As this chapter shows, the performance tools available in Linux overlap a lot in the information they provide. Memory information can be displayed with top, vmstat, free, and sar, for example. A system administrator doesn't need to be an expert in all the tools. However, it is important to know how to find and interpret all the performance information you need, no matter which tools you decide to use. Thus, we recommend spending a lot of time getting familiar with the tools and their output.