# Apache Server Frequently Asked Questions

$Revision: 1.99 $ ($Date: 2010/12/10 10:13:45 $)

Please note that this document refers to a version of the product which has been deprecated, and declared "end of life", in favor of the more recent version of the server. Information obtained here is likely to be outdated and inaccurate.

The latest version of this FAQ is available on the HTTP Server Wiki, at <`http://httpd.apache.org/docs/1.3/misc/FAQ.html`>. This version is no longer maintained, and contains inaccurate and grossly outdated information.

## The Questions

1. Configuration Questions
   1. Why can't I run more than <n> virtual hosts?
   2. Can I increase `FD_SETSIZE` on FreeBSD?
   3. Why doesn't my `ErrorDocument 401` work?
   4. Why does Apache send a cookie on every response?
   5. Why don't my cookies work, I even compiled in `mod_cookies`?
   6. Why do my Java app[let]s give me plain text when I request an URL from an Apache server?
   7. How do I get Apache to send a MIDI file so the browser can play it?
   8. How do I add browsers and referrers to my logs?
   9. 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`)?
   10. Why doesn't mod_info list any directives?
   11. I upgraded to Apache 1.3 and now my virtual hosts don't work!
   12. I'm using RedHat Linux and my .htm files are showing up as HTML source rather than being formatted!
   13. My `.htaccess` files are being ignored.
   14. Why do I get a "`Forbidden`" message whenever I try to access a particular directory?
   15. Why do I get a "`Forbidden/You don't have permission to access / on this server`" message whenever I try to access my server?
   16. 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?
   17. My site is accessible under many different hostnames; how do I redirect clients so that they see only a single name?
   18. 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?
   19. How do I turn automatic directory listings on or off?
   20. Why do my Options directives not have the desired effect?
   21. How can I change the information that Apache returns about itself in the headers?
   22. Why do I see requests for other sites appearing in my log files?

## The Answers

### E. Configuration Questions

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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".

9. 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.

   The other thing that can occasionally cause this symptom is a misunderstanding of the Alias directive, resulting in an alias working with a trailing slash, and not without one. The `Alias` directive is very literal, and aliases what you tell it to. Consider the following example:

               Alias /example/ /home/www/example/

   The above directive creates an alias for URLs starting with `/example/`, but does not alias URLs starting with `/example`. That is to say, a URL such as `http://servername.com/example/` will get the desired content, but a URL such as `http://servername.com/example` will result in a "file not found" error.

   The following `Alias`, on the other hand, will work for both cases:

               Alias /example /home/www/example

10. 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.

11. 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.

12. 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.)

13. 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.

14. 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 (i.e., chmod +x /directory/path) by the web server in order for the content to be accessible.

15. 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.

16. 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.

17. 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>`

18. 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.)

19. 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. For example:

    > `<Directory /path/to/directory>
    > Options +Indexes
    > </Directory>`

    To turn off automatic directory indexing, remove the `Indexes` keyword from the appropriate `Options` line. To turn off directory listing for a particular subdirectory, you can use `Options -Indexes`. For example:

    > `<Directory /path/to/directory>
    > Options -Indexes
    > </Directory>`

20. 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.

21. How can I change the information that Apache returns about itself in the headers?

    When a client connects to Apache, part of the information returned in the headers is the name "Apache" Additional information that can be sent is the version number, such as "1.3.26", the operating system, and a list of non-standard modules you have installed.

    For example:

    > `Server: Apache/1.3.26 (Unix) mod_perl/1.26`

    Frequently, people want to remove this information, under the mistaken understanding that this will make the system more secure. This is probably not the case, as the same exploits will likely be attempted regardless of the header information you provide.

    There are, however, two answers to this question: the correct answer, and the answer that you are probably looking for.

    The correct answer to this question is that you should use the ServerTokens directive to alter the quantity of information which is passed in the headers. Setting this directive to `Prod` will pass the least possible amount of information:

    > `Server: Apache`

    The answer you are probably looking for is how to make Apache lie about what what it is, ie send something like:

    > `Server: Bob's Happy HTTPd Server`

    In order to do this, you will need to modify the Apache source code and rebuild Apache. This is not advised, as it is almost certain not to provide you with the added security you think that you are gaining. The exact method of doing this is left as an exercise for the reader, as we are not keen on helping you do something that is intrinsically a bad idea.

22. Why do I see requests for other sites appearing in my log files?

    A an access_log entry showing this situation could look like this:

    > `63.251.56.142 - - [25/Jul/2002:12:48:04 -0700] "GET http://www.yahoo.com/ HTTP/1.0" 200 1456`

    The question is: why did a request for `www.yahoo.com` come to your server instead of Yahoo's server? And why does the response have a status code of 200 (success)?

    This is usually the result of malicious clients trying to exploit open proxy servers to access a website without revealing their true location. If you find entries like this in your log, the first thing to do is to make sure you have properly configured your server not to proxy for unknown clients. If you don't need to provide a proxy server at all, you should simply assure that the ProxyRequests directive is not set `on`. If you do need to run a proxy server, then you must ensure that you secure your server properly so that only authorized clients can use it.

    If your server is configured properly, then the attempt to proxy through your server will fail. If you see a status code of `404` (file not found) in the log, then you know that the request failed. If you see a status code of `200` (success), that does not necessarily mean that the attempt to proxy succeeded. RFC2616 section 5.1.2 mandates that Apache must accept requests with absolute URLs in the request-URI, even for non-proxy requests. Since Apache has no way to know all the different names that your server may be known under, it cannot simply reject hostnames it does not recognize. Instead, it will serve requests for unknown sites locally by stripping off the hostname and using the default server or virtual host. Therefore you can compare the size of the file (1456 in the above example) to the size of the corresponding file in your default server. If they are the same, then the proxy attempt failed, since a document from your server was delivered, not a document from `www.yahoo.com`.

    If you wish to prevent this type of request entirely, then you need to let Apache know what hostnames to accept and what hostnames to reject. You do this by configuring name-virtual hosts, where the first listed host is the default host that will catch and reject unknown hostnames. For example:

    >     NameVirtualHost *

    >     <VirtualHost *>
    >       ServerName default.only
    >       <Location />
    >         Order allow,deny
    >         Deny from all
    >       </Location>
    >     </VirtualHost>

    >     <VirtualHost *>
    >       ServerName realhost1.example.com
    >       ServerAlias alias1.example.com alias2.example.com
    >       DocumentRoot /path/to/site1
    >     </VirtualHost>

    >     ...