How can I keep my server running when I power down the computer where I have set up the ssh session

I have never set up a server before but since Parse announced that they are closing down I thought I might give it a shot. I have followed along with this tutorial and have managed to migrate my Parse database across to digital ocean.

When I call npm run start everything works fine. I can query for data and create new objects all from my iOS app. But there is just one problem. How do I keep the server up and running even when the computer where the ssh session started has been powered down?

When I call npm run start this is what gets logged in terminal:

> parse-server-example@1.0.0 start /var/www/parse
> node index.js

[TypeError: Cannot read property 'Kerberos' of undefined]
DATABASE_URI not specified, falling back to localhost.
parse-server-example running on port 1337.

I know that this is probably a noob question and yes my knowledge is quite limited, so if you could help me then that would be great!

Thanks for your time!