Manage a user environment using Nix
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Frequently Asked Questions (FAQ)

Why is there a collision error when switching generation?

Home Manager currently installs packages into the user environment, precisely as if the packages were installed through nix-env --install. This means that you will get a collision error if your Home Manager configuration attempts to install a package that you already have installed manually, that is, packages that shows up when you run nix-env --query.

For example, imagine you have the hello package installed in your environment

$ nix-env --query

and your Home Manager configuration contains

home.packages = [ pkgs.hello ];

Then attempting to switch to this configuration will result in an error similar to

$ home-manager switch
these derivations will be built:
Activating installPackages
replacing old ‘home-manager-path’
installing ‘home-manager-path’
building path(s) ‘/nix/store/b5c0asjz9f06l52l9812w6k39ifr49jj-user-environment’
Wide character in die at /nix/store/ line 79.
collision between ‘/nix/store/fmwa4axzghz11cnln5absh31nbhs9lq1-home-manager-path/bin/hello’ and ‘/nix/store/c2wyl8b9p4afivpcz8jplc9kis8rj36d-hello-2.10/bin/hello’; use ‘nix-env --set-flag priority NUMBER PKGNAME’ to change the priority of one of the conflicting packages
builder for ‘/nix/store/b37x3s7pzxbasfqhaca5dqbf3pjjw0ip-user-environment.drv’ failed with exit code 2
error: build of ‘/nix/store/b37x3s7pzxbasfqhaca5dqbf3pjjw0ip-user-environment.drv’ failed

The solution is typically to uninstall the package from the environment using nix-env --uninstall and reattempt the Home Manager generation switch.

Why are the session variables not set?

Home Manager is only able to set session variables automatically if it manages your Bash or Z shell configuration. If you don’t want to let Home Manager manage your shell then you will have to manually source the


file in an appropriate way. In Bash and Z shell this can be done by adding

. "$HOME/.nix-profile/etc/profile.d/"

to your .profile and .zshrc files, respectively. The file should work in most Bourne-like shells.

How do set up a configuration for multiple users/machines?

A typical way to prepare a repository of configurations for multiple logins and machines is to prepare one “top-level” file for each unique combination.

For example, if you have two machines, called “kronos” and “rhea” on which you want to configure your user “jane” then you could create the files

  • kronos-jane.nix,
  • rhea-jane.nix, and
  • common.nix

in your repository. On the kronos and rhea machines you can then make ~jane/.config/nixpkgs/home.nix be a symbolic link to the corresponding file in your configuration repository.

The kronos-jane.nix and rhea-jane.nix files follow the format

{ ... }:

  imports = [ ./common.nix ];

  # Various options that are specific for this machine/user.

while the common.nix file contains configuration shared across the two logins. Of course, instead of just a single common.nix file you can have multiple ones, even one per program or service.

You can get some inspiration from the Post your home-manager home.nix file! Reddit thread.