LPIC-1 System Architecture Practice Question
A system administrator is troubleshooting a Linux server that fails to boot. The server has a software RAID 1 configuration using mdadm, with the root filesystem located on /dev/md0. During boot, the system halts with the following error: 'VFS: Unable to mount root fs on unknown-block(0,0)'. The admin verifies that the BIOS recognizes all disks and that the RAID array was properly assembled prior to the last shutdown. The system was working after a recent kernel update, but now fails. Which of the following actions is the most likely solution?
⚠ Common exam trap
A common mix-up: candidates confuse a root filesystem mount failure with filesystem corruption (fsck) or bootloader issues, but the specific 'unknown-block(0,0)' error points to a missing kernel module or initramfs problem after a kernel update.
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
✓
Rebuild the initramfs to include the mdadm module and the RAID metadata.
After a kernel update, the new kernel may lack the necessary mdadm module or RAID metadata support in the initramfs. The error 'unknown-block(0,0)' indicates the kernel cannot find the root device because the initramfs does not contain the required RAID drivers or assembly instructions. Rebuilding the initramfs with the correct mdadm configuration ensures the kernel can assemble and mount /dev/md0 during boot.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Use a live CD to run fsck on /dev/md0.
Why it's wrong here
Filesystem corruption would not produce 'unknown-block(0,0)', which indicates the kernel cannot locate the root device at all; fsck requires a mountable filesystem. Running fsck from a live CD is tempting for general boot failures, and it would be correct if the array assembled but the filesystem itself were damaged or inconsistent.
- ✓
Rebuild the initramfs to include the mdadm module and the RAID metadata.
Why this is correct
A kernel update can produce an initramfs lacking the mdadm module, so the kernel cannot assemble /dev/md0 and reports unknown-block(0,0). Rebuilding initramfs with mdadm and RAID metadata satisfies the requirement to mount the root filesystem at boot.
- ✗
Check the /etc/fstab file for incorrect root device.
Why it's wrong here
The error occurs before the initramfs hands off to the real root, so /etc/fstab is not yet read; an incorrect fstab entry produces a different failure later. Checking fstab is tempting because it defines mount points, and it would be the right action if the system mounted the root but failed to mount secondary filesystems.
- ✗
Reinstall the bootloader on the MBR.
Why it's wrong here
A missing or misconfigured bootloader yields GRUB errors or a blank screen, not a VFS mount failure; the kernel is already running when this message appears. Reinstalling the bootloader is tempting for any unbootable server, and it would be correct if GRUB itself were corrupted or the MBR overwritten.
Quick reference
RAID Level Comparison
| RAID Level | Min Disks | Fault Tolerance | Read | Write | Usable Capacity |
|---|---|---|---|---|---|
| RAID 0 | 2 | None | Excellent | Excellent | 100% |
| RAID 1 | 2 | 1 disk | Good | Moderate | 50% |
| RAID 5 | 3 | 1 disk | Good | Moderate | 67–94% |
| RAID 6 | 4 | 2 disks | Good | Lower | 50–88% |
| RAID 10 | 4 | 1 disk per mirror | Excellent | Good | 50% |
RAID is not a backup strategy — it protects against disk failure but not against accidental deletion, ransomware, or site-level events.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.