XK0-006 Troubleshooting Practice Question
A Linux administrator is troubleshooting a service that fails to start. They want to view the most recent log entries for that service using systemd's journal. Which command should they use?
⚠ Common exam trap
It's easy for candidates to confuse systemctl status, which gives a summary, with journalctl -u, which provides the full log history for the service.
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
✓
journalctl -u servicename
The journalctl -u command filters the systemd journal by unit, providing all log messages for that service. This is the correct tool to diagnose why a service fails to start, as it captures the service's standard output, error messages, and systemd's own messages about the unit.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
dmesg | grep servicename
Why it's wrong here
dmesg displays kernel ring buffer messages, which are related to hardware and kernel events, not user-space service logs. It will not contain systemd service output. Grepping for the service name is unlikely to yield relevant information about why the service failed to start.
- ✗
systemctl status servicename
Why it's wrong here
systemctl status shows the current state of the service and a few recent log lines, but it is not a full log viewer. While it can indicate failure, it does not provide the complete journal history for the service. For detailed troubleshooting, journalctl -u is more comprehensive.
- ✓
journalctl -u servicename
Why this is correct
journalctl -u filters the journal by the specified systemd unit, showing all log entries for that service. This is the most direct way to see why the service failed. It includes messages from the service's startup, errors, and dependencies, making it ideal for troubleshooting a failed start.
- ✗
tail -f /var/log/messages
Why it's wrong here
/var/log/messages is a traditional syslog file and may not contain systemd service logs, especially on systems using journald exclusively. It also shows all system messages, not filtered by service. This command is not the correct way to view service-specific logs in systemd.
Go deeper
Related to this question
Learn chapter
Linux Fundamentals and History
Key term
Linux
Linux is an open-source operating system that manages computer hardware and software, widely used in servers, desktops, and embedded systems.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official CompTIA exam blueprint
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.