You have this error when you try to install bigbluebutton : bbb-install you must remove apache2
in this case you should know that is because both apache 2 and nginx will use the 80 port, so for prevention bbb-install dont allow the install
to delete apache2 you have to execute theses commands
$ sudo service apache2 stop
$ sudo apt --purge remove apache2 apache2-data apache2-utils apache2-bin apache2-commonnow you can continue the install of bigbluebutton ^^