According to what I know, the shell and its child processes are in the same session which have the same (controlling) terminal. I read that they are interactive processes because they have the same terminal associated with. For now, I accept it although does not feel right because the real interaction is between user and the shell.How about GUI programs (e.g. browser, text editor), window manager and desktop environment? Are they child processes to X11?correction: each command pipeline in a shell has different PGID. so, child processes of shell do not have same PGID with the shell's.
Processes group (session) of GUI processes
x11;process