Hi i am running Tomcat server in production server(A Ubuntu machine), but i have checked after 3-4 days when i am browse application through URL its not responding when i cheked server through login on production server by following command 

```
ps -ef|grep tomcat

```

It showing `PID` it mean Tomcat is running but when i am trying to access application it is not available.
Then i have to restart the server again then everything work fine. What would be cause of this issue and what all thing i have to check i checked log file of Tomcat no any blunder i found on that .

Can any one tell me what can be reason of this issue and how can we resolve this? Also any open source tool to Monitor Tomcat from local machine. So it would send mail if any issue arise on Tomcat server