This LFCS practice question tests your understanding of service configuration. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
An administrator configures a systemd service with Restart=on-failure and RestartSec=10. What happens if the service exits with a non-zero exit code?
It restarts immediately
Why wrong: RestartSec introduces a delay.
It retries infinitely regardless of exit code
Why wrong: on-failure only triggers on failure, not success.
It does not restart
Why wrong: on-failure restarts on exit code != 0.
It waits 10 seconds before restarting
RestartSec defines the delay between restart attempts.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
It waits 10 seconds before restarting
Option D is correct because when Restart=on-failure is set, systemd only restarts the service if it exits with a non-zero exit code or is terminated by a signal (excluding SIGHUP, SIGINT, SIGTERM, and SIGPIPE). The RestartSec=10 directive then introduces a 10-second delay before the restart attempt, preventing rapid restart loops and giving the system time to stabilize.
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.
It restarts immediately
Why it's wrong here
RestartSec introduces a delay.
It retries infinitely regardless of exit code
Why it's wrong here
on-failure only triggers on failure, not success.
It does not restart
Why it's wrong here
on-failure restarts on exit code != 0.
It waits 10 seconds before restarting
Why this is correct
RestartSec defines the delay between restart attempts.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse Restart=on-failure with Restart=always, assuming any exit triggers a restart, or they forget that RestartSec applies even when Restart=on-failure is set, leading them to choose 'immediately' (Option A).
Detailed technical explanation
Under the hood, systemd tracks the service's main PID exit status via waitid() and compares it against the Restart= policy. The RestartSec= timer is implemented using the event loop's timerfd, ensuring precise delays even under load. A real-world scenario: if a database service crashes with a segfault (non-zero exit), RestartSec=10 prevents immediate restart, allowing the kernel to release resources and avoiding a thundering herd problem if multiple dependent services also restart.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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: It waits 10 seconds before restarting — Option D is correct because when Restart=on-failure is set, systemd only restarts the service if it exits with a non-zero exit code or is terminated by a signal (excluding SIGHUP, SIGINT, SIGTERM, and SIGPIPE). The RestartSec=10 directive then introduces a 10-second delay before the restart attempt, preventing rapid restart loops and giving the system time to stabilize.
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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