Daemon

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This is a pun

In UNIX a Daemon is a software program that operates in the background performing a task or running a service. For example, most kinds of servers are daemons, not all daemons are servers though, HAL the "hardware abstraction layer" and Cron, which runs scheduled tasks are good examples of this.

Daemons are named after Maxwell's Demon, which worked in the background of that famous thought experiment, moving molecules. Daemon is spelled with an "A" (that is not pronounced) to emphasize the analogy with the servant entities of Greek mythology, rather than undesirable satanic connotations.

Regardless of this, the FreeBSD version of UNIX has a cute cartoon-demon character as an official mascot. This version is holding a trident (a fork-like weapon) which is a punning reference the process for "daemonizing" a process.

Strictly speaking a process only becomes a daemon if its parent process "dies", the process releases any controlling TTY and the process is adopted by the master-process (init). This is known as "forking".

Early UNIX humor included the legendary t-shirt showing Daemons running around on a mass of pipes, carrying forks and with a barrel labeled "null", all punning references to UNIX technology.

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