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XK0-006 Practice Question: A Linux engineer is troubleshooting a server that…
A Linux engineer is troubleshooting a server that fails to boot. The server displays a message indicating 'Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)'. Which TWO actions should the engineer take to resolve this issue? (Choose TWO.)
⚠ Common exam trap
It's easy for candidates to confuse a kernel panic about root filesystem mounting with a bootloader or filesystem corruption issue, leading them to choose GRUB reinstallation (A) or fsck (C) instead of addressing the initramfs or kernel command line.
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
✓
Boot from a rescue disk and rebuild the initramfs with the necessary filesystem modules
The error 'VFS: Unable to mount root fs on unknown-block(0,0)' means the kernel cannot locate or mount the root filesystem, which typically stems from a missing/incorrect root= kernel parameter or an initramfs lacking the driver for the root device. Option B is correct because booting from a rescue disk and rebuilding the initramfs (e.g., with dracut or mkinitramfs) restores the storage/filesystem modules the kernel needs to access the root device at early boot. Option D is correct because verifying and fixing the root= parameter in the bootloader configuration (e.g., GRUB's /etc/default/grub or grub.cfg) ensures the kernel is pointed at the actual root device (such as /dev/mapper/vg-root or UUID=...). Option A is not appropriate because reinstalling GRUB to the MBR only fixes bootloader-stage problems, not a kernel that has already loaded but cannot mount root. Option C is not the primary fix here since fsck addresses filesystem corruption, not an unknown-block root device error. Option E is unrelated because disabling SELinux does not resolve the kernel's inability to mount the root filesystem.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Reinstall GRUB to the Master Boot Record
Why it's wrong here
Reinstalling GRUB addresses bootloader-stage failures such as a missing stage 1.5 or grub prompt, not a kernel that has already loaded but cannot mount root. The unknown-block(0,0) panic points to a missing or incorrect root filesystem driver in the initramfs.
- ✓
Boot from a rescue disk and rebuild the initramfs with the necessary filesystem modules
Why this is correct
The panic occurs because the initramfs lacks the storage driver needed to mount the root filesystem. Booting a rescue disk lets the engineer rebuild the initramfs with the correct filesystem modules, restoring the kernel's ability to mount root at boot.
- ✗
Run fsck on the root partition to check for filesystem corruption
Why it's wrong here
fsck repairs filesystem corruption once a device is mountable, but unknown-block(0,0) means the kernel found no block device for root at all. The fault lies in the initramfs or root= kernel parameter, so filesystem checking cannot address it.
- ✓
Check the kernel command line in the bootloader configuration for the correct root= parameter
Why this is correct
The panic shows the kernel cannot locate the root filesystem, so the root= parameter in the bootloader configuration likely points to a wrong or missing device. Correcting it lets the kernel mount root and continue booting.
- ✗
Disable SELinux by adding selinux=0 to the kernel command line
Why it's wrong here
SELinux denials occur after the root filesystem mounts, producing AVC messages, not a VFS mount panic. Disabling SELinux leaves the actual fault — an initramfs lacking the storage driver or wrong root= parameter — unresolved, so the kernel still cannot mount root.
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Networking Fundamentals and Configuration
Key term
GRUB
GRUB (Grand Unified Bootloader) is a boot loader package that loads and manages the operating system startup process on Linux and other Unix-like systems.
Key term
Linux
Linux is an open-source operating system that manages computer hardware and software, widely used in servers, desktops, and embedded systems.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA 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 XK0-006 exam.