Xinetd

Xinetd, short for extended Internet services daemon, is a network service super-server for Unix-like operating systems. It listens for connections on configured ports and, when a request arrives for a defined service, starts the corresponding server process on demand. This on-demand model helps conserve resources and centralizes management of multiple network services.

Xinetd provides enhanced control and security features beyond the traditional inetd. It supports per-service access control and filtering, including restrictions based on host or network, and it offers flexible logging options. Services can be limited in concurrency through the instances and per_source directives, and access can be restricted with parameters such as only_from or bind. Other commonly used directives include server and server_args to specify the program to run and its arguments, user and group to drop privileges, and banner, redirect, or disable to control behavior. Logging can be configured for success and failure events, and various thresholds, banners, and banners can be customized per service.

Configuration is stored in a set of files, typically including /etc/xinetd.conf and per-service files in /etc/xinetd.d. A service block defines how xinetd should handle that service, including protocol (often tcp), port, socket_type, wait, and the path to the server executable along with any arguments. The wait setting generally determines whether xinetd handles connections sequentially for a port or spawns new instances to handle connections concurrently.

Xinetd remains available on many Unix-like systems as an alternative to inetd, while newer init and service management systems sometimes favor socket activation features provided by other daemons.