1. apache2.conf
2. httpd.conf
3. ports.conf
4. envvars
5. conf.d
   1. apache2-doc
   2. charset
   3. phpmyadmin.conf
   4. ......
6. mods
   1. mods-available
   2. mods-enable
   3. a2enmod
   4. a2dismod
7. sites
   1. sites-available
   2. sites-enable
   3. a2ensite
   4. a2dissite