Linux Kernel Panic #

A kernel panic is a critical error where the Linux kernel cannot recover, forcing the system to halt. Below is a breakdown of its causes, a real-world example, and step-by-step solutions.

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1. What is a Kernel Panic? #

• Definition: A fatal system crash where the kernel detects an unrecoverable error.
• Symptoms:
  • System freezes with an error message (e.g., Kernel panic - not syncing: VFS: Unable to mount root fs).
  • Reboot loops.
  • Blank screen with a blinking cursor.

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2. Real-World Example #

Scenario: “Unable to Mount Root Filesystem” #

Error Message: #

Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

What Happened? #

• The kernel couldn’t find or mount the root (/) filesystem.
• Possible causes:
  • Corrupt initramfs (initial RAM disk).
  • Missing or incorrect root device in GRUB.
  • Hard drive failure (e.g., SSD/HDD disconnection).

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3. Common Causes of Kernel Panics #

Cause	Description
Hardware Failure	Faulty RAM, dying SSD, or disconnected disk.
Corrupt initramfs	Missing drivers needed to mount /.
Incorrect Kernel Parameters	Wrong root= or rd.lvm.lv in GRUB.
Missing Kernel Modules	Required drivers not loaded (e.g., NVMe, LVM).
Buggy Kernel Update	New kernel has unresolved bugs.
Filesystem Corruption	Improper shutdown or disk errors.

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4. How to Fix a Kernel Panic #

Solution 1: Boot into Rescue Mode #

1. Reboot and hold Shift (BIOS) or spam Esc (UEFI) to open GRUB.
2. Select “Advanced options” → Choose an older kernel (if available).
3. If successful:
   • Rebuild initramfs:bashCopyDownloadsudo update-initramfs -u -k all # Debian/Ubuntu sudo dracut –force # RHEL/Fedora
   • Reinstall GRUB:bashCopyDownloadsudo grub-install /dev/sdX sudo update-grub

Solution 2: Check Kernel Parameters #

1. In GRUB, press e to edit boot entry.
2. Verify root= points to the correct device (e.g., root=/dev/mapper/vg-root).
3. Add nomodeset if GPU drivers are causing issues.

Solution 3: Fix Filesystem Corruption #

1. Boot from a Live USB (e.g., Ubuntu ISO).
2. Mount the root partition:bashCopyDownloadsudo mount /dev/sdXn /mnt
3. Run fsck:bashCopyDownloadsudo fsck -y /dev/sdXn

Solution 4: Hardware Diagnostics #

• Test RAM:bashCopyDownloadsudo memtest86+
• Check disk health:bashCopyDownloadsudo smartctl -a /dev/sdX # For HDD/SSD

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5. Preventing Kernel Panics #

• Regularly update kernels (but test before production).
• Use ext4 or btrfs (more resilient than ext3).
• Monitor disk health (smartctl, badblocks).
• Avoid forced shutdowns (use sync before power-off).

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Final Thoughts #

• If panic persists, boot a Live USB and check logs (/var/log/kern.log).
• For servers, configure kernel crash dumping (kdump).