enabled versus active

Two independent states, printed on two different lines of systemctl status nginx. Loaded: loaded (/usr/lib/systemd/system/nginx.service; enabled; preset: enabled) says what happens the next time the machine boots; Active: active (running) since … says what is happening now. Neither implies the other. systemctl start nginx sets the second and leaves the first alone, which is why a service installed, started and forgotten disappears three weeks later when the machine reboots for a kernel update. Nothing failed — it was never enabled. Being enabled is a symlink under /etc/systemd/system/multi-user.target.wants/ and nothing else, so enable on its own leaves a service enabled and stopped. systemctl enable --now nginx does both, and systemctl is-enabled nginx answering disabled is the whole diagnosis.