the client is capable of accepting.
  
  Virtual Hosts
  
  A much requested feature, sometimes known as multi-homed servers. This allows the server to distinguish between requests made to different IP addresses or names (mapped to the same machine). Apache also offers dynamically configurable mass-virtual hosting.
  
  Configurable Reliable Piped Logs
  
  You can configure Apache to generate logs in the format that you want. In addition, on most Unix architectures, Apache can send log files to a pipe, allowing for log rotation, hit filtering, real-time splitting of multiple vhosts into separate logs, and asynchronous DNS resolving on the fly.
How and why was Apache created?
The About Apache document explains how the Apache project evolved from its beginnings as an outgrowth of the NCSA httpd project to its current status as one of the fastest, most efficient, and most functional web servers in existence.
Why the name "Apache"?
A cute name which stuck. Apache is "A PAtCHy server". It was based on some existing code and a series of "patch files".

For many developers it is also a reverent connotation to the Native American Indian tribe of Apache, well-known for their superior skills in warfare strategy and inexhaustible endurance. For more information on the Apache Nation, we suggest searching Google, Northernlight, or AllTheWeb.
OK, so how does Apache compare to other servers?
For an independent assessment, see Web Compare.

Apache has been shown to be substantially faster, more stable, and more feature-full than many other web 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.
How thoroughly tested is Apache?
Apache is run on over 6 million Internet servers (as of February 2000). 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 half 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.
What are the future plans for Apache?
- to continue to be an "open source" no-charge-for-use HTTP server,
- to keep up with advances in HTTP protocol and web developments in general,
- to collect suggestions for fixes/improvements from its users,
- to respond to needs of large volume providers as well as occasional users.
Whom do I contact for support?
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 the bug report page. Other questions should be directed to the Apache HTTP Server Users List or the comp.infosystems.www.servers.unix or comp.infosystems.www.servers.ms-windows newsgroup (as appropriate for the platform you use), where some of the Apache team lurk, in the company of many other httpd gurus who should be able to help.

Commercial support for Apache is, however, available from a number of third parties.
Is there any more information available on Apache?
Indeed there is. See the main Apache web site. There is also a regular electronic publication called Apache Week available. Links to relevant Apache Week articles are included below where appropriate. There are also some Apache-specific books available.
Where can I get Apache?
You can find out how to download the source for Apache at the project's main web page.
May I use the Apache logo on my product or Web site?
You may NOT use any original artwork from the Apache Software Foundation, nor make or use modified versions of such artwork, except under the following conditions:
- You may use the 'Powered by Apache' graphic on a Web site that is being served by the Apache HTTP server software.
- You may use the aforementioned 'Powered by Apache' graphic or the Apache Software Foundation logo in product description and promotional material IF and ONLY IF such use can in no way be interpreted as anything other than an attribution. Using the Apache name and artwork in a manner that implies endorsement of a product or service is strictly forbidden.

B. General Technical Questions

"Why can't I ...? Why won't ... work?" What to do in case of problems
If you are having trouble with your Apache server software, you should take the following steps:
1. Check the errorlog!
  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 & fix the problem yourself (such as file permissions or the like). The default location of the error log is /usr/local/apache/logs/error_log, but see the ErrorLog directive in your config files for the location on your server.
2. Check the FAQ!
  The latest version of the Apache Frequently-Asked Questions list can always be found at the main Apache web site.
3. Check the Apache bug database
  Most problems that get reported to The Apache Group are recorded in the bug database. Please check the existing reports, open and closed, before adding one. If you find that your issue has already been reported, please don't 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 submitter, because there may be an email exchange going on about the issue that isn't getting recorded in the database.
4. Ask in a user support group.
  A lot of common problems never make it to the bug database because there's already high Q&A traffic about them in the Users mailing list or comp.infosystems.www.servers.unix and related newsgroups. These newsgroups are also available via Google. Many Apache users, and some of the developers, can be found roaming their 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 don't see your question already posted.
5. If all else fails, report the problem in the bug database
  If you've gone through those steps above that are appropriate and have obtained no relief, then please do let The Apache Group know about the problem by logging a bug report.
  
  If your problem involves the server crashing and generating a core dump, please include a backtrace (if possible). As an example,
  
  # cd ServerRoot # dbx httpd core (dbx) where
  
  (Substitute the appropriate locations for your ServerRoot and your httpd and core files. You may have to use gdb instead of dbx.)
How compatible is Apache with my existing NCSA 1.3 setup?
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.

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.

Friendly interaction between Apache and NCSA developers should ensure that fundamental feature enhancements stay consistent between the two servers for the foreseeable future.
Is Apache Year 2000 compliant?
Yes, Apache is Year 2000 compliant.

Apache internally never stores years as two digits. On the HTTP protocol level RFC1123-style addresses are generated which is the only format a HTTP/1.1-compliant server should generate. To be compatible with older applications Apache recognizes ANSI C's asctime() and RFC850-/RFC1036-style date formats, too. The asctime() format uses four-digit years, but the RFC850 and RFC1036 date formats only define a two-digit year. If Apache sees such a date with a value less than 70 it assumes that the century is 20 rather than 19.

Although Apache is Year 2000 compliant, you may still get problems if the underlying OS has problems with dates past year 2000 (e.g., OS calls which accept or return year numbers). Most (UNIX) systems store dates internally as signed 32-bit integers which contain the number of seconds since 1^st January 1970, so the magic boundary to worry about is the year 2038 and not 2000. But modern operating systems shouldn't cause any trouble at all.

Users of Apache 1.2.x should upgrade to a current version of Apache 1.3 (see year-2000 improvements in Apache 1.3 for details).

The Apache HTTP Server project is an open-source software product of the Apache Software Foundation. The project and the Foundation cannot offer legal assurances regarding any suitability of the software for your application. There are several commercial Apache support organizations and derivative server products available that may be able to stand behind the software and provide you with any assurances you may require. You may find links to some of these vendors at <http://www.apache.org/info/support.cgi>.

The Apache HTTP server software is distributed with the following disclaimer, found in the software license:
```
   THIS SOFTWARE IS PROVIDED BY THE APACHE GROUP ``AS IS'' AND ANY
   EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE APACHE GROUP OR
   ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   OF THE POSSIBILITY OF SUCH DAMAGE.
 
```
How do I submit a patch to the Apache Group?
The Apache Group encourages patches from outside developers. There are 2 main "types" of patches: small bugfixes and general improvements. Bugfixes should be submitting using the Apache bug report page. Improvements, modifications, and additions should follow the instructions below.

In general, the first course of action is to be a member of the dev@httpd.apache.org mailing list. This indicates to the Group that you are closely following the latest Apache developments. Your patch file should be generated using either 'diff -c' or 'diff -u' against the latest CVS tree. To submit your patch, send email to dev@httpd.apache.org with a Subject: line that starts with [PATCH] and includes a general description of the patch. In the body of the message, the patch should be clearly described and then included at the end of the message. If the patch-file is long, you can note a URL to the file instead of the file itself. Use of MIME enclosures/attachments should be avoided.

Be prepared to respond to any questions about your patches and possibly defend your code. If your patch results in a lot of discussion, you may be asked to submit an updated patch that incorporate all changes and suggestions.
Why has Apache stolen my favourite site's Internet address?
The simple answer is: "It hasn't." This misconception is usually caused by the site in question having migrated to the Apache Web server software, but not having migrated the site's content yet. When Apache is installed, the default page that gets installed tells the Webmaster the installation was successful. The expectation is that this default page will be replaced with the site's real content. If it doesn't, complain to the Webmaster, not to the Apache project -- we just make the software and aren't responsible for what people do (or don't do) with it.
Why am I getting spam mail from the Apache site?
The short answer is: "You aren't." Usually when someone thinks the Apache site is originating spam, it's because they've traced the spam to a Web site, and the Web site says it's using Apache. See the previous FAQ entry for more details on this phenomenon.

No marketing spam originates from the Apache site. The only mail that comes from the site goes only to addresses that have been requested to receive the mail.
May I include the Apache software on a CD or other package I'm distributing?
The detailed answer to this question can be found in the Apache license, which is included in the Apache distribution in the file LICENSE. You can also find it on the Web at <http://www.apache.org/LICENSE.txt>.
What's the best hardware/operating system/... How do I get the most out of my Apache Web server?
Check out Dean Gaudet's performance tuning page.
What are "regular expressions"?
Regular expressions are a way of describing a pattern - for example, "all the words that begin with the letter A" or "every 10-digit phone number" or even "Every sentence with two commas in it, and no capital letter Q". Regular expressions (aka "regex"s) are useful in Apache because they let you apply certain attributes against collections of files or resources in very flexible ways - for example, all .gif and .jpg files under any "images" directory could be written as /\/images\/.*(jpg|gif)$/.

The best overview around is probably the one which comes with Perl. We implement a simple subset of Perl's regex support, but it's still a good way to learn what they mean. You can start by going to the CPAN page on regular expressions, and branching out from there.
Why isn't there a binary for my platform?
The developers make sure that the software builds and works correctly on the platforms available to them; this does not necessarily mean that your platform is one of them. In addition, the Apache HTTP server project is primarily source oriented, meaning that distributing valid and buildable source code is the purpose of a release, not making sure that there is a binary package for all of the supported platforms.

If you don't see a kit for your platform listed in the binary distribution area (<URL:http://httpd.apache.org/dist/httpd/binaries/>), it means either that the platform isn't available to any of the developers, or that they just haven't gotten around to preparing a binary for it. As this is a voluntary project, they are under no obligation to do so. Users are encouraged and expected to build the software themselves.

The sole exception to these practices is the Windows package. Unlike most Unix and Unix-like platforms, Windows systems do not come with a bundled software development environment, so we do prepare binary kits for Windows when we make a release. Again, however, it's a voluntary thing and only a limited number of the developers have the capability to build the InstallShield package, so the Windows release may lag somewhat behind the source release. This lag should be no more than a few days at most.

C. Building Apache

Why do I get an error about an undefined reference to "__inet_ntoa" or other __inet_* symbols?
If you have installed BIND-8 then this is normally due to a conflict between your include files and your libraries. BIND-8 installs its include files and libraries /usr/local/include/ and /usr/local/lib/, while the resolver that comes with your system is probably installed in /usr/include/ and /usr/lib/. If your system uses the header files in /usr/local/include/ before those in /usr/include/ but you do not use the new resolver library, then the two versions will conflict.

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 -lbind to the EXTRA_LDFLAGS line in your Configuration file, then re-running Configure, should resolve the problem. (Apache versions 1.2.* and earlier use EXTRA_LFLAGS instead.)

Note:As of BIND 8.1.1, the bind libraries and files are installed under /usr/local/bind 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:

EXTRA_CFLAGS=-I/usr/local/bind/include EXTRA_LDFLAGS=-L/usr/local/bind/lib EXTRA_LIBS=-lbind
Why won't Apache compile with my system's cc?
If the server won't compile on your system, it is probably due to one of the following causes:
- The Configure script doesn't recognize your system environment.
  This might be either because it's completely unknown or because the specific environment (include files, OS version, et cetera) isn't explicitly handled. If this happens, you may need to port the server to your OS yourself.
- Your system's C compiler is garbage.
  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 gcc.
- Your include files may be confused.
  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.
- Your operating system or compiler may be out of revision.
  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.
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 problem report. Be sure to include complete details, such as the compiler & OS versions and exact error messages.
Why do I get complaints about redefinition of "struct iovec" when compiling under Linux?
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:
- Remove the definition of struct iovec from your C library includes. It is located in /usr/include/sys/uio.h. Or,
- Add -DNO_WRITEV to the EXTRA_CFLAGS line in your Configuration and reconfigure/rebuild. This hurts performance and should only be used as a last resort.
I'm using gcc and I get some compilation errors, what is wrong?
GCC parses your system header files and produces a modified subset which it uses for compiling. This behavior ties GCC tightly to the version of your operating system. So, for example, if you were running IRIX 5.3 when you built GCC and then upgrade to IRIX 6.2 later, you will have to rebuild GCC. Similarly for Solaris 2.4, 2.5, or 2.5.1 when you upgrade to 2.6. Sometimes you can type "gcc -v" and it will tell you the version of the operating system it was built against.

If you fail to do this, then it is very likely that Apache will fail to build. One of the most common errors is with readv, writev, or uio.h. This is not a bug with Apache. You will need to re-install GCC.
I'm using RedHat Linux 5.0, or some other glibc-based Linux system, and I get errors with the crypt function when I attempt to build Apache 1.2.
glibc puts the crypt function into a separate library. Edit your src/Configuration file and set this:

EXTRA_LIBS=-lcrypt

Then re-run src/Configure and re-execute the make.

D. Error Log Messages and Problems Starting Apache

Why do I get "setgid: Invalid argument" at startup?
Your Group directive (probably in conf/httpd.conf) needs to name a group that actually exists in the /etc/group file (or your system's equivalent). This problem is also frequently seen when a negative number is used in the Group directive (e.g., "Group #-1"). Using a group name -- not group number -- found in your system's group database should solve this problem in all cases.
Why am I getting "httpd: could not set socket option TCP_NODELAY" in my error log?
This message almost always indicates that the client disconnected before Apache reached the point of calling setsockopt() 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.
Why am I getting "connection reset by peer" in my error log?
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 "Stop" 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.
The errorlog says Apache dumped core, but where's the dump file?
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 setuid() 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.

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 is a documented way of bypassing it, it is recommended that you bypass it only for the httpd server process if possible.

The canonical location for Apache's core-dump files is the ServerRoot directory. As of Apache version 1.3, the location can be set via the CoreDumpDirectory directive to a different directory. Make sure that this directory is writable by the user the server runs as (as opposed to the user the server is started as).
When I run it under Linux I get "shmget: function not found", what should I do?
Your kernel has been built without SysV IPC support. You will have to rebuild the kernel with that support enabled (it's under the "General Setup" submenu). Documentation for kernel building is beyond the scope of this FAQ; you should consult the Kernel HOWTO, or the documentation provided with your distribution, or a Linux newsgroup/mailing list. As a last-resort workaround, you can comment out the #define USE_SHMGET_SCOREBOARD definition in the LINUX section of src/conf.h and rebuild the server (prior to 1.3b4, simply removing #define HAVE_SHMGET would have sufficed). This will produce a server which is slower and less reliable.
Server hangs, or fails to start, and/or error log fills with "fcntl: F_SETLKW: No record locks available" or similar messages
These are symptoms of a fine locking problem, which usually means that the server is trying to use a synchronization file on an NFS filesystem.

Because of its parallel-operation model, the Apache Web server needs to provide some form of synchronization when accessing certain resources. One of these synchronization methods involves taking out locks on a file, which means that the filesystem whereon the lockfile resides must support locking. In many cases this means it can't be kept on an NFS-mounted filesystem.

To cause the Web server to work around the NFS locking limitations, include a line such as the following in your server configuration files:

LockFile /var/run/apache-lock

The directory should not be generally writable (e.g., don't use /var/tmp). See the LockFile documentation for more information.
Why am I getting "Expected </Directory> but saw </Directory>" when I try to start Apache?
This is a known problem with certain versions of the AIX C compiler. IBM are working on a solution, and the issue is being tracked by problem report #2312.
I'm using RedHat Linux and I have problems with httpd dying randomly or not restarting properly
RedHat Linux versions 4.x (and possibly earlier) RPMs contain various nasty scripts which do not stop or restart Apache properly. These can affect you even if you're not running the RedHat supplied RPMs.

If you're using the default install then you're probably running Apache 1.1.3, which is outdated. From RedHat's ftp site you can pick up a more recent RPM for Apache 1.2.x. This will solve one of the problems.

If you're using a custom built Apache rather than the RedHat RPMs then you should rpm -e apache. In particular you want the mildly broken /etc/logrotate.d/apache script to be removed, and you want the broken /etc/rc.d/init.d/httpd (or httpd.init) script to be removed. The latter is actually fixed by the apache-1.2.5 RPMs but if you're building your own Apache then you probably don't want the RedHat files.

We can't stress enough how important it is for folks, especially vendors to follow the stopping Apache directions given in our documentation. In RedHat's defense, the broken scripts were necessary with Apache 1.1.x because the Linux support in 1.1.x was very poor, and there were various race conditions on all platforms. None of this should be necessary with Apache 1.2 and later.
I upgraded from an Apache version earlier than 1.2.0 and suddenly I have problems with Apache dying randomly or not restarting properly
You should read the previous note about problems with RedHat installations. It is entirely likely that your installation has start/stop/restart scripts which were built for an earlier version of Apache. Versions earlier than 1.2.0 had various race conditions that made it necessary to use kill -9 at times to take out all the httpd servers. But that should not be necessary any longer. You should follow the directions on how to stop and restart Apache.

As of Apache 1.3 there is a script src/support/apachectl which, after a bit of customization, is suitable for starting, stopping, and restarting your server.
When I try to start Apache from a DOS window, I get a message like "Cannot determine host name. Use ServerName directive to set it manually." What does this mean?
It means what it says; the Apache software can't determine the hostname of your system. Edit your conf\httpd.conf file, look for the string "ServerName", and make sure there's an uncommented directive such as

ServerName localhost

or

ServerName www.foo.com

in the file. Correct it if there one there with wrong information, or add one if you don't already have one.

Also, make sure that your Windows system has DNS enabled. See the TCP/IP setup component of the Networking or Internet Options control panel.

After verifying that DNS is enabled and that you have a valid hostname in your ServerName directive, try to start the server again.
When I try to start Apache for Windows, I get a message like "Unable To Locate WS2_32.DLL...". What should I do?
Short answer: You need to install Winsock 2, available from http://www.microsoft.com/windows95/downloads/

Detailed answer: Prior to version 1.3.9, Apache for Windows used Winsock 1.1. Beginning with version 1.3.9, Apache began using Winsock 2 features (specifically, WSADuplicateSocket()). WS2_32.DLL implements the Winsock 2 API. Winsock 2 ships with Windows NT 4.0 and Windows 98. Some of the earlier releases of Windows 95 did not include Winsock 2.
Apache for Windows does not start. Error log contains this message: "[crit] (10045) The attempted operation is not supported for the type of object referenced: Parent: WSADuplicateSocket failed for socket ###". What does this mean?
We have seen this problem when Apache is run on systems along with Virtual Private Networking clients like Aventail Connect. Aventail Connect is a Layered Service Provider (LSP) that inserts itself, as a "shim," between the Winsock 2 API and Window's native Winsock 2 implementation. The Aventail Connect shim does not implement WSADuplicateSocket, which is the cause of the failure.

The shim is not unloaded when Aventail Connect is shut down. Once observed, the problem persists until the shim is either explicitly unloaded or the machine is rebooted. Instructions for temporarily removing the Aventail Connect V3.x shim can be found here: "How to Remove Aventail Connect v3.x from the LSP Order for Testing Purposes."

Another potential solution (not tested) is to add apache.exe to the Aventail "Connect Exclusion List". See this link for details: "How to Add an Application to Aventail Connect's Application Exclusion List."

Apache is affected in a similar way by any firewall program that isn't correctly configured. Assure you exclude your Apache server ports (usually port 80) from the list of ports to block. Refer to your firewall program's documentation for the how-to.
When I try to start Apache on Windows, I get a message like "System error 1067 has occurred. The process terminated unexpectedly." What does this mean?
This message means that the Web server was unable to start correctly for one reason or another. To find out why, execute the following commands in a DOS window:
```
    c:
    cd "\Program Files\Apache Group\Apache"
    apache
 
```
(If you don't get the prompt back, hit Control-C to cause Apache to exit.)

The error you see will probably be one of those preceding this question in the FAQ.

As of Apache 1.3.14, first check the Windows NT Event Log for Application errors using the Windows NT/2000 Event Viewer program. Any errors that occur prior to opening the Apache error log will be stored here, if Apache is run as a Service on NT or 2000. As with any error, also check your Apache error log.
On a SuSE Linux system, I try and configure access control using basic authentication. Although I follow the example exactly, authentication fails, and an error message "admin: not a valid FDN: ...." is logged.
In the SuSE distribution, additional 3rd party authentication modules have been added and activated by default. These modules interfere with the Apache standard modules and cause Basic authentication to fail. Our recommendation is to comment all those modules in /etc/httpd/suse_addmodule.conf and /etc/httpd/suse_loadmodule.conf which are not actually required for running your server.
Why do I have weird entries in my logs asking for default.ida and cmd.exe?
The host requesting pages from your website and creating those entries is a Windows machine running IIS that has been infected by an Internet worm such as Nimda or Code Red. You can safely ignore these error messages as they do not affect Apache. ApacheWeek has an article with more information.

E. Configuration Questions

Why can't I run more than <n> virtual hosts?
You are probably running into resource limitations in your operating system. The most common limitation is the per-process limit on file descriptors, 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 gethostbyname()) which needs file descriptors and doesn't complain intelligibly when it can't get them.

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 Listen directive also needs a file descriptor.

Typical values for <n> 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.

As to what you can do about this:
1. Reduce the number of Listen 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.
2. Reduce the number of log files. You can use mod_log_config 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. Such a script is provided with the Apache 1.3 distribution in the src/support/split-logfile file.
3. Increase the number of file descriptors available to the server (see your system's documentation on the limit or ulimit commands). For some systems, information on how to do this is available in the performance hints page. There is a specific note for FreeBSD below.
  For Windows 95, try modifying your C:\CONFIG.SYS file to include a line like
  
  FILES=300
  
  Remember that you'll need to reboot your Windows 95 system in order for the new value to take effect.
4. "Don't do that" - try to run with fewer virtual hosts
5. Spread your operation across multiple server processes (using Listen for example, but see the first point) and/or ports.
Since this is an operating-system limitation, there's not much else available in the way of solutions.

As of 1.2.1 we have made attempts to work around various limitations involving running with many descriptors. More information is available.
Can I increase FD_SETSIZE on FreeBSD?
On versions of FreeBSD before 3.0, the FD_SETSIZE 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:

options FD_SETSIZE nnn

to your kernel config file. Starting at version 2.2, this is no longer necessary.

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.

In FreeBSD 3.0, the default FD_SETSIZE has been increased to 1024 and the above limitation in the resolver library has been removed.

After you deal with the appropriate changes above, you can increase the setting of FD_SETSIZE at Apache compilation time by adding "-DFD_SETSIZE=nnn" to the EXTRA_CFLAGS line in your Configuration file.
Why doesn't my ErrorDocument 401 work?
You need to use it with a URL in the form "/foo/bar" and not one with a method and hostname such as "http://host/foo/bar". See the ErrorDocument documentation for details. This was incorrectly documented in the past.
Why does Apache send a cookie on every response?
Apache does not automatically send a cookie on every response, unless you have re-compiled it with the mod_usertrack module, and specifically enabled it with the CookieTracking directive. This module has been in Apache since version 1.2. This module may help track users, and uses cookies to do this. If you are not using the data generated by mod_usertrack, do not compile it into Apache.
Why don't my cookies work, I even compiled in mod_cookies?
Firstly, you do not need to compile in mod_cookies in order for your scripts to work (see the previous question for more about mod_cookies). Apache passes on your Set-Cookie 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.
Why do my Java app[let]s give me plain text when I request an URL from an Apache server?
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 "HTTP/1.0" and do not correctly interpret the "HTTP/1.1" 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.

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 your 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.

In the meantime, a workaround is to tell Apache to "fake" 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:

BrowserMatch Java1.0 force-response-1.0 BrowserMatch JDK/1.0 force-response-1.0

More information about this issue can be found in the Java and HTTP/1.1 page at the Apache web site.
How do I get Apache to send a MIDI file so the browser can play it?
Even though the registered MIME type for MIDI files is audio/midi, some browsers are not set up to recognize it as such; instead, they look for audio/x-midi. There are two things you can do to address this:
1. Configure your browser to treat documents of type audio/midi 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.
2. Instruct Apache to send a different Content-type header for these files by adding the following line to your server's configuration files:
  
  AddType audio/x-midi .mid .midi .kar
  
  Note that this may break browsers that do recognize the audio/midi MIME type unless they're prepared to also handle audio/x-midi the same way.
How do I add browsers and referrers to my logs?
Apache provides a couple of different ways of doing this. The recommended method is to compile the mod_log_config module into your configuration and use the CustomLog directive.

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:

CustomLog logs/access_log "%h %l %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-Agent}i\""

This will add the values of the User-agent: and Referer: headers, which indicate the client and the referring page, respectively, to the end of each line in the access log.

You may want to check out the Apache Week article entitled: "Gathering Visitor Information: Customizing Your Logfiles".
Why does accessing directories only work when I include the trailing "/" (e.g., http://foo.domain.com/~user/) but not when I omit it (e.g., http://foo.domain.com/~user)?
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.

Add a ServerName directive to the config file to tell it what the domain name of the server is.
Why doesn't mod_info list any directives?
The mod_info 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 "current" 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 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 User directive), then mod_info cannot read them in order to list their values. An entry will be made in the error log in this event, however.
I upgraded to Apache 1.3 and now my virtual hosts don't work!
In versions of Apache prior to 1.3b2, there was a lot of confusion regarding address-based virtual hosts and (HTTP/1.1) name-based virtual hosts, and the rules concerning how the server processed <VirtualHost> definitions were very complex and not well documented.

Apache 1.3b2 introduced a new directive, NameVirtualHost, which simplifies the rules quite a bit. However, changing the rules like this means that your existing name-based <VirtualHost> containers probably won't work correctly immediately following the upgrade.

To correct this problem, add the following line to the beginning of your server configuration file, before defining any virtual hosts:

NameVirtualHost n.n.n.n

Replace the "n.n.n.n" with the IP address to which the name-based virtual host names resolve; if you have multiple name-based hosts on multiple addresses, repeat the directive for each address.

Make sure that your name-based <VirtualHost> blocks contain ServerName and possibly ServerAlias directives so Apache can be sure to tell them apart correctly.

Please see the Apache Virtual Host documentation for further details about configuration.
I'm using RedHat Linux and my .htm files are showing up as HTML source rather than being formatted!
RedHat messed up and forgot to put a content type for .htm files into /etc/mime.types. Edit /etc/mime.types, find the line containing html and add htm to it. Then restart your httpd server:

kill -HUP `cat /var/run/httpd.pid`

Then clear your browsers' caches. (Many browsers won't re-examine the content type after they've reloaded a page.)
My .htaccess files are being ignored.
This is almost always due to your AllowOverride directive being set incorrectly for the directory in question. If it is set to None then .htaccess files will not even be looked for. If you do have one that is set, then be certain it covers the directory you are trying to use the .htaccess file in. This is normally accomplished by ensuring it is inside the proper Directory container.
Why do I get a "Forbidden" message whenever I try to access a particular directory?
This message is generally caused because either
- The underlying file system permissions do not allow the User/Group under which Apache is running to access the necessary files; or
- The Apache configuration has some access restrictions in place which forbid access to the files.
You can determine which case applies to your situation by checking the error log.

In the case where file system permission are at fault, remember that not only must the directory and files in question be readable, but also all parent directories must be at least searchable by the web server in order for the content to be accessible.
Why do I get a "Forbidden/You don't have permission to access / on this server" message whenever I try to access my server?
Search your conf/httpd.conf file for this exact string: <Files ~>. If you find it, that's your problem -- that particular <Files> container is malformed. Delete it or replace it with <Files ~ "^\.ht"> and restart your server and things should work as expected.

This error appears to be caused by a problem with the version of linuxconf distributed with Redhat 6.x. It may reappear if you use linuxconf again.

If you don't find this string, check out the previous question.
Why do my files appear correctly in Internet Explorer, but show up as source or trigger a save window with Netscape; or, Why doesn't Internet Explorer render my text/plain document correctly?
MS Internet Explorer (MSIE) and Netscape handle mime type detection in different ways, and therefore will display the document differently. In particular, IE sometimes relies on the file extension or the contents of the file to determine the mime type. This can happen when the server specifies a mime type of application/octet-stream or text/plain. This behavior violates the the HTTP standard and makes it impossible to deliver plain text documents to MSIE clients in some cases. More details are available on MSIE's mime type detection behavior in an MSDN article and a note by Alan J. Flavell.

The best you can do as a server administrator is to accurately configure the mime type of your documents by editing the mime.types file or using an AddType directive in the Apache configuration files. In some cases, you may be able to fool MSIE into rendering text/plain documents correctly by assuring they have a .txt filename extension, but this will not work if MSIE thinks the content looks like another file type.
My site is accessible under many different hostnames; how do I redirect clients so that they see only a single name?
Many sites map a variety of hostnames to the same content. For example, www.example.com, example.com and www.example.net may all refer to the same site. It is best to make sure that, regardless of the name clients use to access the site, they will be redirected to a single, canonical hostname. This makes the site easier to maintain and assures that there will be only one version of the site in proxy caches and search engines.

There are two techniques to implement canonical hostnames:
1. Use mod_rewrite as described in the "Canonical Hostnames" section of the URL Rewriting Guide.
2. Use name-based virtual hosting:
  NameVirtualHost * <VirtualHost *> ServerName www.example.net ServerAlias example.com Redirect permanent / http://www.example.com/ </VirtualHost> <VirtualHost *> ServerName www.example.com DocumentRoot /usr/local/apache/htdocs </VirtualHost>
Why can I access my website from the server or from my local network, but I can't access it from elsewhere on the Internet?
There are many possible reasons for this, and almost all of them are related to the configuration of your network, not the configuration of the Apache HTTP Server. One of the most common problems is that a firewall blocks access to the default HTTP port 80. In particular, many consumer ISPs block access to this port. You can see if this is the case by changing any Port and Listen directives in httpd.conf to use port 8000 and then request your site using http://yourhost.example.com:8000/. (Of course, a very restrictive firewall may block this port as well.)
How do I turn automatic directory listings on or off?
If a client requests a URL that designates a directory and the directory does not contain a filename that matches the DirectoryIndex directive, then mod_autoindex can be configured to present a listing of the directory contents.

To turn on automatic directory indexing, find the Options directive that applies to the directory and add the Indexes keyword. To turn off automatic directory indexing, remove the Indexes keyword from the appropriate Options line.
Why do my Options directives not have the desired effect?
Directives placed in the configuration files are applied in a very particular order, as described by How Directory, Location, and Files sections work. In addition, each Options directive has the effect of resetting the options to none before adding the specified options (unless only "+" and "-" options are used). The consequence is that Options set in the main server or virtual host context (outside any directory, location, or files section) will usually have no effect, because they are overridden by more specific Options directives. For example, in the following

<Directory /usr/local/apache/htdocs> Options Indexes </Directory> Options Includes ExecCGI

Includes and ExecCGI will be off in the /usr/local/apache/htdocs directory.

You can usually avoid problems by either finding the Options directive that already applies to a specific directory and changing it, or by putting your Options directive inside the most specific possible <Directory> section.

F. Dynamic Content (CGI and SSI)

How do I enable CGI execution in directories other than the ScriptAlias?
Apache recognizes all files in a directory named as a ScriptAlias 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 "*.cgi" or "*.pl" or whatever. In other words, all files in a ScriptAlias directory are scripts, as far as Apache is concerned.

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 AddHandler directive.
1. In an appropriate section of your server configuration files, add a line such as
  
  AddHandler cgi-script .cgi
  
  The server will then recognize that all files in that location (and its logical descendants) that end in ".cgi" are script files, not documents.
2. Make sure that the directory location is covered by an Options declaration that includes the ExecCGI option.
In some situations, you might not want to actually allow all files named "*.cgi" 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 mod_rewrite and the following steps:
1. Locally add to the corresponding .htaccess file a ruleset similar to this one:
  
  RewriteEngine on RewriteBase /~foo/bar/ RewriteRule ^quux\.cgi$ - [T=application/x-httpd-cgi]
2. Make sure that the directory location is covered by an Options declaration that includes the ExecCGI and FollowSymLinks option.
What does it mean when my CGIs fail with "Premature end of script headers"?
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 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 "premature end of script headers" message. Even if the CGI runs fine from the command line, remember that the environment and permissions may be different when running under the web server. The CGI can only access resources allowed for the User and Group specified in your Apache configuration. In addition, the environment will not be the same as the one provided on the command line, but it can be adjusted using the directives provided by mod_env.

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 print or write statements that send your HTTP headers:

{ local ($oldbar) = $|; $cfh = select (STDOUT); $| = 1; # # print your HTTP headers here # $| = $oldbar; select ($cfh); }

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 off (with $| = 0 or the equivalent) after the statements that send the headers, as displayed above.

If your script isn't written in Perl, do the equivalent thing for whatever language you are using (e.g., for C, call fflush() after writing the headers).

Another cause for the "premature end of script headers" message are the RLimitCPU and RLimitMEM directives. You may get the message if the CGI script was killed due to a resource limit.

In addition, a configuration problem in suEXEC, mod_perl, or another third party module can often interfere with the execution of your CGI and cause the "premature end of script headers" message.
Why do I keep getting "Method Not Allowed" for form POST requests?
This is almost always due to Apache not being configured to treat the file you are trying to POST to as a CGI script. You can not POST to a normal HTML file; the operation has no meaning. See the FAQ entry on CGIs outside ScriptAliased directories for details on how to configure Apache to treat the file in question as a CGI.
How can I get my script's output without Apache buffering it? Why doesn't my server push work?
As of Apache 1.3, CGI scripts are essentially not buffered. Every time your script does a "flush" to output data, that data gets relayed on to the client. Some scripting languages, for example Perl, have their own buffering for output - this can be disabled by setting the $| special variable to 1. Of course this does increase the overall number of packets being transmitted, which can result in a sense of slowness for the end user.

Prior to 1.3, you needed to use "nph-" scripts to accomplish non-buffering. Today, the only difference between nph scripts and normal scripts is that nph scripts require the full HTTP headers to be sent.
Where can I find the "CGI specification"?
The Common Gateway Interface (CGI) specification can be found at the original NCSA site < http://hoohoo.ncsa.uiuc.edu/cgi/interface.html>. This version hasn't been updated since 1995, and there have been some efforts to update it.

A new draft is being worked on with the intent of making it an informational RFC; you can find out more about this project at <http://web.golux.com/coar/cgi/>.
Why isn't FastCGI included with Apache any more?
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 FastCGI web site. When a new version of Apache was released, the version of the FastCGI module included with it would soon be out of date.

You can still obtain the FastCGI module for Apache from the master FastCGI web site.
How do I enable SSI (parsed HTML)?
SSI (an acronym for Server-Side Include) directives allow static HTML documents to be enhanced at run-time (e.g., when delivered to a client by Apache). The format of SSI directives is covered in the mod_include manual; suffice it to say that Apache supports not only SSI but xSSI (eXtended SSI) directives.

Processing a document at run-time is called parsing it; hence the term "parsed HTML" sometimes used for documents that contain SSI instructions. Parsing tends to be resource-consumptive compared to serving static files, 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 next question for more information about this.)

To enable SSI processing, you need to
- Build your server with the mod_include module. This is normally compiled in by default.
- Make sure your server configuration files have an Options directive which permits Includes.
- Make sure that the directory where you want the SSI documents to live is covered by the "server-parsed" content handler, either explicitly or in some ancestral location. That can be done with the following AddHandler directive:
  
  AddHandler server-parsed .shtml
  
  This indicates that all files ending in ".shtml" in that location (or its descendants) should be parsed. Note that using ".html" will cause all normal HTML files to be parsed, which may put an inordinate load on your server.
For additional information, see the Apache Week article on Using Server Side Includes.
Why don't my parsed files get cached?
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 Content-Length or Last-Modified headers. Caches commonly work by comparing the Last-Modified 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.

You can work around this in some cases by causing an Expires header to be generated. (See the mod_expires documentation for more details.) Another possibility is to use the XBitHack Full mechanism, which tells Apache to send (under certain circumstances detailed in the XBitHack directive description) a Last-Modified 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.
How can I have my script output parsed?
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 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.

This is a feature The Apache Group hopes to add in the next major release after 1.3.
SSIs don't work for VirtualHosts and/or user home directories.
This is almost always due to having some setting in your config file that sets "Options Includes" or some other setting for your DocumentRoot but not for other directories. If you set it inside a Directory section, then that setting will only apply to that directory.
How can I use ErrorDocument and SSI to simplify customized error messages?
Have a look at this document. It shows in example form how you can a combination of XSSI and negotiation to tailor a set of ErrorDocuments to your personal taste, and returning different internationalized error responses based on the client's native language.
Why is the environment variable REMOTE_USER not set?
This variable is set and thus available in SSI or CGI scripts if and only if the requested document was protected by access authentication. For an explanation on how to implement these restrictions, see Apache Week's articles on Using User Authentication or DBM User Authentication.

Hint: When using a CGI script to receive the data of a HTML FORM notice that protecting the document containing the FORM is not sufficient to provide REMOTE_USER 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).
How do I allow each of my user directories to have a cgi-bin directory?
Remember that CGI execution does not need to be restricted only to cgi-bin directories. You can allow CGI script execution in arbitrary parts of your filesystem.

There are many ways to give each user directory a cgi-bin directory such that anything requested as http://example.com/~user/cgi-bin/program will be executed as a CGI script. Two alternatives are:
1. Place the cgi-bin directory next to the public_html directory:
  
  ScriptAliasMatch ^/~([^/]*)/cgi-bin/(.*) /home/$1/cgi-bin/$2
2. Place the cgi-bin directory underneath the public_html directory:
  
  <Directory /home/*/public_html/cgi-bin> Options ExecCGI SetHandler cgi-script </Directory>

G. Authentication and Access Restrictions

Why isn't restricting access by host or domain name working correctly?
Two of the most common causes of this are:
1. An error, inconsistency, or unexpected mapping in the DNS registration
  This happens frequently: your configuration restricts access to Host.FooBar.Com, but you can't get in from that host. The usual reason for this is that Host.FooBar.Com is actually an alias for another name, and when Apache performs the address-to-name lookup it's getting the real name, not Host.FooBar.Com. 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.
2. Inadequate checking and verification in your configuration of Apache
  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 -DMAXIMUM_DNS clause to the EXTRA_CFLAGS definition in your Configuration file. For example:
  
  EXTRA_CFLAGS=-DMAXIMUM_DNS
  
  This will cause Apache to be very paranoid about making sure a particular host address is really assigned to the name it claims to be. Note that this can incur a significant performance penalty, however, because of all the name resolution requests being sent to a nameserver.
How do I set up Apache to require a username and password to access certain documents?
There are several ways to do this; some of the more popular ones are to use the mod_auth, mod_auth_db, or mod_auth_dbm modules.

For an explanation on how to implement these restrictions, see Apache Week's articles on Using User Authentication or DBM User Authentication.
How do I set up Apache to allow access to certain documents only if a site is either a local site or the user supplies a password and username?
Use the Satisfy directive, in particular the Satisfy Any directive, to require that only one of the access restrictions be met. For example, adding the following configuration to a .htaccess 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:

Deny from all Allow from .domain.com AuthType Basic AuthUserFile /usr/local/apache/conf/htpasswd.users AuthName "special directory" Require valid-user Satisfy any

See the user authentication question and the mod_access module for details on how the above directives work.
Why does my authentication give me a server error?
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 "authentication failed" messages.

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 http_request handler will give one of the following, confusing, errors:
- check access
- check user. No user file?
- check access. No groups file?