Under systemd Restart=always, the old gateway becomes a zombie (in the
process table, awaiting reap) when the replacement starts. _pid_exists()
reported the zombie as alive, so --replace waited on a PID that never
dies, then aborted with exit 1 — a silent crash loop. Standalone runs are
unaffected because nothing respawns the gateway into a zombie.
The live path is psutil.pid_exists(), which returns True for zombies, so
the check is added there (Process.status() == STATUS_ZOMBIE -> dead). The
psutil-less POSIX fallback also reads /proc/<pid>/stat (state Z) with a ps
state= fallback for macOS/BSD, before the os.kill(pid, 0) liveness probe.
Diagnosis and the /proc + ps POSIX fallback by MorAlekss (PR #44898);
extended to cover the psutil hot path so the fix applies on normal installs.
Co-authored-by: MorAlekss <mor.aleksandr@yahoo.com>
MorAlekss
acca526286