[Post-Install] Upgrade from 25.10 failing to boot with memory error

[oshunluvr]

I have been attempting to upgrade my laptop from 25.10 Kubuntu to 26.04 three times so far with no success. Each time I get

error: out of memory. Press any key to continue..._

followed by

KERNEL PANIC... VFS: Unable to mount root fs on UUID=..."

AI is, as always totally useless.

Attempting booting into recovery mode the results are the same with an additional message of "Loading initial ramdisk..." prior to the above errors.

My belief is that initramfs is failing to load (the "out of memory" error) thus, the boot drive cannot be mounted and used (the kernel panic).

The initrd.img prior to upgrade is 222mb and after 298.3mb. These are both quite large IME but this machine has an nVidia video card so the dkms drivers take up some space. By comparison, my desktop PC with an AMD video card has a 70mb initrd,img.

The laptop specs:

• Lenovo Yoga 730-15IKB
• Intel i7-8550u
• 16GB RAM
• 1tb Samsung nvme
• secure boot disabled.

I have seen/heard about this error before, but it's been many years. Thanks to a working, fresh 26.04 install, I have the ability to roll-back to the un-updated 25.10, but after three tries I'm searching for a final solution. I'd prefer to use an upgraded install rather than having to redo everything on a new install.

I currently am not using the nvidia and instead are using the built-in Intel video to save battery life so I'm considering just removing the nVIdia drivers altogether and re-upgrading, but that's a temporary hack, not a solution.

Is it possible that the/boot/efi partition size is an issue? It's currently 256mb w/217mb available but the initrd.img on the working 25.10 install is over the available size also at 222mb.

[Snowhog]

Only because.....

AI Overview

The "out of memory" error during the upgrade likely filled or corrupted your /boot partition or interrupted the initramfs generation for the new kernel. This causes the subsequent VFS: Unable to mount root fs kernel panic because the system cannot load the required root file system drivers at boot.

How to Fix the Kernel Panic

• Boot an older kernel: Hard-reboot your computer, press and hold Shift (or tap Esc on UEFI) during startup to open the GRUB menu. Select Advanced options for Ubuntu/Kubuntu and choose a working older kernel version from before the upgrade.

• Check disk space: Once logged into your system, check if your boot partition is full using df -h. Clear out old kernels if space is critically low.

• Regenerate initramfs: Find the exact version string of the broken kernel (e.g., via ls /lib/modules), then update the RAM disk image manually via terminal:
  sudo update-initramfs -u -k <version-number-of-broken-kernel>

• Update GRUB: Reconfigure your bootloader configuration so it maps correctly to the regenerated file:
  sudo update-grub

• Reboot: Restart your computer normally into the newly updated kerne