How to keep an eye on the server resources under unix platform? My “server” farm:
currently is under the Cacti control, which is a powerful tool to track anything you want/can on the system and outside it 
Yet another approach is to use a MUNIN. Easy to install, easy to configure, easy to maintain!
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Munin the monitoring tool surveys all your computers and remembers what it saw. It presents all the information in graphs through a web interface. Its emphasis is on plug and play capabilities. After completing a installation a high number of monitoring plugins will be playing with no more effort.Using Munin you can easily monitor the performance of your computers, networks, SANs, applications, weather measurements and whatever comes to mind. It makes it easy to determine “what’s different today” when a performance problem crops up. It makes it easy to see how you’re doing capacity-wise on any resources. “