home-manager/FAQ.md

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
hello-2.10

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:
  /nix/store/xg69wsnd1rp8xgs9qfsjal017nf0ldhm-home-manager-path.drv
[…]
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/64jc9gd2rkbgdb4yjx3nrgc91bpjj5ky-buildenv.pl 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

~/.nix-profile/etc/profile.d/hm-session-vars.sh

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

. "$HOME/.nix-profile/etc/profile.d/hm-session-vars.sh"

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