If the game is ever stopped, you’ll need to start it.
If the game is already running and you want to restart it:
Your game should also automatically restart when the server is rebooted. If that doesn’t happen for some reason, see Auto-Restart After Server Reboot.
Both the game and portal can be started in Debug Mode. This is good for temporary debugging, but the game only stays running as long as you’re logged in. It’s not a permanent solution.