daemon
termprogrammingops cultureIT support
A long-running background process that waits quietly to do its job, named after a benevolent spirit, not a demon.
The term comes from Maxwell's demon in physics, chosen by MIT's Project MAC in the 1960s for a helpful process that works unseen; the conventional -d suffix (sshd, httpd, crond) marks them. A daemon has no controlling terminal and is usually started at boot, which is exactly why a hung one is invisible until something depending on it fails. On Windows the same idea is called a service. BSD even adopted the little horned mascot, insisting it was a daemon and never a demon.
Also known as: daemons, service, background process, -d suffix