JN0-106 User Interfaces Practice Question
You are a network engineer responsible for a Juniper MX240 router in a data center. The router is running Junos 18.2R1 and you need to upgrade it to 19.1R2 to fix a critical security vulnerability. You establish an SSH session to the router and enter configuration mode to prepare the upgrade. While in configuration mode, you notice that the candidate configuration contains several uncommitted changes from a previous engineer that attempted to modify BGP settings but introduced a syntax error. The candidate configuration fails any commit operation due to this error. The currently active configuration is stable and the router is handling production traffic. The upgrade process requires you to change the boot media and specify the new image. Which action should you take to clear the candidate configuration and proceed with the upgrade?
⚠ Common exam trap
Watch out — candidates often think a reboot is needed to clear uncommitted changes (Option A) or that 'commit force' can bypass syntax errors (Option D), when in fact Junos provides a dedicated 'rollback' command to safely discard the candidate configuration without impacting the active state.
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
✓
Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands.
The 'rollback 0' command discards all uncommitted changes in the candidate configuration and replaces it with the active, committed configuration. This clears the syntax error without affecting the running router, allowing you to proceed with the upgrade commands (e.g., 'request system software add') without a reboot or forced commit.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Reboot the router to clear the candidate configuration and then start the upgrade.
Why it's wrong here
Rebooting an MX240 restarts the Junos OS but does not touch the candidate configuration, which resides in a separate database (juniper.conf) and persists across reboots. The upgrade process requires a valid configuration to commit; rebooting will simply load the active configuration while the problematic candidate remains staged, so the same syntax error will still block any subsequent commit or upgrade step.
- ✓
Execute the 'rollback 0' command to discard the candidate and replace it with the active configuration, then proceed with the upgrade commands.
Why this is correct
The 'rollback 0' command is the correct recovery action because it discards the entire candidate configuration and copies the last committed active configuration into the candidate, giving you a clean, syntactically valid starting point. This operation is local to the configuration database and does not affect the running system until you commit, so you can safely rollback, verify with 'show configuration', and then proceed with the standard software upgrade commands such as 'request system software add'.
- ✗
Run the 'load override terminal' command and paste the active configuration from memory, then commit and upgrade.
Why it's wrong here
Using `load override terminal` replaces the candidate configuration with pasted text, but the candidate already contains a syntax error that prevents any commit. Pasting the active configuration from memory would still fail because the commit operation validates the entire candidate configuration before activating it, and the syntax error remains uncorrected in the pasted text. This option is tempting because `load override terminal` is normally used to replace the entire candidate configuration with a clean, manually entered or copied configuration, and would be correct if the pasted configuration were syntactically valid and free of errors.
- ✗
Use the 'commit force' command to override the syntax error and commit the candidate, then perform the upgrade.
Why it's wrong here
The 'commit force' command does not exist in Junos; the closest commands are 'commit check' for validating the candidate and 'commit confirmed' for reverting after a timeout, but neither can override a syntax error. A commit operation always performs a full syntax check on the candidate configuration and fails if any error exists, so there is no way to force-commit an invalid configuration; the only path to commit is to repair or replace the candidate with a valid configuration.
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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.