FtpServer Logging
FtpServer uses SLF4J throughout its internal code allowing the developer to choose a logging configuration that suits their needs, e.g java.util.logging or Log4J. SLF4J provides FtpServer the ability to log hierarchically across various log levels without needing to rely on a particular logging implementation.
MDC logging
FtpServer supports MDC logging. Basically, it provides session based information for the logger. Of primary interest in the case of FtpServer are the user name and remote IP address for each session. The log4j example below shows how to enable these to be logged.
log4j
If you need to setup detailed logging from within FtpServer's code, then you can use a simple log4j configuration. Note that this logging can be very verbose depending on the log level you chose to use. The log4j jar is bundled with the binary distribution. This is an optional jar file.
The log4j configuration file location is <INSTALL_DIR>/common/classes/log4j.properties. You can modify this file to configure log4j.
log4j.rootLogger=DEBUG, R log4j.appender.R=org.apache.log4j.RollingFileAppender log4j.appender.R.File=./res/log/log.gen log4j.appender.R.MaxFileSize=10MB log4j.appender.R.MaxBackupIndex=10 log4j.appender.R.layout=org.apache.log4j.PatternLayout log4j.appender.R.layout.ConversionPattern=[%5p] %d [%X{userName}] [%X{remoteIp}] %m%n
This log4j configuration sets up a file called log.gen in your FTP Server ./res/log folder with a maximum file size of 10MB and up to 10 backups. DEBUG log level is specified.
You should consult the log4j documentation for more options.