- A
The device mapper target is not set for the disk.
Why wrong: Device mapper is for LVM/multipath, not for by-id links.
- B
The disk does not have a valid partition table.
Why wrong: Partition table is not required for /dev/disk/by-id links.
- C
The scsi_mod kernel module is not loaded.
Why wrong: If the disk is detected, scsi_mod is loaded.
- D
The udev daemon has not processed the device yet; run 'udevadm trigger' to generate links.
udev creates symbolic links; if not triggered, links may not appear immediately.
Question 444 of 513
LFCS Storage Management Practice Question
This LFCS practice question tests your understanding of storage management. 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.
A storage administrator is troubleshooting a system where a new SCSI disk is detected by the kernel but not visible in /dev/disk/by-id/. 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.
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 udev daemon has not processed the device yet; run 'udevadm trigger' to generate links.
When a new SCSI disk is detected by the kernel, the kernel creates the device node (e.g., /dev/sdb), but the symbolic links under /dev/disk/by-id/ are generated by udev based on the device's WWID or other identifiers. If udev has not yet processed the uevent for the new disk, those persistent by-id links will not exist. Running 'udevadm trigger' forces udev to reprocess all pending or missed uevents, which creates the missing links.
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 device mapper target is not set for the disk.
Why it's wrong here
Device mapper is for LVM/multipath, not for by-id links.
- ✗
The disk does not have a valid partition table.
Why it's wrong here
Partition table is not required for /dev/disk/by-id links.
- ✗
The scsi_mod kernel module is not loaded.
Why it's wrong here
If the disk is detected, scsi_mod is loaded.
- ✓
The udev daemon has not processed the device yet; run 'udevadm trigger' to generate links.
Why this is correct
udev creates symbolic links; if not triggered, links may not appear immediately.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a missing partition table or device mapper target is the cause, but the question explicitly states the disk is detected by the kernel, meaning the issue is with udev link creation, not with kernel-level detection or partitioning.
Detailed technical explanation
How to think about this question
Under the hood, when the kernel detects a new SCSI disk, it sends a uevent to udev via netlink. The udev daemon (systemd-udevd) then matches rules in /lib/udev/rules.d/ (e.g., 60-persistent-storage.rules) to create symlinks under /dev/disk/by-id/ using the device's WWID (SCSI inquiry data) or other unique identifiers. If udev is busy, slow, or the uevent is lost (e.g., during early boot or hotplug storms), the links may be missing until manually triggered. In real-world scenarios, this often occurs after a storage array rescan or when using 'echo "- - -" > /sys/class/scsi_host/hostN/scan' without waiting for udev to settle.
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 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
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.
- →
Storage Management — study guide chapter
Learn the concepts, then practise the questions
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FAQ
Questions learners often ask
What does this LFCS question test?
Storage Management — This question tests Storage Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The udev daemon has not processed the device yet; run 'udevadm trigger' to generate links. — When a new SCSI disk is detected by the kernel, the kernel creates the device node (e.g., /dev/sdb), but the symbolic links under /dev/disk/by-id/ are generated by udev based on the device's WWID or other identifiers. If udev has not yet processed the uevent for the new disk, those persistent by-id links will not exist. Running 'udevadm trigger' forces udev to reprocess all pending or missed uevents, which creates the missing links.
What should I do if I get this LFCS 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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