13.1. Introduction

Daemons are processes that live for a long time. They are often started when the system is bootstrapped and terminate only when the system is shut down. Because they don't have a controlling terminal, we say that they run in the background. UNIX systems have numerous daemons that perform day-to-day activities.

In this chapter, we look at the process structure of daemons and how to write a daemon. Since a daemon does not have a controlling terminal, we need to see how a daemon can report error conditions when something goes wrong.

For a discussion of the historical background of the term daemon as it applies to computer systems, see Raymond [1996].