Troubleshooting Dying Jenkins Server

New to Jenkins, I'm having an issue troubleshooting Jenkins -- specifically why it's dying...

I couldn't see any gripes in /var/log/jenkins/jenkins.log -- just normal startup notifications...

But the jenkins service keeps dying.

After some searching for "jenkins ci die", I found these resources:

So I installed the Monitoring plugin... and let's see...
Not running any jobs... it's just sitting there.
Will check it tomorrow.