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internet daemon

Posted on 2006-04-06
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what does internet daemon do
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Question by:teera
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by:Irwin Santos
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by:xDamox
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Hi,

Internet daemons provide services over the internet such as; POP3, SMTP, BIND
whereas certain services only provide services to local LANS
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A daemon refers to a piece of software that runs in the background servicing requests.

An internet daemon is a daemon that answers requests or makes requests through an
Internet Protocol such as TCP/IP streams, or UDP datagrams.

In Linux, one of very the popular internet daemons is called Inetd, or The Internet Daemon.

This is a superserver, a small program, that is configured to receive requests on behalf of other
server software designed for Inetd operation that has properly been configured with Inetd  
(using /etc/inetd.conf).

This contrasts to a configuration of a server program where the program runs in the background,
wait for incoming requests itself (a true daemon mode of operation).

Instead of server software itself staying in the background, listening for requests, some
server software can be configured with inetd -- in this case,  inetd will handle all that daemon
stuff, and be the program constantly listening on a port, Inetd will wait for a request, and pass
control along to the appropriate server program, by running the command, and redirecting
input and output channels to + from the user.

The advantage of this approach is that the server software has less work to do -- since Inetd
managed the request and piped the output, the server software itself did not need to wait for
a request.

This is supposed to allow a server program (like Remote login, Telnetd, or FTPd, for instance), to be
built as a simple interactive application, without worrying about the network; so the daemon could
be simpler, your server application might even be a shell script (highly inadvisable, however).

In fact, the server program didn't even have to be running -- without inetd, every daemon
would have to be running at all times,  inetd allows the system to start up the server program
just in time to handle an incoming request.

Inetd knows which program to start, because it has a list of services it handles, usually in /etc/inetd.conf,
and the service port numbers are standard ones which can be viewed in /etc/services


At other times, the server itself doesn't run, only inetd needs to keep running; normally, no copies
of the server program are running, unless there's an active connection -- and every new connection
launches a new instance of the client daemon.



Contrast this to a program which cannot be run from inetd normally -- such as the Apache web server;
to function, it must be running at all times, waiting for requests.  This reduces startup overhead, and is
ideal for a heavily loaded server.

If your web server only had 1 web request to service a day, it would be wasteful to have Apache running
all day: an Inetd based daemon could be more efficient.


On the other hand, if your web server needed to handle 10-20 simultaneous web requests, inetd would
be inefficient and slow, because (1) Each request would involve starting up a new instance of the web server,
this is inefficient, and would create a big slowdown (2) There would in effect be a copy running for each
concurrent user, this is an even bigger inefficiency, 1000 simultaneous requests could bring the whole
inetd system down.


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by:Irwin Santos
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cool..thank you.
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