--with-expat=/usr: Uses system installed expat. If you have installed expat and do not use this switch, the apache installation may overwrite some files from the expat installation. --enable-mods-shared=all: We want modules to be compiled and used as Dynamic Shared Objects (DSOs) so they can be included and excluded from the server using the run-time configuration directives. --enable-ssl: Use this switch to create the mod_ssl module and enable SSL support.