The Linux Programming Interface

DAEMONS

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:

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

system is shut down.

z It runs in the background and has no controlling terminal. The lack of a control-

ling 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:

z cron: a daemon that executes commands at a scheduled time.

z sshd: the secure shell daemon, which permits logins from remote hosts using a

secure communications protocol.