I used a simple configuration by properties like:
log4cplus::PropertyConfigurator::doConfigure( logFileName );
but now I found another possible config by a thread watcher:
log4cplus::ConfigureAndWatchThread watcher( logFileName.c_str(), 5*1000 );
This one checks every 5 seconds the configuration file and updateds the logging
So by changing the properties, the logging of the running process can be configured.
I've teste this with MinGW on Windows.