How to diagnose the root cause of tomcat crash

I have a tomcat server 7.0.54 running on SUSE linux 11 SP3. It crashes occasionally.

I checked the catalina.out and found the log “INFO: Stopping service Catalina” which looked like tomcat got an abnormal shutdown signal. There is no error log before this Stopping log. This is very weird.

It does not look like a jvm crash because it has a process: pause -> stop -> destroy. But it seems not be shut down by the shutdown.sh through the shutdown port normally. Because it should have an important log “org.apache.catalina.core.StandardServer await” if it was shut down by the shutdown port.

This may have two reasons:

1. System.exit was executed. I checked the code and there is no thiskind of code.
2. It got a system signal, e.g. SIGHUP.

How to find which signal it got and which program sent the signal?

Any suggestion/comments to find the root cause are appreciated. Thanks