[SOLVED] Upgrade from 25.10 failing to boot with memory error - and no keyboard/mouse after fixing boot issue

[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

[oshunluvr]

As I said. AI is useless. None of that applies.

[oshunluvr]

So I've tried removing the nvidia driver altogether, reducing the initramfs size as small as I can, expanding intram memory - nothing helps.

Oddly, a new 26.04 install works perfectly.

[oshunluvr]

Clearly the issue lies with the initrd.img :

After removing the nVIdia driver from the 25.10 install, the initrd.img file went from 288MB to 213MB. Upgrading to 26.04 brought the initrd.img to 302MB with nvidia driver and 238mb without the NVidia driver.

The initrd.img file on a new 26.04 install on the same computer without the nVidia driver is only 88MB and boots both kernels.

I changed every setting I know about to "fix" the initrd.img but no kernels will boot when upgrading from 25.10 to 26.04.

[oshunluvr]

More research into initrrd.img revealed that one big change from 25.10 to 26.04 re. initrd.img is removal of initramfs tools and replacing them with dracut tools. I booted my 25.10 install and purged initramfs and installed dracut and rebuilt initrd.img. It went from 288mb to 122mb!

Still 40 MB larger than a "clean" 26.04 install, but trimming more than half the initramfs size is astonishing.

I'm re-attempting the upgrade to 26.04 now...

[oshunluvr]

This time, after the upgrade, the system booted to either kernel! During the upgrade, the nvidia drivers were re-installed but with dracut the initrd.img files were 198mb - 100mb smaller than before and apparently, a bootable size.

However - NO keyboard, mouse, or the touch screen would work AT ALL. I was unable to log in.

Thankfully, I had SSH setup from the 25.10 install and the upgrade kept it. I was able to log in remotely and troubleshoot. It turned out x11 had not been installed and my input devices did not work until I installed x11, reset the ksmserver, and rebooted. Here's the command that fixed it:

sudo apt install xorg plasma-session-x11 -y
sudo apt install qtchooser
qdbus org.kde.ksmserver /KSMServer logout 0 0 0
sudo reboot

After reboot, I could boot to and log in with both kernels 6.17 and 7.0.

Additional note: Ubuntu ESM Pro no longer loaded ESM updates. I just had to detach and re-attach EDM Pro to get it to work. Probable due to the change from 25.10 to 26.04.