Logging w/log4net

Feb. 05 2019


This article will detail how to setup log4net within your Visual Studio - C# .Net project. The log4net manual can be a bit wordy, so I'll try to break it down into three steps: Installation, Configuration, and Usage.



  • Create or open an existing project.
  • Right-click the project root from within the Solution Explorer tab.
  • Select Manage NuGet Packages... from the drop-down menu.

  • Search for "log4net" in the Browse tab.
  • Select log4net from the list and Install.

NuGet will now download and install the library files so that you project can access them at runtime.


Add the following to the bottom of your Properties/AssemblyInfo.cs file. This will tell log4net to parse the App.config (or Web.config) file.

[assembly: log4net.Config.XmlConfigurator(Watch = true)]

Next, open the App.config file.

Note: You may need to create the App.config file if it doesn't already exist.

You must first register the <log4net> otherwise config file parser won't know how to process it.

    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />

Now, start another root <log4net> (now that it's been registered from above). In order for log4net to know where to log to (i.e. output destination) we'll first need to set up at least one <appender>. Appenders can be thought of as output destinations.

    <appender name="TraceAppender" type="log4net.Appender.TraceAppender">
      <layout type="log4net.Layout.PatternLayout">
        <conversionPattern value="[%date] %level (%logger:%line) - %message%newline" />
      <level value="INFO" />
      <appender-ref ref="TraceAppender" />

The <root> element is optional. You can use it to set sets configurations for the default logging level.

For more information regarding configurations see [More On Configurations](#More On Configurations).


Use the code snippet below as reference for using logging in your own project.

  • It's recommended that every class gets it's own logger.
  • _logger has several methods to call varying log levels (i.e. info, debug).
using System;
using log4net;

namespace Project
    public static class Program
        private static readonly ILog _logger = LogManager.GetLogger(

        static void Main()

More On Configurations

Logging Levels

Level Description
OFF Log nothing; essentially used to disable an Appender
FATAL Issue caused the program to crashed.
ERROR Problem occurred, but didn't yet crash the program.
WARN Potential problem.
INFO Informational message.
DEBUG Used strictly for debugging purposes.
ALL Log everything regardless of level.

Layout - ConversionPattern

These patterns are used to format the log output.

Pattern Details
%date Logs date of logging event in the local time zone.
%file Logs the file name of where the logging event occured.
%line Logs the line number where the logging event occurred.
%method Logs the method where the logging event occurred.
%level Level specified for event.
%message Message passed through the log event.
%newline Newline character.

You can reference the list below or see a full listing here.


Type Description
AdoNetAppender Writes log events to a database.
FileAppender Writes log events to a file you specify.
RollingFileAppender Writes log events to a file you specify, while performing archived file cleanup.
TraceAppender Writes log events to Visual Studio's Output interface.

For a full list of Appenders check here.


You should now have log4net setup and working. Check out the further reading below for more in-depth reading on the topic.

Further Reading