Quick Answer
The answer is mkfs.ext4 -m 2 /dev/sdb1. This command is correct because the -m flag in mkfs.ext4 directly sets the reserved block percentage for the superuser, overriding the default of 5% to reserve exactly 2% of the filesystem blocks on /dev/sdb1. On the Linux Foundation Certified System Administrator LFCS exam, this tests your ability to manage filesystem overhead and understand that reserved blocks prevent non-root users from filling the disk completely, which could crash critical system processes. A common trap is forgetting that the -m value is a percentage, not a block count, or assuming the default is already 2% when it is actually 5% for ext4. To remember, think of the mnemonic “minus m for minimum reserved,” where the number after -m is the percentage you want to keep for root.
This LFCS practice question tests your understanding of storage management. 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.
A system administrator needs to create a new ext4 filesystem on /dev/sdb1 with a reserved block percentage of 2% instead of the default 5%. Which command should be used?
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 -m 2 /dev/sdb1
Correct: -m sets reserved blocks percentage.
mkfs.ext4 -R 2 /dev/sdb1
Why wrong: Incorrect: -R is not a valid option for mkfs.ext4.
mkfs.ext4 -r 2 /dev/sdb1
Why wrong: Incorrect: -r is for RAID stride.
tune2fs -m 2 /dev/sdb1
Why wrong: Incorrect: tune2fs modifies an existing filesystem, not creation.
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 -m 2 /dev/sdb1
Option A is correct because the `-m` flag in `mkfs.ext4` sets the reserved block percentage for the superuser, and specifying `-m 2` overrides the default of 5% to reserve only 2% of the blocks on the new ext4 filesystem on /dev/sdb1.
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 -m 2 /dev/sdb1
Why this is correct
Correct: -m sets reserved blocks percentage.
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 -R 2 /dev/sdb1
Why it's wrong here
Incorrect: -R is not a valid option for mkfs.ext4.
mkfs.ext4 -r 2 /dev/sdb1
Why it's wrong here
Incorrect: -r is for RAID stride.
tune2fs -m 2 /dev/sdb1
Why it's wrong here
Incorrect: tune2fs modifies an existing filesystem, not creation.
Common exam traps
The trap here is that candidates confuse `-m` (reserved block percentage) with `-r` (revision number) or `-R` (RAID stride), or they incorrectly choose `tune2fs` which modifies an existing filesystem rather than creating a new one.
Detailed technical explanation
The reserved block percentage (default 5%) ensures that a privileged user (root) can still write to the filesystem even when it is full, preventing system services from failing due to disk exhaustion. In production environments, reducing this to 2% on large data volumes (e.g., >1 TB) can reclaim significant space, but on root or system partitions, keeping the default 5% is often recommended to maintain system stability under low-disk conditions.
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 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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Storage Management — study guide chapter
Learn the concepts, then practise the questions
Storage Management practice questions
Targeted practice on this topic area only
All LFCS questions
513 questions across all exam domains
Linux Foundation Certified System Administrator LFCS study guide
Full concept coverage aligned to exam objectives
LFCS practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise LFCS questions linked to User and Group Management.
Practise LFCS questions linked to Operation of Running Systems.
Practise LFCS questions linked to Essential Commands.
Practise LFCS questions linked to Networking.
Practise LFCS questions linked to Service Configuration.
Practise LFCS questions linked to Storage Management.
Practise LFCS questions linked to LFCS fundamentals.
Practise LFCS questions linked to LFCS scenario.
Practise LFCS questions linked to LFCS troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Storage Management — This question tests Storage Management — Read the scenario before looking for a memorised answer..
The correct answer is: mkfs.ext4 -m 2 /dev/sdb1 — Option A is correct because the `-m` flag in `mkfs.ext4` sets the reserved block percentage for the superuser, and specifying `-m 2` overrides the default of 5% to reserve only 2% of the blocks on the new ext4 filesystem on /dev/sdb1.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
Last reviewed: Jun 11, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.