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diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node81.html b/sag-0.6.1-www/Invisible/sag-0.6/node81.html new file mode 100644 index 0000000..4b7df40 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node81.html @@ -0,0 +1,75 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Logins via the network</TITLE> +<META NAME="description" CONTENT="Logins via the network"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html1333" HREF="node82.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1331" HREF="node79.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1325" HREF="node80.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1335" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1336" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1334" HREF="node82.html">What login does</A> +<B>Up:</B> <A NAME="tex2html1332" HREF="node79.html">Logging In And Out</A> +<B> Previous:</B> <A NAME="tex2html1326" HREF="node80.html">Logins via terminals</A> +<BR> <P> +<H1><A NAME="SECTION00920000000000000000">Logins via the network</A></H1> +<P> + Two computers in the same network are usually linked via a single + physical cable. When they communicate over the network, the programs + in each computer that take part in the communication are linked + via a <b>virtual connection</b>, a sort of imaginary cable. + As far as the programs at either end of the virtual connection + are concerned, they have a monopoly on their own cable. However, + since the cable is not real, only imaginary, the operating systems + of both computers can have several virtual connections share + the same physical cable. This way, using just a single cable, + several programs can communicate without having to know of or + care about the other communications. It is even possible to + have several computers use the same cable; the virtual + connections exist between two computers, and the other computers + ignore those connections that they don't take part in. +<P> + That's a complicated and over-abstracted description of the + reality. It might, however, be good enough to understand + the important reason why network logins are somewhat different + from normal logins. The virtual connections are established + when there are two programs on different computers that + wish to communicate. Since it is in principle possible to + login from any computer in a network to any other computer, + there is a huge number of potential virtual communications. + Because of this, it is not practical to start a <tt>getty</tt><A NAME="2636"> </A> + for each potential login. +<P> + There is a single process inetd (corresponding + to <tt>getty</tt><A NAME="2638"> </A>) that handles <em>all</em> network logins. + When it notices an incoming network login (i.e., it notices + that it gets a new virtual connection to some other computer), + it starts a new process to handle that single login. The + original process remains and continues to listen for new + logins. +<P> + To make things a bit more complicated, there is more than + one communication protocol for network logins. The two + most important ones are <tt>telnet</tt><A NAME="2640"> </A> and <tt>rlogin</tt><A NAME="2642"> </A>. In + addition to logins, there are many other virtual connections + that may be made (for FTP, Gopher, HTTP, and other network services). + It would be ineffective to have a separate process listening + for a particular type of connection, so instead there is only + one listener that can recognize the type of the connection and + can start the correct type of program to provide the service. + This single listener is called <tt>inetd</tt><A NAME="2644"> </A>; see the + ``Linux Network Administrators' Guide'' for more information. +<P> +<HR><A NAME="tex2html1333" HREF="node82.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1331" HREF="node79.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1325" HREF="node80.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1335" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1336" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1334" HREF="node82.html">What login does</A> +<B>Up:</B> <A NAME="tex2html1332" HREF="node79.html">Logging In And Out</A> +<B> Previous:</B> <A NAME="tex2html1326" HREF="node80.html">Logins via terminals</A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |