LPIC-2 Linux Kernel and System Startup Practice Question
During boot, the system displays 'unable to mount root fs on unknown-block'. What is the most likely cause?
⚠ Common exam trap
Candidates often confuse a missing driver with a wrong root= parameter, but the error message 'unknown-block' specifically points to a driver/module issue, not a path or UUID mismatch.
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
✓
Missing filesystem driver in initramfs
The error 'unable to mount root fs on unknown-block' indicates that the kernel cannot find a driver for the filesystem or block device containing the root filesystem. This typically occurs when the initramfs lacks the necessary kernel module (e.g., ext4, xfs, or a storage controller driver like ahci or nvme) to access the root device. The initramfs is responsible for loading essential drivers before the kernel mounts the real root filesystem; if the driver is missing, the mount fails.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Corrupted init binary
Why it's wrong here
A corrupted init binary would cause a panic after mounting root, not a mount failure.
- ✓
Missing filesystem driver in initramfs
Why this is correct
The kernel cannot access the root filesystem because the necessary driver (e.g., ext4) is not loaded; it must be in the initramfs.
- ✗
Wrong block device order
Why it's wrong here
Device order is handled by the initramfs and udev; 'unknown-block' indicates the driver is missing.
- ✗
Incorrect root= parameter
Why it's wrong here
An incorrect root= would give a 'no root device' or 'cannot find root' message, not 'unknown-block'.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LPIC-2 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-2 exam.