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<document>

	<properties>
		<author email="nicko at apache dot org">Nicko Cadell</author>
		<title>log4net Manual - Frequently Asked Questions</title>
	</properties>

	<meta name="keywords" content="log4net frequently asked questions, log4net faq, log4net" />

	<body>
		<section id="main" name="log4net Manual - Frequently Asked Questions">
			<sectionMenu name="Contents" />
			
			<section id="information" name="Information">
			
				<section id="what-is-log4net" name="What is log4net?">
					<p>
						log4net is a tool to help the programmer output log statements to a variety of 
						output targets.
					</p>
					<p>
						In case of problems with an application, it is helpful to enable logging so 
						that the problem can be located. With log4net it is possible to enable logging at 
						runtime without modifying the application binary. The log4net package is designed 
						so that log statements can remain in <i>production</i> code without incurring a 
						high performance cost. It follows that the speed of logging (or rather not 
						logging) is crucial.
					</p>
					<p>
						At the same time, log output can be so voluminous that it quickly becomes 
						overwhelming. One of the distinctive features of log4net (and common to all of
						the log4x libraries) is the notion of <i>hierarchical 
						loggers</i>. Using these loggers it is possible to selectively control 
						which log statements are output at arbitrary granularity.
					</p>
					<p>
						log4net is designed with two distinct goals in mind: speed and flexibility. There 
						is a tight balance between these two requirements.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="reliability" name="Is log4net a reliable logging system?">
					<p>
						No. log4net is not reliable. It is a best-effort and <em>fail-stop</em> logging system.
					</p>
					<p>
						By fail-stop, we mean that log4net will not throw unexpected exceptions at 
						run-time potentially causing your application to crash. <b>If for any reason, log4net 
						throws an uncaught exception</b> (except for <span class="code">ArgumentException</span> and 
						<span class="code">ArgumentNullException</span> which may be thrown), <b>please send an email 
						to the <a href="mailto:log4net-user@logging.apache.org">
						log4net-user@logging.apache.org</a> mailing list</b>. Uncaught exceptions 
						are handled as serious bugs requiring immediate attention.
					</p>
					<p>
						Moreover, log4net will not revert to <span class="code">System.Console.Out</span>
						or <span class="code">System.Console.Error</span> when its designated 
						output stream is not opened, is not writable or becomes full. This avoids 
						corrupting an otherwise working program by flooding the user's terminal because 
						logging fails. However, log4net will output a single message to 
						<span class="code">System.Console.Error</span> and <span>System.Diagnostics.Trace</span>
						indicating that logging can not be performed.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="prerequisites" name="What are the prerequisites for log4net?">
					<p>
						log4net runs on many different frameworks and each framework has its own requirements.
						As a rule of thumb you will need an ECMA-335 compliant CLI runtime, for example, 
						the Microsoft .NET runtime 1.0 (1.0.3705) or 1.1 (1.1.4322).
					</p>
					<p>
						Not all frameworks are created equal and some features have been excluded from 
						some of the builds. See the <a href="../framework-support.html">Framework Support</a> 
						document for more information.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="examples" name="Is there example code for using log4net?">
					<p>
						There is a directory containing examples in <span class="code">log4net\examples</span>. 
						The examples are broken down by framework.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="features" name="What are the features of log4net?">
					<ul>
						<li>
							log4net is optimized for speed.</li>
						<li>
							log4net is based on a named logger hierarchy.</li>
						<li>
							log4net is fail-stop but not reliable.</li>
						<li>
							log4net is thread-safe.</li>
						<li>
							log4net is not restricted to a predefined set of facilities.</li>
						<li>
							Logging behavior can be set at runtime using a configuration file. 
							Configuration files are in XML format.</li>
						<li>
							log4net is designed to handle exceptions from the start.</li>
						<li>
							log4net can direct its output to many sinks including: a file, the console, the NT EventLog or even e-mail.</li>
						<li>
							log4net categorizes logging into levels: DEBUG, INFO, WARN, ERROR and FATAL.</li>
						<li>
							The format of the log output can be easily changed by implementing a new layout class.</li>
						<li>
							The target of the log output as well as the writing strategy can be altered by 
							writing a new appender class.</li>
						<li>
							log4net supports multiple output appenders per logger.</li>
					</ul>
					<p>
						See the <a href="../features.html">features</a> overview document for more information on the features of log4net.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="thread-safe" name="Is log4net thread-safe?">
					<p>
						Yes, log4net is thread-safe.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="output" name="What does log output look like?">
					<p>
						The log output can be customized in many ways. Moreover, one can completely 
						override the output format by implementing one's own <span class="code">ILayout</span>
					</p>
					<p>
						Here is an example output using <span class="code">PatternLayout</span> with the conversion 
						pattern <span class="code">%timestamp [%thread] %-5level %logger{2} %ndc - %message%newline</span>
					</p>
					<source language="text"><![CDATA[
176 [main] INFO  examples.Sort - Populating an array of 2 elements in reverse order.
225 [main] INFO  examples.SortAlgo - Entered the sort method.
262 [main] DEBUG SortAlgo.OUTER i=1 - Outer loop.
276 [main] DEBUG SortAlgo.SWAP i=1 j=0 - Swapping intArray[0] = 1 and intArray[1] = 0
290 [main] DEBUG SortAlgo.OUTER i=0 - Outer loop.
304 [main] INFO  SortAlgo.DUMP - Dump of integer array:
317 [main] INFO  SortAlgo.DUMP - Element [0] = 0
331 [main] INFO  SortAlgo.DUMP - Element [1] = 1
343 [main] INFO  examples.Sort - The next log statement should be an error message.
346 [main] ERROR SortAlgo.DUMP - Tried to dump an uninitialized array.
467 [main] INFO  examples.Sort - Exiting main method.]]></source>
					<p>
						The first field is the number of milliseconds elapsed since the start of the 
						program. The second field is the thread outputting the log statement. The third 
						field is the level of the log statement. The fourth field is the rightmost 
						two components of the name of the logger making the log request. The fifth field (just 
						before the '-') is the <em>nested diagnostic context</em> (<span class="code">NDC</span>). Note the 
						nested diagnostic context may be empty as in the first two statements. The text 
						after the '-' is the message of the statement.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="loggers" name="What are Loggers?">
					<p>
						The logger concept lies at the heart of log4net's configuration. Loggers are organized into a 
						hierarchy and give the programmer <em>run-time</em> control on which logging statements 
						are printed or not.
					</p>
					<p>
						Loggers are assigned levels through the configuration of log4net. A log statement is 
						routed through to the appender depending on its level <em>and</em> its logger.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
				<section id="contributing" name="Why should I donate my extensions to log4net back to the project?">
					<p>
						Contrary to the GNU Public License (GPL) the Apache Software License does not 
						make any claims over your extensions. By extensions, we mean totally new code 
						that invokes existing log4net code. <em>You are free to do whatever you wish with 
						your proprietary log4net extensions.</em> In particular, you may choose to 
						never release your extensions to the wider public. For details see the
						<a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.
					</p>
					<p>
						We are very careful not to unnecessarily change the log4net client API so that newer log4net 
						releases are backward compatible with previous versions. We are a lot less 
						scrupulous with the internal log4net API. Thus, if your extension is designed to 
						work with the internals of a specific log4net version, then when the next release
						of log4net comes out, you will probably need to adapt your proprietary extensions to the 
						new release. Thus, you will be forced to spend precious resources in order to 
						keep up with log4net changes. This is commonly referred to as the "stupid-tax". 
						By donating the code and making it part of the standard distribution, you save 
						yourself the unnecessary maintenance work.
					</p>
					<p>
						If your extensions are useful then someone will eventually write an extension 
						providing the same or very similar functionality. Your development effort will 
						be wasted.
					</p>
					<p>
						Unless the proprietary log4net extension is business critical, there is little 
						reason for not donating your extensions back to the project.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="contributing-guidelines" name="What should I keep in mind when contributing code?">
					<ol>
						<li>
							Stick to the existing indentation style even if you hate it.
							<p>
								Alternating between indentation styles makes it hard to understand the source 
								code. Make it hard on yourself but easier on others.
							</p>
						</li>
						<li>
							<b>Thoroughly test your code.</b>
							<p>
								There is nothing more irritating than finding the bugs in debugging (i.e. logging) code.
							</p>
						</li>
						<li>
							Keep it simple, small and fast.
							<p>
								It's all about the application not about logging.
							</p>
						</li>
						<li>
							Did I mention sticking with the indentation style?</li>
					</ol>
				</section>
				<p><a href="#top">Back to Top</a></p>
				

				<section id="bug-fixes" name="How fast do bugs in log4net get fixed?">
					<p>
						As fast as they get reported ;-)
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="history" name="What is the history of log4net?">
					<p>
						log4net is a port of the popular <a href="http://logging.apache.org/log4j/">log4j</a> logging library.
						The initial port was done in June 2001, since then we have tried to remain in the
						spirit of the original log4j. See the log4net <a href="../history.html">history</a> page for more details.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
						

				<section id="download" name="Where can I find the latest distribution of log4net?">
					<p>
						The log4net <a href="http://logging.apache.org/log4net/">home page</a> is a good place to start.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
								
			</section>

			<section id="configuration" name="Configuration">

				<section id="dynamic" name="How can I change log behavior at runtime?">
					<p>
						Logging behavior can be set using configuration files which are parsed at runtime. 
						Using configuration files the programmer can define loggers and set their 
						levels.
					</p>
					<p>
						Configuration files are specified in XML. See <span class="code">log4net.Config.XmlConfigurator</span>
						for more details.
					</p>
					<p>
						See the various <span class="code">log4net.Layout</span> and <span class="code">log4net.Appender</span>
						components for specific configuration options.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="runtime-disable" name="How do I completely disable all logging at runtime?">
					<p>
						Setting the <span class="code">Threshold</span> on the Hierarchy to Level OFF will disable all
						logging from that Hierarchy. This can be done in the log4net configuration file
						by setting the "threshold" attribute on the log4net configuration element to "OFF".
						For example:
					</p>
					<source language="xml"><![CDATA[
<log4net threshold="OFF" />]]></source>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				<section id="appender-options" name="What are the configurable options for an appender?">
					<p>
						log4net uses public properties to configure components such as
						Appenders, Layouts, Loggers etc.
					</p>
					<p>
						Thus, any writable public property in on the appender corresponds to a 
						configurable option. For example, in <span class="code">RollingFileAppender</span> the 
						<span class="code">public int MaxSizeRollBackups { set; }</span> property corresponds to 
						the <span class="code">MaxSizeRollBackups</span> option.
					</p>
					<p>
						Layouts options are also defined by their writable properties. Same goes for most 
						other log4net components. 
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				

				<section id="appender-level" name="Is it possible to direct log output to different appenders by level?">
					<p>
						Yes it is. Setting the <span class="code">Threshold</span> option of any appender extending 
						<span class="code">AppenderSkeleton</span>, (most log4net appenders extend 
						<span class="code">AppenderSkeleton</span>) will filter out all log events 
						with a <em>lower</em> level than the value of the threshold option.
					</p>
					<p>
						For example, setting the threshold of an appender to DEBUG will also allow INFO, 
						WARN, ERROR and FATAL messages to log along with DEBUG messages. (DEBUG is the 
						lowest level). This is usually acceptable as there is little use for DEBUG 
						messages without the surrounding INFO, WARN, ERROR and FATAL messages. 
						Similarly, setting the threshold of an appender to ERROR will filter out DEBUG, 
						INFO and WARN messages but not ERROR or FATAL messages.
					</p>
					<p>
						This policy usually best encapsulates what the user actually wants to do, as 
						opposed to her mind-projected solution.
					</p>
					<p>
						If you must filter events by exact level match, then you can attach a 
						<span class="code">LevelMatchFilter</span> to any appender to filter out logging 
						events by exact level match.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>

				
				<section id="config-reload" name="Is there a way to get log4net to automatically reload a configuration file if it changes?">
					<p>
						Yes. The <span class="code">XmlConfigurator</span> supports automatic 
						reloading through the <span class="code">ConfigureAndWatch</span> APIs. See the API 
						documentation for more details.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="appender-assembly" name="Can I load an appender from another assembly?">
					<p>
						Yes. When specifying the type in the configuration file you can give the assembly
						qualified name of the type. For example:
					</p>
					<source language="xml"><![CDATA[
<appender name="..." type="MyNamespace.MyAppender, MyAssembly">]]></source>
					<p>
						The .NET runtime will try to locate the assembly called <i>MyAssembly</i>.
						How .NET locates assemblies is beyond the scope of this FAQ.
					</p>
					<p>
						When loading an assembly from the GAC the fully qualified assembly name,
						including the version, culture and public key must be specified. This is 
						in the standard syntax supported by <span class="code">System.Type.GetType</span>.
						See the next FAQ on how to get the version and public key for an assembly.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>

				
				<section id="assembly-public-key" name="How do I get the Public Key for an assembly?">
					<p>
						The fully qualified name for an assembly includes the version, culture and
						public key. The public key is derived from the strong name used to identify
						the publisher. When referencing an assembly from the GAC the fully qualified
						name must be used. To get the version, culture and public key you can use a
						tool like the excellent .NET Reflector from Lutz Roeder available from
						<a href="http://www.aisto.com/roeder/dotnet">http://www.aisto.com/roeder/dotnet</a>.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
				<section id="layout-header-xml-newlines" name="How do I insert newlines into the layout header?">
					<p>
						Newlines in the config file need to be escaped using an XML numeric character reference.
						The sequence that represents a CR LF is &amp;#13; &amp;#10;. The following example adds
						a header and footer to the output each followed by a newline.
					</p>
					<source language="xml"><![CDATA[
<layout type="log4net.Layout.PatternLayout">
	<header value="[Header]&#13;&#10;" />
	<footer value="[Footer]&#13;&#10;" />
	<conversionPattern value="%date [%thread] %-5level %logger - %message%newline" />
</layout>]]></source>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
				<section id="pattern-string" name="How do I use a pattern to set the value of a string property?">
					<p>
						Log4net supports a pattern syntax for setting string properties similar to the 
						<span class="code">PatternLayout</span> used to format the output messages.
						This pattern syntax can be used by specifying <span class="code">type="log4net.Util.PatternString"</span>
						on the string property in the config file. This tells the config parser to pass the
						value to the <span class="code">PatternString</span> type before converting the result
						to a string. For details on the patterns supported see the <a href="sdk/log4net.Util.PatternString.html">
						PatternString SDK Reference</a>.
					</p>
					<p>
						The following example sets the file name for a <span class="code">FileAppender</span> to include the 
						current process id by specifying the <span class="code">%processid</span> pattern in the
						<span class="code">File</span> property.
					</p>
					<source language="xml"><![CDATA[
<appender name="LogFileAppender" type="log4net.Appender.FileAppender">
	<file type="log4net.Util.PatternString" value="log-file-[%processid].txt" />
	<layout type="log4net.Layout.PatternLayout" value="%date [%thread] %-5level %logger - %message%newline" />
</appender>]]></source>
				</section>
				<p><a href="#top">Back to Top</a></p>
		
		
			</section>

			<section id="implementing" name="Implementing Logging">
			
				<section id="naming" name="Are there any suggested ways for naming loggers?">
					<p>
						Yes, there are.
					</p>
					<p>
						You can name logging loggers by <strong>locality</strong>. It turns out that 
						instantiating a logger in each class, with the logger name equal to the 
						fully-qualified name of the class, is a useful and straightforward approach of 
						defining loggers. This approach has many benefits:
					</p>
					<ul>
						<li>
							It is very simple to implement.</li>
						<li>
							It is very simple to explain to new developers.</li>
						<li>
							It automatically mirrors your application's own modular design.</li>
						<li>
							It can be further refined at will.</li>
						<li>
							Printing the logger automatically gives information on the locality of the 
							log statement.</li>
					</ul>
					<p>
						However, this is not the only way for naming loggers. A common alternative 
						is to name loggers by <strong>functional areas</strong>. For example, the 
						"database" logger, "remoting" logger, "security" logger, or the "XML" 
						logger.
					</p>
					<p>
						You may choose to name loggers by functionality and subcategorize by 
						locality, as in "DATABASE.MyApp.MyClass" or 
						"DATABASE.MyApp.MyModule.MyOtherClass".
					</p>
					<p>
						<em>You are totally free in choosing the names of your loggers.</em> The 
						log4net package merely allows you to manage your names in a hierarchy. However, 
						it is your responsibility to define this hierarchy.
					</p>
					<p>
						<b>Note:</b> by naming loggers by locality one tends to name things by 
						functionality, since in most cases the locality relates closely to 
						functionality.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				

				<section id="static-class-name" name="How do I get the fully-qualified name of a class in a static block?">
					<p>
						You can easily retrieve the fully-qualified name of a class in a static block 
						for class <span class="code">X</span>, with the statement <span class="code">typeof(X).Name</span>. 
						Note that <span class="code">X</span> is the class name and span an instance.
						However because the <span class="code">LogManager.GetLogger</span> method is overloaded
						to take an instance of <span class="code">Type</span> as well as <span class="code">string</span>
						usually only the type of the class is required.
					</p>
					<p>
						Here is the suggested usage template:
					</p>
					<source language="C#"><![CDATA[
public class Foo
{
	private static readonly ILog log = LogManager.GetLogger(typeof(Foo));
	... other code
}]]></source>
					<p>
						An equivalent and more portable solution, though slightly longer, is to use the declaring type 
						of the static constructor.
					</p>
					<source language="C#"><![CDATA[
public class Foo
{
	private static readonly ILog log = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod().DeclaringType);
	... other code
}]]></source>
					<p>
						<b>Note:</b> the .NET Compact Framework 1.0 does not support <span class="code">System.Reflection.MethodBase.GetCurrentMethod()</span>.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="perf-not-logging" name="What is the fastest way of (not) logging?">
					<p>
						For some logger <span class="code">log</span>, writing,
					</p>
					<source language="C#"><![CDATA[
log.Debug("Entry number: " + i + " is " + entry[i]);]]></source>
					<p>
						incurs the cost of constructing the message parameter, that is converting both 
						integer <span class="code">i</span> and <span class="code">entry[i]</span> to 
						a string, and concatenating intermediate strings. This, regardless of whether 
						the message will be logged or not.
					</p>
					<p>
						If you are worried about speed, then write
					</p>
					<source language="C#"><![CDATA[
if(log.IsDebugEnabled) 
{
	log.Debug("Entry number: " + i + " is " + entry[i]);
}]]></source>
					<p>
						This way you will not incur the cost of parameter construction if debugging is 
						disabled for logger <span class="code">log</span>. On the other hand, if the logger is 
						debug enabled, you will incur the cost of evaluating whether the logger is 
						enabled or not, twice: once in <span class="code">IsDebugEnabled</span> and once in <span class="code">Debug</span>. 
						This is an insignificant overhead since evaluating a logger takes less than 
						1% of the time it takes to actually log a statement.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="perf-not-logging2" name="What is REALLY the FASTEST way of (not) logging?">
					<p>
						So you don't think that the previous FAQ is really the fastest way
						of not logging? Well there is a faster way but it does have some
						drawbacks. Starting from: 
					</p>
					<source language="C#"><![CDATA[
if(log.IsDebugEnabled) 
{
	log.Debug("Entry number: " + i + " is " + entry[i]);
}]]></source>
					<p>
						It is possible to further eliminate the calls to <span class="code">IsDebugEnabled</span>
						so that the call is only made once per logger. If you are using one logger 
						for each class then you can store the enabled state for the logger in a static
						variable in the class and then test against this variable:
					</p>
					<source language="C#"><![CDATA[
public class FastLogger
{
	private static readonly ILog log = LogManager.GetLogger(typeof(FastLogger));
	private static readonly bool isDebugEnabled = log.IsDebugEnabled;

	public void MyMethod()
	{
		if(isDebugEnabled) 
		{
			log.Debug("Entry number: " + i + " is " + entry[i]);
		}
	}
}]]></source>
					<p>
						So why exactly is this faster? Well to start with the <span class="code">IsDebugEnabled</span>
						is not called for each log statement, it is called once per logger. Furthermore as the
						<span class="code">isDebugEnabled</span> variable is <span class="code">private static readonly</span>
						the JIT compiler can at <em>run-time</em> optimize out the <span class="code">if</span> test altogether. 
						This means that at runtime the JIT compiler won't even compile the logging statements into native code, i.e.
						all the logging just disappears.
					</p>
					<p>
						So what is the downside to using this? Well one of the clever features of log4net is that
						you can change the logging configuration while your program is running. If you need to 
						investigate an issue in your application, you don't have to stop the application, setup the
						logging and restart the application, you can change the logging configuration and the
						log4net will reload it (see <span class="code">XmlConfigurator.ConfigureAndWatch</span> APIs for more 
						information). However if the JIT has compiled out all of the logging statements
						then they are gone and you can't get them back by reloading the configuration file. Effectively
						this means that the logging configuration can only be set when the application loads and
						it cannot be changed at runtime. It is up to you to decide if you need ultimate speed or need
						to be able to reload the logging configuration while the application is running.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="multiple-files" name="Can the outputs of multiple client request go to different log files?">
					<p>
						Many developers are confronted with the problem of distinguishing the log 
						output originating from the same class but different client requests. They come 
						up with ingenious mechanisms to fan out the log output to different files. In 
						most cases, this is not the right approach.
					</p>
					<p>
						It is simpler to use a context property or stack (<span class="code">ThreadContext</span>). 
						Typically, one would <span class="code">ThreadContext.Properties["ID"] = "XXX"</span>
						client specific information, such as the client's hostname, ID or any other 
						distinguishing information when starting to handle the client's request. 
						Thereafter, log output will automatically include the context data
						so that you can distinguish logs from different client requests even if they 
						are output to the same file.
					</p>
					<p>
						See the <span class="code">ThreadContext</span> and the <span class="code">PatternLayout</span> classes for more 
						information.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="remove-logger" name="Logger instances seem to be create only. Why isn't there a method to remove logger instances?">
					<p>
						It is quite nontrivial to define the semantics of a "removed" logger which is 
						still referenced by the user.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="single-file" name="How do I get multiple process to log to the same file?">
					<p>
						By default the <span class="code">FileAppender</span> holds an exclusive write 
						lock on the log file while it is logging. This prevents other processes from 
						writing to the file. The <span class="code">FileAppender</span> can be configured
						to use a different locking model, <span class="code">MinimalLock</span>, that
						only acquires the write lock while a log is being written. This allows multiple
						processes to interleave writes to the same file, albeit with a loss in performance.
						See the <a href="config-examples.html#fileappender">FileAppender config examples</a>
						for an example <span class="code">MinimalLock</span> configuration.
					</p>
					<p>
						While the <span class="code">MinimalLock</span> model may be used to interleave
						writes to a single file it may not be the optimal solution, especially when
						logging from multiple machines. Alternatively you may have one or more processes
						log to <span class="code">RemotingAppenders</span>. 
						Using the <span class="code">RemoteLoggingServerPlugin</span> (or 
						<span class="code">IRemoteLoggingSink</span>) a process can receive all the events and 
						log them to a single log file.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				

				<section id="distributed" name="If I have many processes across multiple hosts (possibly across multiple time zones) logging to the same file using the RemotingAppender, what happens to timestamps?">
					<p>
						The timestamp is created when the logging event is created. That is so say, 
						when the <span class="code">Debug</span>, <span class="code">Info</span>, 
						<span class="code">Warn</span>, <span class="code">Error</span>
						or <span class="code">Fatal</span> method is invoked. This is unaffected by the time at 
						which they may arrive at a remote server. Since the timestamps are 
						transmitted in UTC format by the <span class="code">RemotingAppender</span>, 
						they all appear in the same time zone as 
						the host creating the logfile. Since the clocks of various machines may not be 
						synchronized, this may account for time interval inconsistencies between events 
						generated on different hosts.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
				<section id="first-log" name="When should I log my first message?">
					<p>
						The simple answer is as soon as possible. The long answer is more complex.
					</p>
					<p>
						If you are configuring log4net programmatically, i.e. by calling the 
						<span class="code">XmlConfigurator.Configure</span> method then you should do so
						before you begin logging and it is reasonable to do this very soon after application
						start.
					</p>
					<p>
						If you are configuring log4net by specifying assembly level attributes on 
						your assembly then the configuration will be loaded once the first call to
						the <span class="code">LogManager.GetLogger</span> is made. It is necessary
						that the first call to <span class="code">LogManager.GetLogger</span> made
						during the process (or AppDomain) is made from the assembly that has the
						configuration attributes. Log4net will look only once and only on the first 
						calling assembly for the configuration attributes.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
			</section>
			
			<section id="customization" name="Customization">

				<section id="custom-output" name="Can the log output format be customized?">
					<p>
						Yes. You can implement the <span class="code">log4net.Layout.ILayout</span> 
						interface to create you own customized log format, or you can extend the 
						<span class="code">LayoutSkeleton</span> class which provides a default
						implementation of the <span class="code">ILayout</span> interface.
						Appenders can be parameterized to use the layout of your choice.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
				
				<section id="custom-appender" name="Can I write a custom appender?">
					<p>
						Yes. You can implement the <span class="code">log4net.Appender.IAppender</span> 
						interface to create you own customized appender. We recommend that you extend the
						<span class="code">log4net.Appender.AppenderSkeleton</span> class rather than
						starting from scratch. You should implement your custom code in a assembly
						separate from the log4net assembly. To get started it is worth looking at the
						source of the <span class="code">log4net.Appender.TraceAppender</span> as an
						example of the minimum amount of code required to get an appender working.
					</p>
					<p>
						To configure log4net to use your custom appender you need to specify the
						assembly qualified name of the appender type in the config file. For
						example:
					</p>
					<source language="xml"><![CDATA[
<appender name="..." type="MyNamespace.MyAppender, MyAssembly">]]></source>
					<p>
						The .NET runtime will try to locate the assembly called <i>MyAssembly</i>.
						How .NET locates assemblies is beyond the scope of this FAQ.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>

			</section>

			<section id="troubleshooting" name="Troubleshooting">

				<section id="internalDebug" name="How do I enable log4net internal debugging?">
					<p>
						There are 2 different ways to enable internal debugging in log4net.
						These are listed below. The preferred method is to specify
						the <span class="code">log4net.Internal.Debug</span> option in the application's
						config file.
					</p>
					<ul>
						<li>
							<p>
								Internal debugging can also be enabled by setting a value in the application's
								configuration file (not the log4net configuration file, unless the log4net config
								data is embedded in the application's config file). The <span class="code">log4net.Internal.Debug</span>
								application setting must be set to the value <span class="code">true</span>.
								For example:
							</p>
							<div class="syntax"><pre class="code">
&lt;?xml version="1.0" encoding="utf-8" ?&gt;
&lt;configuration&gt;
	&lt;appSettings&gt;
		&lt;add key="log4net.Internal.Debug" value="true"/&gt;
	&lt;/appSettings&gt;
&lt;/configuration&gt;</pre></div>
							<p>
								This setting is read immediately on startup an will cause all internal
								debugging messages to be emitted.
							</p>
						</li>
						<li>
							<p>
								To enable log4net's internal debug programmatically you need
								to set the <span class="code">log4net.Util.LogLog.InternalDebugging</span>
								property to <span class="code">true</span>. Obviously the sooner this
								is set the more debug will be produced.
							</p>
						</li>
					</ul>
					<p>
						Internal debugging messages are written to the console and to the 
						<span class="code">System.Diagnostics.Trace</span>
						system. If the application does not have a console the messages logged
						there will be lost. Note that an application can redirect the console
						stream by setting the <span class="code">System.Console.Out</span>. The
						Trace system will by default send the message to an attached debugger
						(where the messages will appear in the output window). If the process
						does not have a debugger attached then the messages are sent to the 
						system debugger. A utility like DebugView from 
						<a href="http://www.sysinternals.com">http://www.sysinternals.com</a>
						may be used to capture these messages.
					</p>
					<p>
						As log4net internal debug messages are written to the <span class="code">System.Diagnostics.Trace</span>
						system it is possible to redirect those messages to a local file. You can define
						a trace listener by adding the following to your application's .config file:
					</p>
					<div class="syntax"><pre class="code">
&lt;configuration&gt;
	...
	
	&lt;system.diagnostics&gt;
		&lt;trace autoflush="true"&gt;
			&lt;listeners&gt;
				&lt;add 
					name="textWriterTraceListener" 
					type="System.Diagnostics.TextWriterTraceListener" 
					initializeData="C:\tmp\log4net.txt" /&gt;
			&lt;/listeners&gt;
		&lt;/trace&gt;
	&lt;/system.diagnostics&gt;

	...
&lt;/configuration&gt;</pre></div>
					<p>
						Make sure that the process running your application has permission 
						to write to this file.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="trouble-EventLog" name="Why doesn't the EventLogAppender work?">
					<p>
						If you are not getting events delivered to the event log this usually indicates 
						a permissions problem. Basically if the event log does not exist the EventLogAppender 
						tries to create it, but you need local administrator permissions to create event logs 
						(just to write into the right bit of the registry). You don't need administrator 
						permissions to log to an existing event log, but it must exist. If you are using the 
						event log from a web application or service using the event log can be a little tricky. 
					</p>
					<p>
						A web application will run as the user account ASPNET. This account deliberately has 
						few permissions to reduce the chances of someone hacking into the web server. While the 
						account has permission to write to the event log it does not have permission to create 
						event sources (registry create and write access), which are needed to write to the event log.
					</p>
					<p>
						There are a couple of solutions:
					</p>
					<ol>
						<li>
							<p>
								Make the ASPNET user a member of the Administrators group. This will work because the 
								user will then have the required permissions. This is <strong>not recommended</strong>
								for production use.
							</p>
						</li>
						<li>
							<p>
								As the event source only needs to be created once for the machine, create an installer
								and configure it to create the event source. 
								The installer will need to be run as Administrator (don't they all). See 
								<span class="code">System.Diagnostics.EventLogInstaller</span> in the Microsoft .NET 
								Framework SDK for an example of how to create a simple event log installer.
							</p>
						</li>
					</ol>
					<p>
						There is a Microsoft Knowledge Base article that covers this issue and how to resolve
						it. <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;329291">
							PRB: "Requested Registry Access Is Not Allowed" Error Message When ASP.NET 
							Application Tries to Write New EventSource in the EventLog</a>.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="trouble-file-perm" name="Why can't I log to a FileAppender from a web application?">
					<p>
						The web application runs as a special user account on the web server
						called ASPNET. This account has restricted permissions to protect the 
						web server from attacks. By default this account may not have permission
						to write to the file system. Make sure that the ASPNET account has 
						permission to create and write to files in the directory chosen for
						logging.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="trouble-service" name="Why doesn't the logging in my service work?">
					<p>
						A windows service runs as a user account specified in the services
						control panel. This account may have restricted permissions, make 
						sure that the account has permission to create and write to files 
						in the directory chosen for logging.
					</p>
					<p>
						A windows service is launched by windows. The current directory in
						a service is set to the windows system directory (e.g. 
						<span class="code">C:\Windows\System32</span>). If you are loading
						the configuration file from the current directory then be aware
						that this path will not be the location of your assemblies.
						The best way to get the path to your assemblies is to use
						<span class="code">AppDomain.BaseDirectory</span>.
						Note that the log4net internals never use the current directory.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>

				
				<section id="trouble-db" name="I am having trouble using the AdoNetAppender to connect to my database?">
					<p>
						For details on the different ways in which ADO.NET can connect to a database see:
						<a href="http://msdn.microsoft.com/library/en-us/cpguide/html/cpconadonetconnections.asp">Connecting to a Data Source Using ADO.NET</a>.
					</p>
					<p>
						If you need to use ODBC to connect to your database then please note that the
						ADO.NET ODBC drivers are not included in the standard .NET framework redistributable.
						You can download the drivers from microsoft download at: 
						<a href="http://www.microsoft.com/downloads/details.aspx?FamilyID=6ccd8427-1017-4f33-a062-d165078e32b1">ODBC .NET Data Provider</a>.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


				<section id="report-bugs" name="How do I report bugs?">
					<p>
						See the <a href="../support.html">support</a> page for details.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>


			</section>
			
			<section id="misc" name="Miscellaneous">
			
				<section id="vsnet-add-reference" name="How do I make log4net appear in the Visual Studio Add References dialog?">
					<p>
						There is a good discussion of this topic on Robert McLaws blog:
						<a href="http://weblogs.asp.net/rmclaws/archive/2003/11/15/37743.aspx">Building a Better Server Control Experience, Part 2</a>.
					</p>
				</section>
				<p><a href="#top">Back to Top</a></p>
				
			</section>
			
		</section>

	</body>
</document>
