LFCS Operation of Running Systems Practice Question
A developer reports that a custom daemon fails to start after a reboot. The daemon's unit file is located in /etc/systemd/system/custom.service. Which of the following is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The service is not enabled.
The most likely cause is that the service is not enabled (systemctl enable). Even though the unit file exists in /etc/systemd/system, systemd only starts services automatically at boot if they are enabled. Option B is correct. Option A is incorrect because manually starting the service after installation would work but does not affect boot behavior. Option C is unlikely because SELinux policy blocks would produce a different error (e.g., denial messages). Option D is incorrect because firewall rules do not prevent systemd from starting a service; they affect network connectivity.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The service was not started manually after installation.
Why it's wrong here
A unit file placed in /etc/systemd/system is not enabled automatically, so systemd never starts it at boot; the missing step is systemctl enable. Manual start is irrelevant after reboot. This option tempts because services do need starting once, but persistence across reboots requires the enable symlink.
- ✓
The service is not enabled.
Why this is correct
An enabled unit creates the symlink under the target's `.wants` directory, which is what triggers the start at boot; a unit merely present in `/etc/systemd/system` is loaded but never pulled in. Since the daemon runs fine manually, only the missing enablement explains the reboot-specific failure.
- ✗
The SELinux policy blocks the service.
Why it's wrong here
SELinux denials typically log AVC messages and usually surface only when a service is manually started, not specifically after reboot; a unit in /etc/systemd/system that fails only post-reboot points to missing enablement or dependency ordering. SELinux confinement is the right focus when a daemon starts manually but is denied under enforcing mode.
- ✗
A firewall rule is blocking inbound connections.
Why it's wrong here
A firewall blocking inbound connections prevents clients reaching the daemon, not systemd launching the process at boot. It is tempting because unreachable services appear down, but the stem describes the daemon itself failing to start, which points to unit configuration rather than network filtering.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the LFCS exam.