Terms and Definitions in Nix Project

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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
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. When evaluated, it creates one or more entries in the Nix Store. The nix-instantiate command is the command which creates entries in the Nix Store, while the nix-env and nix-build commands are its user-friendly interface. Nix Manual: Glossary -> Derivation
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"

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