inetd

The inetd(8) daemon handles incoming network connections for less frequently used network services. Most systems don't have a steady stream of incoming FTP requests, so why have the FTP daemon running all the time? Instead, inetd listens to the network for incoming FTP requests. When an FTP request arrives, inetd(8) starts the FTP server and hands off the request. Other common programs that rely on inetd are telnet, tftp, and POP3.

inetd also handles functions so small and rarely used that they're easier to implement within inetd, rather than route them through a separate program. This includes discard (which dumps any data received into the black hole of /dev/null), chargen (which pours out a stream of characters), and other functions. These ...

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