Difference between apachectl and httpd.worker?

[Gloria]

What is the difference between the mentioned ways of starting the apache server?

[NikkyG]

Apachectl is nothing but a wrapper over the httpd as well as it sets some environment variables and adds functionality such as configtest, you can find more details about it here. Whereas, httpd.worker is just like httpd, but is enabled with the worker module for further functionality.