Linux Box monitoring solution

[Jatin]

Hi all

I am a performance test engineer. I am into performance testing of 
network management products. I am looking out for an open source product 
that can monitor all my linux boxes. I basically need the following:

1. To monitor all the linux boxes in my lab using a single UI remotely
2. Would require all the system level resource utilization parameter as 
well process level resource utilization parameters.
3. Tool should allow me to configure the intervals at which the required 
data should be sampled from the linux boxes.
4. Parameters such as CPU , Memory , Network , Disk I/O and process 
utilization are the most important things that i am looking for.

Please suggest me some useful open source tools that can do all these 
things.

Thanks
Jatin