Preface
This FAQ section provides help with logging-related issues.
As you read these questions, please keep in mind that Tomcat's internal logging is separate from your own webapp's logging. You would typically be concerned only with your own webapp's logging. You would modify Tomcat's internal logging settings if you are debugging a possible issue or running into other problems. It is anticipated that Tomcat's out-of-the-box logging configuration will be fine for the vast majority of users and environments.
Questions
[#Q1 Does Tomcat have built-in logging capabilities, and if so how do I use them?]
[#Q2 What role does commons-logging play in logging?]
[#Q3 What role does JULI and log4j play in logging?]
[#Q4 How do I configure commons-logging for use with Tomcat?]
[#Q5 How should I log in my own webapps?]
[#Q6 Where does System.out go? How do I rotate catalina.out?]
[#Q7 Where are the logs when running Tomcat as a Windows service?]
[#Q8 How do I customize the location of the tomcat logging.properties file?]
Answers
Does Tomcat have built-in logging capabilities, and if so how do I use them?
The Servlet Specification requires Servlet Containers like Tomcat to provide at least a rudimentary implementation of the ServletContext#log method. Tomcat provides a much richer implementation than required by the Spec, as follows:
Prior to Tomcat 5.5, Tomcat provided a Logger element that you could configure and extend according to your needs. If you are using a Tomcat version previous to Tomcat 5.5, make sure to read the [http://tomcat.apache.org/tomcat-4.1-doc/config/logger.html Logger configuration reference].
Starting with Tomcat 5.5, Logger was removed and [http://jakarta.apache.org/commons/logging Jakarta Commons-Logging]
Logis used everywhere in Tomcat. Read the Commons-Logging documentation if you'd like to know how to better use and configure Tomcat's internal logging. See also [http://tomcat.apache.org/tomcat-5.5-doc/logging.html]To enable request logging similar to the Apache HTTP server, you may include the following line in the server.xml file, in the <Engine> tag:
<Valve className="org.apache.catalina.valves.AccessLogValve"
directory="logs" prefix="localhost_access_log." suffix=".log"
pattern="common" resolveHosts="false"/>
This will produce a log file for each day, such as logs/localhost_access_log.2008-03-10.log, containing the files requested, IP address of the requester, and similar information.
128.34.123.121 - - [10/Mar/2008:15:55:57 -0500] "GET /upload/ClickPoints.jsp HTTP/1.1" 200 2725
In addition, Tomcat does not swallow the System.out and System.err JVM output streams. You may use these streams for elementary logging if you wish, but a more robust approach such as commons-logging or [http://logging.apache.org/log4j Log4J] is recommended for production applications.
What role does commons-logging play in logging?
Tomcat wants to support multiple logging implementations, so it uses commons-logging. In case that's unclear, think of it like this. You are a Tomcat developer. The car you drive when logging is the commons-logging car. The engine of that car is either JULI or log4j. Without one of these engines, the car goes no where. However regardless of whether you use JULI or log4j, the steering wheel, break, gas pedal, etc. are the same.
Related FAQ:
What role does JULI and log4j play in logging?
What role does JULI and log4j play in logging?
First see:
What role does commons-logging play in logging?
Note in addition that in your own applications you could log directly with JULI or log4j. But once you choose one, you can't easily switch to the other later. If you use commons-logging you can.
How do I configure commons-logging for use with Tomcat?
You need to specify a commons-logging configuration file and, if you wish, a logging implementation that supports commons-logging. JDK 1.4 (and later) java.util.Logging and Log4j are the two most commonly used logging toolkits for Tomcat. If you supply an external logging toolkit such as Log4J, it needs to be located in the $CATALINA_HOME/common/lib directory (for Tomcat 5.0 and earlier). Tomcat 5.5 and later uses commons-logging while bootstrapping so some people suggest adding Log4j to the bootstrap classpath by using the scripts in $CATALINA_HOME/bin (see [http://markmail.org/message/3sgxfol3njcfutsm Need for it to be in bootstrap classpath?]). A better approch apparently working is:
- Put jog4j.jar in the $CATALINA_HOME/common/lib directory 2. Put the full commons-logging.jar in the $CATALINA_HOME/common/lib directory, even if you see the reduced API version there, named commons-logging-api.jar
Through some classloading voodoo during bootstrapping, if you have the full commons-logging.jar file in your common/lib directory, it replaces the classes from the commons-logging-api.jar file and will reinitialize the logging system and attempt to locate log4j or whatever other logging system you may be using. (see [http://markmail.org/message/3sgxfol3njcfutsm#query:+page:1+mid:7oce37bngiq2otlu+state:results this thread]).
For more detailed instructions, see these mailing list discussions:
[http://marc.theaimsgroup.com/?l=tomcat-user&m=106623436423859&w=2 A log4j example]
[http://marc.theaimsgroup.com/?l=tomcat-user&m=108330970225012&w=2 Logging Configuration]
[http://marc.theaimsgroup.com/?l=tomcat-user&m=108578233003073&w=2 Example with JSVC and running on port 80.]
[http://minaret.biz/tips/tomcatLogging.html Tomcat and Log4j Configuration (and Velocity), addressing and solving the bootstrap commons-logging.jar problem]
How should I log in my own webapps?
While you can use System.out and System.err to log, we strongly recommend using a toolkit like Log4J or JDK 1.4's java.util.logging package. With these toolkits, you have significantly more functionality (for example, sending emails, logging to a database, controlling at runtime the logging level of different classes, inspecting the logs with a graphical viewer, etc.) than with Tomcat's built-in default logging configuration.
We also recommend that you separate your logging from Tomcat's internal logging. That means you should bundle your logging toolkit with your webapp. If you're using Log4J, for example, place the Log4J jar in the WEB-INF/lib directory of your webapp and the Log4J configuration file in the WEB-INF/classes directory of your webapp. This way different web applications can have different logging configurations and you don't need to worry about them interfering with each other.
Where does System.out go? How do I rotate catalina.out?
System.out and System.err both print to catalina.out. But you can suppress this via the swallowOutput property and sent to different log files. catalina.out does not rotate. But it should not be an issue because nothing should be printing to standard output since you are using a logging package, right? [http://marc.theaimsgroup.com/?t=105544472600001&r=1&w=2a thread about rotation of catalina.out]
Where are the logs when running Tomcat as a Windows service?
See these mailing list archive threads:
[http://markmail.org/message/3fjakrf77dqmy5nz Where are the Tomcat logs when running as a Windows service?]
How do I customize the location of the tomcat logging.properties file?
Set the following property when starting tomcat:
java.util.logging.config.file
Example:
-Djava.util.logging.config.file=/etc/tomcat/logging.properties
For another example of how to set this look in catalina.sh for Tomcat 6.0.16 on lines 182-185. The statements look like this:
# Set juli [LogManager] if it is present if [-r "$CATALINA_BASE"/conf/logging.properties ]; then
JAVA_OPTS="$JAVA_OPTS "-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager" "-Djava.util.logging.config.file="$CATALINA_BASE/conf/ logging.properties" fi
Projects such as JPackage that repackage Tomcat for Linux typically move the configuration to a directory dictated by the FHS standard (http://www.pathname.com/fhs/), and therefore use the java.util.logging.config.file property to set the location of the logging.properties file in the Tomcat startup script.
On Fedora the startup script in typically located in /etc/rc.d/init.d/ and on Gentoo linux it is located in /etc/init.d/.