Hi!
According to https://spark.apache.org/docs/0.9.0/configuration.html#configuring-logging, changing log-level is just a matter of creating a log4j.properties (which is in the classpath of spark) and changing log level there for the root logger. I did this steps on every node in the cluster (master and worker nodes). However, after restart there is still no debug output as desired, but only the default info log level.
