Howtoforge posted a guide about system monitoring with sar and ksar

sar is one of the old and famous commandline utilities, which is often overlooked. It provides a wealth of information when you have kind of performance bottlenecks. By itself it only provides lengthy columns of numerical data, kind of hard to interpret. sar exists on most Linux distributions, for example Ubuntu, Debian, CentOS, Gentoo, and is also available on Solaris, AIX, and other commercial Unices. ksar, on the other hand, is a Java based front end for sar's numerical data. It produces friendly graphs which could be exported to .pdf and some other formats.

  System Monitoring With sar And ksar