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I can't seem to get Trace level log information outputted after upgrading to .NET Core 2.0 (+ASP.NET Core 2.0).

In fact, if I do a dotnet new webproject and add the code below in Startup for Configure, I do not get any trace or debug log messages, but I get the Information and Error messages twice. Commenting out the .AddConsole()call will output these (Information and Error) only once - suggesting that it gets configured automatically with a console provider by default. Keep in mind, this is a "File -> New" project experience, there is nothing setup in Program.cs for logging or configuration at all for this - except for what I've added. Anyone seen things? Or should I register a GitHub issue for it.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory) { loggerFactory.AddConsole(Microsoft.Extensions.Logging.LogLevel.Trace); if (env.IsDevelopment()) { app.UseDeveloperExceptionPage(); } app.Run(async (context) => { var logger = loggerFactory.CreateLogger("Blah"); logger.LogTrace("Hello world : Trace"); logger.LogDebug("Hello world : Debug"); logger.LogInformation("Hello world : Information"); logger.LogError("Hello world : Error"); await context.Response.WriteAsync("Hello World!"); }); }
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  • will give me them once What do you mean by that? Commented Aug 20, 2017 at 12:01
  • Edited; I get Info and Error twice - but if I take out my AddConsole() line - I get the Info and Error once - but no Trace nor Debug messages at all with our without my explicit line to say console and Trace level. Commented Aug 20, 2017 at 12:14
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    Are you running in development? Default environment now is Production.. you can try set ASPNETCORE_ENVIRONMENT=Development; dotnet run Commented Aug 20, 2017 at 12:15
  • I ran into a similar issue. Adding a await Task.Delay(1) after the logging statements gets the Console to display logs. If It take it out, only partial logs are displayed on the Console. The accepted answer doesn't actually do anything. It seems to be a threading issue. Commented Jan 12, 2018 at 20:15

4 Answers 4

Reset to default
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The way logging is configured has changed a little... The recommended way (and it's pretty well documented in this GitHub issue/announcement to do it now is to configure the loggers on the AddLogging method, such as 

services.AddLogging(builder => { builder.AddConfiguration(Configuration.GetSection("Logging")) .AddConsole() .AddDebug(); });

And have an appsettings.json like

Notice

Seems a few people are confused, because the example only demonstrates the configuration of Console provider and not all loggers.

The LogLevel section configures logging level for all namespaces (Default key) or for a specific namespace (System overrides the default value for all classes logging whose namespace starts with System.*.

This is for the class used in T in ILogger<T>). This allows to set a higher or lower than default logging level for loggers from this namespace. 

{ "ApplicationInsights": { "InstrumentationKey": "" }, "Logging": { "IncludeScopes": false, "LogLevel": { "Default": "Information", "System": "Warning", "Microsoft": "Information" }, "Console": { "LogLevel": { "Default": "Warning", "System": "Information", "Microsoft": "Information" } } } }

Please note that the structure of the appsettings.json changed from what it used to be in .NET Core 1.x and that Logging entry in the appsettings.json now has logger provider names in it, which allows you to configure logging levels per logging provider.

Previously, the entry in appsettings.json would only be applicable to the console logger.

Alternatively, the logging can now be moved within the WebHostBuilder instead. 

public static void Main() { var host = new WebHostBuilder() .UseKestrel() .UseContentRoot(Directory.GetCurrentDirectory()) .ConfigureAppConfiguration((hostingContext, config) => { var env = hostingContext.HostingEnvironment; config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true) .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true) .AddJsonFile("hosting.json", optional: false) .AddEnvironmentVariables(); }) .ConfigureLogging((webhostContext, builder) => { builder.AddConfiguration(webhostContext.Configuration.GetSection("Logging")) .AddConsole() .AddDebug(); }) .UseIISIntegration() .UseStartup<Startup>() .UseApplicationInsights() .Build(); host.Run(); }

Update

In case one doesn't want to use the appsettings.json, one can register the filters in code too. 

services.AddLogging(builder => { builder.AddConfiguration(Configuration.GetSection("Logging")) // filter for all providers .AddFilter("System", LogLevel.Debug) // Only for Debug logger, using the provider type or it's alias .AddFilter("Debug", "System", LogLevel.Information) // Only for Console logger by provider type .AddFilter<DebugLoggerProvider>("System", LogLevel.Error) .AddConsole() .AddDebug(); });
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11 Comments

Thanks.. In fact, just adding an appsettings.json file with the Logging configuration without any logging setup at all seems to give me what I need.
or just builder.SetMinimumLevel(LogLevel.Trace);
Note that using AddConfiguration requires the Microsoft.Extensions.Configuration package.
Does any of this enable actual debug messages to be written to the log? That is with "LogLevel Default: Debug" the output of Debug.WriteLine ends up in the log. Because if not it's not much use, because 1) I don't want to have to inject Microsoft's logging class into every single low level component in my app and replace every single WriteLine with _log.LogDebug, 2) If I'm using a third party component I may not be able to inject Microsoft's logging class into these components.
I found your example of appsettings.json to be incorrect for .NET Core 2.1, this one worked for me learn.microsoft.com/en-us/aspnet/core/fundamentals/logging/…
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I spent almost twenty minutes to realize that since Configuration.GetSection("Logging") in the Startup.cs file reads the section "Logging" from the config in the appsettings.json file, which was configured as "Error". Changing it to "Information" or anything lower, fixed the issue.

Here's what the appsettinsg.json file looks now:

{ "Logging": { "IncludeScopes": true, "Debug": { "LogLevel": { "Default": "Information" } }, "Console": { "LogLevel": { "Default": "Information" } } } }

To find out more about the levels of logging (such as in "Information"), check out this link, that also provides general information on ASP.NET Core logging.

I'm just posting here, just in case you bump into any trouble with getting the logging to work, make sure you've been through that JSON file.

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Nothing of the above works for me The only workaround was to write a method

private void ConfigLogging( ILoggingBuilder builder ) { builder.SetMinimumLevel( LogLevel.Trace ); //... additional configuration... }

and when using the AddLogging extension method write it as

services.AddLogging( ConfigLogging );
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3 Comments

You sure your appsettings.json had the correct format? Or if the value was overriden by one of the other config sources (developing settings, environment variables etc)?
I solved it by adding this line: .ConfigureLogging((hostingContext, logging) => { ... logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging")); ... })
It's almost as if "Trace" is treated specially and will only be honored as a log level if in the declared code and NOT the config file. But I see no documentation of that.
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The following structure of appsettings.json seems to work fine:

{ "Logging": { "LogLevel": { "Default": "Information", "System": "Information", "Microsoft": "Information" }, "Console": { "IncludeScopes": true } } }

Taken from https://learn.microsoft.com/en-us/aspnet/core/fundamentals/logging/?view=aspnetcore-2.1

Also, see what your start up calls are, I find the following works for me:

public class Startup { public Startup(IHostingEnvironment env) { var logger = new LoggerConfiguration() .MinimumLevel.Information() .WriteTo.Sink(jsonSink) .Enrich.WithExceptionDetails() .CreateLogger(); Log.Logger = logger; } }
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