superservers

A superserver is a server design that manages and runs other services on demand rather than keeping every service loaded in memory. It operates as a central process that listens on one or more sockets and, when a request arrives, starts the appropriate service to handle that request. This on-demand approach can reduce resource usage and simplify administration on systems with many daemons.

The concept originated in Unix with inetd, the internet super-server, introduced in the 1980s to multiplex multiple services over shared ports. It was followed by enhancements such as xinetd that added access control and logging. In modern operating systems, socket activation features in init systems like systemd and launchd implement a similar gatekeeping role, effectively serving as superservers that launch services only when needed.

Operation typically involves a configuration that maps sockets or ports to the commands or executables that provide the corresponding service. When a connection arrives, the superserver consults this configuration and either spawns the designated service process or forwards the connection to a pool of pre-existing workers. Designs may be per-connection, where each request starts a new process, or pooled, where multiple requests share a set of workers.

Advantages include reduced memory footprint, lower background activity, and improved on-demand scalability, especially on systems with many services. Drawbacks can include latency for the first connection to a service, potential single-point-of-failure concerns, and increased complexity in configuration and security management.

See also inetd, xinetd, systemd, and socket activation. These concepts describe related mechanisms for on-demand service startup and management.