<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.
