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 wants to run a script daily at 2 AM. They create a timer unit and a service unit. The service unit uses Type=oneshot. Which of the following timer configurations is correct?
OnUnitActiveSec=24h
Why wrong: OnUnitActiveSec triggers after the service last started, not at a fixed time.
OnBootSec=1d
Why wrong: OnBootSec triggers a fixed time after boot, not at a specific clock time.
OnActiveSec=24h
Why wrong: OnActiveSec triggers after activation of the timer, not at a specific time.
OnCalendar=*-*-* 02:00:00
This sets a calendar event to run daily at 2:00 AM.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
OnCalendar=*-*-* 02:00:00
Option D is correct because `OnCalendar=*-*-* 02:00:00` specifies an absolute calendar event that triggers the timer at 2:00 AM every day, regardless of when the system booted or when the service last ran. This matches the requirement to run a script daily at a fixed time, and it works correctly with a `Type=oneshot` service unit.
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.
OnUnitActiveSec=24h
Why it's wrong here
OnUnitActiveSec triggers after the service last started, not at a fixed time.
OnBootSec=1d
Why it's wrong here
OnBootSec triggers a fixed time after boot, not at a specific clock time.
OnActiveSec=24h
Why it's wrong here
OnActiveSec triggers after activation of the timer, not at a specific time.
OnCalendar=*-*-* 02:00:00
Why this is correct
This sets a calendar event to run daily at 2:00 AM.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates confuse `OnUnitActiveSec` (relative to last activation) with a fixed daily schedule, or they invent non-existent directives like `OnActiveSec`, while overlooking the correct `OnCalendar=` syntax for absolute time triggers.
Detailed technical explanation
In systemd, timer units use `OnCalendar=` for absolute, calendar-based scheduling, which is evaluated using the `systemd.time(7)` calendar event format. The expression `*-*-* 02:00:00` means any year, any month, any day at 02:00:00, effectively creating a daily trigger. For `Type=oneshot` services, the timer ensures the service runs exactly at the specified calendar time, and if the system is off at that moment, systemd can use `Persistent=true` to catch up missed runs.
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: OnCalendar=*-*-* 02:00:00 — Option D is correct because `OnCalendar=*-*-* 02:00:00` specifies an absolute calendar event that triggers the timer at 2:00 AM every day, regardless of when the system booted or when the service last ran. This matches the requirement to run a script daily at a fixed time, and it works correctly with a `Type=oneshot` service unit.
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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