This LFCS practice question tests your understanding of service configuration. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 company runs a monitoring agent service (monitor.service) that must start after the network is fully up and the DNS resolver is ready. The service currently has the following dependencies in its unit file:
The service starts, but often fails to resolve hostnames because DNS is not yet available. Which change should be made to the unit file to ensure the service only starts after DNS is ready?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a dependency: After=nss-lookup.target
Option B is correct because `nss-lookup.target` is a synchronization point that indicates the hostname resolution subsystem (including DNS) is fully operational. By adding `After=nss-lookup.target`, the monitor service will not start until DNS resolution is available, solving the hostname resolution failures. The existing `Wants=network.target` is insufficient because `network.target` only signals that basic network interfaces are configured, not that DNS services are ready.
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.
✗
Replace After=network.target with After=network-online.target and add Requires=network-online.target
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse `network-online.target` with DNS readiness, assuming network connectivity automatically implies DNS resolution is available, but DNS is a separate service that may not be synchronized with network interface activation.
Detailed technical explanation
How to think about this question
`nss-lookup.target` is a systemd target that is pulled in by services like `systemd-resolved` or `nscd` when they are ready to serve hostname lookups. It is part of the systemd boot sequence and is typically reached after the network is online and the local resolver is initialized. In real-world scenarios, a monitoring agent that performs DNS queries on startup will fail if the resolver is not yet available, even if the network interface is up; using `nss-lookup.target` ensures the service waits for the Name Service Switch (NSS) subsystem, which includes DNS, mDNS, and other resolution backends.
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.
Service Configuration — This question tests Service Configuration — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add a dependency: After=nss-lookup.target — Option B is correct because `nss-lookup.target` is a synchronization point that indicates the hostname resolution subsystem (including DNS) is fully operational. By adding `After=nss-lookup.target`, the monitor service will not start until DNS resolution is available, solving the hostname resolution failures. The existing `Wants=network.target` is insufficient because `network.target` only signals that basic network interfaces are configured, not that DNS services are ready.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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