Apache: The Definitive Guide, Second Edition

1.5. What Happens at the Server End?

We assume that the server is well set up and running Apache. What does Apache do? In the simplest terms, it gets a URL from the Internet, turns it into a filename, and sends the file (or its output)^[§§] back down the Internet. That's all it does, and that's all this book is about!

^[§§] Usually. We'll see later that some URLs may refer to information generated completely within Apache.

Three main cases arise:

•    The Unix server has a standalone Apache that listens to one or more ports (port 80 by default) on one or more IP addresses mapped onto the interfaces of its machine. In this mode (known as standalone mode ), Apache actually runs several copies of itself to handle multiple connections simultaneously.

•    The server is configured to use the Unix utility inetd , which listens on all ports it is configured to handle. When a connection comes in, it determines from its configuration file, /etc/inetd.conf, which service that port corresponds to and runs the configured program, which can be an Apache in inetd mode. It is worth noting that some of the more advanced features of Apache are not supported in this mode, so it should only be used in very simple cases. Support for this mode may well be removed in future releases of Apache.

•    On Windows, ...