.net – Log4Net: set Max backup files on RollingFileAppender with rolling Date

This behaviour is because of the fact that RollingFileAppender (and many other appenders as well as filters) implements the IOptionHandler interface which "allows an object to defer activation of its options until all options have been set. This is required for components which have related options that remain ambiguous until all are set".

And further: "The ActivateOptions method must be called on this object after the configuration properties have been set. Until ActivateOptions is called this object is in an undefined state and must not be used."

When configuring adapters via xml files you won't have to think about activation since it is done by the log4net configurator.

Here's my settings. It rolls only on date:

<log4net>
    <appender name="RollingFile" type="log4net.Appender.RollingFileAppender">
        <file value="c:\Logs\Today.log"/>
        <rollingStyle value="Date"/>
        <datePattern value="yyyyMMdd"/>
        <appendToFile value="true"/>
        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%level %logger %date{ISO8601} - %message%newline"/>
        </layout>
    </appender>
    <root>
        <!-- Options are "ALL", "DEBUG", "INFO", "WARN", "ERROR", "FATAL" and "OFF". -->
        <level value="ERROR"/>
        <appender-ref ref="RollingFile"/>
    </root>
</log4net>

Changes to your web.config, will restart the application automatically (so you'll lose sessions, etc).