Resource usage
 

I usually use "top" command to check the resource usage , it is very good and simple method to know the status ( loading , CPU , memory usage ), but we have many servers so we can't check the servers frequently , so we can't find the problem before the problem happens

can advise any method / script that I can implement to send us a alert mail if the resource usage reach a specific level , for example , if the CPU usage reach 90% , then send us a alert mail , what can i do ? thx

We use Nagios to monitor servers for CPU, disc space, services etc. and it has been serving us well. You can set up NRPE on each of the clients such that it reports all the services you choose to monitor to the Nagios server.

http://nagios.sourceforge.net/docs/nrpe/NRPE.pdf