daemon

operating system /day'mn/ or /dee'mn/ (From the mythological

meaning, later rationalised as the acronym "Disk And Execution

MONitor") A program that is not invoked explicitly, but lies

dormant waiting for some condition(s) to occur. The idea is

that the perpetrator of the condition need not be aware that a

daemon is lurking (though often a program will commit an

action only because it knows that it will implicitly invoke a

daemon).

For example, under ITS writing a file on the LPT spooler's

directory would invoke the spooling daemon, which would then

print the file. The advantage is that programs wanting files

printed need neither compete for access to, nor understand any

idiosyncrasies of, the LPT. They simply enter their

implicit requests and let the daemon decide what to do with

them. Daemons are usually spawned automatically by the

system, and may either live forever or be regenerated at

intervals.

Unix systems run many daemons, chiefly to handle requests

for services from other hosts on a network. Most of these

are now started as required by a single real daemon, inetd,

rather than running continuously. Examples are cron (local

timed command execution), rshd (remote command execution),

rlogind and telnetd (remote login), ftpd, nfsd (file

transfer), lpd (printing).

Daemon and demon are often used interchangeably, but seem to

have distinct connotations (see demon). The term "daemon"

was introduced to computing by CTSS people (who pronounced

it /dee'mon/) and used it to refer to what ITS called a

dragon.

[Jargon File]

(1995-05-11)