Quick Answer
The answer is the `monitor start messages` command. This is the correct choice because it initiates a real-time, tail-like display of the `/var/log/messages` file, allowing an engineer to view real time system logs as new syslog entries are generated on a Junos device. Unlike static commands like `show log messages`, which only display the file’s current contents, `monitor start messages` continuously updates the terminal, making it essential for live troubleshooting. On the JNCIA-Junos exam, this command tests your understanding of operational monitoring versus file viewing; a common trap is confusing it with `monitor traffic` or `show log`, which serve different purposes. The exam expects you to know that `monitor start` is the Junos equivalent of the Linux `tail -f` command for syslog files. A helpful memory tip: think of “monitor” as “watch live,” and “start” as “begin the stream”—so “monitor start” means “start watching the live stream of messages.”
This JNCIA-JUNOS practice question tests your understanding of user interfaces. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
During troubleshooting, an engineer needs to view real-time logging messages on a Junos device. Which command should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
file show /var/log/messages
Why wrong: Shows file content, not real-time.
monitor start messages
Displays real-time log messages.
show log messages
Why wrong: Shows log file, not real-time.
traceoptions
Why wrong: Configuration statement, not a command.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
monitor start messages
The 'monitor start messages' command enables real-time, tail-like display of the /var/log/messages log file on a Junos device, allowing the engineer to view new log entries as they are generated. This is the correct command for live troubleshooting because it continuously updates the terminal with incoming syslog messages, unlike static file viewing commands.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
file show /var/log/messages
Why it's wrong here
Shows file content, not real-time.
monitor start messages
Why this is correct
Displays real-time log messages.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
show log messages
Why it's wrong here
Shows log file, not real-time.
traceoptions
Why it's wrong here
Configuration statement, not a command.
Common exam traps
The trap here is that candidates often confuse 'show log messages' (a static snapshot) with 'monitor start messages' (a live streaming view), because both involve the 'messages' log file, but only the latter provides real-time output.
Trap categories for this question
Command / output trap
Shows file content, not real-time.
Detailed technical explanation
The 'monitor start' command uses the 'tail -f' mechanism under the hood to follow the log file, and it can be stopped with 'monitor stop'. In a real-world scenario, an engineer troubleshooting a routing protocol flapping issue would use 'monitor start messages' to see real-time BGP or OSPF state changes as they happen, without needing to repeatedly re-run a show command.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
User Interfaces — This question tests User Interfaces — Read the scenario before looking for a memorised answer..
The correct answer is: monitor start messages — The 'monitor start messages' command enables real-time, tail-like display of the /var/log/messages log file on a Junos device, allowing the engineer to view new log entries as they are generated. This is the correct command for live troubleshooting because it continuously updates the terminal with incoming syslog messages, unlike static file viewing commands.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
Read the scenario before looking for a memorised answer.
About these practice questions
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Same concept, more angles
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. A network engineer wants to view the OSPF log entries in real time. They type 'show log messages | match ospf' and get output, but it does not update. What should they do to see real-time updates of OSPF log entries?
mediumWhy A: Option A is correct because the 'monitor start messages' command in Junos OS enables real-time streaming of syslog messages to the terminal, similar to 'tail -f' on a log file. Piping the output through '| match ospf' filters the live feed to show only OSPF-related entries. In contrast, 'show log messages' is a one-time snapshot that does not update automatically.
Variation 2. An engineer wants to view system log messages as they are generated in real-time. Which command should they use?
mediumWhy B: The 'monitor log messages' command in Junos OS provides a real-time view of system log messages as they are generated, similar to the 'tail -f' command on Unix systems. It streams new log entries to the terminal without requiring manual refresh, making it ideal for live monitoring of events.
Variation 3. A technician wants to view the system log messages in real time. Which command should they use?
easyWhy B: The 'monitor start messages' command is used in Junos OS to display system log messages in real time as they are generated. This is the correct command for live monitoring of system events, similar to 'tail -f' on Unix systems.
Last reviewed: Jun 11, 2026
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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