Modern Linux systems are often asked to perform many functions. Because of the broad appeal of Linux, its use is in everything from firewalls to set-top boxes. Because of this, there are many network services that are commonly seen on a Linux system. These services oftentimes do not see constant use, but need to be active and available when the need arises. Some examples of these important but often seldom used services are ftp, finger, telnet, imap, and pop3.
You may notice that these examples all represent network services that are considered relatively “old” (at least in terms of modern day computing). This is essentially true. Years ago, when hardware was more expensive and harder to come by, the amount of system resources, especially memory, that each process consumed was of great importance. The problem was that administrators wanted to consolidate a lot of their network services on one Linux machine, but were running into memory limitations. The solution was to come up with a listening service, or “super-server,” that handled incoming connections and started the correct networking service to handle them. Thus the inetd service was born.
The inetd service has two important characteristics: It is a single process that can listen on multiple ports for incoming connections, starting the appropriate service when a connection comes in and connecting the inbound connection with the service. Also, inetd supports a sophisticated security scheme for allowing and disallowing ...