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A systems administrator troubleshoots a connectivity issue and needs to determine whether port 449 is open locally. Which of the following commands should the administrator use?
In Linux troubleshooting, identifying which ports are listening for connections is a foundational skill. According to CompTIA Linux+ V8, the ss (socket statistics) utility is the modern replacement for the older netstat command. It is used to dump socket statistics and provides information similar to netstat, but it is faster and can display more detailed TCP and state information.
To check if a specific port (like 449) is open locally, the administrator would run ss -an | grep 449.
-a: Displays both listening and non-listening (for established connections) sockets.
-n: Shows numerical port numbers instead of attempting to resolve them to service names (e.g., showing 443 instead of https).
| grep 449: Filters the output to show only lines containing the desired port number.
If the output shows a line with the state LISTEN on port *:449 or 127.0.0.1:449, the service is successfully running and bound to that port.
The other options are incorrect for the following reasons: ip link (Option A) is used to manage network interfaces (layer 2) and does not show port information (layer 4). dig (Option B) is a DNS lookup tool and cannot check port status. tracepath (Option C) is used to trace the network path to a host and detect MTU issues; it does not report on the state of specific local ports.
Therefore, ss is the verified tool for this troubleshooting task.