The Network Server uses the derby.log file to log problems that it encounters. It also logs connections and disconnections when the property derby.drda.logConnections is set to true. The derby.log file is created when the Derby server is started. The Network Server then records the time and version. If a log file exists, it is overwritten, unless the property derby.infolog.append is set to true.
java org.apache.derby.drda.NetworkServerControl logconnections on [-h <hostname>] [-p <portnumber>]
java org.apache.derby.drda.NetworkServerControl logconnections off [-h <hostname>][-p <portnumber>]