JN0-106 Junos OS Fundamentals Practice Question
A technician notices that the /var partition on a Junos device is 95% full. Which action will immediately free up disk space without affecting device operation?
⚠ Common exam trap
Test-takers frequently think rebooting (Option B) clears all temporary files and logs, but Junos does not automatically delete persistent log files on reboot; only volatile /tmp is cleared, so /var remains full.
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
✓
Clear log files using 'clear log messages'
The 'clear log messages' command immediately removes the contents of the active log files (e.g., messages, interactive-commands) without requiring a reboot or affecting running processes. This directly frees up space in /var/log, which is a primary consumer of the /var partition, while leaving the directory structure intact so logging continues normally.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Delete unused software packages using 'request system software delete'
Why it's wrong here
Deleting software packages with 'request system software delete' can free space under /var, but it is not a fast or immediate remedy: you must first remove the package, then commit the change, and in many cases reboot for the cleanup to fully take effect. During the commit/reboot window, the partition may remain critically full, and the process can introduce operational downtime that is disproportionate to the goal of freeing space.
- ✗
Reboot the device
Why it's wrong here
Rebooting the device merely restarts the Junos OS and its processes; it does not remove or compress any files residing in /var, such as log files, core dumps, or temporary files. In fact, a reboot can add new log messages and potentially generate additional core dumps, worsening the space issue rather than resolving it. It also causes a service outage, which is an unacceptable side effect when only filesystem space is the concern.
- ✗
Remove the /var/log directory
Why it's wrong here
Removing the /var/log directory is dangerous and ineffective: /var/log is a live system directory actively used by the logging daemon, and deleting it will immediately break log rotation, audit, and troubleshooting capabilities. The directory may be recreated on reboot, but all historical logs would be lost, and active processes holding file handles could behave unpredictably. This action compromises operational visibility and risks system instability, making it far worse than the original problem.
- ✓
Clear log files using 'clear log messages'
Why this is correct
Using 'clear log messages' is the correct immediate action because it truncates the active log files under /var/log (specifically /var/log/messages) and instantly releases all allocated blocks to the filesystem, freeing space in /var without requiring a reboot or commit. The syslog daemon continues writing to the file, which is recreated/truncated gracefully, so no logging interruption or packet loss occurs. This targeted approach addresses the symptom—a full /var partition—while preserving all other system files and services.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks 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 JN0-106 exam.