apache2ctl – Apache HTTP server control interface

show all loaded modules

apache2ctl -M

show all vhosts

apache2ctl -S

run syntax check for config files

apache2ctl -t

References
http://csuca.org/manual/en/programs/apachectl.html
https://manpages.ubuntu.com/manpages/trusty/man8/apache2ctl.8.html