Unifying Audio with Pipewire

ALSA. Jack. PulseAudio. MIDI. Musescore. Jamulus.

My musical interactions with Linux are not the most complex in the world, but they ain’t trivial. The complexity of the Linux audio landscape has been a stumbling block so far. Pipewire has just gotten me past that.

The title of this article implies that you need to do something other than install Pipewire. So far, this is not true. On my system, at least, it Just works.

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Updating config.sub in a bitbake recipe

config.sub is used to determine, among other things, the architecture of the machine. This is used in the configure script for an autotools based make file.

Older config.sub files don’t know how to handle aarch64, the generic name used for ARM64 servers in the build process. We have a recipe that pulls in code using an older config.sub file and I need to update.

My first approach was to build a patch. This works fine, and it was my fallback, but it is tedious to do for every recipe that needs this update, every time it needs it. It turns out we have a better approach that follows the guide of “don’t repeat yourself.”

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Jamulus Server with a Low Latency Kernel on F33

I’m trying to run a Jamulus server . I got it running, but the latency was high. My first step was to add the real time kernel from CCRMA.

CCRMA no longer ships a super-package for core. The main thing missing seems to be the rtirq package.

  • installed the ccrma repo file.
  • installed the real time Kernel
  • Set the RT kernel as the default.
  • installed the rtirq scripts rpm
  • enabler the systemd module for rtirq
  • rebooted
  • cloned the Jamulus repo from git
  • configure, built, and installed Jamulus from the sources
  • added a systemd module for Jamulus
  • set selinux to permissive mode (starting Jamulus failed without this)
  • started Jamulus
  • ensured I could connect to it
  • stopped jamulus
  • set selinux to enforcing mode
  • restarted Jamulus from systemctl
  • connected from my desktop to the Jamulus server
  • Jammed

It does not seem to have much impact on the latency I am seeing. I think that is bound more by network.

Setting the Default Kernel on Fedora 33

I have a server that I want to run the Real Time Kernel from CCRMA. Once I followed the steps to get the kernel installed, I had to reboot to use it.

Rebooting on a server with a short timeout for grub is frustrating.

Since the Fedora Kernel is installed, and I want to be able to run it as a backup kernel, I had to figure out how to change the default Kernel for Grub2. Most of the docs out there assume that you can list the menu-items in the grub2 config file, but that is a thing of the past. The lines are now auto-generated from a regex match of the places where one might place the vmlinuz files.

I ended up booting the machine and looking at the grub menu, which showed three Kernels installed; two Fedora Kernels and the RT from CCRMA. The RT Kernel was the second one on the list. But Grub is 0 relative, so to set the default Kernel:

sudo grub2-set-default 1

The next time it booted, it was set to the RT kernel;

$ uname -r
5.10.2-200.rt20.1.fc33.ccrma.x86_64+rt


Working with the beaker command line

A graphical User interface has the potential ability to guide users on their journey from n00b13 to power user. If a user has never used a system before, the graphical user interface can provide a visual orientation to the system that is intuitive and inviting.

Once a user starts to depend on a system and use it regularly, they often want to automate tasks performed in that system.

I am reminded of these principals as I start making use of my company’s beaker server. I need short term access to machines of various architectures develop and test our Yocto based coding efforts.

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Getting hostname information from the beaker command line

We use Beaker to allocate and loan computer hardware. If you want to talk to it via the comand line, you can use the bkr executable. Some of the information comes back as json, but beaker tends to speak xml. To look up a host name from a job, you need to be able to parse the xml. To do that, I used the xq execuable from the python yq package. Yes, x and y.

I installed yq via pip. That puts both the xq and yq executablees into ~/.local/bin.

If i know the job ID, I can parse it using the following syntax.

bkr job-results 'J:5078388' | xq -r  ".job | .recipeSet | .recipe| .task | .[] | .roles | .role | .system | .\"@value\""
hpe-apollo-cn99xx-14-vm-12.khw4.lab.eng.bos.redhat.com
hpe-apollo-cn99xx-14-vm-12.khw4.lab.eng.bos.redhat.com

UPDATE: So here is a useful script that makes use of bkr, jq, and xq to list the hostnames of the hosts I currently have on loan from beaker.

for job in $( bkr job-list -o $USER  --unfinished | jq -r '.[]' ) ; do bkr job-results $job | xq -r  ".job | .recipeSet | .recipe| .task | .[] | .roles | .role | .system | .\"@value\"" ; done