The Network Server uses the derby.log file to log problems that it encounters. It also logs connections 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.
When the Network Server is logging connections, it also logs the Connection Number; this log message is written both to the derby.log file and to the Network Server console.
java org.apache.derby.drda.NetworkServerControl logconnections on [-h <hostname>] [-p <portnumber>]
java org.apache.derby.drda.NetworkServerControl logconnections off [-h <hostname>][-p <portnumber>]