Debian – cpu 100% with tomcat 7 on Debian 8

If the process is dying it could be:

1. JVM exited because of an unhandeled Java exception - you should see something in catalina.out or in the file used to redirect the STDOUT and STDERR - read as in application crash.
2. OS send a signal that was not trapped by JVM - you should see something in STDOUT or STDERR that are redirected usually to catalina.out- read as in JVM crash.

Find where the STDOUT and STDERR is logged:

sudo -u tomcat6 ls -l /proc/$(pgrep java)/fd/{1,2}

Analise the java exception. If you do not find it, then search for a JVM creash.

Enable core dumps: http://en.linuxreviews.org/HOWTO_enable_core-dumps

Analise the core: http://www.freebsd.org/doc/en/books/developers-handbook/debugging.html#AEN1012

gdb /path.../java core
(gdb) bt

Analise the stack where JVM crashed.

EDIT: For high JVM load you can see which thread is generating the load. Use: top -Hp $(pgrep java) to find out the thread id that has the highest CPU usage. Then generate 2-3 thread dumps at 10 seconds apart with pkill -3 java. Convert to hex lowercase the PID of the thread from top output, then search for that number after nid= in catalina.out. That is the stack trace of the most expansive thread.

Also check if the JVM is not doing too much full GCs because the memory is not configured properly. See: http://java.sun.com/developer/technicalArticles/Programming/GCPortal/, http://www.oracle.com/technetwork/java/gc-tuning-5-138395.html, http://www.oracle.com/technetwork/java/faq-140837.html

Some useful tools: http://java.sun.com/developer/technicalArticles/J2SE/jconsole.html and https://visualvm.dev.java.net/

There is obviously a thread that is hanging.

kill -3 processid

Will show a list of the running threads in the java-app. Collect these and send it back to the dev.