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daemon: /day´mn/, /dee´mn/, n. [from Maxwell's Demon, later incorrectly retronymed as ‘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 (2003) usage.
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