How to show listening TCP sockets with ss

Checking listening TCP sockets with ss confirms whether a service is actually bound to the expected port before firewall rules, reverse proxies, or application logs become the focus. It is a fast first check when a daemon should be accepting connections but clients still fail to connect.

The ss utility reads socket state from the kernel and, with -ltnp, limits the output to listening TCP sockets, prints numeric addresses and ports, and shows the owning process when the kernel allows it. The result is a short table that highlights which local address and port each listener is bound to.

Wildcard listeners such as 0.0.0.0:80 or [::]:443 accept connections on all matching local interfaces, while loopback listeners such as 127.0.0.1:5432 stay local to the host. Process details from -p are permission-sensitive, so a regular user may see the socket but not the owning program until the command is re-run with sudo.

1. Open a terminal application.
2. Run the listening TCP socket query.

   $ ss -ltnp
   State  Recv-Q Send-Q Local Address:Port Peer Address:PortProcess
   LISTEN 0      5            0.0.0.0:8080      0.0.0.0:*    users:(("python3",pid=3080,fd=3))

   The -l, -t, -n, and -p flags limit the output to listening TCP sockets, keep addresses numeric, and request process details.

3. Read the Local Address:Port column to confirm where the service is bound.

   Entries such as 0.0.0.0:8080 listen on all local IPv4 interfaces, while 127.0.0.1:8080 accepts connections only from the local host.

4. Re-run the query with sudo when the Process column is blank and ownership matters.

   $ ss -ltnp
   State  Recv-Q Send-Q Local Address:Port Peer Address:PortProcess
   LISTEN 0      5            0.0.0.0:8080      0.0.0.0:*
   
   $ sudo ss -ltnp
   State  Recv-Q Send-Q Local Address:Port Peer Address:PortProcess
   LISTEN 0      5            0.0.0.0:8080      0.0.0.0:*    users:(("python3",pid=3080,fd=3))

   Without elevated privileges, ss -p usually shows process details only for sockets owned by the current user.