Among many monitoring tools that available, most people use "top" (a part of procps package). Top provide almost everything we need to monitor our system's resource usage within single shot. In this article, all the information are based on procps 3.2.5 running on top of Linux kernel 2.6.x
Here, we assume that procps package is already installed and run well in your Linux system. No previous experience with top is needed here, but if you had given it a try briefly, that would be an advantage.
Read the full thing at http://www.linuxforums.org/articles/using-top-more-efficiently_89.html