Daemon, occasionally referred to as a “background process”, is a computer program that runs as a background process, rather than being under the direct control of an user. The term was coined in the context of Unix-like computer systems, but certain Windows operating system components are daemons as well.
Essentially, a daemon is a computer application designed to run independently of a user’s direct control. Daemon programs often run continuously on computers, and are necessary in keeping the computer functioning as expected. The responsibility of a daemon ranges from maintaining system resources to performing a task when a user requests it.
For example, a UNIX system often has the following daemons running as services: cron, which executes scheduled commands; fuser, which confirms the users on the system; sshd, which provides secure remote access; and inetd, which listens for network connections and passes them to the appropriate program.
Many of a computer’s services are made possible by daemons. Another example is a software update daemon, which checks for updates of software requested by the user. The daemon software launches, downloads the update, and installs the update itself.
For a user to interact with a daemon, he could use commands such as “service stop” to stop a service. This control of daemons is generally done in a command line or graphical environment.
