Exercise 3: What ws1's "systemctl restart apache2" Was Actually Asking systemd to Do — Possible Solution
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Explanation:

Using only this chapter's own PID-1/process-supervision material --
before systemctl's full syntax is covered in systemd1-2 -- "systemctl
restart apache2" is a command directed at systemd, the process
running as PID 1 on the Debian system ws1 targets. Since PID 1 is the
ancestor process ultimately responsible for supervising every other
process on the system (per this chapter's own description of PID 1's
role), asking it to "restart apache2" is really asking systemd, in
its role as process supervisor, to stop whichever process is
currently running as the Apache web server and start a fresh instance
of it in its place.

This connects directly to the chapter's own reaping material as well:
when systemd stops the old Apache process, it's systemd itself --
already established as the process responsible for tracking and
cleaning up process lifecycles on the system -- that oversees that
process's termination and then starts the new one, rather than some
separate, unrelated mechanism. The command is fundamentally a request
made to the one process (systemd, PID 1) that the kernel itself
designated as having special, systemwide responsibility over how
processes come and go -- exactly the role this chapter establishes,
even without yet knowing the specific unit-file mechanics systemd1-2
and systemd1-3 will cover.

WHY THIS WORKS AS AN ANSWER
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This answers using only the material this specific chapter has
actually established (PID 1's supervisory role) rather than reaching
ahead into unit files or systemctl syntax not yet covered, directly
connecting the ws1 command back to systemd's own PID-1 identity and
process-lifecycle responsibility.