Quick Answer
The correct answer is that both the 'show log messages' and 'monitor start messages' commands are used to view system log messages on a Juniper device. The 'show log messages' command reads and displays the static contents of the default system log file, /var/log/messages, which stores kernel, daemon, and system-level events, making it ideal for historical review. In contrast, 'monitor start messages' provides a real-time tail of the same file, allowing you to watch live log entries as they are written, which is essential for troubleshooting ongoing issues. On the JNCIA-Junos exam, this question tests your understanding of Junos operational commands for system monitoring, and a common trap is confusing 'show log' with 'show log messages'—the former requires a specific filename, while the latter defaults to /var/log/messages. A helpful memory tip is to think of 'show' as a snapshot of the past and 'monitor start' as a live feed, just like the difference between reading a book and watching a live stream.
This JNCIA-JUNOS practice question tests your understanding of operational monitoring and maintenance. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Which TWO commands can be used to view the system log messages on a Juniper device? (Select two.)
show log dcd
Why wrong: Shows a specific log, not the main messages.
show log messages
Displays and tails the current log messages.
monitor start messages
Tails live log messages.
show log file
Why wrong: Not a standard command; usually specifies a file.
show system messages
Why wrong: Not a valid 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
show log messages
Option B is correct because 'show log messages' displays the contents of the default system log file, /var/log/messages, which contains kernel, daemon, and system-level messages. Option C is correct because 'monitor start messages' provides a real-time tail of the same /var/log/messages file, allowing live monitoring of system log entries as they are written.
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.
show log dcd
Why it's wrong here
Shows a specific log, not the main messages.
show log messages
Why this is correct
Displays and tails the current log messages.
Related concept
Read the scenario before looking for a memorised answer.
monitor start messages
Why this is correct
Tails live log messages.
Related concept
Read the scenario before looking for a memorised answer.
show log file
Why it's wrong here
Not a standard command; usually specifies a file.
show system messages
Why it's wrong here
Not a valid command.
Common exam traps
The trap here is that candidates confuse the generic 'show log' syntax with a nonexistent 'show log file' command, or they mistakenly think 'show system messages' is valid because of similarity to other vendors' commands like 'show logging' on Cisco IOS.
Trap categories for this question
Command / output trap
Shows a specific log, not the main messages.
Detailed technical explanation
Junos stores system log messages in /var/log/messages by default, controlled by the syslog daemon. The 'show log' command reads the file from disk, while 'monitor start' uses the 'tail -f' mechanism to follow the file in real time. In production, 'monitor start messages' is invaluable for troubleshooting live issues like interface flaps or routing protocol changes without repeatedly polling the log file.
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.
Operational Monitoring and Maintenance — study guide chapter
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FAQ
Operational Monitoring and Maintenance — This question tests Operational Monitoring and Maintenance — Read the scenario before looking for a memorised answer..
The correct answer is: show log messages — Option B is correct because 'show log messages' displays the contents of the default system log file, /var/log/messages, which contains kernel, daemon, and system-level messages. Option C is correct because 'monitor start messages' provides a real-time tail of the same /var/log/messages file, allowing live monitoring of system log entries as they are written.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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. Which TWO commands can be used to monitor system log messages in real-time?
mediumWhy D: Option D is correct because the 'monitor start interactive-commands' command in Junos OS enables real-time monitoring of interactive commands executed on the device, displaying them as they occur. Option E is correct because 'monitor start messages' streams the contents of the /var/log/messages file in real-time, allowing you to see new syslog entries as they are generated. Both commands use the 'monitor start' family, which is specifically designed for real-time log monitoring, unlike 'show log' which only displays historical data.
Last reviewed: Jun 24, 2026
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