Troubleshooting mount -a Failure Due to Missing Device
This EX200 practice question tests your understanding of configure local storage. 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.
Exhibit
# cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Mon Jul 19 10:15:30 2021
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=12345678-1234-1234-1234-123456789abc / xfs defaults 0 0
UUID=abcdef12-3456-7890-abcd-ef1234567890 /boot ext4 defaults 1 2
UUID=deadbeef-cafe-babe-1234-567890abcdef swap swap defaults 0 0
/dev/vdb1 /mnt/data ext4 defaults 0 0
# blkid /dev/vdb1
/dev/vdb1: UUID="a1b2c3d4-e5f6-7890-abcd-ef1234567890" TYPE="ext4"
# mount -a
mount: /mnt/data: can't find /dev/vdb1 in /etc/fstab.
Refer to the exhibit. An administrator attempts to mount all filesystems using 'mount -a' and receives an error. What is the most likely cause?
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.
Exhibit
# cat /etc/fstab
#
# /etc/fstab
# Created by anaconda on Mon Jul 19 10:15:30 2021
#
# Accessible filesystems, by reference, are maintained under '/dev/disk/'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=12345678-1234-1234-1234-123456789abc / xfs defaults 0 0
UUID=abcdef12-3456-7890-abcd-ef1234567890 /boot ext4 defaults 1 2
UUID=deadbeef-cafe-babe-1234-567890abcdef swap swap defaults 0 0
/dev/vdb1 /mnt/data ext4 defaults 0 0
# blkid /dev/vdb1
/dev/vdb1: UUID="a1b2c3d4-e5f6-7890-abcd-ef1234567890" TYPE="ext4"
# mount -a
mount: /mnt/data: can't find /dev/vdb1 in /etc/fstab.
A
The ext4 filesystem on /dev/vdb1 is corrupted.
Why wrong: The error indicates the device is not found in /etc/fstab, not filesystem corruption.
B
The filesystem type specified in /etc/fstab is incorrect.
Why wrong: The blkid output shows it is ext4, matching the fstab entry.
C
The entry for /dev/vdb1 in /etc/fstab uses a device name that does not exist.
The /dev/vdb1 device is not present (maybe the disk was removed or the device name changed). The fstab entry uses a device path that is not available, causing mount -a to fail.
D
The mount point /mnt/data does not exist.
Why wrong: The error message says 'can't find /dev/vdb1', not that the mount point is missing.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The entry for /dev/vdb1 in /etc/fstab uses a device name that does not exist.
The error occurs because the entry in /etc/fstab for /dev/vdb1 references a device name that does not exist on the system. When 'mount -a' is executed, it reads /etc/fstab and attempts to mount each filesystem; if the device node is missing (e.g., due to a typo, incorrect kernel name, or the device not being attached), the mount fails with an error like 'mount: special device /dev/vdb1 does not exist'. This is the most likely cause given the scenario.
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 ext4 filesystem on /dev/vdb1 is corrupted.
Why it's wrong here
The error indicates the device is not found in /etc/fstab, not filesystem corruption.
✗
The filesystem type specified in /etc/fstab is incorrect.
Why it's wrong here
The blkid output shows it is ext4, matching the fstab entry.
✓
The entry for /dev/vdb1 in /etc/fstab uses a device name that does not exist.
Why this is correct
The /dev/vdb1 device is not present (maybe the disk was removed or the device name changed). The fstab entry uses a device path that is not available, causing mount -a to fail.
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 mount point /mnt/data does not exist.
Why it's wrong here
The error message says 'can't find /dev/vdb1', not that the mount point is missing.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Red Hat RHCSA often tests the distinction between errors caused by a missing device node versus a missing mount point or filesystem corruption, and candidates mistakenly assume the error is due to a missing mount point or a corrupted filesystem without reading the exact error message.
Trap categories for this question
Command / output trap
The blkid output shows it is ext4, matching the fstab entry.
Detailed technical explanation
How to think about this question
Under the hood, 'mount -a' parses /etc/fstab line by line and calls the mount(2) system call for each entry. The kernel first checks for the existence of the block device via the device node in /dev; if the node is missing, the system call returns ENOENT (No such file or directory). This is different from a missing mount point (ENOENT on the target directory) or a corrupted filesystem (EIO or wrong superblock). In real-world scenarios, this often happens when a disk is removed, renamed (e.g., after a kernel update changes device ordering), or when using stale persistent names like /dev/sdb1 that no longer match the current device enumeration.
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 EX200 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.
Configure local storage — This question tests Configure local storage — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The entry for /dev/vdb1 in /etc/fstab uses a device name that does not exist. — The error occurs because the entry in /etc/fstab for /dev/vdb1 references a device name that does not exist on the system. When 'mount -a' is executed, it reads /etc/fstab and attempts to mount each filesystem; if the device node is missing (e.g., due to a typo, incorrect kernel name, or the device not being attached), the mount fails with an error like 'mount: special device /dev/vdb1 does not exist'. This is the most likely cause given the scenario.
What should I do if I get this EX200 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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