Raspberry Pi4B / (64bit 21.04): 5.11 kernel tree's -1014-raspi / 1015-raspi apt update kills the OS

in flag

I've now got two of my RPi4B installations (Xubuntu, 64bit) of 21.04 into a non-bootable state after a normal apt update with the kernel tree update to 5.11.0-1014-raspi or 5.11.0-1015-raspi. I made the first error report on that thing a week or so back when the first one of my RPi4B builds booted into the Rainbow of Death and I warned the devs that there is an issue with that. I thought it'd been safe to update on another RPi4B running the same OS, now it's booting to the underscore of doom.

How can I fix the bootloader, if at all? Any help is appreciated. I have no clue whatsoever what goes into the whole uboot segment and so forth, and I sure as hell wouldn't want to reinstall the entire OS from scratch.

The first unbootable unit shows absolutely nothing going wrong in /var/log/ , here's the last of the logs from that one:

My main question is; can I somehow bring the bootloader back to life, since that is what seems to be the problem here? When the first unit got zapped because of an apt-update, I did copy the boot partition data from the then-still-working one and tried rsyncing the data, to no avail.

There is absolutely no documentation on how Ubuntu's Uboot works on RPi4B's, at least I haven't found any. If someone can point me to the Raspberry Pi 4B U-boot documentation, I would be very happy to read it. Now I'm just out of luck with two non-functional OS builds that worked perfectly well before the routine kernel update.

Please advice. Thanks.

UPDATE 1: I got a fresh USB stick, flashed Ubuntu Server 64-bit for the RPi4B with rpi-imagerand booted into a fresh system. After running apt updates and upgrades, it too updated to the -1015-raspi, after which I rebooted and it went itno the "rainbow of death" with four blinks in a row (which would indicate that a bootloader was not found).

So, another one bites the dust. I was hoping to maybe be able to get a working bootloader that way, but no such luck.

UPDATE 2: There's now a bugreport at

UPDATE 3: SOLVED I solved it on my own without having to reinstall by waiting for a new apt update on the kernel packages and then just copied the boot partition data from a fresh install to the broken OS's one. (See the answer below.)

Nmath avatar
ng flag
You are not using the term "bricked" correctly. It seems that your hardware is functional. If this is about a **bug** then the question is off-topic. You should file a bug report. If your installation is corrupted beyond repair, then you should reinstall the OS. Otherwise, if you have a specific problem that you want help with, you should provide more context and actionable details. Your narrative descriptions of the steps you took to reproduce this problem are not clear and specific enough to help.
The Pthyister avatar
in flag
I corrected the wording; sorry -- what I meant is that the OS is in a completely non-booting state. I ran the apt-update on both of those OS installs as I regularly do; as is appropriate, and it seems that in both instances, the kernetree update from to broke the OS's. The first one boots straight into the "rainbow of death", the second one into the "underscore of doom". I also updated my question.
Nmath avatar
ng flag
The nature of bugs is that they need to be fixed by developers. Bugs can't be fixed if developers don't know about them. You should file a bug report, and in the meantime, do not use the kernel that is not working for your hardware
in flag

I got this fixed on my own by just waiting for a new kernel update to be out on the 64bit Ubuntu on RPi4B. I wrote the latest image of Ubuntu Server 64bit on to a USB stick using rpi-imager and then ran the initial setup on the RPi4B on it. I then ran an install on all the available apt update / apt upgrade packages, and made sure it was booting without problems after these updates.

I then copied all the boot-partition's files from the healthy new Ubuntu Server to the damaged OS's boot partition, excluding meta-data, network-config and user-data files as well as the cmdline.txt and config.txt.

Plugged in and prayed, after a while of fscking in the four-dotted (. . . .) Ubuntu screen, both of the OS's came back to life! I am extremely happy now.

So yep, it was a bootloader problem like I thought. Just a word of advice to keep an eye out on this potential pitfall, lest you end up in the same type of limbo after a kernel-related apt update. Back up often! :o)

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