5.1. Troubleshooting, Debugging, Profiling, and Monitoring
Logging is easy to control through the console, with commands grouped under log shell. To learn about the available logging commands type:
Typical usage is:
log:setto dynamically change the global log level
- Execute the problematic operation
log:display-exceptionto display the log
Worst Case Scenario
If you end up with a Karaf in a really bad state (i.e. you can not boot it anymore) or you just want to revert to a clean state quickly, you can safely remove the
data directory just in the installation directory. This folder contains transient data and will be recreated if you remove it and relaunch Karaf.
You may also want to remove the files in the
deploy folder to avoid them being automatically installed when Karaf is started the first time.
Usually, the easiest way to debug Karaf or any application deployed onto it is to use remote debugging.
Remote debugging can be easily activated by setting the
KARAF_DEBUG environment variable to
This can be done using the following command on Unix systems:
On Windows, use the following command
Then, you can launch Karaf using the usual way:
Last, inside your IDE, connect to the remote application (the default port to connect to is 5005).
This option works fine when we have to debug a project deployed top of Apache Karaf. Nervertheless, you will be blocked if you would like to debug the server Karaf. In this case, you can change the following parameter suspend=y in the karaf.bat script file. That will cause the JVM to pause just before running main() until you attach a debugger then it will resume the execution. This way you can set
your breakpoints anywhere in the code and you should hit them no matter how early in the startup they are
and on Windows,
You need a few steps to be able to profile Karaf using YourKit.
The first one is to edit the
etc/config.properties configuration file and add the following property:
Then, set the
JAVA_OPTS environment variable:
or, on Windows
Run Karaf from the console, and you should now be able to connect using YourKit standalone or from your favorite IDE.
Karaf uses JMX for monitoring and management of all Karaf components.
The JMX connection could be:
- local using the process id
- remote using the
rmiRegistryPortproperty defined in
Using JMX, you can have a clean overview of the running Karaf instance:
- A overview with graphics displaying the load in terms of thread, heap/GC, etc:
- A thread overview:
- A memory heap consumption, including "Perform GC" button:
- A complete JVM summary, with all number of threads, etc:
You can manage Karaf features like you are in the shell. For example, you have access to the Admin service MBean, allowing you to create, rename, destroy, change SSH port, etc Karaf instances:
You can also manage Karaf features MBean to list, install, uninstall Karaf features: