Setsid

Setsid is a Unix utility that runs a program in a new session, thereby detaching it from the current controlling terminal and from the current process group. It is commonly used to start long-running tasks in the background, such as daemons, without being affected by terminal hangups or job control from the launching shell.

Technical overview: When invoked with a command, setsid forks a child process that creates a new session, becomes the session leader of that session, and disassociates from any controlling terminal. The specified program is then executed inside this new session. The effect is that the started process runs in isolation from the terminal that launched it, reducing the chance that terminal actions will signal or interfere with it.

Usage: The typical syntax is setsid [PROGRAM [ARG]...]. If a program is provided, it is started in the new session; if not, behavior can vary by implementation. In practice, users employ setsid to launch services or commands that should keep running independently of the initiating shell or terminal.

Common use cases: daemonizing a process, starting background jobs from scripts, or ensuring that a command does not receive terminal-related signals when the terminal is closed. Setsid is often used in combination with other tools such as nohup or disown to further detach a process from terminals and sessions.

See also: nohup, disown, daemon, session, process group.