29.1. init: the primordial process
init is the first process to run after the system boots, and in many ways it is the most important daemon. It always has a PID of 1 and is an ancestor of all user processes and all but a few system processes.
At startup, init either places the system in single-user mode or begins to execute the scripts needed to bring the system to multiuser mode. When you boot the system into single-user mode, init runs the startup scripts after you terminate the single-user shell by typing exit or <Control-D>.
In multiuser mode, init is responsible for making sure that processes are available to handle logins on every login-enabled device. Logins on serial ports are generally handled by some variant of getty (e.g., ...
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