Den apache process auf dem system stoppen und mit option -X -f und vermutlich -d auf der Kommando Zeile als root starten.
Siehe man page:
-X Run apache2 in debug mode. Only one worker will be started and the server will not detach from the console.
-f config
Uses the directives in the file config on startup. If config does not begin with a /, then it is taken to be a path relative to the ServerRoot. The default is
/etc/apache2/apache2.conf.
-d serverroot
Set the initial value for the ServerRoot directive to serverroot. This can be overridden by the ServerRoot directive in the configuration file.
-e level
Sets the LogLevel to level during server startup. This is useful for temporarily increasing the verbosity of the error messages to find problems during startup.