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9.6.  inetd 超级服务

Inetd(常被称为“网络超级服务”)是一个服务器服务。它按需求运行一些不常用的服务,而且不需要连续运行。
/etc/inetd.conf 文件列出这些服务和他们常用的端口。 inetd 命令监听列出的所有端口;当探测到任意其中端口的连接,它就运行相应的服务程序。
/etc/inetd.conf 文件中每行通过七个区段(有空格分开)描述一个服务:
下面的例子阐释最常见的情况:

例 9.1. 摘自 /etc/inetd.conf

talk   dgram  udp wait    nobody.tty /usr/sbin/in.talkd in.talkd
finger stream tcp nowait  nobody     /usr/sbin/tcpd     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 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.