Replacing Ubuntu kernel on Pi 4B

[phantomgtr-1]

I used to enable Ubuntu realtime kernel or lowlatency kernel in my other x64 machines (i.e. pro enable realtime-kernel). Yet I can’t do it on Pi. Now I got 3 kernels inside Pi, viz, ordinary one, RT, and lowlatency, but only the ordinary kernel is boot.




As I can’t find the answer in Google, may I know how to do it on Pi 4B? Or was Ubuntu simply not supporting RT kernel in Pi?
Thanks all.

[MAFoElffen]

No it does not support RT Kernel for Pi.

Not just for Raspberry Pi. Ubuntu Pro services are not available for the ARM architecture at all. The Pro package is installable on ARM, but it provides nothing that is usable.

I asked the Ubuntu Pro Support if that is for future compatibility in case they ever decided to support ARM... and they didn't know. LOL.

[phantomgtr-1]

No it does not support RT Kernel for Pi.

Not just for Raspberry Pi. Ubuntu Pro services are not available for the ARM architecture at all. The Pro package is installable on ARM, but it provides nothing that is usable.

I asked the Ubuntu Pro Support if that is for future compatibility in case they ever decided to support ARM... and they didn't know. LOL.

MAFoElffen, Thanks a lot. That's pity. And may I know how about lowlatency kernel?

[MAFoElffen]

Wait a second... Let me go back on what I said.

I thought you were talking about Ubuntu Pro, where they are offering "Realtime kernel patching" during updates, where they if a kernel updates, and it applies it (in memory) until the system is rebooted. Ubuntu Pro, with all of it's servcies does not work for ARM architecture...

I am right, but still, I was also wrong. (In a way.) They are not generally available from the repo's & not from Ubuntu Pro, but...

When I started looking for low-latency kernels in ARM and I see them for arm64. But look what else I found:

https://ubuntu.com/blog/what-is-real-time-linux-i
(As of February 2023... So still fresh and new.)
https://ubuntu.com/engage/an-introdu...eal-time-linux
https://ubuntu.com/blog/real-time-kernel-technical

But it still has no mention of ARM or ARM64... And does state how it is applied, is still through Ubuntu Pro, like I said, which doesn't work with with ARM or ARM64...

But then I saw this, which is very 'different':
https://metebalci.com/blog/latency-o...ux-4.9-kernel/
https://metebalci.com/blog/latency-o...x-4.19-kernel/

That got me looking again, and then I struck Gold!!!
https://discourse.ubuntu.com/t/insta...berry-pi/34833
^^^
Experimental, new, & Experimental... The PPA is linked in that blog post there. Use at your own risk.

lowlatency kernels for arm64? Yes, I see those at the port repo... I have not used them, but i know they exist for arm64.

But then this:
https://forum.snapcraft.io/t/snappin...berry-pi/20462

[phantomgtr-1]

That got me looking again, and then I struck Gold!!!
https://discourse.ubuntu.com/t/insta...berry-pi/34833
^^^
Experimental, new, & Experimental... The PPA is linked in that blog post there. Use at your own risk.

lowlatency kernels for arm64? Yes, I see those at the port repo... I have not used them, but i know they exist for arm64.

Thanks a lot, MAFoElffen. I've come across that post, too. By that time I wish to try the official one before going for others. Now I learnt there is no official one for Pi, then I'll try this one.

Thanks again

[martinr]

Ubuntu Pro services are not available for the ARM architecture at all. The Pro package is installable on ARM, but it provides nothing that is usable.

Hi @MAFoElffen,

Let me quickly chime in on the Ubuntu Pro support for ARM and especially for RPi.

Supported architectures eligible for Ubuntu Pro are stated on this page.

It states:
Architectures supported with ESM: Ubuntu 22.04 LTS (Jammy Jellyfish) Until 2032: amd64, s390x, amd64, arm64, s390x, ppc64el, RISC-V.

No mention about RT Kernel, so no support for that unfortunately, but esm-apps and esm-infra security updates should be available for arm64 architectures.

Now it's important to know which architecture your RPi is, because some are 32 bit and others 64 bit. That can be checked by running:

$ dpkg --print-architecture

on your RPi.

Check your available Pro services with:

$ pro status

But be aware that the pro app has (had) some trouble in correctly presenting supported services on RPi (see here and here).
It used to show that realtime-kernel was available for armhf architecture and that is not the case. That bug seems to be gone now.