cat brain.stuff > wordpress

Determine the process id (PID) of the process that has high CPU load.

The culprit:

16397 tomcat    24   0 2809m 1.2g  26m S 197.4 14.8 112:28.42 java

Use top, ps or the java jps tool. I used jps here.

sudo -u tomcat jps -l

Output:

16397 org.apache.catalina.startup.Bootstrap
8985 sun.tools.jps.Jps

We then try to create a thread dump with the java jstack tool.

sudo jstack 16397 > stacktrace.dmp

Output:

16397: Unable to open socket file: target process not responding or HotSpot VM not loaded
The -F option can be used when the target process is not responding

sudo jstack -F 16397 > stacktrace.dmp

If that is also not working you can try quitting the process.

sudo -u tomcat kill -QUIT 16397

You will need to check the logs to see the stacktrace.

You can then check out the running threads and their state. I found that some threads were in a blocking state due to a few java.lang.OutOfMEmoryError errors.

To get more detailed information we can also use the jmap command to do a little deeper digging.

sudo jmap -dump:file=thread_dump.16379.dmp -F 16397