The answer is the /var filesystem. This is the correct choice because /var is the partition on Junos devices that stores dynamic system data, including rotating log files like messages and interactive-commands, as well as core dumps and temporary files that can rapidly consume disk space. When investigating Junos disk space issues, /var is the most common culprit for low space alerts, as these logs and crash data accumulate over time without manual cleanup. On the JNCIA-Junos exam, this question tests your understanding of Junos filesystem roles and common troubleshooting scenarios—a frequent trap is confusing /var with /config or /tmp, but remember that /config holds configuration files and is rarely the source of bloat. A useful memory tip: think of /var as the “variable” space where everything changes and grows, so when disk space is tight, always check /var first.
JNCIA-JUNOS Junos OS Fundamentals Practice Question
This JNCIA-JUNOS practice question tests your understanding of junos os fundamentals. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 only 19% used.
✗
/ (root)
Why it's wrong here
Root is at 66% usage, which is not critically full.
✗
/dev
Why it's wrong here
/dev is a virtual filesystem at 100% but it is a devfs; it does not represent physical disk space.
✓
/var
Why this is correct
/var is at 97% usage, closest to capacity.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Junos uses a separate /var partition to isolate volatile data from the core OS, preventing log floods from crashing the system. The 'show system storage' command reveals usage per mount point, and 'file list /var/log' helps identify large log files. In real-world scenarios, a misconfigured syslog server or a repeated crash can fill /var, causing the device to drop logs or fail to generate core dumps.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the JNCIA-JUNOS exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Junos OS Fundamentals — This question tests Junos OS Fundamentals — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: /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.
What should I do if I get this JNCIA-JUNOS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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