Apache is the most commonly user web server, and it's the one I've been using for the last 20 years. So I thought I knew it pretty well.
I set up a server with Fedora 22 (that's the latest version) and Apache/2.4.12. No problems, except when I started it up, it failed.
One of the things I do, is I take the log output of apache, and pipe it into an analysis program, which alerts me via email to any naughty stuff. That's easy to do,
CustomLog "|/home/engine/analyser.pl" vlog
For reasons I really don't understand, it wasn't working. It seemed to be claiming that it couldn't access the file.
I removed the quote marks, and it worked. I put the quote marks back ... and it still worked.