User Package Management

NixOS allows users to manage packages independently from the base system. Service and normal users can install packages from nixpkgs or other sources in their user profile. This is a powerful mechanism to tailor an application’s runtime environment to the exact needs of the deployment. You can also use this approach to install tools that you want to use interactively.

User packages are installed to ~/.nix-profile, consisting of the usual subdirectories like bin, include, lib, etc

Installing packages that are already present in the system environment is safe. This doesn’t use additional space if it’s exactly the same package. Other versions, newer or older than system packages, can be installed without conflicts.

Custom User Environments

The user profile can be customized by building an environment with buildEnv and installing it. Packages from arbitrary sources can be mixed and pinned to specific versions.

Create a file like myproject_env.nix which specifies the packages to be installed:

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let
  # Imports. Which package sources should be used?
  # Use a pinned NixOS version, see https://nixos.org/channels
  pkgs = import (fetchTarball https://releases.nixos.org/nixos/19.09/nixos-19.09.2149.58a9acf75a3/nixexprs.tar.xz) {};
  # ...or just use the current NixOS version of the platform, currently 19.03
  # pkgs = import <nixpkgs> {};
in
pkgs.buildEnv {
  name = "myproject-env";
  paths = with pkgs; [
    libjpeg
    zlib
    ffmpeg
    nodejs-10_x
    electron
  ];
  extraOutputsToInstall = [ "dev" ];
}

The code shown above defines an environment with 5 packages installed from a specific build of NixOS 19.09. The pinned NixOS version can be newer or older than the installed system version.

Pinning the version of the import prevents unwanted changes in your application’s dependencies but you are responsible for updating the imports to get security fixes from upstream.

See https://nixos.org/nixos/packages.html for a list of packages. Use the attribute name from the list and include it in paths. The attribute name can differ from the package name. For some packages, multiple versions are available.

Dry-run this expression with:

nix-build myproject_env.nix

A result symlink now points to the generated environment. It can be inspected and used manually, but is not yet an active part of the user profile.

Run

nix-env -i -f myproject_env.nix

to install the env in your profile. Now its binaries are available in PATH and libraries/include files should get found by the compiler.

To update, install the environment again with the same command. This picks up changes in myproject_env.nix and package updates (if the imports are not pinned to a specific version).

Collisions With Existing Packages

Packages included in an environment can collide with packages from other environments or with separately installed packages (we recommend not to do this).

You may encounter an error like this:

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$ nix-env -if myproject_env.nix
installing 'myproject-env'
building '/nix/store/c3qwfxvdhjgirvzxdhc2h0wpa59fplvk-user-environment.drv'...
error: packages '/nix/store/s1vqsx5jd7xxq3ihwxz4sc6h1fwnh3v1-myproject-env/lib/libz.so' and '/nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/lib/libz.so' have the same priority 5; use 'nix-env --set-flag priority NUMBER INSTALLED_PKGNAME' to change the priority of one of the conflicting packages (0 being the highest priority)
builder for '/nix/store/c3qwfxvdhjgirvzxdhc2h0wpa59fplvk-user-environment.drv' failed with exit code 1
error: build of '/nix/store/c3qwfxvdhjgirvzxdhc2h0wpa59fplvk-user-environment.drv' failed

You can check for potential collisions by viewing the list of packages in the user profile:

nix-env -q --installed

To avoid/resolve conflicts, remove the package and install the user env afterwards:

nix-env -e zlib-1.2.11
nix-env -if myproject_env.nix

Multiple Package Outputs

Packages can have multiple “outputs” which means that not all files are installed by default. If you want to install libraries to build against, including dev in extraOutputsToInstall should be sufficient. You can check which outputs are available with the following command:

nix show-derivation -f '<nixpkgs>' zlib | jq '.[].env.outputs'

This shows the outputs for zlib: out, dev and static. -f sets the inspected NixOS version, which can be an URL like in myproject_env.nix.

Assume we have an user env with just zlib. If extraOutputsToInstall is empty, these files would be installed:

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$ nix-build myproject_env.nix && tree -l result
/nix/store/s1vqsx5jd7xxq3ihwxz4sc6h1fwnh3v1-myproject-env
result
├── lib -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/lib
│   ├── libz.so -> libz.so.1.2.11
│   ├── libz.so.1 -> libz.so.1.2.11
│   └── libz.so.1.2.11
└── share -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/share
    └── man
        └── man3
            └── zlib.3.gz

If you add dev to extraOutputsToInstall, include and lib/pkgconfig would be installed, too:

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$ nix-build myproject_env.nix && tree -l result
/nix/store/a078dzvn7w7pp3mn0gxig8mpc14p2g4s-myproject-env
result
├── include -> /nix/store/ww7601vx7qrcwwfnwzs1cwwx6zcqdjz3-zlib-1.2.11-dev/include
│   ├── zconf.h
│   └── zlib.h
├── lib
│   ├── libz.so -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/lib/libz.so
│   ├── libz.so.1 -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/lib/libz.so.1
│   ├── libz.so.1.2.11 -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/lib/libz.so.1.2.11
│   └── pkgconfig -> /nix/store/ww7601vx7qrcwwfnwzs1cwwx6zcqdjz3-zlib-1.2.11-dev/lib/pkgconfig
│       └── zlib.pc
└── share -> /nix/store/iiymx8j7nlar3gc23lfkcscvr61fng8s-zlib-1.2.11/share
    └── man
        └── man3
            └── zlib.3.gz

Mixing Packages From Different Sources

You can import packages from different NixOS versions or other sources:

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let
  pkgs = import <nixpkgs> {};
  pkgs_19_09 = import (fetchTarball https://releases.nixos.org/nixos/19.09/nixos-19.09.2149.58a9acf75a3/nixexprs.tar.xz) {};
in
pkgs.buildEnv {
  name = "myproject-env";
  paths = with pkgs; [
    pkgs_19_09.libjpeg
    zlib
  ];
  extraOutputsToInstall = [ "dev" ];
}

This installs the zlib from the platform NixOS version but libjpeg from NixOS 19.09.