NLog creates several log files instead of one

Question

I try to plug NLog to my project, and do it for the first time, code looks like this:

static class Program
{
private static readonly Logger logger = LogManager.GetCurrentClassLogger();

private static void Main(string[] args)
{
    logger.Trace("Enter Main");

    MyClass.DoWork();

    logger.Trace("Exit Main");
}

class MyClass
{
    private static readonly Logger logger = LogManager.GetCurrentClassLogger();

    public static void DoWork()
    {
        logger.Trace("Enter DoWork");

        var mgc = new MyGreatClass();
        var task = mgc.RunAsync(...);

        logger.Trace("Exit DoWork");        
    }
}

class MyGreatClass
{
   private static readonly Logger logger = LogManager.GetCurrentClassLogger();

   async Task<bool> RunAsync()
   {
       logger.Trace("Log something");
       await DoSomethig();
   }
}

And Nlog.config file looks like this:

<targets>
    <target name="file" xsi:type="File" fileName="${basedir}/logdata${date:format=HH-mm-ss}.log" 
      layout="${date:format=HH\:mm\:ss}|${message}" />
  </targets>

  <rules>
    <logger name="*" minlevel="Trace" writeTo="file" />
  </rules>

But while logging it creates 3 different log files, how to make Nlog to create and log in one file only? Is it good practice to create many log files while running one application?

Answer 1

This is happening because of the target filename in your Nlog.config file. Every time a log message is being generated, it's creating a new log file using:

fileName="${basedir}/logdata${date:format=HH-mm-ss}.log"

The date:format... portion is a call to DateTime.Now . My code was doing the same thing. Once I set a variable of DateTime.Now at the beginning of my code, I then passed that variable into the Nlog.config setup as the name and only one log file was created.

DateTime localDate = DateTime.Now;

string currentDateString = localDate.ToString("yyyyMMdd-hhmmss"); 

fileTarget.FileName = baseDirectory + @"\logs\" + currentDateString + "-LOGS.txt";

Answer 2

NLog will render a new filename every second when using this layout:

fileName="${basedir}/logdata${date:format=HH-mm-ss}.log" 

Instead consider doing this:

fileName="${basedir}/logdata${processinfo:StartTime:format=HH-mm-ss:cached=true}.log" 

Then NLog will use the process-startup-timestamp, that will not change every second.

See also: https://github.com/NLog/NLog/wiki/ProcessInfo-Layout-Renderer