The Linux Programming Interface

37DAEMONS

This chapter examines the characteristics of daemon processes and looks at the steps required to turn a process into a daemon. We also look at how to log messages from a daemon using the syslog facility.

37.1 Overview

A daemon is a process with the following characteristics:

• It is long-lived. Often, a daemon is created at system startup and runs until the system is shut down.

• It runs in the background and has no controlling terminal. The lack of a controlling terminal ensures that the kernel never automatically generates any job-control or terminal-related signals (such as SIGINT, SIGTSTP, and SIGHUP) for a daemon.

Daemons are written to carry out specific tasks, as illustrated by the following examples:

• cron: a daemon that executes ...