Apache

Possibly the most used open source software in the world, Apache is a web (HTTP) server. Since the creation of the web server, the The Apache Software Foundation now hosts many open source projects in addition to its web server.

Installing

Apache is available (if not pre-installed) on most Linux distributions, pre-installed on Mac OS X (where it's called "Web Sharing"), and available for Windows (and not to be confused with IIS, Microsoft's own proprietary web server).

Debian/Ubuntu

sudo apt-get install apache2

Modules

Current installs of apache break up different common configuration options into "modules" (actually just lots of little text files containing the necessary commands / parameters). You can use the commands: a2enmod and a2dismod to enable and disable a particular module.

userdir

For instance to activate having a public_html folder in your home, simply switch on the "userdir" option with:

sudo a2enmod userdir

Reloading changes

Apache generally only reads the configuration files when it starts up, so if you make changes, you can restart the server to make sure they get loaded again:

/etc/init.d/apache2 restart