public static void ModifyAppenders<T>(this ILoggerRepository repository, Action<T> modify) where T:log4net.Appender.AppenderSkeleton

{

    var appenders = from appender in log4net.LogManager.GetRepository().GetAppenders()

                        where appender is T

                        select appender as T;

    foreach (var appender in appenders)

    {

        modify(appender);

        appender.ActivateOptions();

    }

}

log4net.LogManager.GetRepository().ModifyAppenders<FileAppender>(a =>

                {

                    a.File = Path.Combine(settings.ConfigDirectory,

                                          Path.GetFileName(a.File));

                });

 private void TurnOnLogging()

        {

            log4net.Repository.ILoggerRepository[] repositories= log4net.LogManager.GetAllRepositories();

            //Configure all loggers to be at the debug level.

            foreach (log4net.Repository.ILoggerRepository repository in repositories)

            {

                repository.Threshold = repository.LevelMap["DEBUG"];

                log4net.Repository.Hierarchy.Hierarchy hier = (log4net.Repository.Hierarchy.Hierarchy)repository;

                log4net.Core.ILogger[] loggers=hier.GetCurrentLoggers();

                foreach (log4net.Core.ILogger logger in loggers)

                {

                    ((log4net.Repository.Hierarchy.Logger) logger).Level = hier.LevelMap["DEBUG"];

                }

            }

            //Configure the root logger.

            log4net.Repository.Hierarchy.Hierarchy h = (log4net.Repository.Hierarchy.Hierarchy)log4net.LogManager.GetRepository();

            log4net.Repository.Hierarchy.Logger rootLogger = h.Root;

            rootLogger.Level = h.LevelMap["DEBUG"];

        }