- A
The filesystem is mounted read-only
Why wrong: The mount output shows (rw) indicating read-write.
- B
The vfat filesystem does not support Unix permissions, and the mount options (fmask/dmask) restrict write access to root only
Correct. The vfat filesystem does not store Unix permissions; the fmask and dmask options control the permissions shown. With fmask=0022, files get 755 permissions, but the owner is root (default unless uid/gid options are used). So only root can write.
- C
The filesystem is mounted with the 'noexec' option, preventing write
Why wrong: The mount output does not show 'noexec'; it shows 'rw' and other options, but noexec is not present.
- D
The file's permissions are 644, so the user does not have write access
Why wrong: The file shows -rw-r--r--, which allows owner write, but the owner is root, not the user.
LPIC-1 Devices, Filesystems and FHS Practice Question
This LPIC-1 practice question tests your understanding of devices, filesystems and fhs. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Refer to the exhibit. A user tries to write to /mnt/usb/myfile.txt as a non-root user and receives a permission denied error. What is the most likely reason?
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 choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
The vfat filesystem does not support Unix permissions, and the mount options (fmask/dmask) restrict write access to root only
Option B is correct because the vfat filesystem does not store Unix-style permissions; instead, it relies on mount options like fmask and dmask to set the effective permissions for all files and directories. If these masks are set to restrict write access to root only (e.g., fmask=0133), non-root users will receive a 'permission denied' error even if the filesystem is mounted read-write. This is a common cause of write failures on USB drives formatted with FAT/VFAT.
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 mounted read-only
Why it's wrong here
The mount output shows (rw) indicating read-write.
- ✓
The vfat filesystem does not support Unix permissions, and the mount options (fmask/dmask) restrict write access to root only
Why this is correct
Correct. The vfat filesystem does not store Unix permissions; the fmask and dmask options control the permissions shown. With fmask=0022, files get 755 permissions, but the owner is root (default unless uid/gid options are used). So only root can write.
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.
- ✗
The filesystem is mounted with the 'noexec' option, preventing write
Why it's wrong here
The mount output does not show 'noexec'; it shows 'rw' and other options, but noexec is not present.
- ✗
The file's permissions are 644, so the user does not have write access
Why it's wrong here
The file shows -rw-r--r--, which allows owner write, but the owner is root, not the user.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the 'permission denied' error must be due to file permissions (option D) or a read-only mount (option A), but they overlook that vfat does not store Unix permissions and that mount masks are the actual controlling mechanism.
Trap categories for this question
Command / output trap
The mount output shows (rw) indicating read-write.
Detailed technical explanation
How to think about this question
Under the hood, the vfat driver in the Linux kernel uses the fmask and dmask mount options to compute the effective permission bits for files and directories, respectively. For example, 'fmask=0133' results in files having permissions 644 (rw-r--r--), but the mask is applied to the owner, group, and others; if the mask denies write to others, non-root users cannot write. In real-world scenarios, a user might plug in a FAT32 USB drive and find they cannot write because the system's udisks2 or automounter applied a restrictive mask (e.g., 0007) for security reasons, which can be overridden by remounting with 'uid=1000,gid=1000,fmask=0113,dmask=0002'.
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 network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
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.
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Devices, Filesystems and FHS — study guide chapter
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FAQ
Questions learners often ask
What does this LPIC-1 question test?
Devices, Filesystems and FHS — This question tests Devices, Filesystems and FHS — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The vfat filesystem does not support Unix permissions, and the mount options (fmask/dmask) restrict write access to root only — Option B is correct because the vfat filesystem does not store Unix-style permissions; instead, it relies on mount options like fmask and dmask to set the effective permissions for all files and directories. If these masks are set to restrict write access to root only (e.g., fmask=0133), non-root users will receive a 'permission denied' error even if the filesystem is mounted read-write. This is a common cause of write failures on USB drives formatted with FAT/VFAT.
What should I do if I get this LPIC-1 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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Last reviewed: Jul 4, 2026
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