If you have the problem that starting a server (e.g. tomcat/8080) leads to an error because the port is already blocked. You can use this call:

sudo lsof -i -P -n | grep LISTEN

This will result into something like following output:

apache2   3085        www-data    4u  IPv6  42617      0t0  TCP *:80 (LISTEN)
apache2   3086        www-data    4u  IPv6  42617      0t0  TCP *:80 (LISTEN)
docker-pr 3805            root    4u  IPv6  47126      0t0  TCP *:5000 (LISTEN)
docker-pr 3822            root    4u  IPv6  43660      0t0  TCP *:8088 (LISTEN)
docker-pr 3887            root    4u  IPv6  41565      0t0  TCP *:8443 (LISTEN)
docker-pr 3899            root    4u  IPv6  48297      0t0  TCP *:8080 (LISTEN)
dnsmasq   4180 libvirt-dnsmasq    6u  IPv4  48409      0t0  TCP (LISTEN)

And I see, in this case docker some docker process is blocking port 8080.

For the example of docker, you could see what containers are running on what port:

sudo docker ps
CONTAINER ID        IMAGE                         COMMAND                  CREATED             STATUS                    PORTS                                            NAMES
09b4d248ce0e        fawserver:latest              "/entrypoint.sh"         6 days ago          Up 3 hours      >8080/tcp,>8443/tcp   fawserver```

Here we go, my docker-version of the server is still running.

sudo docker stop fawserver

And the port is available again :+1: