This LPIC-2 practice question tests your understanding of block devices, filesystems and advanced storage. 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.
An administrator needs to create an ext4 filesystem on /dev/sdb1 with a block size of 4096 bytes and reserve 2% of blocks for root. Which command accomplishes this?
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.
mkfs.ext4 --block-size 4096 -m 2 /dev/sdb1
Why wrong: The flag for block size is -b, not --block-size.
mkfs.ext4 -B 4096 -m 2 /dev/sdb1
Why wrong: -B is not a valid flag for mkfs.ext4; block size is set with -b.
mkfs.ext4 -b 4096 -m 2 /dev/sdb1
-b sets block size to 4096 bytes; -m sets reserved percentage to 2.
mkfs.ext4 -b 4096 -M 2 /dev/sdb1
Why wrong: -M is invalid; use -m for reserved blocks percentage.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
mkfs.ext4 -b 4096 -m 2 /dev/sdb1
Option C is correct because mkfs.ext4 uses the `-b` option to specify the block size in bytes (4096) and `-m` to set the reserved blocks percentage for root (2%). The `-b` flag is the standard short form for block size in the mke2fs family of tools, and `-m` accepts a percentage value directly.
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.
mkfs.ext4 --block-size 4096 -m 2 /dev/sdb1
Why it's wrong here
The flag for block size is -b, not --block-size.
mkfs.ext4 -B 4096 -m 2 /dev/sdb1
Why it's wrong here
-B is not a valid flag for mkfs.ext4; block size is set with -b.
mkfs.ext4 -b 4096 -m 2 /dev/sdb1
Why this is correct
-b sets block size to 4096 bytes; -m sets reserved percentage to 2.
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.
mkfs.ext4 -b 4096 -M 2 /dev/sdb1
Why it's wrong here
-M is invalid; use -m for reserved blocks percentage.
Common exam traps
The trap here is that candidates confuse the `-b` (block size) and `-m` (reserved blocks percentage) flags with similar-looking but incorrect flags like `-B` or `-M`, or mistakenly use long options like `--block-size` without verifying the exact syntax supported by mkfs.ext4.
Detailed technical explanation
The `-m` option in mkfs.ext4 reserves a percentage of filesystem blocks for the superuser (root) to prevent non-root users from filling the disk entirely, which could cause system instability. The default reserved percentage is 5%, but reducing it to 2% is common for data partitions where root access is not critical. The block size (`-b`) must be a power of 2 between 1024 and 65536, and 4096 is the default for most modern ext4 filesystems, balancing performance and metadata overhead.
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 LPIC-2 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
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FAQ
Block Devices, Filesystems and Advanced Storage — This question tests Block Devices, Filesystems and Advanced Storage — Read the scenario before looking for a memorised answer..
The correct answer is: mkfs.ext4 -b 4096 -m 2 /dev/sdb1 — Option C is correct because mkfs.ext4 uses the `-b` option to specify the block size in bytes (4096) and `-m` to set the reserved blocks percentage for root (2%). The `-b` flag is the standard short form for block size in the mke2fs family of tools, and `-m` accepts a percentage value directly.
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 25, 2026
This LPIC-2 practice question is part of Courseiva's free LPI 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 LPIC-2 exam.
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