Develop Reference

Log4net error - patternstring not working

I am creating a logging component using log4net in my project. I've created an xml file to configure the log4net settings including an append-er and logger definition. I'm using PatternString to pick up properties' value from the appsetting.config file. However when I build and run the project, it throws the following error:
log4net:ERROR Undefined level [%property{Level}] on Logger [Test].
Does anyone know what might be causing it?
XML:
<?xml version="1.0" encoding="UTF-8" ?>
<log4net>
<logger name="Test">
<level type="log4net.Util.PatternString" value="%property{Level}" />
<appender-ref ref="JsonFileAppender" />
</logger>
</log4net>
appsetting.config:
<appSettings>
<add key="Level" value="ALL"/>
</appSettings>
In case it's useful the log4net version is: version:2.0.8

Good question!
I learnt from this, a lot.
Please don't forget to call this method before start logging.
log4net.Config.XmlConfigurator.Configure();
app.config is.
if you need apply pattern, use <layout> element.
and if you want to use some value from "appSettings",
use like this, %appSetting{Environment}
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
</configSections>
<log4net>
<appender name="ConsoleAppender" type="log4net.Appender.ConsoleAppender" >
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%ndc] - %message%newline" />
</layout>
</appender>
<root>
<level value="%appSetting{Environment}" />
<appender-ref ref="ConsoleAppender" />
</root>
</log4net>
<appSettings>
<add key="Environment" value="INFO" />
<!-- this is optional flag.-->
<add key="log4net.Internal.Debug" value="True" />
</appSettings>
</configuration>
Here is where I learned
Accessing appSettings config values from log4net config section
https://logging.apache.org/log4net/release/manual/configuration.html
https://www.paraesthesia.com/archive/2010/11/12/log4net-appsettings-keys.aspx/

The reason for this error is because the level of a logger can't be configured via a PatternString.
The <level> elements expects a wellknown value, like eg. ALL, DEBUG, INFO, WARN, ERROR,
eg.:
<logger name="Test">
<level value="All" />
</logger>
From your setup I read that you are trying to apply a setting from AppSettings.config upon the log level of a logger in your Log4net configuration.
As explained above, this can't be done.
Either keep all Log4net related settings within its own xml - in the end it is also configuration.
Or set the level programmatically;
you will have to translate the string value in appsettings.config to a Level yourself.
logger = LogManager.GetLogger("Test");
Level level = // Parse from ConfigurationManager.AppSettings["Level"]
((Logger)logger.Logger).Level = level;

Log4Net Error: Failed to find configuration section 'log4net' in the application's .config file

I currently use a class library to store a class that handles logging using log4net. This class is used in other projects.
I've read a lot of other questions and answers, but I haven't been able to fix it yet...
I enabled internal debugging of log4net because it would not write to a file, and this is the error I get:
log4net:ERROR Failed to find configuration section 'log4net' in the application's .config file. Check your .config file for the <log4net> and <configSections> elements. The configuration section should look like: <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
These are my files:
log4net.config
<log4net debug="true">
<appender name="LogFileAppender" type="log4net.Appender.FileAppender">
<param name="File" value="Logs/log4net.log" />
<param name="AppendToFile" value="true" />
<layout type="log4net.Layout.PatternLayout">
<param name="Header" value="[Header]\r\n" />
<param name="Footer" value="[Footer]\r\n" />
<param name="ConversionPattern" value="%d [%t] %-5p %c %m%n" />
</layout>
</appender>
<root>
<level value="ALL" />
<appender-ref ref="LogFileAppender" />
</root>
</log4net>
App.config
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
</configSections>
<appSettings>
<add key="log4net.Internal.Debug" value="true"/>
</appSettings>
<parameter>
<parameterName value="#BlogId" />
<dbType value="Int32" />
<layout type="log4net.Layout.RawPropertyLayout">
<key value="BlogId" />
</layout>
</parameter>
</configuration>
AssemblyInfo.cs (just last line)
[assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net.config", Watch = true)]
Logger.cs
public class Logger : ILogger
{
private static ILog logger = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
public Logger()
{
XmlConfigurator.Configure();
logger.Info("NEW LOGGER INSTANCE CREATED");
}
}
UPDATE
I fixed it by letting the class that uses my Logger.cs give its own .config file for log4net. Now log4net reads the given .config files and it works.

You have defined that the log4net section is in your app.config with:
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
</configSections>
that means you should add the content of the log4net.config to the app.config file.

If you're trying to implement a wrapper over log4net where the log4net lives in its own class library and not in the main executable of your application, try something like this in a static constructor of your wrapper class:
static Logger()
{
log4net.Config.XmlConfigurator.Configure(new System.IO.FileInfo
(System.IO.Path.GetDirectoryName
(System.Reflection.Assembly.GetExecutingAssembly().Location)));
}
The static constructor solution ensures that if you load the class library, the configuration code will run.
You will also need to do something to copy the log4net.config file from that class library project into the same folder as the executable. You can do this by hand when deploying the application; however, to do it automatically when debugging a post-build step with something like this (from the class library project) will put the config file into the right folder:
XCOPY "$(TargetDir)*.config" ".\..\..\..\..\bin\Debug" /S /Y /I
XCOPY "$(TargetDir)*.config" ".\..\..\..\..\bin\Release" /S /Y /I
// Where those paths point to the main executable /bin folders
// and build configuration target dirs
A good reason to use this approach is that if you're leveraging something like MEF, you can bring in your logger wrapper class as an interface and you don't need to reference log4net in more than one project in your solution. You can interface with the logger with an abstract interface of your own choosing, and use log4net as the Impl. (Bridge pattern)
Good luck!

redirect log4net logs from third party

I have a third party using a configuration file that looks like this:
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
<!--Others sections-->
</configSections>
<log4net>
<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file value=".\logs\logclient.txt" />
<appendToFile value="false" />
<rollingStyle value="Date" />
<maximumFileSize value="1000KB" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%ndc] - %message%newline" />
</layout>
</appender>
<root>
<level value="DEBUG" />
<appender-ref ref="RollingFileAppender" />
</root>
</log4net>
</configuration>
The code in the third party looks like :
LogManager.GetRepository(Assembly.GetCallingAssembly()), configFile);
LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);
I would like the third party dll to use my own appender defined in my own configuration file. How can I managed this ?
NB :
the third party need to use its own configuration file because others
sections are mandatory and I can not add them in my file
I can modify the third party configuration file, I can not modify mine

There are two existing questions that propose a solution to dynamically edit log4net configuration:
Dynamically reconfigure Log4Net
How can I change the file location programmatically? (see JackAce answer).

As far as I understand, you must use the third party configuration file and you can modify it.
The configSource property/attribute should work to redirect the log4net configuration section of your third party configuration file.
In the third party configuration file :
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler,log4net" />
</configSections>
<log4net configSource="pathtoyourlog4net.config" />

log4net library is a tool to help the programmer output log statements
to a variety of output targets.
You can also configure log4net in code instead of using a config file,this SO post clearly explains the question.
Change appender dynamically:
public static void ChangeFilePath(string appenderName, string newFilename)
{
log4net.Repository.ILoggerRepository repository = log4net.LogManager.GetRepository();
foreach (log4net.Appender.IAppender appender in repository.GetAppenders())
{
if (appender.Name.CompareTo(appenderName) == 0 && appender is log4net.Appender.FileAppender)
{
log4net.Appender.FileAppender fileAppender = (log4net.Appender.FileAppender)appender;
fileAppender.File = System.IO.Path.Combine(fileAppender.File, newFilename);
fileAppender.ActivateOptions();
}
}
}
Reference post

If your .NET app is referencing the thirdparty.dll, at runtime the app will ignore the thirdparty.dll.config completely. Also, the thirdparty.dll will not pickup the settings in the thirdparty.dll.config as it is expecting these to be loaded by the exe.
What you have to do is to merge (or replicate) the content of the thirdparty.dll.config into your own app.config. Both your app and the thirdparty.dll will be able to pickup the settings in your app.exe.config and you only need to maintain one .config file.
Furthermore, you can then add additional appenders to the log4net section and it will be picked-up by both your app and the thirdparty.dll.

Log4Net Not Writing to Output File

I'm having serious trouble getting log4net to work with a Windows service (multi-project solution).
I first added reference to log4net.dll to the appropriate projects via NuGet. I then created a new Log4Net.config file in the root folder of the Windows service project. In the file's properties, I set Copy to Output Directory = Copy always. Below is the config file:
<?xml version="1.0"?>
<configuration>
<log4net>
<appender name="TestServiceLog" type="log4net.Appender.RollingFileAppender">
<file value="C:\Temp\Test.log" />
<appendToFile value="true" />
<rollingStyle value="Size" />
<maxSizeRollBackups value="100" />
<maximumFileSize value="10MB" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %level %logger - %message%newline" />
</layout>
</appender>
<root>
<level value="INFO" />
<priority value="ALL" />
<appender-ref ref="TestServiceLog" />
</root>
</log4net>
</configuration>
In my Windows service project, in the AssemblyInfo.cs file, I added this line:
[assembly: log4net.Config.XmlConfigurator(ConfigFile = "Log4Net.config", Watch = true)]
In my main TestService.cs class, I referenced log4net and initialized the logger like so (omitted non-logging code):
public partial class TestService : ServiceBase
{
private ILog Log { get; set; }
protected override void OnStart(string[] args)
{
Log = LogManager.GetLogger(this.GetType());
Log.Info("Hear me log.");
}
}
I then installed and ran the service. I validated the service is running normally, but no log file is created/written to. No exceptions are being thrown. Everything appears in order when debugging. I turned on log4net's internal debugging and got this:
log4net: Creating repository for assembly [TestService, Version=3.6.5570.17497, Culture=neutral, PublicKeyToken=null]
log4net: Assembly [TestService, Version=3.6.5570.17497, Culture=neutral, PublicKeyToken=null] Loaded From [C:\ProgramData\Company\Applications\TestService\TestService\TestService.exe]
log4net: Assembly [TestService, Version=3.6.5570.17497, Culture=neutral, PublicKeyToken=null] does not have a RepositoryAttribute specified.
log4net: Assembly [TestService, Version=3.6.5570.17497, Culture=neutral, PublicKeyToken=null] using repository [log4net-default-repository] and repository type [log4net.Repository.Hierarchy.Hierarchy]
log4net: repository [log4net-default-repository] already exists, using repository type [log4net.Repository.Hierarchy.Hierarchy]
The output does not seem to hint at any issues. I've also tried adding the following line to my configuration, but it didn't do the trick:
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" requirePermission="false"/>
I added a WinForms project to the solution with the exact same configuration and logging worked fine, so I'm confident it's not my setup. Any other ideas on steps I may have missed?

I was able to get it to work by making the Log variable static and instantiating it like this:
private static ILog Log = LogManager.GetLogger(typeof(TestService));
I'm not quite sure why this was necessary. Hopefully someone else knows the answer.

Log4Net doesn’t write log in release mode - Console Application

I have a console application and have a class library which wraps the Log4Net methods. Now when run the application in debug mode it writes log but when it is built in release mode it doesn’t write log file. What would be the solution for this? The sample code and config file is given below
My development environment is
Visual Studio 2013 and .NET Framework 4.5
Console Application
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
log4net.GlobalContext.Properties["LogFileName"] = "TestLogin.txt";
Logger log = new Logger(typeof(Program));
log.Info("Logging is enabled!!");
}
}
}
App.config in Console Application
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
</configSections>
<startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
</startup>
<log4net>
<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file type="log4net.Util.PatternString" value ="%property{LogFileName}"/>
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %level - %message%newline%exception" />
</layout>
</appender>
<root>
<level value="ALL" />
<appender-ref ref="RollingFileAppender" />
</root>
</log4net>
</configuration>
Class Library
using log4net;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
[assembly: log4net.Config.XmlConfigurator(Watch = true)]
namespace Logging
{
public class Logger
{
private readonly ILog log = null;
public Logger(Type type)
{
log = LogManager.GetLogger(type);
}
public void Info(object message)
{
log.Info(message);
}
}
}
I have followed the post and it didn’t help me to figure out why Log4Net doesn’t write in log file in release mode?
log4net doesn't log when running a .Net 4.0 Windows application built in Release mode

There are a few workarounds for this.
You could add the [MethodImpl(MethodImplOptions.NoInlining)]
attribute to your Logger constructor methods in your class library.
You could add [assembly: log4net.Config.XmlConfigurator(Watch =
true)] to AssemblyInfo.cs in your Console Project (not the class library project)
You can add log4net.Config.XmlConfigurator.Configure(); at the
start of your Logger constructor.
I think the reason this is happening is that in release mode, your class library is inlined and so when log4net attempts to find the attribute, it thinks the calling assembly is your exe which does not contain the attribute.
PS.
I presume you are aware that your Logger class will mean that you lose the ability to filter by method names, as log4net will only see the Logger.Info method name.

The line [assembly: log4net.Config.XmlConfigurator(Watch = true)] should be added to your AssemblyInfo.cs file in the Properties folder.

For users with an MVC app that already have the lines [assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net.config", Watch = true)] in AssemblyInfo.cs and log4net.Config.XmlConfigurator.Configure(); in Global.asax.cs, but it's still not writing, make sure that the Application Pool user has permissions to write to the location where you're writing the log.
To get around this, I simply created a log directory on the IIS server NOT inside inetpub, gave it adequate permissions (I suppose it can be "Everyone", "Full Control" if it's just a child log directory and you're feeling lazy), and wrote the full path in the log4net.config (or Web.config, if you didn't isolate it).
Here's my config file:
<?xml version="1.0"?>
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
</configSections>
<log4net>
<root>
<level value="ALL"/>
<appender-ref ref="RollingFileAppender"/>
</root>
<appender name="RollingFileAppender" type="log4net.Appender.RollingFileAppender">
<file value="C:/absolute/path/to/logfile.log" />
<appendToFile value="true" />
<rollingStyle value="Size" />
<maximumFileSize value="10MB"/>
<datePattern value="yyyyMMdd'-FULL.log'" />
<maxSizeRollBackups value="-1"/>
<staticLogFileName value="false"/>
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
</layout>
</appender>
</log4net>
</configuration>

Make sure that the log4net.config file is added in your final release binary and corresponds to the path mentioned in ConfigFile = "log4Net.config".
I had the same problem, then I realized that I was simply missing out this config file in my release binary.

I have this in my Logging.dll and my Program.exe assembly.cs. Then it works in both debug and release mode. My program is a windows service.
[assembly: log4net.Config.XmlConfigurator(ConfigFile = "log4net.config", Watch = true)]