pyrox.dev
1# Declarative Package Management {#sec-declarative-package-mgmt}
2
3With declarative package management, you specify which packages you want
4on your system by setting the option
5[](#opt-environment.systemPackages). For instance, adding the
6following line to `configuration.nix` enables the Mozilla Thunderbird
7email application:
8
9```nix
10{
11 environment.systemPackages = [ pkgs.thunderbird ];
12}
13```
14
15The effect of this specification is that the Thunderbird package from
16Nixpkgs will be built or downloaded as part of the system when you run
17`nixos-rebuild switch`.
18
19::: {.note}
20Some packages require additional global configuration such as D-Bus or
21systemd service registration so adding them to
22[](#opt-environment.systemPackages) might not be sufficient. You are
23advised to check the [list of options](#ch-options) whether a NixOS
24module for the package does not exist.
25:::
26
27You can get a list of the available packages as follows:
28
29```ShellSession
30$ nix-env -qaP '*' --description
31nixos.firefox firefox-23.0 Mozilla Firefox - the browser, reloaded
32...
33```
34
35The first column in the output is the *attribute name*, such as
36`nixos.thunderbird`.
37
38Note: the `nixos` prefix tells us that we want to get the package from
39the `nixos` channel and works only in CLI tools. In declarative
40configuration use `pkgs` prefix (variable).
41
42To "uninstall" a package, remove it from
43[](#opt-environment.systemPackages) and run `nixos-rebuild switch`.
44
45```{=include=} sections
46customizing-packages.section.md
47adding-custom-packages.section.md
48```