580 lines
18 KiB
XML
580 lines
18 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="ch-configuration">
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<title>Configuring NixOS</title>
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<para>This chapter describes how to configure various aspects of a
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NixOS machine through the configuration file
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<filename>/etc/nixos/configuration.nix</filename>. As described in
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<xref linkend="sec-changing-config" />, changes to that file only take
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effect after you run <command>nixos-rebuild</command>.</para>
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<!--===============================================================-->
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<section><title>Package management</title>
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<para>This section describes how to add additional packages to your
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system. NixOS has two distinct styles of package management:
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<itemizedlist>
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<listitem><para><emphasis>Declarative</emphasis>, where you declare
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what packages you want in your
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<filename>configuration.nix</filename>. Every time you run
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<command>nixos-rebuild</command>, NixOS will ensure that you get a
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consistent set of binaries corresponding to your
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specification.</para></listitem>
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<listitem><para><emphasis>Ad hoc</emphasis>, where you install,
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upgrade and uninstall packages via the <command>nix-env</command>
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command. This style allows mixing packages from different Nixpkgs
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versions. It’s the only choice for non-root
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users.</para></listitem>
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</itemizedlist>
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</para>
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<para>The next two sections describe these two styles.</para>
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<section><title>Declarative package management</title>
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<para>With declarative package management, you specify which packages
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you want on your system by setting the option
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<option>environment.systemPackages</option>. For instance, adding the
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following line to <filename>configuration.nix</filename> enables the
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Mozilla Thunderbird email application:
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<programlisting>
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environment.systemPackages = [ pkgs.thunderbird ];
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</programlisting>
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The effect of this specification is that the Thunderbird package from
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Nixpkgs will be built or downloaded as part of the system when you run
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<command>nixos-rebuild switch</command>.</para>
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<para>You can get a list of the available packages as follows:
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<screen>
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$ nix-env -qaP '*' --description
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nixos.pkgs.firefox firefox-23.0 Mozilla Firefox - the browser, reloaded
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<replaceable>...</replaceable>
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</screen>
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The first column in the output is the <emphasis>attribute
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name</emphasis>, such as
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<literal>nixos.pkgs.thunderbird</literal>. (The
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<literal>nixos</literal> prefix allows distinguishing between
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different channels that you might have.)</para>
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<para>To “uninstall” a package, simply remove it from
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<option>environment.systemPackages</option> and run
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<command>nixos-rebuild switch</command>.</para>
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<section><title>Customising packages</title>
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<para>Some packages in Nixpkgs have options to enable or disable
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optional functionality or change other aspects of the package. For
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instance, the Firefox wrapper package (which provides Firefox with a
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set of plugins such as the Adobe Flash player) has an option to enable
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the Google Talk plugin. It can be set in
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<filename>configuration.nix</filename> as follows:
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<filename>
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nixpkgs.config.firefox.enableGoogleTalkPlugin = true;
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</filename>
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</para>
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<warning><para>Unfortunately, Nixpkgs currently lacks a way to query
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available configuration options.</para></warning>
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<para>Apart from high-level options, it’s possible to tweak a package
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in almost arbitrary ways, such as changing or disabling dependencies
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of a package. For instance, the Emacs package in Nixpkgs by default
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has a dependency on GTK+ 2. If you want to build it against GTK+ 3,
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you can specify that as follows:
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<programlisting>
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environment.systemPackages = [ (pkgs.emacs.override { gtk = pkgs.gtk3; }) ];
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</programlisting>
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The function <varname>override</varname> performs the call to the Nix
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function that produces Emacs, with the original arguments amended by
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the set of arguments specified by you. So here the function argument
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<varname>gtk</varname> gets the value <literal>pkgs.gtk3</literal>,
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causing Emacs to depend on GTK+ 3. (The parentheses are necessary
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because in Nix, function application binds more weakly than list
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construction, so without them,
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<literal>environment.systemPackages</literal> would be a list with two
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elements.)</para>
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<para>Even greater customisation is possible using the function
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<varname>overrideDerivation</varname>. While the
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<varname>override</varname> mechanism above overrides the arguments of
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a package function, <varname>overrideDerivation</varname> allows
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changing the <emphasis>result</emphasis> of the function. This
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permits changing any aspect of the package, such as the source code.
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For instance, if you want to override the source code of Emacs, you
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can say:
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<programlisting>
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environment.systemPackages =
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[ (pkgs.lib.overrideDerivation pkgs.emacs (attrs: {
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name = "emacs-25.0-pre";
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src = /path/to/my/emacs/tree;
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}))
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];
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</programlisting>
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Here, <varname>overrideDerivation</varname> takes the Nix derivation
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specified by <varname>pkgs.emacs</varname> and produces a new
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derivation in which the original’s <literal>name</literal> and
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<literal>src</literal> attribute have been replaced by the given
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values. The original attributes are accessible via
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<varname>attrs</varname>.</para>
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<para>The overrides shown above are not global. They do not affect
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the original package; other packages in Nixpkgs continue to depend on
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the original rather than the customised package. This means that if
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another package in your system depends on the original package, you
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end up with two instances of the package. If you want to have
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everything depend on your customised instance, you can apply a
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<emphasis>global</emphasis> override as follows:
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<screen>
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nixpkgs.config.packageOverrides = pkgs:
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{ emacs = pkgs.emacs.override { gtk = pkgs.gtk3; };
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};
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</screen>
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The effect of this definition is essentially equivalent to modifying
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the <literal>emacs</literal> attribute in the Nixpkgs source tree.
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Any package in Nixpkgs that depends on <literal>emacs</literal> will
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be passed your customised instance. (However, the value
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<literal>pkgs.emacs</literal> in
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<varname>nixpkgs.config.packageOverrides</varname> refers to the
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original rather than overriden instance, to prevent an infinite
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recursion.)</para>
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</section>
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<section><title>Adding custom packages</title>
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<para>It’s possible that a package you need is not available in NixOS.
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In that case, you can do two things. First, you can clone the Nixpkgs
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repository, add the package to your clone, and (optionally) submit a
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patch or pull request to have it accepted into the main Nixpkgs
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repository. This is described in detail in the <link
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xlink:href="http://hydra.nixos.org/job/nixpkgs/trunk/tarball/latest/download-by-type/doc/manual">Nixpkgs
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manual</link>. In short, you clone Nixpkgs:
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<screen>
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$ git clone git://github.com/NixOS/nixpkgs.git
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$ cd nixpkgs
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</screen>
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Then you write and test the package as described in the Nixpkgs
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manual. Finally, you add it to
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<literal>environment.systemPackages</literal>, e.g.
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<programlisting>
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environment.systemPackages = [ pkgs.my-package ];
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</programlisting>
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and you run <command>nixos-rebuild</command>, specifying your own
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Nixpkgs tree:
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<screen>
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$ nixos-rebuild switch -I nixpkgs=/path/to/my/nixpkgs</screen>
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</para>
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<para>The second possibility is to add the package outside of the
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Nixpkgs tree. For instance, here is how you specify a build of the
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<link xlink:href="http://www.gnu.org/software/hello/">GNU Hello</link>
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package directly in <filename>configuration.nix</filename>:
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<programlisting>
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environment.systemPackages =
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let
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my-hello = with pkgs; stdenv.mkDerivation rec {
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name = "hello-2.8";
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src = fetchurl {
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url = "mirror://gnu/hello/${name}.tar.gz";
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sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6";
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};
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};
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in
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[ my-hello ];
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</programlisting>
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Of course, you can also move the definition of
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<literal>my-hello</literal> into a separate Nix expression, e.g.
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<programlisting>
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environment.systemPackages = [ (import ./my-hello.nix) ];
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</programlisting>
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where <filename>my-hello.nix</filename> contains:
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<programlisting>
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with <nixpkgs> {}; # bring all of Nixpkgs into scope
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stdenv.mkDerivation rec {
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name = "hello-2.8";
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src = fetchurl {
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url = "mirror://gnu/hello/${name}.tar.gz";
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sha256 = "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6";
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};
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}
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</programlisting>
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This allows testing the package easily:
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<screen>
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$ nix-build my-hello.nix
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$ ./result/bin/hello
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Hello, world!
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</screen>
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</para>
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</section>
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</section>
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<section><title>Ad hoc package management</title>
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<para>With the command <command>nix-env</command>, you can install and
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uninstall packages from the command line. For instance, to install
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Mozilla Thunderbird:
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<screen>
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$ nix-env -iA nixos.pkgs.thunderbird</screen>
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If you invoke this as root, the package is installed in the Nix
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profile <filename>/nix/var/nix/profiles/default</filename> and visible
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to all users of the system; otherwise, the package ends up in
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<filename>/nix/var/nix/profiles/per-user/<replaceable>username</replaceable>/profile</filename>
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and is not visible to other users. The <option>-A</option> flag
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specifies the package by its attribute name; without it, the package
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is installed by matching against its package name
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(e.g. <literal>thunderbird</literal>). The latter is slower because
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it requires matching against all available Nix packages, and is
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ambiguous if there are multiple matching packages.</para>
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<para>Packages come from the NixOS channel. You typically upgrade a
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package by updating to the latest version of the NixOS channel:
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<screen>
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$ nix-channel --update nixos
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</screen>
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and then running <literal>nix-env -i</literal> again. Other packages
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in the profile are <emphasis>not</emphasis> affected; this is the
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crucial difference with the declarative style of package management,
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where running <command>nixos-rebuild switch</command> causes all
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packages to be updated to their current versions in the NixOS channel.
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You can however upgrade all packages for which there is a newer
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version by doing:
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<screen>
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$ nix-env -u '*'
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</screen>
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</para>
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<para>A package can be unstalled using the <option>-e</option>
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flag:
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<screen>
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$ nix-env -e thunderbird
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</screen>
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</para>
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<para>Finally, you can roll back an undesirable
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<command>nix-env</command> action:
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<screen>
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$ nix-env --rollback
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</screen>
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</para>
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<para><command>nix-env</command> has many more flags. For details,
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see the
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<citerefentry><refentrytitle>nix-env</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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manpage or the Nix manual.</para>
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</section>
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</section>
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<!--===============================================================-->
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<section><title>User management</title>
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<para>NixOS supports both declarative and imperative styles of user
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management. In the declarative style, users are specified in
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<filename>configuration.nix</filename>. For instance, the following
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states that a user accound named <literal>alice</literal> shall exist:
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<programlisting>
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users.extraUsers.alice =
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{ createHome = true;
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home = "/home/alice";
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description = "Alice Foobar";
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extraGroups = [ "wheel" ];
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isSystemUser = false;
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useDefaultShell = true;
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openssh.authorizedKeys.keys = [ "ssh-dss AAAAB3Nza... alice@foobar" ];
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};
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</programlisting>
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Note that <literal>alice</literal> is a member of the
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<literal>wheel</literal> group, which allows her to use
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<command>sudo</command> to execute commands as
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<literal>root</literal>. Also note the SSH public key that allows
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remote logins with the corresponding private key. Users created in
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this way do not have a password by default, so they cannot log in via
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mechanisms that require a password. However, you can use the
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<command>passwd</command> program to set a password, which is retained
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across invocations of <command>nixos-rebuild</command>.</para>
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<para>A user ID (uid) is assigned automatically. You can also specify
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a uid manually by adding
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<programlisting>
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uid = 1000;
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</programlisting>
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to the user specification.</para>
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<para>Groups can be specified similarly. The following states that a
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group named <literal>students</literal> shall exist:
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<programlisting>
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users.extraGroups.students.gid = 1000;
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</programlisting>
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As with users, the group ID (gid) is optional and will be assigned
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automatically if it’s missing.</para>
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<warning><para>Currently declarative user management is not perfect:
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<command>nixos-rebuild</command> does not know how to realise certain
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configuration changes. This includes removing a user or group, and
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removing group membership from a user.</para></warning>
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<para>In the imperative style, users and groups are managed by
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commands such as <command>useradd</command>,
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<command>groupmod</command> and so on. For instance, to create a user
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account named <literal>alice</literal>:
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<screen>
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$ useradd -m alice</screen>
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The flag <option>-m</option> causes the creation of a home directory
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for the new user, which is generally what you want. The user does not
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have an initial password and therefore cannot log in. A password can
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be set using the <command>passwd</command> utility:
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<screen>
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$ passwd alice
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Enter new UNIX password: ***
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Retype new UNIX password: ***
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</screen>
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A user can be deleted using <command>userdel</command>:
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<screen>
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$ userdel -r alice</screen>
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The flag <option>-r</option> deletes the user’s home directory.
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Accounts can be modified using <command>usermod</command>. Unix
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groups can be managed using <command>groupadd</command>,
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<command>groupmod</command> and <command>groupdel</command>.</para>
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</section>
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<!--===============================================================-->
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<section><title>Networking</title>
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<section><title>Secure shell access</title>
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<para>Secure shell (SSH) access to your machine can be enabled by
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setting:
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<programlisting>
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services.openssh.enable = true;
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</programlisting>
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By default, root logins using a password are disallowed. They can be
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disabled entirely by setting
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<literal>services.openssh.permitRootLogin</literal> to
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<literal>"no"</literal>.</para>
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<para>You can declaratively specify authorised RSA/DSA public keys for
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a user as follows:
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<!-- FIXME: this might not work if the user is unmanaged. -->
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<programlisting>
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users.extraUsers.alice.openssh.authorizedKeys.keys =
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[ "ssh-dss AAAAB3NzaC1kc3MAAACBAPIkGWVEt4..." ];
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</programlisting>
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</para>
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</section>
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<section><title>IPv4 configuration</title>
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<para>By default, NixOS uses DHCP (specifically,
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(<command>dhcpcd</command>)) to automatically configure network
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interfaces. However, you can configure an interface manually as
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follows:
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<programlisting>
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networking.interfaces.eth0 = { ipAddress = "192.168.1.2"; prefixLength = 24; };
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</programlisting>
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(The network prefix can also be specified using the option
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<literal>subnetMask</literal>,
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e.g. <literal>"255.255.255.0"</literal>, but this is deprecated.)
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Typically you’ll also want to set a default gateway and set of name
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servers:
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<programlisting>
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networking.defaultGateway = "192.168.1.1";
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networking.nameservers = [ "8.8.8.8" ];
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</programlisting>
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</para>
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<note><para>Statically configured interfaces are set up by the systemd
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service
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<replaceable>interface-name</replaceable><literal>-cfg.service</literal>.
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The default gateway and name server configuration is performed by
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<literal>network-setup.service</literal>.</para></note>
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<para>The host name is set using <option>networking.hostName</option>:
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<programlisting>
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networking.hostName = "cartman";
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</programlisting>
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The default host name is <literal>nixos</literal>. Set it to the
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empty string (<literal>""</literal>) to allow the DHCP server to
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provide the host name.</para>
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||
</section>
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<section><title>IPv6 configuration</title>
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<para>IPv6 is enabled by default. Stateless address autoconfiguration
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is used to automatically assign IPv6 addresses to all interfaces. You
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can disable IPv6 support globally by setting:
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<programlisting>
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networking.enableIPv6 = false;
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</programlisting>
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</para>
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</section>
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<section><title>Firewall</title>
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<para>NixOS has a simple stateful firewall that blocks incoming
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connections and other unexpected packets. The firewall applies to
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both IPv4 and IPv6 traffic. It can be enabled as follows:
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<programlisting>
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networking.firewall.enable = true;
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</programlisting>
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You can open specific TCP ports to the outside world:
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<programlisting>
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networking.firewall.allowedTCPPorts = [ 80 443 ];
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</programlisting>
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Note that TCP port 22 (ssh) is opened automatically if the SSH daemon
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is enabled (<option>services.openssh.enable = true</option>). UDP
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ports can be opened through
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<option>networking.firewall.allowedUDPPorts</option>. Also of
|
||
interest is
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<programlisting>
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networking.firewall.allowPing = true;
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</programlisting>
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to allow the machine to respond to ping requests. (ICMPv6 pings are
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always allowed.)</para>
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||
</section>
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|
||
<section><title>Wireless networks</title>
|
||
|
||
<para>
|
||
NixOS will start wpa_supplicant for you if you enable this setting:
|
||
|
||
<programlisting>
|
||
networking.wireless.enable = true;
|
||
</programlisting>
|
||
|
||
NixOS currently does not generate wpa_supplicant's
|
||
configuration file, <literal>/etc/wpa_supplicant.conf</literal>. You should edit this file
|
||
yourself to define wireless networks, WPA keys and so on (see
|
||
wpa_supplicant.conf(5)).
|
||
</para>
|
||
|
||
<para>
|
||
If you are using WPA2 the <command>wpa_passphrase</command> tool might be useful
|
||
to generate the <literal>wpa_supplicant.conf</literal>.
|
||
|
||
<screen>
|
||
$ wpa_passphrase ESSID PSK > /etc/wpa_supplicant.conf</screen>
|
||
|
||
After you have edited the <literal>wpa_supplicant.conf</literal>,
|
||
you need to restart the wpa_supplicant service.
|
||
|
||
<screen>
|
||
$ systemctl restart wpa_supplicant.service</screen>
|
||
</para>
|
||
|
||
|
||
</section>
|
||
|
||
|
||
<section><title>Ad-hoc configuration</title>
|
||
|
||
<para>You can use <option>networking.localCommands</option> to specify
|
||
shell commands to be run at the end of
|
||
<literal>network-setup.service</literal>. This is useful for doing
|
||
network configuration not covered by the existing NixOS modules. For
|
||
instance, to statically configure an IPv6 address:
|
||
|
||
<programlisting>
|
||
networking.localCommands =
|
||
''
|
||
ip -6 addr add 2001:610:685:1::1/64 dev eth0
|
||
'';
|
||
</programlisting>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
<!-- TODO: OpenVPN, NAT -->
|
||
|
||
|
||
</section>
|
||
|
||
|
||
<!-- TODO: declarative package installation; X11; user management;
|
||
Apache; libvirtd virtualisation -->
|
||
|
||
|
||
</chapter>
|