Pax Logging: loggers log level

As you probably know, Apache Karaf uses Pax Logging as logging system.

Pax Logging is an OPS4j project (Open Participation Software 4 Java) which provide a fully OSGi compliant framework for logging. Pax Logging leverages a bunch of logging frameworks like slf4j, logback, log4j, avalong, etc. It gathers all the configuration and the actual logging mechanisms in a central way. It means that, in your applications/bundles, you can use slf4j or log4j, it doesn’t matter, behind the hood you will use Pax Logging.

Karaf provides a bunch of shell commands and MBean for logging:

  • log:display to see the log
  • log:display-exception to see only the exceptions
  • log:tail to display and “follow on the fly” the log
  • log:set to change the log level of a particular logger (or the rootLogger)
  • log:get to get the current log level of a particular logger (or the rootLogger)

The default configuration is a log4j configuration described in etc/org.ops4j.pax.logging.cfg. It’s where you especially define the loggers with the level and the appenders with the the conversion pattern.

However, sometimes, you may want to disable logging in a particular class or package. A typical example is when you use the Karaf webcontainer (provided by Pax Web), and you have a monitoring tool (like Naggios or Zabbix) which access to a URL in a “bad manner”. By “bad manner”, I mean that the monitoring tool send just a “ping” most of the time, not a complete valid HTTP request.

In that case, you may see “WARNING” messages in the log, coming from the Jetty web server. The messages look like:


22:25:20,948 | WARN | tp2029485198-177 | pse.jetty.servlet.ServletHandler 514 | 54 - org.eclipse.jetty.util - 7.6.7.v20120910 | /system/console/bundles
java.lang.reflect.UndeclaredThrowableException
    at org.ops4j.pax.web.service.internal.$Proxy10.service(Unknown Source)[71:org.ops4j.pax.web.pax-web-runtime:1.1.4]
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:652)[62:org.eclipse.jetty.servlet:7.6.7.v20120910]
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:447)[62:org.eclipse.jetty.servlet:7.6.7.v20120910]
...

As you know the source of this warn message, you may want to “increase” the log level to ERROR (to avoid to see WARN messages), or to completely disable the log messages coming from the Jetty ServletHandler.

To change the log level, in etc/org.ops4j.pax.logging.cfg, you can create a new logger dedicated to jetty, and define the log level for this logger:


log4j.logger.org.eclipse.jetty=ERROR

or you can completely disable the logging coming from the servlet handler:


log4j.logger.org.eclipse.jetty.servlet.ServletHandler=OFF

OFF is a “special” log level which disable the logging.

Another “use case” for this is about the sshd server embedded in Karaf. You may know that you can access to Karaf using a simple ssh client (OpenSSH on Unix, Putty on Windows, or the client provided with Karaf). By default, the Karaf sshd server log all session connections in DEBUG. So if you turn the rootLogger to DEBUG, you will see a lot of “noise” in the log. So, it makes sense to change the sshd server log level to INFO, just for the channel session:


log4j.logger.org.apache.mina.sshd.server.channel.ChannelSession=INFO

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