A single Linux system can provide dozens, even hundreds, of network
services. For example, when you use the telnet program, you are accessing
the telnet service on a remote system. Likewise, when you use the ftp
program, you are connecting to the ftp service on the remote system.
In order to provide these services, the remote system either runs an
instance of each server to accept connections (for example
/usr/sbin/in.telnetd and /usr/sbin/in.ftpd), or runs inetd. The inetd
program accepts each incoming connection and starts the appropriate
services to handle the connection based on its type. For this reason,
inetd is also known as the "Internet superserver."
On a typical Linux installation, inetd handles most incoming
connections. Only a few programs (such as sshd and lpd) handle their
own network communication without relying on inetd to accept incoming
connections.