Terms and Definitions in Nix Project

Terms and Definitions

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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. This is an important concept further explored in User Environment. Profiles and generations are closely related.	Nix Manual - Basic Package Management chapter Nix Manual - Profiles chapter Nix Manual - nix-env
(User) Profile	Nix	Most generally, a profile is a link to a generation, and there's a profiles (note the s) folder which collects types of profiles together so that they form lists of generations. In standalone Nix (e.g. on a different Linux distro), it's primary use is user profiles. In NixOS, there's also the system profile, which manages system-wide configuration (e.g. /etc, the kernel, initrd, systemd). Tools like Home Manager also have their own profile (which would also be per-user). The user's active profile is defined in ~/.nix-profile, and is what all nix-env commands would operate on by default. ❯ ls -l ~/.nix-profile lrwxrwxrwx 1 username users ... /home/username/.nix-profile -> /nix/var/nix/profiles/per-user/username/profile	Nix Manual: Profiles Nix Pills - The first profile
Generation	Nix	A revision of a user environment, newly created every time the system is updated (with old ones being preserved until manually removed). Technically, each generation is simply a link to a specific user environment in the Nix store. This term connotes the cloning and modification of an existing user environment. Nix's environment rollback facilities rely on Generations. The current generation is a user's currently selected user environment, and is generally selected via the active profile (which is just a symlink, normally in /nix/var/nix/profiles/).	Nix Manual: Profiles
Derivation	Nix	A Nix expression which describes a build action. High-level derivations (like the ones describing packages in Nixpkgs), get evaluated into low-level derivations (called store derivations — because they wind up in the Nix store). nix-instantiate is the command which translates high-level derivations into low-level ones. nix-store --realise can then check and finish their build for the nix store, producing output path(s). nix-build is a user-friendly wrapper for the previous commands. Derivations are analogous to package definitions in other package managers.	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.	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"