$ Linux Command

System

setsid

Run a command in a new session.

processsessiondaemonprocess-group

Additional Notes

setsid runs a program in a new session, detaching it from the current terminal's session and process group. This is commonly used to properly daemonize processes, ensuring they are not tied to the controlling terminal and do not receive SIGHUP when the terminal closes.

A session is a collection of process groups. When a program runs with setsid, it becomes the session leader of a new session with no controlling terminal. This is similar to what daemon programs do internally when they call setsid() system call during initialization.

Syntax

setsid [options] program [arguments...]

Parameters

  • program: The command or program to execute.
  • arguments: Arguments to pass to the program.

Common Options

  • -c, --ctty: Set the controlling terminal to the current terminal.
  • -f, --fork: Fork before executing the program (creates a child process that runs the command).
  • -w, --wait: Wait for the program to exit before returning.
  • -V, --version: Show version information.

Examples

setsid daemon-process

Run daemon-process in a new session, detached from the terminal.

setsid -w mycommand

Run mycommand in a new session and wait for it to complete.

setsid -f myprogram &

Fork and run myprogram in the background, completely detached from the shell.

setsid ping 8.8.8.8

Run ping in a new session so it survives the terminal being closed.

Practical Notes

  • Without setsid, background jobs may receive SIGHUP when the terminal closes.
  • The shell builtin disown is an alternative for keeping jobs running after logout.
  • setsid is more reliable than using nohup for full daemonization.
  • The -f flag combined with & is a common pattern for launching detached processes.
  • Process monitoring tools like supervisord or systemd are preferred for production daemon management.