Rohit Gupta

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By Default we have the following values for following properties of RollingFileAppender

  • staticLogFileName = true
  • countDirection = –1
  • rollingStyle = Composite
  • maxSizeRollBackups = 0 // be careful with this
  • maximumFileSize = “10MB”
  • datePattern = ".yyyy-MM-dd"

staticLogFileName indicates whether you need to keep writing (log) to the same file all the time. You will need to set it to false when using Date as the rolling style and you have large number of backups.

Optionally file.log.yyyy-mm-dd for current formated datePattern can by the currently logging file (or file.log.curSizeRollBackup (rollingStyle=Size) or even file.log.yyyy-mm-dd.curSizeRollBackup --- (rollingStyle=Composite)) This will make time based roll overs with a large number of backups much faster -- it won't have to rename all the backups!

Recommend to leave it at its default value “true”

countDirection when its value is –1, then newest logfile backup will always be file.log.1.. hence this would involve more number of file renaming.

By default newer files have lower numbers. (countDirection < 0) ie. log.1 is most recent, log.5 is the 5th backup, etc... countDirection > 0 does the opposite ie. log.1 is the first backup made, log.5 is the 5th backup made, etc. For infinite backups use countDirection > 0 to reduce rollOver costs.

rollingStyle can be either Date, Size or Composite. the default setting Composite, uses a combination of Size and Date settings. Thus if you have the datePattern set to “.yyyy-MM-dd” and maxSizeRollBackups set to 10, themn it will maintain 10 log backups for each day.

If you have the DatePattern set to “.yyyy-MM-dd HH:mm” and maxSizeRollbackups = 10 then it will maintain 10 logfile backups per minute


   1: <appender name="RollingFileAppenderV1" type="log4net.Appender.RollingFileAppender">
   2:     <file type="log4net.Util.PatternString" value="F:\HornetFeed\%property{LogName}" />
   3:     <appendToFile value="true" />
   4:     <rollingStyle value="Size" />
   5:     <maxSizeRollBackups value="-1" />
   6:     <maximumFileSize value="5000KB" />
   7:     <staticLogFileName value="true" />
   8:     <countDirection value="1"/>
   9:     <layout type="log4net.Layout.PatternLayout">
  10:         <conversionPattern value="%m%n" />
  11:     </layout>
  12:     <filter type="log4net.Filter.PropertyFilter">
  13:         <Key value="Version" />
  14:         <StringToMatch value="1" />
  15:     </filter>
  16:     <filter type="log4net.Filter.DenyAllFilter" />
  17: </appender>

This will create infinite file backups with the countdirection > 0 so that the newest file has the latest/greatest name i.e. log.5 for the newest backup (5th backup)

   1: <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
   2:         <file value="logfile" />
   3:         <appendToFile value="true" />
   4:         <rollingStyle value="Composite" />
   5:         <datePattern value=".yyyyMMdd-HHmm" />
   6:         <maxSizeRollBackups value="10" />
   7:         <maximumFileSize value="1MB" />
   8:         <countDirection value="1"/>
   9:         <layout type="log4net.Layout.PatternLayout">
  10:             <conversionPattern value="%date [%thread] %-5level %logger [%property{NDC}] - %message%newline" />
  11:         </layout>
  12:     </appender>

This is a Composite RollingFileAppender which keeps max of 10 1MB log backups every minute

posted on Tuesday, March 3, 2009 3:50 PM


# re: Tips on using log4net RollingFileAppender 7/13/2009 3:55 AM Anonymous
Nice tip, Thank you!

# re: Tips on using log4net RollingFileAppender 10/20/2009 3:14 AM G B
Thanks buddy for the tips. I used it to solve a problem with the config.

# re: Tips on using log4net RollingFileAppender 3/19/2010 12:07 PM Scott Leckie
Good post, thanks. It's funny that everyone has their own fave log4net configs.
Mine has a static filename, as yours does, but I restrict the size to 2MB and then manage up to ten archive folders.


# re: Tips on using log4net RollingFileAppender 3/15/2011 1:25 PM Randall Price
Many thanks for a great post! I have been trying for a long time now to get my log files to look like:


and finally got it.

# re: Tips on using log4net RollingFileAppender 3/31/2011 7:36 AM Seb
Hi Randall,
Could you please share with us your config file, because I want to have the same log Filename.
Thank you,

# re: Tips on using log4net RollingFileAppender 4/21/2011 2:18 AM Ravi
very useful!!!

# re: Tips on using log4net RollingFileAppender 8/19/2011 6:31 PM dunk sb mid
It is very rare that you find relevant information on the network, but your article also provide information to me.

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