Fedora™ Unleashed, 2008 edition

files residing in the /var/www/cgi-bin directory and are used to dynamically generate data (usually HTML) for the remote browser when requested.

mod_dir and mod_env

The mod_dir module is used to determine which files are returned automatically when a user tries to access a directory. The default is index.html. If you have users who create web pages on Windows systems, you should also include index.htm, like this:

DirectoryIndex index.html index.htm

mod_env controls how environment variables are passed to CGI and SSI scripts.

mod_expires

mod_expires is used to add an expiration date to content on your site by adding an Expires header to the HTTP response. Web browsers or cache servers don't cache expired content.

mod_headers

mod_headers is used to manipulate the HTTP headers of your server's responses. You can replace, add, merge, or delete headers as you see fit. The module supplies a Header directive for this. Ordering of the Header directive is important. A set followed by an unset for the same HTTP header removes the header altogether. You can place Header directives almost anywhere within your configuration files. These directives are processed in the following order:

1. Core server

2. Virtual host

3. <Directory> and .htaccess files

4. <Location>

5. <Files>

mod_info and mod_log_config

mod_info provides comprehensive information about your server's configuration. For example, it displays all the installed modules, as well as all the directives used in its configuration files.

mod_log_config defines how your log files should look. See the 'Logging' section for further information about this subject.

mod_mime and mod_mime_magic

The mod_mime module tries to determine the MIME type of files from their extensions.

The mod_mime_magic module tries to determine the MIME type of files by examining portions of their content.

mod_negotiation

Using the mod_negotiation module, you can select one of several document versions that best suits the client's capabilities. You can select from among several options for which criteria to use in the negotiation process. You can, for example, choose among different languages, graphics file formats, and compression methods.

mod_proxy

mod_proxy implements proxy and caching capabilities for an Apache server. It can proxy and cache FTP, CONNECT, HTTP/0.9, and HTTP/1.0 requests. This isn't an ideal solution for sites that have a large number of users and therefore have high proxy and cache requirements. However, it's more than adequate for a small number of users.

mod_rewrite

mod_rewrite is the Swiss army knife of URL manipulation. It enables you to use powerful regular expressions to perform any imaginable manipulation of URLs. It provides rewrites, redirection, proxying, and so on. There's very little that you can't accomplish with this module.

TIP

See http://localhost/manual/misc/rewriteguide.html for a cookbook that gives you an in-depth explanation of what the mod_rewrite module is capable of.

mod_setenvif

mod_setenvif allows manipulation of environment variables. Using small snippets of text- matching code known as regular expressions, you can conditionally change the content of environment variables. The order in which SetEnvIf directives appear in the configuration files is important. Each SetEnvIf directive can reset an earlier SetEnvIf directive when used on the same environment variable. Be sure to keep that in mind when using the directives from this module.

mod_speling

mod_speling is used to enable correction of minor typos in URLs. If no file matches the requested URL, this module builds a list of the files in the requested directory and extracts those files that are the closest matches. It tries to correct only one spelling mistake.

mod_status

You can use mod_status to create a web page containing a plethora of information about a running Apache server. The page contains information about the internal status as well as statistics about the running Apache processes. This can be a great aid when you're trying to configure your server for maximum performance. It's also a good place to see whether something's amiss with your Apache server.

mod_ssl

mod_ssl provides Secure Sockets Layer (version 2 and 3) and transport layer security (version 1) support for Apache. At least 30 directives exist that deal with options for encryption and client authorization and that can be used with this module.

mod_unique_id

mod_unique_id generates a unique request identifier for every incoming request. This ID is put into the UNIQUE_ID environment variable.

mod_userdir

The mod_userdir module enables mapping of a subdirectory in each user's home directory into your web tree. The module provides several ways to accomplish this.

mod_vhost_alias

mod_vhost_alias supports dynamically configured mass virtual hosting, which is useful for Internet service providers (ISPs) with many virtual hosts. However, for the average user, Apache's ordinary virtual hosting support should be more than sufficient.

There are two ways to serve virtual hosts on an Apache server. You can have one IP address with multiple CNAMEs, or you can have multiple IP addresses with one name per address. Apache has different sets of directives to handle each of these options. (You learn more about virtual hosting in Apache in the next section of this chapter.)

Again, the available options and features for Apache modules are too numerous to describe completely in this chapter. You can find complete information about the Apache modules in the online documentation for the server included with Fedora or at the Apache Software Foundation's website.

Virtual Hosting

One of the more popular services to provide with a web server is to host a virtual domain. Also known as a virtual host, a virtual domain is a complete website with its own domain name, as if it were a standalone machine, but it's hosted on the same machine as other websites. Apache implements this capability in a simple way with directives in the httpd.conf configuration file.

Apache now can dynamically host virtual servers by using the mod_vhost_alias module you