I struggled with this today whilst trying to figure out Apache’s config options.

On Ubuntu you can do the following:

$ dpkg --get-selections |grep apache
apache2						install
apache2-mpm-prefork				install
apache2-prefork-dev				install
apache2-utils					install
apache2.2-bin					install
apache2.2-common				install
libapache2-mod-php5				install
libapache2-mod-wsgi				install

This tells me that I have mpm-prefork.