The answer is that another process is already using port 8080. This is correct because the journalctl output for a service failure will log a bind error with the specific errno EADDRINUSE, which translates directly to “Address already in use.” When a service attempts to start and bind to a port that is already occupied, the kernel rejects the request, and systemd captures this failure in the journal. On the Linux Foundation Certified System Administrator LFCS exam, this scenario tests your ability to read journalctl logs and map common errno values to real-world problems—a core troubleshooting skill for managing systemd services. A common trap is assuming the service itself is misconfigured, but the key clue is the explicit “Address already in use” message. Memory tip: think of EADDRINUSE as “E-A-DDR-IN-USE” — if you see that, a port is occupied, so run `ss -tuln | grep 8080` to find the culprit.
LFCS Operation of Running Systems Practice Question
This LFCS practice question tests your understanding of operation of running systems. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Exhibit
Refer to the exhibit.
$ sudo journalctl -u myapp.service --since "1 hour ago"
-- Logs begin at Mon 2025-03-10 08:30:15 UTC, end at Mon 2025-03-10 12:45:22 UTC. --
Mar 10 11:30:17 server1 myapp[1234]: Starting application...
Mar 10 11:30:18 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:18 server1 myapp[1234]: [INFO] Retrying in 5 seconds...
Mar 10 11:30:23 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:23 server1 myapp[1234]: [INFO] Retrying in 10 seconds...
Mar 10 11:30:33 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:33 server1 myapp[1234]: [FATAL] Exiting after repeated failures
Mar 10 11:30:33 server1 systemd[1]: myapp.service: main process exited, code=exited, status=1/FAILURE
Mar 10 11:30:33 server1 systemd[1]: myapp.service: Unit entered failed state.
Based on the journalctl output, what is the most likely cause of the service failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Refer to the exhibit.
$ sudo journalctl -u myapp.service --since "1 hour ago"
-- Logs begin at Mon 2025-03-10 08:30:15 UTC, end at Mon 2025-03-10 12:45:22 UTC. --
Mar 10 11:30:17 server1 myapp[1234]: Starting application...
Mar 10 11:30:18 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:18 server1 myapp[1234]: [INFO] Retrying in 5 seconds...
Mar 10 11:30:23 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:23 server1 myapp[1234]: [INFO] Retrying in 10 seconds...
Mar 10 11:30:33 server1 myapp[1234]: [ERROR] Failed to bind to port 8080: Address already in use
Mar 10 11:30:33 server1 myapp[1234]: [FATAL] Exiting after repeated failures
Mar 10 11:30:33 server1 systemd[1]: myapp.service: main process exited, code=exited, status=1/FAILURE
Mar 10 11:30:33 server1 systemd[1]: myapp.service: Unit entered failed state.
A
Another process is already using port 8080.
The repeated 'Address already in use' errors clearly indicate a port conflict.
B
The service configuration file has a syntax error.
Why wrong: The log shows the service starting and then failing on bind, not a config parse error.
C
The system is out of memory.
Why wrong: There are no out-of-memory messages; the service fails due to port conflict.
D
The service is trying to write to a read-only filesystem.
Why wrong: No logs indicate filesystem issues; the error is specifically about port binding.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Another process is already using port 8080.
The journalctl output shows a bind error on port 8080 with 'Address already in use'. This indicates that another process is already listening on that port, preventing the service from starting. In systemd, such a failure is logged with the specific errno EADDRINUSE, which directly points to a port conflict.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Another process is already using port 8080.
Why this is correct
The repeated 'Address already in use' errors clearly indicate a port conflict.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The service configuration file has a syntax error.
Why it's wrong here
The log shows the service starting and then failing on bind, not a config parse error.
✗
The system is out of memory.
Why it's wrong here
There are no out-of-memory messages; the service fails due to port conflict.
✗
The service is trying to write to a read-only filesystem.
Why it's wrong here
No logs indicate filesystem issues; the error is specifically about port binding.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may confuse a bind error with a configuration syntax error, but the specific 'Address already in use' message uniquely identifies a port conflict, not a parsing issue.
Trap categories for this question
Command / output trap
The log shows the service starting and then failing on bind, not a config parse error.
Detailed technical explanation
How to think about this question
When a service binds to a TCP port, the kernel's socket layer checks the port's state in the TCP control block. If the port is already in the TIME_WAIT or ESTABLISHED state for the same address/port tuple, bind() returns EADDRINUSE. The SO_REUSEADDR socket option can allow binding to a port in TIME_WAIT, but not if another process is actively listening. In production, this often occurs after a service restart without proper cleanup or when a monitoring tool inadvertently occupies the same port.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Operation of Running Systems — This question tests Operation of Running Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Another process is already using port 8080. — The journalctl output shows a bind error on port 8080 with 'Address already in use'. This indicates that another process is already listening on that port, preventing the service from starting. In systemd, such a failure is logged with the specific errno EADDRINUSE, which directly points to a port conflict.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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