Log4Net Tutorial in C# .NET – Logging Levels Explained with Examples

log4net is one of the most widely used logging frameworks for .NET applications. It helps developers capture logs for debugging, performance monitoring, and troubleshooting. In this tutorial, we’ll not only show how to log messages in a file but also explain the different log4net logging levels – DEBUG, INFO, WARN, ERROR, and FATAL – with examples. By the end of this guide, you’ll know how to configure log4net and choose the right logging level for your application.

Write Log in procedures are given below-

1. Download log4net from http://logging.apache.org/log4net/download.html

2. Open visual studio and create a new website.

3. Add to the project a reference to the \bin\net\2.0\release\log4net.dll assembly in the log4net distribution.

4. write the main method like this

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Text;
using log4net;
using log4net.Config;
using log4net.Core;
using log4net.Repository.Hierarchy;
using log4net.Appender;
using System.Collections.Generic;
using System.Xml.Schema;
public partial class _Default : System.Web.UI.Page
{

  protected void Page_Load(object sender, EventArgs e)

  {

  }

  protected void btn_Click(object sender, EventArgs e)

  {

      int a = 23, b = 0;
              try

              {



                  int result = a / b;



              }



              catch (Exception ex)

              {



                  // Divide by Zero exception occurred and in the next line we are going to log tha

               log4net.ILog log =log4net.LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

               log4net.Config.XmlConfigurator.Configure();

                 log.Debug(ex.Message);

                  log.Error(ex.Message);

                  log.Warn(ex.Message);

                  log.Info(ex.Message);

                  log.Fatal(ex.Message);



              }

          }

}

5.Now put this web.config/app.config file in configuration tag.

<configsections>

<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,Log4net">

</section>

<log4net>

<root>

<level value="DEBUG">

<appender-ref ref="LogFileAppender">

</appender-ref>

<appender name="LogFileAppender" type="log4net.Appender.RollingFileAppender">

<param name="File" value="C:\ErrorLogFile\log.txt">

<param name="AppendToFile" value="true">

<rollingstyle value="Size">

<maxsizerollbackups value="10">

<maximumfilesize value="10MB">

<staticlogfilename value="true">

<layout type="log4net.Layout.PatternLayout">

<param name="ConversionPattern" value="%-5p%d{yyyy-MM-dd hh:mm:ss} â�� %m%n">

</layout>

</staticlogfilename>

</maximumfilesize></maxsizerollbackups></rollingstyle></appender></level></root></log4net></configsections>

If you run this code log file show in the C:\ErrorLogFile\log.txt

FAQs about log4net Logging Levels

What are the log4net logging levels?

log4net supports five main levels: DEBUG, INFO, WARN, ERROR, and FATAL. Each indicates the severity of the log message.

Which log level should I use in production?

Typically, INFO and WARN are enabled in production, while DEBUG is used during development. ERROR and FATAL are logged for issues that need immediate attention.

Can I create custom log levels in log4net?

Yes, log4net supports custom log levels, though most applications use the built-in ones.

What is the difference between ERROR and FATAL?

ERROR indicates a problem that does not stop the application. FATAL means a critical issue that may cause the application to stop running.