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 percentage of filesystem blocks reserved exclusively for the root user, overriding the default of 5% to the required 2%. On the LPIC-1 exam, this tests your understanding of filesystem creation options and the purpose of reserved blocks—preventing a full disk from locking out the superuser for critical system processes. A common trap is confusing `-m` with block size or inode options, or forgetting that the default is 5%, not zero. The exam often pairs this with questions about tuning ext4 performance or troubleshooting disk space issues. Remember the mnemonic: **m** for **m**inimum root reserve—think of the `-m` flag as “make room for the master.”
This LPIC-1 practice question tests your understanding of devices, filesystems and fhs. 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 a new ext4 filesystem on /dev/sdb1 and wants to reserve 2% of the blocks for the root user. 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 specifies reserved blocks percentage.
tune2fs -m 2 /dev/sdb1
Why wrong: tune2fs modifies an existing filesystem, but the filesystem must already exist.
mke2fs -r 2 /dev/sdb1
Why wrong: -r is not a valid option for mke2fs.
mkfs.ext4 -R 2 /dev/sdb1
Why wrong: -R is used for RAID options, not reserved blocks.
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` specifies the percentage of filesystem blocks reserved for the root user (superuser). By default, ext4 reserves 5% of blocks; using `-m 2` reduces this to 2%, as required. This command creates a new ext4 filesystem on `/dev/sdb1` with the specified reserved block percentage.
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 specifies 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.
tune2fs -m 2 /dev/sdb1
Why it's wrong here
tune2fs modifies an existing filesystem, but the filesystem must already exist.
mke2fs -r 2 /dev/sdb1
Why it's wrong here
-r is not a valid option for mke2fs.
mkfs.ext4 -R 2 /dev/sdb1
Why it's wrong here
-R is used for RAID options, not reserved blocks.
Common exam traps
The trap here is that candidates confuse `-m` (reserved block percentage) with `-r` (revision level) or assume `tune2fs` can be used to create a filesystem, when in fact `tune2fs` only modifies existing filesystems.
Detailed technical explanation
The reserved blocks percentage (set via `-m`) is a key feature of ext2/3/4 filesystems, ensuring that root can always write to the filesystem even when it is full, preventing system failures from disk-full conditions. This reservation is stored in the superblock and can be adjusted later with `tune2fs -m`. In practice, reducing reserved blocks from the default 5% to 2% is common on large data partitions to reclaim space, but it must be done cautiously on system partitions to avoid out-of-space issues for critical processes.
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-1 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
Devices, Filesystems and FHS — This question tests Devices, Filesystems and FHS — 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` specifies the percentage of filesystem blocks reserved for the root user (superuser). By default, ext4 reserves 5% of blocks; using `-m 2` reduces this to 2%, as required. This command creates a new ext4 filesystem on `/dev/sdb1` with the specified reserved block percentage.
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 11, 2026
This LPIC-1 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-1 exam.
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