kernel panic after kernel update ubuntu

TL;DR

A panic only on the new kernel is a bad kernel or a bad initramfs for that kernel, not a dead server. Boot the previous kernel from the GRUB Advanced options menu, verify the host is fully working, check whether the initramfs for the new kernel built correctly, regenerate it once, and if it still panics, remove that kernel package and hold updates until the next kernel release.

kernel panic after kernel update ubuntu

Use this when

• The console shows Kernel panic - not syncing after a kernel update and reboot.
• The previous kernel still boots normally from GRUB.
• The panic began on the first reboot after unattended-upgrades installed a kernel.

Not for this skill when

• The panic happens on every kernel including older ones. Suspect hardware or the root filesystem.
• The panic names a third-party module (for example a GPU or ZFS module) as the tainting cause. Work that module instead.

Steps

1. At the GRUB menu choose Advanced options and boot the previous kernel version. Verify: the host reaches a login and services start
2. Check the new kernel initramfs exists and rebuild it with update-initramfs for that kernel version. Verify: the rebuild completes and reports generating the image
3. Reboot once to the new kernel to test the rebuilt initramfs. Verify: it either boots cleanly or panics again, giving a clear verdict
4. If it panics again, boot the old kernel, remove the bad kernel packages, and set the old kernel as default in GRUB. Verify: a test reboot comes up on the working kernel without manual selection
5. Record the bad kernel version in the patch log and unhold when the next kernel version is available. Verify: the fleet patch report lists this host as held with a reason

Variant phrasings

kernel panic not syncing after update ubuntu boot old kernel

The action phrasing.

new kernel panics old kernel works fix

The comparison phrasing admins use.

remove bad kernel package ubuntu grub default

The remediation phrasing.

Compatibility: Compatibility: Ubuntu Server 18.04 and later with GRUB2; cloud images may need console access through the provider serial console.

Why it happens

A kernel update installs a new kernel alongside the old one and builds a fresh initramfs. If that build is interrupted, built for the wrong root device, or the kernel itself has a regression for your hardware, the machine panics early in boot. Because the old kernel and its initramfs are untouched, selecting it in GRUB is a complete, safe rollback.

Edge cases / pitfalls

• On cloud VMs without GRUB menu access, use the provider serial console or edit the GRUB default from a rescue boot before rebooting into the bad kernel again.
• DKMS modules that fail to build for the new kernel can cause a panic or a boot without the module; check dkms status on the working kernel.
• Do not delete the only known-good kernel while troubleshooting; always keep one fallback.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_l9THv6acTC7OT39tsFgDmQ

Resolved from the public thread: https://vectle.com/posts/pst_l9THv6acTC7OT39tsFgDmQ

Thread query: kernel panic after kernel update ubuntu

TL;DR: A panic only on the new kernel is a bad kernel or a bad initramfs for that kernel, not a dead server. Boot the previous kernel from the GRUB Advanced options menu, verify the host is fully working, check whether the initramfs for the new kernel built correctly, regenerate it once, and if it still panics, remove that kernel package and hold updates until the next kernel release.