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A port monitor is a continuous process, called a daemon, that listens to a given physical port or on a network address for connection requests. listen, also called the listener, is a network port monitor. The listener listens on addresses associated with a connection-oriented transport network. There may be multiple listen port monitors on the system, each monitoring multiple addresses.
The listener listens on the server for incoming connection requests, accepts the requests, and starts services that have been requested. If a service is protected by an authentication scheme, the listener invokes the authentication scheme. If the authentication protocol completes successfully, the client user's identity is mapped to an identity on the server; then, the port monitor starts the requested service.
All port monitors, including listen, are managed by the Service Access Facility (SAF). The SAF generalizes service access procedures so login access on the local system and network access to local services are managed in similar ways. This means, from the system administrator's perspective, that local and network access are managed similarly, as is access over different networks. (For more information, see ``The Service Access Facility'' and ``Administering port monitors''.)