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    In Umbraco v8.0+ we have changed the underlying logging framework from Log4Net to Serilog.

    Out of the box for v8.0+ we will write a JSON log file that contains a more rich logfile, that allows tools to perform searches & correlation on log patterns a lot easier.

    The default location of this file is written to App_Data/Logs and contains the Machine name, along with the date too:

    • /App_Data/Logs/UmbracoTraceLog.DELLBOOK.20181108.json

    Structured logging

    Serilog is a logging framework that allows us to do structured logging or write log messages using the message template format. This allows us to have a more detailed log message, rather than the traditional text message in a long txt file.

    2018-11-12 08:34:50,419 [P27004/D2/T1] INFO   Umbraco.Core.Runtime.CoreRuntime - Booted. (4586ms) [Timing 9e76e5f]

    Here is an example of the same log message represented as JSON, you can see here we have much more information that would allow us to search & filter logs based on these properties with an appropriate logging system.

      "@t": "2018-11-12T08:34:50.4190399Z",
      "@mt": "{EndMessage} ({Duration}ms) [Timing {TimingId}]",
      "EndMessage": "Booted.",
      "Duration": 4586,
      "TimingId": "9e76e5f",
      "SourceContext": "Umbraco.Core.Runtime.CoreRuntime",
      "ProcessId": 27004,
      "ProcessName": "iisexpress",
      "ThreadId": 1,
      "AppDomainId": 2,
      "AppDomainAppId": "LMW3SVC2ROOT",
      "MachineName": "DELLBOOK",
      "Log4NetLevel": "INFO ",
      "HttpRequestNumber": 1,
      "HttpRequestId": "557f45ba-0888-4216-8723-e226d795a2f7"

    To learn more about structured logging and message templates you can read more about it over on the https://messagetemplates.org website or alternatively watch this video from the Serilog creator - https://www.youtube.com/watch?v=OhmNp8UPEEg

    Writing to the log

    Umbraco writes log messages, but you are also able to use the Umbraco logger to write the log file as needed, so you can get further insights and details about your implementation.

    Here is an example of using the logger to write an Information message to the log which will contain one property of Name which will output the name variable that is passed into the method

    using Umbraco.Web.WebApi;
    using Umbraco.Core.Logging;
    namespace MyNamespace
        public class MyApiController : UmbracoApiController
            public string GetSayHello(string name)
                Logger.Info<MyApiController>("We are saying hello to {Name}", name);
                return $"Hello {name}";

    The incorrect way to log the message would be use string interpolation or string concatenation such as

    //GOOD - Do use :)
    Logger.Info<MyApiController>("We are saying hello to {Name}", name);
    //BAD - Do not use :(
    Logger.Info<MyApiController>($"We are saying hello to {name}");
    //BAD - Do not use :(
    Logger.Info<MyApiController>("We are saying hello to " + name);

    The bad examples above will write to the log file, but we will not get a separate property logged with the message. This means we can't find them by searching for log messages that use the message template We are saying hello to {Name}

    If you are writing classes that inherit from one of these special Umbraco base classes:

    • RenderMvcController
    • SurfaceController
    • UmbracoApiController
    • UmbracoAuthorizedApiController

    Then you can access the logging functionality via a special 'Logger' property included in those base classes and use the friendlier syntax of Logger.Info<T> to pass the type, if you add a reference to Umbraco.Core.Logging as a Using statement.

    Outside of these places, eg a ContentFinder or your own custom code, you can get a reference to the logger via Dependency Injection. While using Dependency Injection is the recommended way, it is possible to use Current.Logger instead, if DI is not an option.

    using Umbraco.Core.Logging;
    using Umbraco.Web.Routing;
    namespace MyNamespace
        public class MyContentFinder : IContentFinder
            private readonly ILogger _logger;
            public MyContentFinder(ILogger logger)
                _logger = logger;
            public bool TryFindContent(PublishedRequest frequest)
                _logger.Info<MyContentFinder>("Trying to find content for url {RequestUrl}", frequest.Uri);
                //Do Content Finder Logic...

    You will need to register your ContentFinder using a Composer

    Log Levels

    Serilog uses levels as the primary means for assigning importance to log events. The levels in increasing order of importance are:

    1. Verbose - tracing information and debugging minutiae; generally only switched on in unusual situations
    2. Debug - internal control flow and diagnostic state dumps to facilitate pinpointing of recognised problems
    3. Information - events of interest or that have relevance to outside observers; the default enabled minimum logging level
    4. Warning - indicators of possible issues or service/functionality degradation
    5. Error - indicating a failure within the application or connected system
    6. Fatal - critical errors causing complete failure of the application

    The default log levels we ship with in Umbraco v8.0+ are:

    • .txt file Debug
    • .json file Verbose


    Serilog can be configured and extended by using the two XML configuration files on disk.

    • /config/serilog.config is used to modify the main Umbraco logging pipeline
    • /config/serilog.user.config which is a sublogger and allows you to make modifications without affecting the main Umbraco logger

    Info on the Serilog config here.


    Full C# control over Serilog configuration

    If you like using Serilog but prefer to use C# to configure the logging pipeline then you can do so with the following example. This sets the minimum logging level from a web.config AppSetting, allowing you to set different minimum logging levels in different environments using web config transforms.

    using System;
    using System.Configuration;
    using Umbraco.Web;
    using Umbraco.Core;
    using Umbraco.Web.Runtime;
    using Umbraco.Core.Logging.Serilog;
    using Serilog;
    using Serilog.Core;
    using Serilog.Events;
    namespace MyNamespace
        public class FineTuneLoggingApplication : UmbracoApplication
            protected override IRuntime GetRuntime()
                var logLevelSetting = ConfigurationManager.AppSettings["YourMinimumLoggingLevel"]; //Warning, Debug, Information, etc
                const bool ignoreCase = true; //this is to clarify the function of the boolean second parameter in the TryParse
                if (!Enum.TryParse(logLevelSetting, ignoreCase, out LogEventLevel minimumLevel))
                    minimumLevel = LogEventLevel.Information;//set to this level if the config setting is missing or doesn't match a valid enumeration
                var levelSwitch = new LoggingLevelSwitch { MinimumLevel = minimumLevel };
                var loggerConfig = new LoggerConfiguration()
                var logger = new SerilogLogger(loggerConfig);
                var runtime = new WebRuntime(this, logger, GetMainDom(logger));
                return runtime;

    You will then need to update the global.asax file on disk to use our FineTuneLogging class like so

    <%@ Application Inherits="MyNamespace.FineTuneLoggingApplication" Language="C#" %>

    The logviewer dashboard

    Learn more about the logviewer dashboard in the backoffice and how it can be extended.

    The logviewer desktop app

    This is a tool for viewing & querying JSON log files from disk in the same way as the built in log viewer dashboard.

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    Serilog project/references shipped

    Umbraco v8.0+ ships with the following Serilog projects, where you can find further information & details with the GitHub readme files as needed.

    Further Resources

    If you are interested in learning more then the following resources will beneficial: