It has been itching me for a long time to know what the historical reason for calling daemon programs or threads "daemon"
Lat: daemon, latin version of the Greek "δαίμων" ("godlike power, fate, god")
- god,
- a subordinate deity, as the genius of a place or a person's attendant spirit
There are numerous questions clarifying what daemons are and how they behave, but none explaining the origins of the term "daemon" for programs that run in the background like sshd.
Why do we title programs that run in the background as daemons?
See the wiki
According to Fernando J. Corbató who worked on Project MAC in 1963 his team is the first to use the term daemon. The use of the term daemon was inspired by Maxwell's daemon, in physics and thermodynamics as an imaginary agent which helped to sort molecules.
"We fancifully began to use the word daemon to describe background processes which worked tirelessly to perform system chores."
In the Unix System Administration Handbook, Evi Nemeth states the following about daemons:
"Many people equate the word "daemon" with the word "demon", implying some kind of satanic connection between UNIX and the underworld. This is an egregious misunderstanding. "Daemon" is actually a much older form of "demon"; daemons have no particular bias towards good or evil, but rather serve to help define a person's character or personality. The ancient Greeks' concept of a "personal daemon" was similar to the modern concept of a "guardian angel"—eudaemonia is the state of being helped or protected by a kindly spirit. As a rule, UNIX systems seem to be infested with both daemons and demons."