Understanding your Linux daemons

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A Unix daemon is a program that runs in the “background,” enabling you to do other work in the “foreground,” and is independent of control from a terminal. Daemons can either be started by a process, such as a system startup script, where there is no controlling terminal, or by a user at a terminal without “tying up” that terminal as the daemon runs. But which daemons can you safely play with? Which should you leave running?

An introduction to daemons

The real-world (i.e., non-computer) definition of “daemon” is either a spirit (an evil one) or an inner or private voice. It’s interesting to note that each of the real-world definitions actually does apply to Unix daemon programs. Like mythological daemons, Unix daemon programs skulk around unseen in the background just as a daemon would. And daemons act like an inner voice in that they can run continuously and, like a conscience, can always be accessed. The word “daemon” is one of those cases of chicken and egg computer acronyms in search of a definition and supposedly is based on “Disk And Execution MONitor” program.

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