Quick Answer
The answer is to use the command show log messages | match "error". This is the most efficient method because the show log messages command displays the contents of the primary system log file, /var/log/messages, and piping the output to the match filter isolates only those lines containing the keyword "error," allowing you to quickly pinpoint interface failure issues without sifting through irrelevant entries. On the JNCIA-Junos exam, this question tests your ability to efficiently navigate Junos operational mode and apply filters to system logs, a common task for troubleshooting. A frequent trap is using show log without a filter, which dumps the entire log and wastes time, or using a grep-like command incorrectly. Remember the memory tip: "Pipe to match for a catch" — always pair show log with match to zero in on specific error messages.
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.
An administrator is asked to check the system log files for any error messages related to interface failures. Which command would be most efficient?
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.
monitor start messages | match "error"
Why wrong: Monitors live log start, not a static search.
show log file messages | match "error"
Efficiently filters for errors in the log file.
show log messages
Why wrong: Shows all log messages without filtering.
show system syslog 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 file messages | match "error"
Option B is correct because 'show log messages' displays the contents of the /var/log/messages file, and piping the output to 'match "error"' filters for lines containing 'error', making it the most efficient command to check system log files for interface failure errors. The 'show log' command is the standard way to view log files in JUNOS, and the 'match' filter allows targeted searching without overwhelming the administrator with irrelevant data.
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.
monitor start messages | match "error"
Why it's wrong here
Monitors live log start, not a static search.
show log file messages | match "error"
Why this is correct
Efficiently filters for errors in the log file.
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 all log messages without filtering.
show system syslog messages
Why it's wrong here
Not a valid command.
Common exam traps
The trap here is that candidates may confuse 'monitor start messages' with 'show log messages', thinking the real-time monitor is more efficient for checking logs, but the question asks for checking existing log files, not monitoring live events.
Trap categories for this question
Command / output trap
Shows all log messages without filtering.
Detailed technical explanation
In JUNOS, system log files are stored in /var/log/ by default, with 'messages' being the primary log file for general system events, including interface state changes and errors. The 'show log <filename>' command reads the specified log file from disk, and when combined with 'match', it uses a grep-like pattern matching engine to filter lines, which is efficient because it only processes the file once and outputs matching lines. In a real-world scenario, an administrator troubleshooting recurring interface flapping would use 'show log messages | match "interface.*down"' to quickly isolate relevant events without scrolling through thousands of lines.
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
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 file messages | match "error" — Option B is correct because 'show log messages' displays the contents of the /var/log/messages file, and piping the output to 'match "error"' filters for lines containing 'error', making it the most efficient command to check system log files for interface failure errors. The 'show log' command is the standard way to view log files in JUNOS, and the 'match' filter allows targeted searching without overwhelming the administrator with irrelevant data.
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.
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Last reviewed: Jun 24, 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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