From a technical perspective, you could say that a web server is just a special kind of file server; all a web server does is hand out files to users that are stored in a directory structure, which is called the document root. To offer these files, a web server uses a certain file format. This format is the Hypertext Markup Language (HTML). HTML files, however, are not the only files that a web server can offer. A web server can offer other types of files as well. Therefore, a web server is a good source for streaming audio and video, accessing databases, displaying animations, showing photos, and much more.
Originally, web content was static. Ever since a few years ago, however, web servers became a platform where people work together to create some content. One of the best examples of this is Wikipedia, the online encyclopedia where people from all over the world work together to create content. However, I won't cover interactive web pages in this chapter; in fact, this subject requires a book on its own.
The web server stores the content, but the client has to use a specific protocol to access this content. This protocol is the Hypertext Transfer Protocol (HTTP). Typically, a client uses a browser to generate HTTP commands that get content stored on a web server as HTML files. In the case of an application server, such as in the Wikipedia example or when using a Java-based service in Tomcat, it is this application that dynamically creates the content and the HTML data, but it is still the Apache web server that manages the HTTP traffic between the server and the client.
The Apache web server comes in two important versions. The most recent version is 2.x. This version is installed by default on SUSE Linux Enterprise Server. You may, however, encounter environments where version 1.3 is still being used. This is especially the case if the developer of some custom scripts has developed those scripts for use in a 1.3 environment. Those with urgent needs to use version 1.3 instead of 2.0, however, are increasingly rare, and therefore, I won't cover version 1.3 of the Apache web server in this chapter.
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