if running as non root user (what's should be the default on web-servers) you get:
(log.c.118) opening errorlog '/var/log/lighttpd/server.log' failed: Permission denied

Fix: create log directory only if not exist and chmod 777 to allow anyone 
to write and create files inside default log directory

Signed-off-by: Christian Schoenebeck <christian.schoenebeck@gmail.com>