LPIC-1 Essential System Services and Networking Practice Question
A system administrator notices that the system time is slowly drifting from the actual time. The system uses chrony for NTP synchronization. The administrator runs 'chronyc sources' and sees no reachable sources. The firewall is enabled and configured. Which action should the administrator take to resolve the time synchronization issue?
⚠ Common exam trap
A common mix-up: candidates assume restarting the service (Option B) will fix connectivity issues, but the root cause is a firewall blocking UDP 123, which requires a firewall rule change, not a service restart.
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
✓
Add a firewall rule to allow UDP 123 outbound to NTP servers.
Chrony uses UDP port 123 for NTP communication. Since the firewall is enabled and configured, and 'chronyc sources' shows no reachable sources, the most likely cause is that outbound NTP traffic is being blocked. Adding a firewall rule to allow UDP 123 outbound to NTP servers will permit chrony to reach its NTP sources and synchronize the system clock, resolving the drift.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure chrony to use a different port for NTP.
Why it's wrong here
NTP uses UDP port 123 by default; changing the port is not standard and may not work with public servers.
- ✗
Restart chronyd service.
Why it's wrong here
Restarting without addressing the firewall will not make sources reachable.
- ✓
Add a firewall rule to allow UDP 123 outbound to NTP servers.
Why this is correct
Opening the correct port allows chrony to communicate with NTP sources.
- ✗
Use ntpdate to set the time manually once.
Why it's wrong here
ntpdate is a one-shot fix and does not maintain ongoing synchronization.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-1 practice question is part of Courseiva's free LPI 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 LPIC-1 exam.