Some common issues if scans doesn’t return any results:
- You don’t have nmap installed or not available within your PATH
- The targets are not answering to an ICMP Echo Request -> Check the Alive Test setting of your Target definition and try some of the other available methods (Further reading: https://docs.greenbone.net/GSM-Manual/gos-4/en/vulnerabilitymanagement.html#creating-a-target).
- SELinux is enabled and blocking the scanner from doing its job.
- You’re using a custom scan configuration which doesn’t include the nmap (NASL wrapper) and Ping Host NVTs from the Port scanners family (Further reading: Hint: Self-created scan configs (copy of “empty” scan config) showing no results).
The mentioned Ping Host plugin allows to configure a Report about unrechable Hosts to yes so you will get at least some notes if a remote host is considered as dead / not reachable. In that case you will get no results.