Commit Check: Syntax Verification and Failure Due to Concurrent Changes
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?
Quick Answer
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.
⚠ Common exam trap
Many candidates 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.
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
✓
The other engineer committed their changes between the commit check and the commit.
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.
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.
- ✗
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.
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Same concept, more angles
1 more way this is tested on JN0-106
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.
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.