Difference between installing via nix-env and configuration.nix?

[jonringer]

@vulcao

I’m new to Nix and NixOS and have been installing new packages by adding them to environment.systemPackages in /etc/nixos/configuration.nix then rebuilding, which I thought was the same as using the package manager

packages listed in configuration.nix get added to a system profile. This also gives you the generations

@vulcao

Today I used nix-env -i hello and realized that it doesn’t put that package in the configuration.nix file.

no, nix-env is meant to give you a similar experience to other package managers, however, i manages it’s own gcroots (what derivations can be cleaned up), and even generations. Generally you should avoid using nix-env for package installation as it doesn’t leverage the power of nix.

@vulcao

What’s the difference between those installation methods? Is it like installing to /Applications vs ~/Applications on macOS?

Somewhat. In terms of user vs system installation, yes. However, nixos is different from normal FHS operating systems in that there’s a layer of indirection when you install something, so your PATH and other environment variables just reference the current “profile” or generation

$ echo $PATH
/run/wrappers/bin:/home/jon//.nix-profile/bin:/etc/profiles/per-user/jon/bin:/nix/var/nix/profiles/default/bin:/run/current-system/sw/bin:/home/jon//.cargo/bin:/home/jon//.config/nixpkgs/bin

/home/jon//.cargo/bin:/home/jon//.config was added by me.