Control Terminals

 

        The concept of a control terminal comes from Ultrix; the idea is for a process to be able to direct output to a place that will be seen by its user (a human being) even when its standard input and standard output have been redirected. A process may or may not have a control terminal. If it does, then the control terminal can be opened by opening a particular device file, which usually has the path name /dev/tty. (OS also provides the OpenControlTerminal procedure; see page .) Normally a new process inherits the control terminal of the process that created it, but this can be overridden (see SetControlTerminal and UnsetControlTerminal, page ). A process with no control terminal automatically acquires as a control terminal the first tty device that it opens.