I installed octoprint today, the newest stable version at the Raspberry PI 3B+.
If I lease the terminal Octoprint goes offfline.
How I can start the octoprint server at the startup of my Raspberry PI?
Did you install OctoPrint vi OctoPi? Then the OctoPrint server should start every time you power up your RasPi.
What exactly do you do when you leave the terminal?
I closed the terminal cause I didn't knew an other way.
I flashed a micro SD with raspian and made a basic install of octoprint.
OctoPrint is meant to be used via the web frontend.
Anyhow, when the OctoPrint server is running, leaving the terminal should not close the server, except you started the server program itself file from that terminal window.