Log4Net config in external file does not work

We are using log4net and want to specify it's configuration in an external config file (as we have done with other sections). To do this we have changed the log4net section in the App.config to:

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

And in the Log.Config file (same directory as the App.config) we have:

<log4net>
  <appender name="General" type="log4net.Appender.FileAppender">
    <file value="myapp.log" />
    <layout type="log4net.Layout.SimpleLayout" />
  </appender>
  <root>
    <appender-ref ref="General" />
  </root>
</log4net>

However, when we run the app, no log file is created (and no logging done). There are no error messages output to the console.

If we move the contents of the Log.config file back into the App.config (replacing the first code line above), it works as expected. Any idea why it is not working in an external file?

Do you have the following attribute in your AssemblyInfo.cs file:

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log4Net.config", Watch = true)]

and code like this at the start of each class that requires logging functionality:

private static readonly ILog log = 
LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);

I have a blog post containing this and other info here.

There is an open defect on this issue. Log4Net does not support the configSource attribute of configuration elements. To use a purely configuration file solution you use the log4net.Config key in appSettings.

Step 1: Include the normal configuration section definition:

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

Step 2: Use the magic log4net.Config key in appSettings.

<appSettings>
      <add key="log4net.Config" value="log4net.simple.config" />
</appSettings>

Step 3: Contribute a patch to fix the handling of configSource.

The step that has been missed is

log4net.Config.XmlConfigurator.Configure(); 

this will cause the configSource to be used. Make sure you call it once before calling GetLogger();

Make sure that your log4net.config file is set with the following properties:

Build Action: Content

Copy to output directory: Copy Always

Either use,

<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
</configSections>
<appSettings>
<add key="log4net.Config" value="Log4Net.config" />
</appSettings>

or just,

log4net.Config.XmlConfigurator.ConfigureAndWatch(new System.IO.FileInfo("Log4Net.config"));

In both cases the file,Log4Net.config, should be there in output directory. You can do this by setting Log4Net.config file properties in solution explorer. Build Action - Content and Copy to Output Directory - Copy always

Watch out for this issue...

In my case everything was configured correctly. The problem is that I used Web Deploy inside Visual Studio 2013 to upload the site to WinHost.com and it reset the ACLs on the server. This in turn revoked all permission on folders and files - log4net could not write the file.

You can read more about it here:

How to stop Web Deploy/MSBuild from messing up server permissions

I asked the support team there to reset the ACLs and then log4net started spitting logs. :)

It is also possible to turn on a Debug mode for log4net. Insert this into the App.config file:

 <appSettings>
      <add key="log4net.Internal.Debug" value="true"/>
 </appSettings>
 <system.diagnostics>
      <trace autoflush="true">
      <listeners>
           <add
             name="textWriterTraceListener"
             type="System.Diagnostics.TextWriterTraceListener"
             initializeData="link\to\your\file.log" />
      </listeners>
      </trace>
 </system.diagnostics>

and you will at least get error messages, from which you can derive what exactly went wrong. In my case I simply forgot to set Copy to output directory to Copy Always.

Assuming you had an external config file called log4net.config that is copied to your deploy directory you can configure it like so:

using System;
using System.Collections.Generic;
using System.Windows.Forms;
using System.Reflection;

using log4net;

namespace MyAppNamespace {
    static class Program {
        //declare it as static and public so all classes in the project can access it
        //like so: Program.log.Error("got an error");
        public static readonly log4net.ILog log = log4net.LogManager.GetLogger(typeof(Program));

        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main() {
             //configure it to use external file
            log4net.Config.XmlConfigurator.Configure(new Uri(Application.StartupPath + "\\log4net.config"));
            //use it
            log.Debug("#############   STARING APPLICATION    #################");


            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new FormMain());
        }
    }
}

I had the same problem, besides having

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net")]

in the running project, I also had the following line in a reference project:

[assembly: log4net.Config.XmlConfigurator]

When I removed this line in the referenced projects, the logs start to appear.

1. add following to AssemblyInfo.cs

   [assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log4Net.config")]

2. Make sure log4net.config is included in project

3. In properties of log4net.config

change CopyToOutputDirctory tag to CopyIfNewer tag

4. Double check log level level value="ALL"

@Mitch, It turns out there is a file with the [assembly:...] declaration, but it did not have the ConfigFile property.

Once I added it and pointed it to Log.config, it started working. I would have thought that it would work like all the other config sections (ie AppSettings) and accept external config files with no modification.

We don't have the second statement you mentioned, as we wrap it in a global static log provider.

In my case I got this error message:

log4net: config file [C:\........\bin\Debug\log4net.config] not found.

And log4net.config the file was in Visual Studio 2017 project, but when I checked the file in bin\Debug folder I could not find it.

My original assembly setup was like this:

[assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net.config", Watch = true)]

After some research time, I change it to the following and it works:

[assembly: log4net.Config.XmlConfigurator(ConfigFile = @"..\..\log4net.config", Watch = true)]

It's also worth pointing out that in a web app it looks in the root directory, not the bin folder, so make sure that's where you put the config file.