This LFCS practice question tests your understanding of operation of running systems. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A service is using a port that conflicts with another application. Which command can be used to identify which process is listening on a specific TCP port?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
ss -tulpn | grep :port
Why wrong: Valid but not the only one.
All of the above
All listed commands can show listening processes.
lsof -i :port
Why wrong: Valid but not the only one.
netstat -tulpn | grep :port
Why wrong: Valid but not the only one.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
All of the above
Option B is correct because all three commands—ss, lsof, and netstat—can be used to identify which process is listening on a specific TCP port. The ss command is the modern replacement for netstat and uses kernel netlink to display socket information, while lsof lists open files including network sockets, and netstat reads /proc/net files. Each command with the appropriate flags (ss -tulpn, lsof -i :port, netstat -tulpn) will show the PID and process name associated with a listening port, making 'All of the above' the accurate answer.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
ss -tulpn | grep :port
Why it's wrong here
Valid but not the only one.
All of the above
Why this is correct
All listed commands can show listening processes.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
lsof -i :port
Why it's wrong here
Valid but not the only one.
netstat -tulpn | grep :port
Why it's wrong here
Valid but not the only one.
Common exam traps
The trap here is that candidates often assume only one command (like netstat or ss) is correct, but the LFCS exam expects you to recognize that multiple tools can achieve the same result, and 'All of the above' is the comprehensive answer when all options are technically valid.
Detailed technical explanation
Under the hood, ss uses the netlink interface to query socket information directly from the kernel, making it faster and more efficient than netstat, which parses /proc/net/tcp and /proc/net/udp files. The -tulpn flags filter for TCP (-t) and UDP (-u) listening sockets (-l), show numeric addresses (-n), and include the process identifier (-p). In real-world scenarios, when a service fails to start due to a port conflict, running any of these commands with grep for the specific port quickly reveals the conflicting PID, allowing you to kill or reconfigure the process.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the LFCS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Operation of Running Systems — This question tests Operation of Running Systems — Read the scenario before looking for a memorised answer..
The correct answer is: All of the above — Option B is correct because all three commands—ss, lsof, and netstat—can be used to identify which process is listening on a specific TCP port. The ss command is the modern replacement for netstat and uses kernel netlink to display socket information, while lsof lists open files including network sockets, and netstat reads /proc/net files. Each command with the appropriate flags (ss -tulpn, lsof -i :port, netstat -tulpn) will show the PID and process name associated with a listening port, making 'All of the above' the accurate answer.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.
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