log4net not working

Question

One gotcha for this type of thing is to make sure to add the XmlConfigurator attribute to the assembly by placing the following line in your AssemblyInfo.cs:

[assembly: log4net.Config.XmlConfigurator]

Otherwise log4net never activates.

I guess that either log4net is not logging at all, or the file is not ending up where you expect it.

Firstly, have you actually called

XmlConfigurator.Configure()

anywhere in your code? If the xml snippet above is in the application configuration file, this call will do the trick. If the xml snippet is in it's own file, you'll need to use the .Configure(string) overload that takes the path to the file. Without this call (or apparently the assembly level attribute mentioned by Kirk Woll), then log4net won't be logging at all.

If you believe this is all done, and log4net should be logging, then maybe you should put a fully qualified path in for the log file while you debug further. That will let you be sure where the file should be.

There is another small gotcha, see here: http://logging.apache.org/log4net/release/manual/configuration.html#dot-config

the [assembly: log4net.Config.XmlConfigurator] method doesn't work with app.config. If you configure log4net from app.config, you must use the log4net.Config.XmlConfigurator.Configure() method.

Here is my checklist for when log4net is proving to be recalcitrant:

• ensure that log4net.config file is copied to the bin\ folder when building (set to 'Copy if newer' in compiler)
  • when dealing with installed code, ensure that the log4net.config came along for the ride (set to 'Content' in compiler)
• ensure that the user that the process runs as has write rights to the folder where the logs are to be written
• if in doubt, give promiscuous permissions to c:\temp\ and get everything to log to there ()
• fire up Sysinternal/Dbgview.exe to see if that tells you anything

For an ASP.NET MVC project adding

log4net.Config.XmlConfigurator.Configure();

to the Global.asax.cs also helps:

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
        AuthConfig.RegisterAuth();

        log4net.Config.XmlConfigurator.Configure();
    }
}

These are the steps which eventually got my file logging working:

• -Check AssemblyInfo.cs contains the following attribute. [assembly: log4net.Config.XmlConfigurator]. This loads log4net.
• Check the log directory has write permissions.
• Check the logger has a format specified. This is done by checking each element in your configuration has a layout element specified. Eg:

<appender name="MainLogger"... <layout type="log4net.Layout.SimpleLayout"/>

• Finally, try turning on log4net internal logging to enable console logging and checking the console. To do this, add <add key="log4net.Internal.Debug" value="true"/> to your appSettings.

I've had experiences where logging systems fail silently without raising exceptions. I suppose this makes sense because if the logger is logging errors then how can it log an error that it's unable to perform logging?

So if the file isn't created on disk, start by looking into file system permissions to ensure the user your application is running under can write a new file to that disk location.

For testing purposes you might want to manually create the file on disk that should be written to and open up permissions for everybody to write to it. If the logger starts writing to it then you know it's permission based rather than configuration based.