JN0-106 Junos OS Fundamentals Practice Question
Exhibit
Refer to the exhibit. From the output of 'show system storage': Filesystem Size Used Avail Use% Mounted on /dev/da0s1a 1.9G 1.2G 600M 66% / devfs 1.0K 1.0K 0B 100% /dev /dev/md0 1.5G 1.4G 42M 97% /var /dev/da0s1e 190M 34M 142M 19% /config
Refer to the exhibit. Which filesystem should the administrator investigate to free up disk space?
⚠ Common exam trap
A common mix-up: candidates assume the root filesystem (/) is the primary space consumer, but Junos intentionally segregates dynamic data into /var, making it the correct target for disk space recovery.
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
✓
/var
The /var filesystem on Junos devices stores system logs, core dumps, and temporary files. When disk space is low, /var is the most common culprit because it contains rotating log files (e.g., messages, interactive-commands) and crash data that can accumulate rapidly. The administrator should investigate /var to free up space by clearing old logs or core files.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
/config
Why it's wrong here
/config is a dedicated partition that stores committed configuration files, not high-churn operational data. At only 19% utilization, it has ample free space and no risk of filling under normal operation, so it cannot be the filesystem closest to full. Its usage grows only when configurations are edited, not from logs or transient files, making it an improbable candidate for administrative concern.
- ✗
/ (root)
Why it's wrong here
The root partition (/) holds the base operating system, installed packages, and core system directories. At 66% usage, it still has roughly one-third of its capacity free, which is not considered critically full. While a full root filesystem would be serious, 66% indicates comfortable headroom, and root is not the partition typically at risk of imminent exhaustion in a Junos device.
- ✗
/dev
Why it's wrong here
/dev is a devfs, a pseudo-filesystem that lives in memory and represents device nodes, not physical disk storage. Its 100% usage is normal and expected because the kernel dynamically allocates entries as devices are probed and the size is not constrained by disk capacity. Therefore, a full /dev does not indicate a real storage problem, and it is not a candidate for replacement or cleanup like a disk-backed filesystem.
- ✓
/var
Why this is correct
/var is the correct answer because it is a disk-backed partition that contains high-write operational data including system logs, temporary files, and core dumps, which accumulate over time. At 97% utilization, it is almost full and poses an imminent risk: if it fills, logging and certain system services may fail, and the device may become unstable. This near-capacity state makes /var the filesystem that should immediately concern an administrator.
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JA
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.