[1] SMF introduces: All these capabilities are made possible by treating Services as "first class objects".
They can be defined to have special states that allow finer control and permit monitoring and probing for diagnosing software failures, rather than having the administrator or dedicated "restarter" modules kill and restart the service as before.
Other services include NFS for sharing files on a network, DHCP for dynamic IP address assignment, and Secure Shell for remote logins.
Even higher level functions can be services, such as specific databases for e-commerce, finance, manufacturing control, etc.
One can have many instances of a defined service, such as multiple webservers listening on different ports referencing different WWW root directories.