daemon
daemon: /day'mn/ or /dee'mn/ n. [from the mythological meaning,
later rationalized 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 (in this example) 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.
Daemon and demon are often used interchangeably, but seem to
have distinct connotations. 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; the prototype was a program
called DAEMON that automatically made tape backups of the file
system. Although the meaning and the pronunciation have drifted, we
think this glossary reflects current (2000) usage.
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