Daemon
/ˈdiː.mən/ · Noun · Hacker Culture · Origin: 1963
Definitions
Daemon is a background process that runs continuously on a computer system without direct user interaction, performing system-level tasks or waiting to handle requests. The term originates from Greek mythology (a supernatural being working behind the scenes) and was first used in computing at MIT in the 1960s. Common Unix daemons include httpd (web server), sshd (secure shell server), cron (scheduled task runner), and systemd (system and service manager). Daemons typically start at boot time, run with elevated privileges, and have no controlling terminal. They are identified by convention with a trailing 'd' in their process name. In Unix systems, creating a daemon involves forking the process, detaching from the terminal, and closing standard file descriptors. On Windows, the equivalent concept is a service. Daemons are essential infrastructure, quietly handling logging, networking, printing, database operations, and countless other background tasks that keep systems running.
In plain English: A program that runs silently in the background on your computer, doing its job automatically without you ever seeing it — like a helpful invisible worker.
Common daemons include httpd (web server), sshd (secure shell), crond (scheduler), and systemd (the init system that manages all other daemons). The trailing 'd' in process names often indicates a daemon. They typically detach from the terminal, run as background processes, and log to files rather than stdout.
Example: 'The nginx daemon keeps crashing at midnight. Check the logs at /var/log/nginx/error.log — daemons don't print to your terminal.'
Source: practical / naming convention
Etymology
- 1867
- James Clerk Maxwell proposes his 'demon' thought experiment
- 1963
- MIT Project MAC team names background processes 'daemons'
- 1988
- BSD adopts the daemon mascot, drawn by John Lasseter
Origin Story
Maxwell's demon became Unix's background process
In thermodynamics, James Clerk Maxwell proposed a thought experiment in 1867: a tiny being (a 'demon') that sits at a gate between two gas chambers, sorting fast molecules from slow ones. This demon works tirelessly in the background, never resting, never interacting with the system in a visible way.
When MIT programmers in the 1960s needed a name for background processes that ran continuously without user interaction on Project MAC, they borrowed Maxwell's concept but changed the spelling. Fernando Corbato, a pioneer of time-sharing systems, is credited with first applying 'daemon' to computing.
The spelling with an 'a' was deliberate — partly to distinguish it from the religious 'demon,' and partly as a nod to the Greek 'daimon' (a guiding spirit, not an evil one). The BSD mascot, a cheerful little devil with a pitchfork, cemented the playful association.
Coined by: Fernando Corbato / MIT Project MAC team
Context: MIT Project MAC, 1960s
Fun fact: The BSD daemon mascot was drawn by John Lasseter, who later co-founded Pixar. Its official name is 'Beastie.'