Every process now has an init process like it has a session, and each
session belong to an init. Orphaned processes are reparented to its init
process. All descendent processes are SIGKILL'd when an init process exits
and creating additional processes/threads fails.
Add setinit(2) for becoming the init process for your child processes and
add getinit(2) for locating your init process.
Add TIOCSCTTY force flag that releases a terminal from its current session
and makes it the controlling terminal for the current session. This ioctl
is essential to transferring the controlling terminal to a nested init,
which has its own session.
Add TIOCUCTTY that releases the terminal as the controlling terminal for
its current session.
Remove INIT_PID as it is replaced by getinit(2).
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