In this chapter, the reader has been taken through many important ideas on the design and implementation of the traditional Unix security model. Among other things, we have covered the traditional Unix permission model, the concepts of process real and effective IDs, APIs to query and set them, sudo(8), saved-set IDs.
Again, it bears repeating: we definitely recommend you also read the following Chapter 8, Process Capabilities! In it, we show how the traditional permissions model is flawed, and how you should use the superior, modern Linux Capabilities model.