[GER] How do I install the Forum via Linux?

and dis

Port 80 appears to already be in use.

This will show you what command is using port 80
./discourse-setup: line 283: lsof: command not found

If you are trying to run Discourse simultaneously with another web
server like Apache or nginx, you will need to bind to a different port

See Run other websites on the same machine as Discourse

If you are reconfiguring an already-configured Discourse, use

./launcher stop app

to stop Discourse before you reconfigure it and try again.