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9.6. The inetd Super-Server

Inetd (often called “Internet super-server”) is a server of servers. It executes rarely used servers on demand, so that they do not have to run continuously.
The /etc/inetd.conf file lists these servers and their usual ports. The inetd command listens to all of them; when it detects a connection to any such port, it executes the corresponding server program.
Each significant line of the /etc/inetd.conf file describes a server through seven fields (separated by spaces):
The following example illustrates some use-cases after installing talkd, nullidentd (ident-server), and fingerd:

Παράδειγμα 9.1. Excerpt from /etc/inetd.conf

#:BSD: Shell, login, exec and talk are BSD protocols.
talk   dgram   udp     wait    nobody.tty   /usr/sbin/in.talkd      in.talkd
ntalk  dgram   udp     wait    nobody.tty   /usr/sbin/in.ntalkd     in.ntalkd

#:INFO: Info services
ident  stream  tcp     nowait  nobody       /usr/sbin/nullidentd    nullidentd
finger stream  tcp     nowait  nobody       /usr/sbin/tcpd          /usr/sbin/in.fingerd
The tcpd program is frequently used in the /etc/inetd.conf file. It allows limiting incoming connections by applying access control rules, documented in the hosts_access(5) manual page, and which are configured in the /etc/hosts.allow and /etc/hosts.deny files. Once it has been determined that the connection is authorized, tcpd executes the real server (like in.fingerd in our example). It is worth noting that tcpd relies on the name under which it was invoked (that is the first argument, argv[0]) to identify the real program to run. So you should not start the arguments list with tcpd but with the program that must be wrapped.