What is a 'daemon' in Linux?

A daemon in Linux is defined as a background process that runs without user intervention. This means that a daemon operates independently of any interactive user sessions and typically performs tasks or provides services that are essential for system operations. For instance, daemons can manage system resources, handle network requests, execute scheduled tasks, or monitor system health, all without requiring direct input from a user.

Common examples of daemons include web servers like Apache, print servers, and database systems, which need to run continuously and wait for requests. These processes usually start when the system boots and are often managed by an init system like systemd or Upstart.

In contrast, a system service that requires user input, a command-line interface for executing scripts, or a user-initiated application that runs in the foreground do not encapsulate the essence of a daemon, as they either necessitate user interaction or operate in the foreground of a user session, which is not characteristic of daemon processes.