The answer is to use logrotate with the copytruncate option to rotate /var/log/app.log and move the rotated file to /var/old_logs/. This is correct because copytruncate allows you to rotate a log file without stopping the application by first copying the current log to a new file and then truncating the original to zero length, preserving the application’s open file descriptor so it continues writing seamlessly. On the LFCS exam, this scenario tests your understanding of log management under resource constraints, specifically how to free disk space on a full root filesystem while maintaining application uptime—a common trap is choosing the standard rotate or create options, which would require restarting the service or risk data loss. The key insight is that copytruncate avoids any downtime by never closing the file handle, making it ideal for critical services. Memory tip: think “copy then chop”—the file is copied away, then the original is chopped to zero, keeping the app happy.
LFCS Essential Commands Practice Question
This LFCS practice question tests your understanding of essential commands. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
You are managing a Linux server that hosts a critical web application. The server is running low on disk space in the root filesystem, and you need to free up space urgently. You run 'df -h' and see that /dev/sda1 is mounted on / and is 95% full. You also notice that /var/log/messages is over 2 GB in size. The application writes logs to /var/log/app.log, which is also large. The server has a separate /var partition that has plenty of free space. The application must continue running with minimal downtime. You need to compress and rotate logs without losing any data, and ensure that the root filesystem has at least 10% free space. Which of the following actions should you take first to achieve this goal?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Clue: "least"
Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use logrotate with the 'copytruncate' option to rotate /var/log/app.log and move the rotated file to /var/old_logs/.
Option C is correct because logrotate with the 'copytruncate' option allows the application to continue writing to the same file descriptor while the current log is copied and then truncated to zero length. This avoids any application downtime and the rotated log can be moved to the separate /var partition (which has free space) for compression or archiving, freeing space on the root filesystem without data loss.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Delete /var/log/app.log and /var/log/messages to free space quickly.
Why it's wrong here
Deleting logs loses data and may violate compliance requirements.
✗
Stop the application, truncate /var/log/app.log, then restart the application.
Why it's wrong here
Stopping the application causes downtime, which is not acceptable.
✓
Use logrotate with the 'copytruncate' option to rotate /var/log/app.log and move the rotated file to /var/old_logs/.
Why this is correct
This rotates the log without interrupting the application and moves it to a partition with space, freeing root.
Clue confirmation
The clue words "first", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Compress /var/log/app.log using gzip and keep it in place.
Why it's wrong here
Compression alone may not free enough space on root, and the file remains on the root filesystem.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose to delete or truncate logs directly, not realizing that running processes hold file descriptors and that truncation does not immediately free disk space until the file descriptor is closed, or they overlook the 'copytruncate' option which allows zero-downtime rotation.
Detailed technical explanation
How to think about this question
The 'copytruncate' option works by first copying the current log file to a new name, then truncating the original file to zero bytes. The application continues writing to the same inode and file descriptor, so no restart is needed. However, there is a small window where log data written between the copy and truncate may be lost; for critical applications, the 'copy' method (which renames the log and creates a new file) is safer but requires application support (e.g., SIGHUP). In this scenario, moving the rotated file to /var/old_logs/ (on the separate partition) alleviates root filesystem pressure.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the LFCS 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
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Essential Commands — This question tests Essential Commands — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use logrotate with the 'copytruncate' option to rotate /var/log/app.log and move the rotated file to /var/old_logs/. — Option C is correct because logrotate with the 'copytruncate' option allows the application to continue writing to the same file descriptor while the current log is copied and then truncated to zero length. This avoids any application downtime and the rotated log can be moved to the separate /var partition (which has free space) for compression or archiving, freeing space on the root filesystem without data loss.
What should I do if I get this LFCS question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first", "least". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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