Apache is a server that responds to requests from Web browsers, or clients, such as Firefox, Netscape, lynx, and Internet Explorer. When you enter the address of a Web page (a URI, page 1113) in a Web browser's location bar, the browser sends a request over the Internet to the (Apache) server at that address. In response, the server sends the requested content back to the browser. The browser then displays or plays the content, which might be a song, picture, video clip, or other information.
Content Aside from add-on modules that can interact with the content, Apache remains oblivious to the content itself. Server administration and content creation are two different aspects of bringing up a Web site. This chapter concentrates on setting up and running an Apache server; it spends little time discussing content creation.
Modules Apache, like the Linux kernel, uses external modules to increase load-time flexibility and allow parts of its code to be recompiled without recompiling the whole program. Rather than being part of the Apache binary, modules are stored as separate files that can be loaded when Apache is started.
Apache uses external modules, called dynamic shared objects (DSOs), for basic and advanced functions; there is not much to Apache without these modules. Apache also uses modules to extend its functionality: Modules can process scripts written in Perl, PHP, Python, and other languages; use several different methods to authenticate users; facilitate publishing content; and process nontextual content, such as audio. The list of modules written by the Apache Group and third-party developers is always growing. For more information refer to "Modules" on page 876.
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