musnix

Real-time audio in NixOS

About

musnix provides a set of simple, high-level configuration options for doing real-time audio work in NixOS, including optimizing the kernel, applying the CONFIG_PREEMPT_RT patch to it, and adjusting various low-level system settings.

Basic Usage

Clone this project.

Add the following to your configuration.nix:

{
  imports =
    [ # ...
      /path/to/musnix/clone
    ];

  musnix.enable = true;
  users.users.johndoe.extraGroups = [ "audio" ];
}

To update musnix, run git pull.

Later sections of this document contain information about the various configuration options.

Using musnix as a channel

As an alternative to the above approach, you can instead add musnix as a channel:

sudo -i nix-channel --add https://github.com/musnix/musnix/archive/master.tar.gz musnix
sudo -i nix-channel --update musnix

Add <musnix> to imports in your configuration.nix:

{
  imports =
    [ # ...
      <musnix>
    ];

  musnix.enable = true;
  users.users.johndoe.extraGroups = [ "audio" ];
}

To update musnix, run:

sudo -i nix-channel --update musnix

Using musnix as a flake

As an alternative to the above approaches, you can also add musnix as a flake:

{
  inputs = {
    nixpkgs = { url = "github:NixOS/nixpkgs/nixos-unstable"; };
    musnix  = { url = "github:musnix/musnix"; };
  };
  outputs = inputs: rec {
    nixosConfigurations = {
      example-config = inputs.nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules =
          [ # ...
            inputs.musnix.nixosModules.musnix
            ./configuration.nix
          ];
        specialArgs = { inherit inputs; };
      };
    };
  };
# ...

Base Options

musnix.enable

Description: Enable musnix, a module for real-time audio.
Type: boolean
Default value: false
NOTE: This option must be set to true to use other musnix base options.
Details: If enabled, this option will do the following:
- Activate the performance CPU frequency scaling governor.
- Set vm.swappiness to 10.
- Set the following udev rules:
```
KERNEL=="rtc0", GROUP="audio"
KERNEL=="hpet", GROUP="audio"
DEVPATH=="/devices/virtual/misc/cpu_dma_latency", OWNER="root", GROUP="audio", MODE="0660"
```
- Set the following PAM limits:
```
@audio  -       memlock unlimited
@audio  -       rtprio  99
@audio  soft    nofile  99999
@audio  hard    nofile  99999
```
- Set the following environment variables to default install locations in NixOS:
  - VST_PATH
  - VST3_PATH
  - LXVST_PATH
  - LADSPA_PATH
  - LV2_PATH
  - DSSI_PATH
- Allow users to install plugins in the following directories:
  - ~/.vst
  - ~/.vst3
  - ~/.lxvst
  - ~/.ladspa
  - ~/.lv2
  - ~/.dssi

musnix.alsaSeq.enable

Description: If enabled, load ALSA Sequencer kernel modules. Currently, this only loads the snd_seq and snd_rawmidi modules.
Type: boolean
Default value: true

musnix.ffado.enable

Description: If enabled, use the Free FireWire Audio Drivers (FFADO).
Type: boolean
Default value: false

musnix.rtcqs.enable

Description: If enabled, install the rtcqs command-line utulity, which analyzes the system and makes suggestions about what to change to make it more audio-friendly.
Type: boolean
Default value: false

musnix.soundcardPciId

Description: The PCI ID of the primary soundcard. Used to set the PCI latency timer.

To find the PCI ID of your soundcard:
```
lspci | grep -i audio
```
Type: string
Default value: ""
Example value: "00:1b.0"
NOTE: If you have a USB sound card, this option is not useful.

Kernel Options

NOTE: The following kernel options can be used without setting musnix.enable = true;

musnix.kernel.realtime

NOTE: Enabling this option will rebuild your kernel.
Description: If enabled, this option will apply the CONFIG_PREEMPT_RT patch to the kernel.
Type: boolean
Default value: false

musnix.kernel.packages

Description: This option allows you to select the real-time kernel used by musnix.
Type: package
Default value: pkgs.linuxPackages_rt
Available packages:
- pkgs.linuxPackages_5_15_rt
- pkgs.linuxPackages_6_1_rt
- pkgs.linuxPackages_6_6_rt
or:
- pkgs.linuxPackages_rt (currently pkgs.linuxPackages_6_1_rt)
- pkgs.linuxPackages_latest_rt (currently pkgs.linuxPackages_6_6_rt)

rtirq Options

NOTES:

The following rtirq options can be used without setting musnix.enable = true;
musnix.kernel.realtime must be set to true to use these options.

musnix can also install and run the rtirq script as a systemd service.

To see a list of options for using this feature, use the following command:

nixos-option musnix.rtirq

To see a description of one of the listed options (in this case enable):

nixos-option musnix.rtirq.enable

Other Options

musnix.das_watchdog.enable

Description: If enabled, start the das_watchdog service. This service will ensure that a realtime process won't hang the machine.
Type: boolean
Default value: true if musnix.kernel.realtime = true, otherwise false

Communication

IRC: #musnix on libera.chat

the-furry-hubofeverything/musnix