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If I were to install the packages linux-ubuntu-modules-2.6.22-14-rt and linux-headers-2.6.22-14-rt , what would be the downfalls of using a realtime kernal?

I'm a musician, and getting JACK set up basically requires a realtime kernal (as does every other music based thing with Linux). However, will I lose any functionality from this?

ie: Graphics, speed, games, development (Tkinter?), Wine, etc.

Also, how can I remove my old 2.4 kernel that came with Ubuntu? I would have two 2.6's as well as two 2.4's (one regular and one realtime of each), and I find the 2.4's burdensome.

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Dani AI

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Short, factual correction and context: the realtime (PREEMPT_RT) kernel changes how the kernel schedules and handles interrupts to reduce latency and jitter — it does not “reserve 95% of the CPU” for an audio program. The common “95” number you’ve seen in many JACK guides is an rtprio (real‑time scheduling priority) value, not a percent of CPU time; real‑time tasks can preempt normal tasks, so a badly configured RT priority can starve other processes, but the kernel itself isn’t carving out CPU slices. (kernel.org)

Pros and cons, tied to the thread: an RT kernel gives much lower and more deterministic audio latency (good for JACK/Ardour), but it can expose driver/module issues (especially with closed‑source or out‑of‑tree drivers), subtle stability/power‑management differences, and slightly different throughput behaviour. The Ubuntu “linux-rt” packages are essentially metapackages that pull in the RT image plus matching modules — install the right module package for the RT image or the hardware drivers may be missing. Keeping a normal kernel as a fallback is the usual, safe approach. (This echoes ’s decision to keep both and ’s advice to remove unwanted kernels via the package manager.) (wiki.ubuntu.com)

Practical checks and safe cleanup: verify the running kernel first with uname -r. Use the package manager (or Synaptic) to remove old 2.4 images and then regenerate the boot menu; a distro‑recommended cleanup (autoremove / purge) is the safest route to free /boot afterward. After removing kernels, run the grub update command so the menu reflects current images. Example checks:

uname -r
sudo update-grub

(askubuntu.com)

JACK checklist (common fixes): create/use an audio group and give it rtprio and memlock limits (example lines), then logout/login; enable threaded IRQs / use an rtirq-style prioritiser; set CPU governor to performance while recording; and confirm the RT kernel has the matching module package installed. Example limits (place in /etc/security/limits.d/audio.conf):

@audio   -  rtprio     95
@audio   -  memlock    unlimited

Restart session after changes and start JACK with realtime enabled. If issues persist, test with the generic (non‑RT) kernel to confirm whether problems are kernel/driver related. (jackaudio.org)

Summary: use the RT kernel for serious audio sessions after setting the audio limits and IRQ priorities, keep the stock kernel for everyday desktop/gaming, and remove the old 2.4 kernels via the package manager only after confirming the running kernel with uname -r. (kernel.org)

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Okay, this is solved on my own, with a little research.

Realtime kernels dedicate 95% of your CPU to the current Audio application running. So if Ardour is recording, 95% of your CPU is dedicated to Ardour, leaving but 5% to your other applications.

So, using a realtime kernel for desktop use isn't the greatest choice. So you should keep a regular and a realtime kernel (or not the latter, if you don't use audio applications too much) to balance your machine.

Also, the package linux-rt is required by the realtime kernel, or else wireless and many other features will not work.

Member Avatar for John A

>Also, how can I remove my old 2.4 kernel that came with Ubuntu?

If I recall correctly, you can remove kernels on a Debian-based system with:

apt-get remove linux-image-version

If you don't know the exact version, try searching through your packages:

dpkg -l "linux-image*2.4*"

Something like that.

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Thanks, John A. I installed the rt kernel, and removed all of my 2.4's. Everything's working now, except JACK. But that's a different thread... (HINT HINT JOHN A)

Member Avatar for John A

I've never used JACK, so can't help you there. :)

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