Daemon

A daemon

example:

Dhcpcd with filename 	dhcpcd 	  also known as    dhcpcd@.service 	   is a DHCP daemon. Hence 'd' as the last letter of the filename 

is a program that runs as a "background" process (without a terminal or user interface), commonly waiting for events to occur and offering services. A good example is a web server that waits for a request to deliver a page, or a ssh server waiting for someone trying to log in. While these are full featured applications, there are daemons whose work is not that visible. Daemons are for tasks like writing messages into a log file (e.g. syslog, metalog) or keeping your system time accurate (e.g. ntpd). For more information see man 7 daemon.

In current Parabola Linux, daemons are managed by systemd. The systemctl command is the user interface used to manage them. It reads name.service files that contain information about how and when to start the associated daemon. Service files are stored in /{etc,usr/lib,run}/systemd/system. See systemd#Using units for details.

Daemon or Dämon is German for demon.