The fundamental unit of administration in the SMF framework is the service instance. Each SMF service has the potential to have multiple versions of it configured. As well, multiple instances of the same version can run on a single Solaris system. An instance is a specific configuration of a service. A web server is a service. A specific web server daemon that is configured to listen on port 80 is an instance. Each instance of the web server service could have different configuration requirements. The service has system-wide configuration requirements, but each instance can override specific requirements, as needed. Multiple instances of a single service are managed as child objects of the service object.
Services are not just the representation for standard long-running system services such as in.dhcpd or nfsd. Services also represent varied system entities that include ISV applications such as Oracle software. In addition, a service can include less traditional entities such as the following:
A physical network device
A configured IP address
Kernel configuration information
Milestones that correspond to system init state, such as the multiuser run level
Generically, a service is an entity that provides a list of capabilities to applications and other services, local and remote. A service is dependent on an implicitly declared list of local services.
A milestone is a special type of service. Milestone services represent high-level attributes of the system. For example, the services which constitute run levels S, 2, and 3 are each represented by milestone services.