Dynamically Changing log4j log level

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What are the different approaches for changing the log4j log level dynamically, so that I will not have to redeploy the application. Will the changes be permanent in those cases?

Changing the log level is simple; modifying other portions of the configuration will pose a more in depth approach.

LogManager.getRootLogger().setLevel(Level.DEBUG);

The changes are permanent through the life cyle of the Logger. On reinitialization the configuration will be read and used as setting the level at runtime does not persist the level change.

UPDATE: If you are using Log4j 2 you should remove the calls to setLevel per the documentation as this can be achieved via implementation classes.

Calls to logger.setLevel() or similar methods are not supported in the API. Applications should remove these. Equivalent functionality is provided in the Log4j 2 implementation classes but may leave the application susceptible to changes in Log4j 2 internals.

Log4j - Reload Logging Levels on Runtime, As soon as a file change is observed, configurationChanged() method is invoked and DOMConfigurator.configure() method is used to again reload the log4j  Questions: What are the different approaches for changing the log4j log level dynamically, so that I will not have to redeploy the application. Will the changes be permanent in those cases? Answers: Changing the log level is simple; modifying other portions of the configuration will pose a more in depth approach.

File Watchdog

Log4j is able to watch the log4j.xml file for configuration changes. If you change the log4j file, log4j will automatically refresh the log levels according to your changes. See the documentation of org.apache.log4j.xml.DOMConfigurator.configureAndWatch(String,long) for details. The default wait time between checks is 60 seconds. These changes would be persistent, since you directly change the configuration file on the filesystem. All you need to do is to invoke DOMConfigurator.configureAndWatch() once.

Caution: configureAndWatch method is unsafe for use in J2EE environments due to a Thread leak

JMX

Another way to set the log level (or reconfiguring in general) log4j is by using JMX. Log4j registers its loggers as JMX MBeans. Using the application servers MBeanServer consoles (or JDK's jconsole.exe) you can reconfigure each individual loggers. These changes are not persistent and would be reset to the config as set in the configuration file after you restart your application (server).

Self-Made

As described by Aaron, you can set the log level programmatically. You can implement it in your application in the way you would like it to happen. For example, you could have a GUI where the user or admin changes the log level and then call the setLevel() methods on the logger. Whether you persist the settings somewhere or not is up to you.

How to change logging level in runtime, Changing the log logging level in runtime is important mainly in FATALLogging​, Enterprise Java, Log4j); with a dynamic logLevel String parameter which represent the logging level you wish to set your system to. If any of  Changing LogLevel Dynamically We do not have a way to change log level from slf4j api and we need to rely on implementation, in our case log4j api. First get rootLogger with log4j then set the level on it. Here is an example code for the same

Log4j2 can be configured to refresh its configuration by scanning the log4j2.xml file (or equivalent) at given intervals. Just add the "monitorInterval" parameter to your configuration tag. See line 2 of the sample log4j2.xml file, which tells log4j to to re-scan its configuration if more than 5 seconds have passed since the last log event.

<?xml version="1.0" encoding="UTF-8" ?>
<Configuration status="warn" monitorInterval="5" name="tryItApp" packages="">

    <Appenders>
        <RollingFile name="MY_TRY_IT"
                     fileName="/var/log/tryIt.log"
                     filePattern="/var/log/tryIt-%i.log.gz">
            <Policies>
                <SizeBasedTriggeringPolicy size="25 MB"/>
            </Policies>
            ...
        </RollingFile>
    </Appenders>


    <Loggers>
        <Root level="error">
            <AppenderRef ref="MY_TRY_IT"/>
        </Root>
    </Loggers>

</Configuration>

There are extra steps to make this work if you are deploying to a tomcat instance, inside an IDE, or when using spring boot. That seems somewhat out of scope here and probably merits a separate question.

How to dynamically change log level in SLF4j Log4J with , LogLevel change based on the log level choosen. Posted by Prateep Gedupudi on December 12, 2015. Many of us already know this, but logging is just a way  Lets look at a few ways to change log levels. First the simple, but not so elegant approach. Don’t get me wrong (about the elegance statement) this approach works. Log4j 1.x API Often applications will have custom log4j properties files. Here we define the appenders and the layouts for the appenders.

With log4j 1.x I find the best way is to use a DOMConfigurator to submit one of a predefined set of XML log configurations (say, one for normal use and one for debugging).

Making use of these can be done with something like this:

  public static void reconfigurePredefined(String newLoggerConfigName) {
    String name = newLoggerConfigName.toLowerCase();
    if ("default".equals(name)) {
      name = "log4j.xml";
    } else {
      name = "log4j-" + name + ".xml";
    }

    if (Log4jReconfigurator.class.getResource("/" + name) != null) {
      String logConfigPath = Log4jReconfigurator.class.getResource("/" + name).getPath();
      logger.warn("Using log4j configuration: " + logConfigPath);
      try (InputStream defaultIs = Log4jReconfigurator.class.getResourceAsStream("/" + name)) {
        new DOMConfigurator().doConfigure(defaultIs, LogManager.getLoggerRepository());
      } catch (IOException e) {
        logger.error("Failed to reconfigure log4j configuration, could not find file " + logConfigPath + " on the classpath", e);
      } catch (FactoryConfigurationError e) {
        logger.error("Failed to reconfigure log4j configuration, could not load file " + logConfigPath, e);
      }
    } else {
      logger.error("Could not find log4j configuration file " + name + ".xml on classpath");
    }
  }

Just call this with the appropriate config name, and make sure that you put the templates on the classpath.

Changing the Logging Level at the Runtime for a Spring Boot , We're going to start by using the /loggers Actuator endpoint to display and change our logging level. The /loggers endpoint is available at actuator  Here's the way to change log level dynamically: LogManager.getRootLogger().setLevel(Level.DEBUG); To use a property from custom file use Properties.loadFromXML to read a file with properties, then determine a level using these properties.

This answer won't help you to change the logging level dynamically, you need to restart the service, if you are fine restarting the service, please use the below solution

I did this to Change log4j log level and it worked for me, I have n't referred any document. I used this system property value to set my logfile name. I used the same technique to set logging level as well, and it worked

passed this as JVM parameter (I use Java 1.7)

Sorry this won't dynamically change the logging level, it requires a restart of the service

java -Dlogging.level=DEBUG -cp xxxxxx.jar  xxxxx.java

in the log4j.properties file, I added this entry

log4j.rootLogger=${logging.level},file,stdout

I tried

 java -Dlogging.level=DEBUG -cp xxxxxx.jar  xxxxx.java
 java -Dlogging.level=INFO-cp xxxxxx.jar  xxxxx.java
 java -Dlogging.level=OFF -cp xxxxxx.jar  xxxxx.java

It all worked. hope this helps!

I have these following dependencies in my pom.xml

<dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
</dependency>

<dependency>
    <groupId>log4j</groupId>
    <artifactId>apache-log4j-extras</artifactId>
    <version>1.2.17</version>
</dependency>

Changing Log4j logging levels dynamically, Turns out your development team did not provide you a feature to change log levels on the fly. Only way you can do that is to restart the  i have an issue, i want to change the logging level of log4j at runtime, i have tried many things with log4j.properties file, i have also tried to written a code which after particular time again reads the properties file and again configure the logger.

Apache Log4j 2 - Apache Logging Services, How do I configure log4j2 in code without a configuration file? How do I change a logger's level in code? How do I dynamically write to separate log files? I'm interested in programmatically changing the log level in Log4j2. I tried looking at their configuration documentation but that didn't seem to have anything. I also tried looking in the package: org.apache.logging.log4j.core.config, but nothing in there looked helpful either.

Dynamically changing log level with Weblogic, log4j, JMX and WLST, how to configure log4j properly in a JEE app to be run on Weblogic; how to dynamically configure the log level using JMX and Weblogic Scripting Tool. The setLogLevelWithParameter() method utilized the logLevel parameter to change the log4j logging level, and the loadLog4jPropertiesFile() method reloads the log4j.properties file so that new changes to the file get reflected in the web application's logging.

Dynamically Changing log4j log level, Questions: What are the different approaches for changing the log4j log level dynamically, so that I will not have to redeploy the application. Changing the log level in Spring Boot 1.5+ can be done with a http-endpoint Add <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency>

Comments
  • stackoverflow.com/questions/1200449/…
  • Very similar to stackoverflow.com/questions/2115900/…
  • Updated question for log4j2: stackoverflow.com/questions/23434252/…
  • For only runtime dependencies LogManager.getLogger(Class.forName("org.hibernate.util.JDBCExceptionReporter")).setLevel(Level.FATAL);
  • Note that the log4j 2 API does not provide a "setLevel" method.
  • But this only sets the root logger , isn't it? If individual levels are set for loggers under root, setting the root logger will have no effect on those LOGGER's. Wouldn't we have to do something like root.getLoggerRepository().getCurrentCategories(), iterate over each instance of the logger and set LEVELs for each logger? @AaronMcIver
  • @ChrisCantrell Log4j 2 does provide a way to do this, although it's not as simple.
  • Log4j2 can be configured to refresh its configuration by scanning the log4j2.xml file (or equivalent) at given intervals. E.g. <Configuration status="warn" monitorInterval="5" name="tryItApp" packages="">
  • A word of caution regarding log4j watchdog approach: "Because the configureAndWatch launches a separate watchdog thread, and because there is no way to stop this thread in log4j 1.2, the configureAndWatch method is unsafe for use in J2EE envrironments where applications are recycled". Reference: Log4J FAQ
  • If i was to use configureAndWatch functionality of Log4j I could stop that watchdog thread in an EJB's @PostDestroy method (that's a good enough indicator of when the container is shutting down) That's it ? Or is there more to it that I am missing..!
  • sorry I meant @PreDestroy method
  • "Log4j registers its loggers as JMX MBeans.". My servlet uses log4j 1.2 I don't see any log4j MBeans.
  • All you need to do is to invoke DOMConfigurator.configureAndWatch() once. How can I achieve this ?
  • @vsingh, are you deploying inside spring boot, tomcat, or a container or with an IDE? Sometimes there can be extra steps in those cases (not the fault of log4j2) -- basically the app can't see the file changing because it's been copied to another location by a framework or tool.