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9.6. The inetd 超級伺服器

Inetd (又稱為 “Internet 超級伺服器”) 是伺服器中的伺服器。依需要啟用甚少用到的伺服器，因此不需持續地執行它。
/etc/inetd.conf 檔案列出伺服器及其通用的埠號。inetd 命令偵測它們；若發現任何埠號已被連結，則執行對應的程式。

DEBIAN POLICY Register a server in /etc/inetd.conf

套件經常需要在 /etc/inetd.conf 檔案登錄新的伺服器，但 Debian 政策禁止任何套件不屬於自身的組態檔。所以有 update-inetd 腳本 (在同名套件內)：管理組態檔案以及其他套件，使其在超級伺服器的組態中登錄新的伺服器。
/etc/inetd.conf 檔案中的每列款目以 7 個欄位 (以空格區分) 描述伺服器：
The following example illustrates some use-cases after installing talkd, nullidentd (ident-server), and fingerd:

範例 9.1. 取自 /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.

社群 Wietse Venema

Wietse Venema, whose expertise in security has made him a renowned programmer, is the author of the tcpd program. He is also the main creator of Postfix, the modular e-mail server (SMTP, Simple Mail Transfer Protocol), designed to be safer and more reliable than sendmail, which features a long history of security vulnerabilities. We will have a closer look at this mail server in 節 11.1, “Mail Server”.

其他 異於 inetd 的命令

While Debian installs openbsd-inetd by default, there is no lack of alternatives: we can mention inetutils-inetd, rlinetd, and xinetd, which all provide the virtual package inet-superserver.
Most of these alternatives share the same configuration file /etc/inetd.conf.
This last incarnation of a super-server however, offers different syntax and very interesting possibilities. Most notably, its configuration can be split into several files (stored, of course, in the /etc/xinetd.d/ directory), which can make an administrator's life easier. It is considered to be more powerful, but also more complex.
Last but not least, it is even possible to emulate inetd's behavior with systemd's socket-activation mechanism (see 節 9.1.1, “systemd 啟動系統”).