Novnc server ubuntu 18

I have an error installing opennebula in Ubuntu 18.0, please if somebody can help me withh this topic, send me some recomendations about it
Failed to start opennebula novnc server

Maybe, you should follow this link to install OpenNebula FrontEnd:

And then install the node:

Make sure to install every package.

I did it on a Virtual Machine running in VirtualBox and it was successful. I also tried on a physical computer and it was fine too.

The only issue I found was about repository.

error2

of course this page was my guide, but I have an error when I put the command systemctl start opennebula. Please If you can help me.