The answer is that the commit failed because another user’s pending commit was applied between the commit check and the commit. This error occurs because Junos uses a transaction-based configuration system where the candidate configuration is a separate copy of the active configuration. When you run commit check, it validates syntax against the current active configuration at that moment, but it does not lock the database. If another user’s commit is applied in the brief interval afterward, the configuration database version changes, and your commit fails with the “configuration database modified by another user” message. On the JNCIA-Junos exam, this scenario tests your understanding of commit check verification and failure scenarios, specifically how concurrent changes can invalidate a successful syntax check. A common trap is assuming commit check guarantees a successful commit, but it only verifies syntax, not database consistency. Memory tip: think of commit check as a “syntax snapshot”—it’s valid only for the exact moment you take it.
JNCIA-JUNOS User Interfaces Practice Question
This JNCIA-JUNOS practice question tests your understanding of user interfaces. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
A network engineer is configuring a Juniper device in a production network. They have applied several changes to the candidate configuration and run 'commit check', which passes. After a brief pause, they run 'commit' but receive the error: 'commit failed: configuration database modified by another user. Please reload the configuration and try again.' The engineer is the only person currently logged into the device, but they know that another engineer was working on the same device earlier and may have left a commit pending. What is the most likely reason for the commit failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The other engineer committed their changes between the commit check and the commit.
Option A is correct because the error message 'configuration database modified by another user' indicates that another user (the earlier engineer) had a pending commit that was not yet applied or discarded. When the current engineer ran 'commit check', it validated the candidate configuration against the current active configuration, but between that check and the actual 'commit', the other engineer's pending commit was applied (or their session was closed, causing their changes to be committed automatically if they had left a commit pending). This changed the configuration database, causing the commit to fail due to a version mismatch.
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.
✓
The other engineer committed their changes between the commit check and the commit.
Why this is correct
This is the most likely cause of the 'configuration database modified by another user' error.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The commit check did not validate the syntax of the new changes.
Why it's wrong here
Commit check validates syntax and passed; this is not the cause.
✗
The candidate configuration has timed out and must be re-entered.
Why it's wrong here
Timeout would result in a different error or require reloading the candidate, but not this specific message.
✗
The device has insufficient storage to write the new configuration.
Why it's wrong here
Insufficient storage would produce a 'no space' error, not a database modification error.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume 'commit check' passes guarantee a successful commit, but they overlook that the configuration database can be modified by another user between the check and the commit, leading to a commit failure even when no other user is currently logged in.
Detailed technical explanation
How to think about this question
Junos uses a two-phase commit model: 'commit check' validates the candidate configuration against the current active configuration, but does not lock the database. If another user commits changes between the check and the commit, the candidate configuration becomes stale (its base revision no longer matches the active configuration). The 'commit' command then fails to prevent conflicting changes from being applied. This is similar to an optimistic concurrency control mechanism, where the commit succeeds only if the candidate configuration was derived from the current active configuration.
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.
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The other engineer committed their changes between the commit check and the commit. — Option A is correct because the error message 'configuration database modified by another user' indicates that another user (the earlier engineer) had a pending commit that was not yet applied or discarded. When the current engineer ran 'commit check', it validated the candidate configuration against the current active configuration, but between that check and the actual 'commit', the other engineer's pending commit was applied (or their session was closed, causing their changes to be committed automatically if they had left a commit pending). This changed the configuration database, causing the commit to fail due to a version mismatch.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An engineer is configuring a firewall filter and wants to verify the syntax of the configuration before committing. Which command should be used?
medium
A.validate
✓ B.commit check
C.show | display inheritance
D.commit confirmed
Why B: The 'commit check' command validates the syntax and configuration semantics of the candidate configuration without activating it. This allows the engineer to verify that the firewall filter configuration is correct before committing, preventing potential service disruption from a faulty commit.
Last reviewed: Jun 24, 2026
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This JNCIA-JUNOS 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 JNCIA-JUNOS exam.
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