All the processes started from the same process share the same session and the same terminal. This is true when started with '&', run on the command-line, or fork/exec within a program.

When setsid() ("set session id") is called we create a new session which does not have a terminal. By default, the process which calls setsid() is moved to the new session (setsid() can take a PID as a parameter). The process is now the only process in the new session, unless it starts new processes itself. It does not have a terminal and ps -ef will show ? against its TTY column. This is the usual way that a daemon disconnects from a terminal since it does not want signals from the keyboard.

(Not copied from doc)

In reply to Re^4: Keep a "system" process running if script is prematurely exited? by cdarke
in thread Keep a "system" process running if script is prematurely exited? by westrock2000

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