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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daemon book n.
"The Design and Implementation of the 4.3BSD UNIX Operating
System", by Samuel J. Leffler, Marshall Kirk McKusick, Michael J.
Karels, and John S. Quarterman (Addison-Wesley Publishers, 1989,
ISBN 0-201-06196-1); or "The Design and Implementation of the 4.4
BSD Operating System" by Marshall Kirk McKusick, Keith Bostic,
Michael J. Karels and John S. Quarterman (Addison-Wesley Longman,
1996, SBN 0-201-54979-4) Either of the standard reference books
on the internals of BSD Unix. So called
because the covers have a picture depicting a little devil (a
visual play on daemon) in sneakers,
holding a pitchfork (referring to one of the characteristic
features of Unix, the fork(2) system call). Also
known as the Devil Book.