unifi does not shut down properly when stopped via systemd (it always exits with
SIGTERM exit status) because systemd wants stop commands to not exit before the
main command is gone and unifi does not comply. the easiest way around this is
to have systemd send an ignored signal after the stop command has exited.
unifi may still throw exceptions during shutdown, but it *does* exit cleanly as
far as systemd is concerned now.
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