Daemon (background computer process)

Characteristics and behavior

Daemons are ordinary user-space processes but follow a set of common practices to run reliably in the background. Typical steps include detaching from any controlling terminal, running in their own session, changing the working directory to a safe location, closing or redirecting standard input/output streams, and creating a process identifier (PID) file so other tools can find and manage them. Daemons usually run with least privilege required for their function and respond to signals for reconfiguration, termination, or log rotation.

Examples and typical uses

• Network servers (for example, a web server or an SSH server such as sshd).
• Logging and monitoring services that collect and store system events.
• Task schedulers and job runners that execute work at set intervals.
• Device or print spoolers that mediate access to hardware.

Common daemon names include httpd (web), sshd (secure shell), cron or crond (scheduled tasks), and syslogd (system logging). Many distributions provide tools and standards for starting, stopping, and supervising daemons.

History and management

The daemon concept predates modern init systems and has evolved alongside them. Traditional initialization schemes started daemons in sequence at boot, while modern service managers provide dependency handling, on-demand activation, and supervision. Administrators interact with daemons using commands provided by the system's init or service manager, read configuration files that control behavior, and monitor logs for errors.

Distinctions and notable facts

While "daemon" is the common term on Unix-like platforms, other operating systems use terms such as "service" or "background process." Functionally the ideas overlap, but management interfaces and lifecycle conventions may differ. A daemon is not inherently privileged: its security posture depends on implementation, configuration, and the privileges with which it runs. For general reference on software concepts, see related documentation and additional resources at technical guides.