This LFCS practice question tests your understanding of service configuration. 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.
A company runs a web application stack consisting of a frontend web server (web.service) and a backend application server (app.service). The app.service uses Restart=on-failure to automatically restart if it crashes. The administrator wants the web.service to automatically restart whenever app.service restarts, so that the frontend remains in sync with the backend. Which directive should be added to the web.service unit file's [Unit] section to achieve this?
BindsTo=app.service
Why wrong: Stops web.service if app.service stops, but does not restart.
PartOf=app.service
Propagates stop/restart from app.service to web.service.
Requires=app.service
Why wrong: Only ensures app.service is started, does not propagate restarts.
Wants=app.service
Why wrong: Weak dependency, no restart propagation.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
PartOf=app.service
Option B (PartOf=app.service) is correct because when app.service stops or restarts, PartOf causes systemd to stop or restart web.service as well, keeping the frontend in sync with the backend. Unlike BindsTo, PartOf does not create a strict dependency that would prevent app.service from starting independently, and it ensures the frontend follows the backend's state changes without requiring the backend to be fully operational for the frontend to start.
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.
BindsTo=app.service
Why it's wrong here
Stops web.service if app.service stops, but does not restart.
PartOf=app.service
Why this is correct
Propagates stop/restart from app.service to web.service.
Related concept
Read the scenario before looking for a memorised answer.
Requires=app.service
Why it's wrong here
Only ensures app.service is started, does not propagate restarts.
Wants=app.service
Why it's wrong here
Weak dependency, no restart propagation.
Common exam traps
The trap here is that candidates confuse PartOf with BindsTo, assuming the stronger dependency is always better, but PartOf is the correct choice because it only propagates restarts without creating a hard binding that would prevent independent startup or cause the frontend to be stopped if the backend fails.
Detailed technical explanation
Under the hood, PartOf= creates a one-way dependency where the target unit's state changes (stop/restart) are propagated to the dependent unit, but not vice versa; this is implemented via systemd's dependency graph and event propagation. A real-world scenario where this matters is in microservice architectures where a frontend must reconnect or reinitialize after a backend restart, but the frontend should not be prevented from starting if the backend is temporarily unavailable. PartOf is often used with BindsTo for stronger coupling, but here PartOf alone suffices because the requirement is only to restart on restart, not to enforce a strict binding.
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
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FAQ
Service Configuration — This question tests Service Configuration — Read the scenario before looking for a memorised answer..
The correct answer is: PartOf=app.service — Option B (PartOf=app.service) is correct because when app.service stops or restarts, PartOf causes systemd to stop or restart web.service as well, keeping the frontend in sync with the backend. Unlike BindsTo, PartOf does not create a strict dependency that would prevent app.service from starting independently, and it ensures the frontend follows the backend's state changes without requiring the backend to be fully operational for the frontend to start.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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