install-nix-action

Installs Nix on GitHub Actions runners for Linux and macOS.

Features

• Quick installation (~4s on Linux / ~20s on macOS)
• Multi-user installation with sandboxing enabled by default on Linux
• Support for self-hosted GitHub runners
• Allows specifying Nix installation URL via install_url (the oldest supported Nix version is 2.3.5)
• Allows specifying extra Nix configuration options via extra_nix_config
• Allows specifying $NIX_PATH and channels via nix_path
• Enables KVM on supported machines: run VMs and NixOS tests with full hardware-acceleration
• Pair with a binary cache from cachix-action to speed up re-builds and share binaries across your team

Usage

Create .github/workflows/test.yml in your repo with the following contents:

name: "Test"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v5
    - uses: cachix/install-nix-action@v31
      with:
        nix_path: nixpkgs=channel:nixos-unstable
    - run: nix-build

Usage with Flakes

name: "Test"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v5
    - uses: cachix/install-nix-action@v31
      with:
        github_access_token: ${{ secrets.GITHUB_TOKEN }}
    - run: nix build
    - run: nix flake check

Inputs

Name	Description	Default
install_url	URL to install Nix from. Useful for testing non-stable releases or pinning a specific Nix version (e.g., https://releases.nixos.org/nix/nix-2.3.7/install)	""
install_options	Additional flags to pass to the Nix installer script	""
extra_nix_config	Additional configuration to append to /etc/nix/nix.conf	""
nix_path	Value to set for the NIX_PATH environment variable (e.g., nixpkgs=channel:nixos-unstable)	""
github_access_token	GitHub token for Nix to use when pulling from GitHub repositories. Helps work around rate limit issues. Has no effect when access-tokens is specified in extra_nix_config.	$GITHUB_TOKEN if available
set_as_trusted_user	Add the current user to the trusted-users list	true
enable_kvm	Enable KVM for hardware-accelerated virtualization on Linux	true

Differences from the default Nix installer

Some settings have been optimised for use in CI environments:

• nix.conf settings. Override these defaults with extra_nix_config:

  • The experimental flakes and nix-command features are enabled. Disable by overriding experimental-features in extra_nix_config.

  • max-jobs is set to auto.

  • show-trace is set to true.

  • $USER is added to trusted-users.

  • $GITHUB_TOKEN is added to access_tokens if no other github_access_token is provided.

  • always-allow-substitutes is set to true.

  • ssl-cert-file is set to /etc/ssl/cert.pem on macOS.

• KVM is enabled on Linux if available. Disable by setting enable_kvm: false.

• $TMPDIR is set to $RUNNER_TEMP if empty.

---

FAQ

How do I print the nixpkgs version I've configured?

- name: Print nixpkgs version
  run: nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'

How do I add a nixpkgs channel?

This action doesn't set up any channels by default. Use nix_path to configure optional channels by picking a channel or pinning nixpkgs to a specific commit.

- uses: cachix/install-nix-action@v31
  with:
    nix_path: nixpkgs=channel:nixos-unstable

See also the tutorial on pinning on nix.dev.

How do I run NixOS tests on Linux?

- uses: cachix/install-nix-action@v31
  with:
    enable_kvm: true
    extra_nix_config: "system-features = nixos-test benchmark big-parallel kvm"

How do I install packages via nix-env from the specified nix_path?

nix-env -i mypackage -f '<nixpkgs>'

How do I add a binary cache?

If the binary cache you want to add is hosted on Cachix and you are using cachix-action, you should use their extraPullNames input like this:

- uses: cachix/cachix-action@v31
   with:
     name: mycache
     authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
     extraPullNames: nix-community

Otherwise, you can add any binary cache to nix.conf using install-nix-action's own extra_nix_config input:

- uses: cachix/install-nix-action@v31
  with:
    extra_nix_config: |
      trusted-public-keys = hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=
      substituters = https://hydra.iohk.io https://cache.nixos.org/

How do I configure steps to use my flake's development environment?

You can configure jobs.<job_id>.steps[*].shell to use nix develop.

  # (optional) pre-build the shell separately to avoid skewing the run time of the next
  #            step and have clear point of failure should the shell fail to build
- name: Pre-build devShell
  run: nix build --no-link .#devShells.$(nix eval --impure --raw --expr 'builtins.currentSystem').default

- name: Run a command with nix develop
  shell: 'nix develop -c bash -e {0}'
  run: echo "hello, pure world!"

How do I pass environment variables to commands run with nix develop or nix shell?

Nix runs commands in a restricted environment by default, called pure mode. In pure mode, environment variables are not passed through to improve the reproducibility of the shell.

You can use the --keep / -k flag to keep certain environment variables:

- name: Run a command with nix develop
  run: nix develop --ignore-environment --keep MY_ENV_VAR --command echo $MY_ENV_VAR
  env:
    MY_ENV_VAR: "hello world"

Or you can disable pure mode entirely with the --impure flag:

nix develop --impure

How do I pass AWS credentials to the Nix daemon?

In multi-user mode, Nix commands that operate on the Nix store are forwarded to a privileged daemon. This daemon runs in a separate context from your GitHub Actions workflow and cannot access the workflow's environment variables. Consequently, any secrets or credentials defined in your workflow environment will not be available to Nix operations that require store access.

There are two ways to pass AWS credentials to the Nix daemon:

• Configure a default profile using the AWS CLI
• Install Nix in single-user mode

Configure a default profile using the AWS CLI

The Nix daemon supports reading AWS credentials from the ~/.aws/credentials file.

We can use the AWS CLI to configure a default profile using short-lived credentials fetched using OIDC:

job:
  build:
    runs-on: ubuntu-latest
    # Required permissions to request AWS credentials
    permissions:
      id-token: write
      contents: read
    steps:
      - uses: actions/checkout@v5
      - uses: cachix/install-nix-action@v31
      - name: Assume AWS Role
        uses: aws-actions/configure-aws-credentials@v5.0.0
        with:
          aws-region: us-east-1
          role-to-assume: arn:aws-cn:iam::123456789100:role/my-github-actions-role
      - name: Make AWS Credentials accessible to nix-daemon
        run: |
          sudo -i aws configure set aws_access_key_id "${AWS_ACCESS_KEY_ID}"
          sudo -i aws configure set aws_secret_access_key "${AWS_SECRET_ACCESS_KEY}"
          sudo -i aws configure set aws_session_token "${AWS_SESSION_TOKEN}"
          sudo -i aws configure set region "${AWS_REGION}"

Install Nix in single-user mode

In some environments it may be possible to install Nix in single-user mode by passing the --no-daemon flag to the installer. This mode is normally used on platforms without an init system, like systemd, and in containerized environments with a single user that can own the entire Nix store.

This approach is more generic as it allows passing environment variables directly to Nix, including secrets, proxy settings, and other configuration options.

However, it may not be suitable for all environments. Consult the Nix manual for the latest restrictions and differences between the two modes.

For example, single-user mode is currently supported on hosted Linux GitHub runners, like ubuntu-latest. It is not supported on macOS runners, like macos-latest.

- uses: cachix/install-nix-action@v31
  with:
    install_options: --no-daemon