This LFCS practice question tests your understanding of essential commands. 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.
A system administrator configures a new server with multiple disks. After partitioning and formatting, they mount a partition to /data. Several days later, they notice that the /data filesystem is full, but 'du -sh /data' reports only 2 GB used, while the partition is 100 GB. 'df -h' shows /data is 98% full. What is the most likely cause and the correct action?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
There are deleted files still held open by processes. Use 'lsof /data' to find and restart those processes.
Option D is correct because when a file is deleted but still held open by a running process, the filesystem does not release the disk blocks until the process closes the file descriptor. This causes 'df' to report the space as used, while 'du' cannot see the deleted file's data, leading to the discrepancy. Using 'lsof /data' identifies the processes holding the deleted files, and restarting them frees the space.
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.
✗
The filesystem is fragmented. Run 'e4defrag' to defragment.
Why it's wrong here
Fragmentation does not affect disk space reporting discrepancy.
✗
The filesystem has reserved blocks for root. Reduce the reserved percentage with 'tune2fs -m 0'.
Why it's wrong here
Reserved blocks are typically only 5% of the filesystem, not enough to explain the discrepancy.
✗
The 'du' command is not counting hidden files (dot files). Use 'du -sh .*' to include them.
Why it's wrong here
'du -sh /data' includes all files, including hidden ones.
✓
There are deleted files still held open by processes. Use 'lsof /data' to find and restart those processes.
Why this is correct
Deleted open files consume space but are not counted by 'du'; 'lsof' can find them.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse the 'du' vs 'df' discrepancy with hidden files or reserved blocks, but the key clue is that 'du' shows far less usage than 'df', which points to unlinked but still-open files.
Detailed technical explanation
How to think about this question
Under the hood, when a file is unlinked (deleted) but still open, the inode remains allocated and the disk blocks are not freed until the file descriptor is closed. The 'df' command queries the filesystem superblock for block usage, which includes these orphaned blocks, while 'du' walks the directory tree and only sees files with directory entries. This is a classic symptom of a file being held open by a process, often seen with log files or database files that are rotated but still written to by a running daemon.
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: There are deleted files still held open by processes. Use 'lsof /data' to find and restart those processes. — Option D is correct because when a file is deleted but still held open by a running process, the filesystem does not release the disk blocks until the process closes the file descriptor. This causes 'df' to report the space as used, while 'du' cannot see the deleted file's data, leading to the discrepancy. Using 'lsof /data' identifies the processes holding the deleted files, and restarting them frees the space.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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