Apache Configuration File Basics

The primary Apache configuration file is called httpd.conf or (for Apache 2.0 on some Linux distributions) httpd2.conf. This file is usually located in /etc/apache, /etc/httpd, or /etc/httpd/conf. Whatever the filename or location, most of the lines in this file are either comments that begin with hash marks (#) or options lines that take the following form:

Directive Value

The Directive is the name of a parameter you want to adjust, and the Value is the value given to the parameter. The Value may be a number, a filename, or an arbitrary string. Some directives appear in named blocks begun and ended with codes enclosed in angle brackets, such as this:

<lfDefine APACHEPROXIED>

Listen 8080 </lfDefine>

This particular example sets the Listen directive to 8080 if the APACHEPROXIED variable is defined. Note that the final line uses the name specified in the first line, but preceded by a slash (/). This arrangement signifies the start and end of a block of options, albeit one that contains just one option in this example.

Apache is designed in a modular way—many of its features can be compiled as separate modules that can be loaded at run time or left unloaded. Precisely which features are compiled as modules and which are compiled into the main Apache executable (typically called apache, httpd, or httpd2) varies from one distribution to another. To load a module, you use the LoadModule directive, and many Apache configuration files have a large number of these directives early in the file. With Apache 1,3.x, you may also need to use the AddModule directive to activate the module after you've loaded it, or to activate the features of a module that's compiled into the main binary. You may want to peruse these modules to see what features are enabled by default.

Tip Commenting out the LoadModule directives for unused features can be a good security measure. For instance, if you have no need to deliver dynamic content, commenting out the cgi_module can reduce the chance that an accidental misconfiguration or intentional cracking will cause damage. Unfortunately, it's hard to know what each module does, so I recommend caution in commenting out module definitions.

In addition to the main configuration file, a handful of additional files are important:

access.conf Not all Apache configurations use this file, which is essentially a supplemental file that tells Apache how to treat specific directories. Many systems roll this information into the main configuration file. For those that don't, an AccessConfig directive in the main file points to the access.conf file.

mime.types orapache-mime.types This file defines assorted Multipurpose Internet Mail Extension (MIME) types, which are codes that help identify the type of a file. HTTP transfers identify files by MIME type, but Linux filesystems don't store MIME type information natively. Therefore, Apache uses this file to map filename extensions (such as .html or .txt) to MIME types. The default file handles most common files you're likely to deliver on your web server, but you may need to add MIME types if you place exotic file types on the server.

magic This file exists in support of a second method of determining a file's MIME type. Rather than rely on filename extensions, this file includes "fingerprints" for many file types based on the files' contents. You shouldn't try to adjust this file unless you have precise instructions on doing so for a particular file type or if you possess a deep understanding of the file's internal format.

These files typically reside in the same directory that holds the main Apache configuration file. You're most likely to need to adjust access.conf, but only on systems that use it by default or if you choose to use this configuration option. If you deliver unusual file types, the best way to associate MIME types with those files is usually by adjusting the mime.types or apache-mime.types file; modifying the magic file is much trickier.

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