This section provides a quick overview of the default locations of the configuration files, binaries, and content associated with the Apache 2 Web server on your Ubuntu system:

/etc/apache2: A directory containing the configuration files for the Apache 2 Web server. The primary configuration file in this directory is the file apache2.conf.

/etc/apache2/conf.d: A directory containing local configuration directives for Apache 2, such as those associated with third-party or locally installed packages.

/etc/apache2/envvars: A file containing environment variables that you want to set in the environment used by the apache2ctl script to manage an Apache 2 Web server.

/etc/apache2/mods-available: A directory containing available Apache 2 modules and their configuration files.

/etc/apache2/mods-enabled: A directory containing symbolic links to actively enable Apache 2 modules and their configuration files, located in the /etc/apache2/mods-available directory. This is analogous to the use of symbolic links to start various processes from the scripts in /etc/init.d at different run levels.

/etc/apache2/sites-available: A directory containing files that define the Web sites supported by this server.

/etc/apache2/mods-enabled: A directory containing symbolic links to actively enabled Web sites for this server, located in the /etc/apache2/mods-available directory. This is analogous to the use of symbolic links to start various processes from the scripts in /etc/init.d at different run levels.

/etc/default/apache2: A configuration file that determines whether the Apache 2 should automatically start at boot time.

/etc/init.d/apache2: A shell script that uses the apache2ctl utility to start and stop an Apache 2 Web server.

/etc/mime.types: The default MIME (Multipurpose Internet Mail Extensions) file types and the extensions that they are associated with.

/usr/lib/cgi-bin: The location in which any CGI-BIN (Common Gateway Interface scripts) for a default Apache 2 Web server will be installed.

/usr/sbin/apache2: The actual executable for the Apache 2 Web server.

/usr/sbin/apache2ctl: An administrative shell script that simplifies starting, stopping, restarting, and monitoring the status of a running Apache 2 Web server.

/usr/share/apache2-doc: A directory that contains the actual Apache 2 manual (in the manual subdirectory). This directory is present only if you’ve installed the apache2-doc package (as suggested earlier).

/usr/share/apache2/error: A directory containing the default error responses delivered.

/usr/share/apache2/icons: A directory containing the default set of icons used by an Apache 2 Web server. This directory is mapped to the directory /icons in your Apache server’s primary configuration file.

/var/log/apache2/access.log: The default access log file for an Apache 2 Web server. This log file tracks any attempts to access this Web site, the hosts that they came from, and so on.

/var/log/apache2/error.log: The default error log file for an Apache 2 Web server. This log file tracks internal Web server problems, attempts to retrieve nonexistent files, and so on.

/var/run/apache2/apache2.pid: A text file used by Apache 2 to record its process ID when it starts. This file is used when terminating or restarting the Apache 2 server using the /etc/init.d/apache2 script.

/var/www/apache2-default: A directory containing the default home page for this Web server. Note that the default Apache 2 Web server does not display the content of this directory correctly—I’ll use that as an example of configuring a Web site in the next section.

Some of these directories, most specifically the /etc/apache2 configuration directory, contain other files that are included or referenced by other files in that same directory.