nixpkgs/nixos/doc/manual/from_md/configuration/declarative-packages.section.xml

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<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude" xml:id="sec-declarative-package-mgmt">
<title>Declarative Package Management</title>
<para>
With declarative package management, you specify which packages you
want on your system by setting the option
<xref linkend="opt-environment.systemPackages" />. For instance,
adding the following line to <literal>configuration.nix</literal>
enables the Mozilla Thunderbird email application:
</para>
<programlisting language="bash">
environment.systemPackages = [ pkgs.thunderbird ];
</programlisting>
<para>
The effect of this specification is that the Thunderbird package
from Nixpkgs will be built or downloaded as part of the system when
you run <literal>nixos-rebuild switch</literal>.
</para>
<note>
<para>
Some packages require additional global configuration such as
D-Bus or systemd service registration so adding them to
<xref linkend="opt-environment.systemPackages" /> might not be
sufficient. You are advised to check the
<link linkend="ch-options">list of options</link> whether a NixOS
module for the package does not exist.
</para>
</note>
<para>
You can get a list of the available packages as follows:
</para>
<programlisting>
$ nix-env -qaP '*' --description
nixos.firefox firefox-23.0 Mozilla Firefox - the browser, reloaded
...
</programlisting>
<para>
The first column in the output is the <emphasis>attribute
name</emphasis>, such as <literal>nixos.thunderbird</literal>.
</para>
<para>
Note: the <literal>nixos</literal> prefix tells us that we want to
get the package from the <literal>nixos</literal> channel and works
only in CLI tools. In declarative configuration use
<literal>pkgs</literal> prefix (variable).
</para>
<para>
To <quote>uninstall</quote> a package, simply remove it from
<xref linkend="opt-environment.systemPackages" /> and run
<literal>nixos-rebuild switch</literal>.
</para>
<xi:include href="customizing-packages.section.xml" />
<xi:include href="adding-custom-packages.section.xml" />
</section>