Correct option is A
In Unix-like systems, the init process (now often systemd) is the first user-space process started by the kernel.
It is assigned PID 1, and it becomes the ancestor of all other user processes.
PID 1 is responsible for starting services, handling orphaned processes (via wait), and coordinating shutdown/reboot.
Because of its critical role, if PID 1 exits or crashes, the system typically panics.
Historically, PID 0 refers to the swapper/scheduler (kernel task), not a regular user-space process.
Therefore, the PID of the init process is 1.
PID 1 is responsible for starting services, handling orphaned processes (via wait), and coordinating shutdown/reboot.
Because of its critical role, if PID 1 exits or crashes, the system typically panics.
Historically, PID 0 refers to the swapper/scheduler (kernel task), not a regular user-space process.
Therefore, the PID of the init process is 1.
Important Key Points
- PID 1: First user-space process; parent of all others.
- Responsibilities: Launch services, reap orphans, manage runlevels/targets.
- Stability: Failure of PID 1 is catastrophic; system may halt/panic.
- Modern init: Often systemd (PID 1), but could be sysvinit, OpenRC, etc.
- PID 0: Kernel’s idle/swapper task (not user-space).
- Signals: PID 1 handles signals specially; e.g., ignores some by default for robustness.
Knowledge Booster
- Why not (b) 0? Not a user-space process; it’s the kernel idle/swapper thread.
- Why not (c) 3 or (d) 4? Ordinary processes get these PIDs later; the first user-space process is always PID 1.
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