I have newly installed greenbone 20.08 on my ubuntu 20.04 system.
I installed greenbone using the link- https://launchpad.net/~mrazavi/+archive/ubuntu/gvm.
All steps works fine but the last command sudo -E -u gvm -g gvm gvmd --rebuild when I run I get an error as “A feed sync is already running ,failed to rebuild nvt cache” .
If you have completed syncing all of the data feeds, it can still take some time for gvmd to ingest all of that data. Let it sit for a while. It sounds like you have everything else. The easiest way to know it’s done is when you see you have the basic scan configs listed. You can also see when it finishes in the gvmd log file as well.