Controlling Terminal of a Process
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One of the attributes of a process is its controlling terminal.
Child processes created with `fork' inherit the controlling terminal
from their parent process. In this way, all the processes in a session
inherit the controlling terminal from the session leader. A session
leader that has control of a terminal is called the "controlling
process" of that terminal.
You generally do not need to worry about the exact mechanism used to
allocate a controlling terminal to a session, since it is done for you
by the system when you log in.
An individual process disconnects from its controlling terminal when
it calls `setsid' to become the leader of a new session. Note:Process
Group Functions.