JN0-106 Junos Configuration Basics Practice Question
Which TWO statements are true about the 'commit' operation in Junos?
⚠ Common exam trap
Many exam-takers confuse the 'commit' operation with saving to persistent storage (like Cisco's 'copy running-config startup-config'), but in Junos, 'commit' only activates the configuration in memory and does not automatically write to a file; persistent storage requires an explicit save command.
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 commit command validates the configuration syntax before applying it.
Option A is correct because when you issue commit in Junos, the candidate configuration is first checked for syntax and semantic errors, and only a valid configuration is merged into the active configuration. Option D is correct because Junos supports commit comment "text", which stores a descriptive comment with the committed configuration for documentation and audit purposes. Option B is not correct because commit applies the candidate configuration to the active configuration; it does not by itself save a configuration file to disk, which is done with save or file-related commands. Option C is not correct because after a commit the candidate configuration remains as the working copy and is not replaced by the active configuration. Option E is not correct because a successful commit does not overwrite the rollback configurations; Junos maintains up to 50 previous committed configurations for rollback.
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 commit command validates the configuration syntax before applying it.
Why this is correct
The commit command validates the configuration syntax before applying it. Junos runs a validation phase that checks for parser errors, unsupported statements, and semantic issues such as incorrect interface references. If validation fails, the commit is aborted and the active configuration remains unchanged. This is distinct from the optional 'commit check' command, which validates without actually applying the configuration.
- ✗
The commit command automatically saves the configuration to a file on the hard disk.
Why it's wrong here
This is incorrect because commit writes the candidate configuration into the active configuration store (the running configuration file), not to a separate or external file. Junos does not require a manual 'save' step, and the 'save' command is an explicit way to copy the configuration to a named file. The commit operation is an activation process, not a file-export operation, so no arbitrary file is created automatically.
- ✗
After a commit, the candidate configuration is replaced with the active configuration.
Why it's wrong here
This statement reverses the relationship between candidate and active configurations. During a commit, the active configuration is updated from the candidate configuration; the candidate buffer is not replaced or overwritten by the active configuration. After a successful commit, the candidate remains available in configuration mode so you can continue editing or compare it with the newly activated configuration.
- ✓
A commit can include a comment for documentation purposes.
Why this is correct
Yes, the commit command supports a 'comment' option, such as 'commit comment "Adding VLAN 100"', which attaches an annotation to the commit. This comment is recorded in the commit history and can be reviewed with 'show system commit', aiding in change documentation and accountability. On dual-Routing Engine platforms, the comment is synchronized to both REs along with the configuration.
- ✗
A successful commit overwrites the rollback configurations.
Why it's wrong here
A successful commit does not overwrite previous rollback configurations. Instead, the current active configuration becomes rollback 0, and every existing rollback point is shifted down one position (0 to 1, 1 to 2, etc.) up to the configured limit, which defaults to 50. Only when that limit is exceeded does the oldest rollback get discarded, but the new configuration never overwrites an existing rollback point.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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