You shouldn't need to start and enable NodeBB every time you reboot the server, once you've enable'd it once, it should come up again every time you reboot.
How to disable dailydigest?
I don't want send dailydigest to users.
Users can opt-out of the daily digest by changing the option in their user profile settings.
We changed the behaviour to be opt-in instead of out-out, as people did not wish to receive emails every day If your NodeBB does not do this, then consider upgrading.