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The Linux Programming Interface by Michael Kerrisk

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Chapter 37. 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.

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 commands ...

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