Terms and Definitions in Nix Project

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Term Context Meaning Related Links
User Environment
Nix A set of "active" applications. These applications usually exist in the Nix store. A single Nix user may have multiple user environments. Profiles and generations are closely related.

Nix Manual - Basic Package Management chapter
Nix Manual - Profiles chapter
Nix Manual - nix-env

(User) Profile Nix Profiles simplify managing and switching between user environments, and thus control which applications and system configurations are in active use. Generally, a profile is a link to a generation, and the corresponding profiles folder collects a list of generations. A standalone Nix installation (i.e. on a Linux distro that is not NixOS) operates mainly on user profiles. In NixOS, there is also a system profile that manages system-wide configuration (e.g. /etc, the kernel, initrd, systemd). Other tools like Home Manager also have their own profiles. By default, a user's active profile is stored at ~/.nix-profile:
$ ls -l ~/.nix-profile
lrwxrwxrwx ... /home/username/.nix-profile ->
Nix Manual: Profiles
Nix Pills - The first profile
Nix An instance of a user environment. When a user makes any change to their environment, such as installing or removing packages, a new generation of the environment is created instead of modifying the environment in-place. This ensures that updates are atomic and the user can easily roll-back to any previous generation if something goes wrong. The current generation is a user's currently active user profile. Nix Manual: Profiles
Derivation Nix A Nix expression which describes a build action. Derivations are analogous to package definitions in other package managers. High-level derivations (such as the ones describing packages in Nixpkgs) get evaluated into low-level derivations (called store derivations), for instance by using the nix-instantiate command. nix-store --realise run the build commands described in the derivation, producing one or more output paths. nix-build is a user-friendly wrapper for the previous two commands. Nix Manual: Glossary - Derivation
Nix Manual: Derivation
Output path Nix A store path produced by a derivation. These are generally analogous to built packages, or pieces of them.
$ ls -ld /nix/store/*-firefox-9*/
dr-xr-xr-x ... /nix/store/v4b8...3d0w-firefox-92.0/
Nix Manual: Derivation
rec { } Nix expressions The { } block contains "mutually recursive" attributes, which means they can refer to each other. Composing the Hello Package
expression evaluator Nix The part of the Nix program which reads and evaluates a Nix expression. Nix Manual: Common Options --arg
Nix Manual: Built-in Functions
stdenv Nix expressions An attribute which contains things expected in the most basic Unix environment. (e.g. Bash shell, gcc, cp, tar, grep, etc.) all-packages.nix: stdenv =]
config.nix or nixpkgs-config.nix NixOS Wiki A Nix expression retrieved by and applied to the all-packages.nix Nix expression. This file enables an end-user to customize the Nix expressions contained in the community-owned NixPkgs list or to define entirely new Nix expressions to use with Nix commands. This file's path can be overridden by the NIXPKGS_CONFIG environment variable. all-packages.nix: config

NixPkgs Release Notes

attribute path nix-env takes this if you pass the `-A` flag [1] an unambiguous identifier for a package
symbolic package name [2] This string represents what you commonly think of as a package. There can be multiple packages with the symbolic name "hello".
selector this term is used in nix-env error messages [3], it seems to be actually a DrvName struct [4] (a derivation name) see "symbolic package name"
selection path nix-shell error message [5] see "attribute path"[6]
derivation name manual[7], source code [8] see "symbolic package name"
package name IRC[9] see "symbolic package name"
attribute selection path source[10] see "attribute path"