Change log4net logging level programmatically

Ken_82793 0
Viewed 50072

This is similar to 650694 but no answer was accepted there, I can't get any of those suggestions to work at all, and I suspect I may be in a slightly different situation.

I'm calling log4net.Config.XmlConfigurator.Configure(). But after that point in the program, I want to change the logging threshold to a value only known at runtime.

From the other question, I tried:

((log4net.Repository.Hierarchy.Logger)mylogger.Logger).Level = log4net.Core.Level.Error;

and:

var appender = new log4net.Appender.ColoredConsoleAppender();
appender.Layout = new log4net.Layout.PatternLayout(@"%date %-5level %message%newline");
appender.Threshold = log4net.Core.Level.Error;
appender.ActivateOptions();
log4net.Config.BasicConfigurator.Configure(appender);

but neither one seems to have any effect: I'm still seeing DEBUG and INFO logging statements on the console.

My hunch is that I'm adding a new appender, which has no effect on the appender declared in the XML config (which tells it to print DEBUG level messages), but I don't have any evidence for this yet.

I've been digging through the log4net API for a while now, and I'm just not seeing it. Is there something simple I'm missing?

log4net logging c#
8 Answers

Finally found a working solution, here.

The big pieces were:

  • need to set the threshold on all loggers, including the "cannot be retrieved by name" root logger
  • need to get the Level from the Hierarchy's LevelMap

Big thanks to Eddie for asking good pointed questions, which led me to google the right words. I never would have figured this out alone.

(Aside: Repository, Hierarchy, Logger, RootLogger, LevelMap -- I had no idea it was even possible to make a logging library this complex. It's got about 20 layers of indirection, which I'm sure makes it flexible enough for anything, but makes it nearly impossible to do simple things like "don't log any messages above threshold X". Gah!)

Ken_827930

If this works for someone, here is how I implemented in my web application a toggle level endpoint exposed via an API call, so I can change the logging level on the fly.

public HttpResponseMessage Post([FromBody] string logLevel)
{
    var newLevel = ToggleLogging(logLevel);

    // Create your own response here.
    return newLevel;
}

And the actual implementationt

private Level ToggleLogging(string logLevel)
{

    Level level = null;

    if (logLevel != null)
    {
        level = LogManager.GetRepository().LevelMap[logLevel];
    }


    if (level == null)
    {
        level = Level.Warn;
    }

    ILoggerRepository[] repositories = LogManager.GetAllRepositories();

    //Configure all loggers to be at the same level.
    foreach (ILoggerRepository repository in repositories)
    {
        repository.Threshold = level;
        Hierarchy hier = (Hierarchy)repository;
        ILogger[] loggers = hier.GetCurrentLoggers();
        foreach (ILogger logger in loggers)
        {
            ((Logger)logger).Level = level;
        }
    }

    //Configure the root logger.
    Hierarchy h = (Hierarchy)LogManager.GetRepository();
    Logger rootLogger = h.Root;
    rootLogger.Level = level;

    return level;
}
user_7966680

JeanT's answer doesnt seem to work with the latest version of log4net.

I adapted it to get it working, this changes to Debug level, but alter as required.

foreach(var r in LogManager.GetAllRepositories()) { ((log4net.Repository.Hierarchy.Hierarchy)r).Root.Level = Level.Debug; ((log4net.Repository.Hierarchy.Hierarchy)r).RaiseConfigurationChanged(EventArgs.Empty); }

user_38023020

In my case I had different default levels for different appenders set the config, but wanted to overide them if the application was in verbose mode.

I used the following:

var log4NetHierarchy = (log4net.Repository.Hierarchy.Hierarchy)LogManager.GetRepository();
foreach (var appender in log4NetHierarchy.GetAppenders())
{
    if (appender is AppenderSkeleton appenderSkeleton)
    {
        appenderSkeleton.Threshold = Level.All;
    }
}
log4NetHierarchy.RaiseConfigurationChanged(EventArgs.Empty);
user_131530
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