Trying to find what process is using a certain port

If you run into the situation where you quickly want to know which process is using a certain (TCP) port, use the following command:

pi@server:~ $ sudo ss -lptn 'sport = :443'
State      Recv-Q Send-Q        Local Address:Port          Peer Address:Port 
LISTEN     0      128                       *:443                      *:*      users:(("nginx",pid=29909,fd=8),("nginx",pid=29908,fd=8),("nginx",pid=29907,fd=8),("nginx",pid=29906,fd=8),("nginx",pid=29905,fd=8))
LISTEN     0      128                      :::443                     :::*      users:(("nginx",pid=29909,fd=9),("nginx",pid=29908,fd=9),("nginx",pid=29907,fd=9),("nginx",pid=29906,fd=9),("nginx",pid=29905,fd=9))