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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 the most common cases:

Example 9.1. Excerpt from /etc/inetd.conf

talk   dgram  udp wait    nobody.tty /usr/sbin/in.talkd in.talkd
finger stream tcp nowait  nobody     /usr/sbin/tcpd     /usr/sbin/in.fingerd
ident  stream tcp nowait  nobody     /usr/sbin/identd   identd -i

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 /usr/bin/in.fingerd in our example).