nixpkgs/doc/configuration.xml

<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="chap-packageconfig">

<title>Global configuration</title>

<para>Nix comes with certain defaults about what packages can and
cannot be installed, based on a package's metadata. By default, Nix
will prevent installation if any of the following criteria are
true:</para>

<itemizedlist>
  <listitem><para>The package is thought to be broken, and has had
  its <literal>meta.broken</literal> set to
  <literal>true</literal>.</para></listitem>

  <listitem><para>The package isn't intended to run on the given system, as none of its <literal>meta.platforms</literal> match the given system.</para></listitem>

  <listitem><para>The package's <literal>meta.license</literal> is set
  to a license which is considered to be unfree.</para></listitem>

  <listitem><para>The package has known security vulnerabilities but
  has not or can not be updated for some reason, and a list of issues
  has been entered in to the package's
  <literal>meta.knownVulnerabilities</literal>.</para></listitem>
</itemizedlist>

<para>Note that all this is checked during evaluation already,
and the check includes any package that is evaluated.
In particular, all build-time dependencies are checked.
<literal>nix-env -qa</literal> will (attempt to) hide any packages
that would be refused.
</para>

<para>Each of these criteria can be altered in the nixpkgs
configuration.</para>

<para>The nixpkgs configuration for a NixOS system is set in the
<literal>configuration.nix</literal>, as in the following example:
<programlisting>
{
  nixpkgs.config = {
    allowUnfree = true;
  };
}
</programlisting>
However, this does not allow unfree software for individual users.
Their configurations are managed separately.</para>

<para>A user's of nixpkgs configuration is stored in a user-specific
configuration file located at
<filename>~/.config/nixpkgs/config.nix</filename>. For example:
<programlisting>
{
  allowUnfree = true;
}
</programlisting>
</para>

<para>Note that we are not able to test or build unfree software on Hydra
due to policy. Most unfree licenses prohibit us from either executing or
distributing the software.</para>

<section xml:id="sec-allow-broken">
  <title>Installing broken packages</title>


  <para>There are two ways to try compiling a package which has been
  marked as broken.</para>

  <itemizedlist>
    <listitem><para>
      For allowing the build of a broken package once, you can use an
      environment variable for a single invocation of the nix tools:

      <programlisting>$ export NIXPKGS_ALLOW_BROKEN=1</programlisting>
    </para></listitem>

    <listitem><para>
      For permanently allowing broken packages to be built, you may
      add <literal>allowBroken = true;</literal> to your user's
      configuration file, like this:

<programlisting>
{
  allowBroken = true;
}
</programlisting>
    </para></listitem>
  </itemizedlist>
</section>

<section xml:id="sec-allow-unsupported-system">
  <title>Installing packages on unsupported systems</title>


  <para>
    There are also two ways to try compiling a package which has been marked as unsuported for the given system.
  </para>

  <itemizedlist>
    <listitem><para>
      For allowing the build of a broken package once, you can use an environment variable for a single invocation of the nix tools:

      <programlisting>$ export NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1</programlisting>
    </para></listitem>

    <listitem>
      <para>
        For permanently allowing broken packages to be built, you may add <literal>allowUnsupportedSystem = true;</literal> to your user's configuration file, like this:

<programlisting>
{
  allowUnsupportedSystem = true;
}
</programlisting>
      </para>
    </listitem>
  </itemizedlist>

  <para>
    The difference between an a package being unsupported on some system and being broken is admittedly a bit fuzzy.
    If a program <emphasis>ought</emphasis> to work on a certain platform, but doesn't, the platform should be included in <literal>meta.platforms</literal>, but marked as broken with e.g. <literal>meta.broken = !hostPlatform.isWindows</literal>.
    Of course, this begs the question of what "ought" means exactly.
    That is left to the package maintainer.
  </para>
</section>

<section xml:id="sec-allow-unfree">
  <title>Installing unfree packages</title>

  <para>There are several ways to tweak how Nix handles a package
  which has been marked as unfree.</para>

  <itemizedlist>
    <listitem><para>
      To temporarily allow all unfree packages, you can use an
      environment variable for a single invocation of the nix tools:

      <programlisting>$ export NIXPKGS_ALLOW_UNFREE=1</programlisting>
    </para></listitem>

    <listitem><para>
      It is possible to permanently allow individual unfree packages,
      while still blocking unfree packages by default using the
      <literal>allowUnfreePredicate</literal> configuration
      option in the user configuration file.</para>

      <para>This option is a function which accepts a package as a
      parameter, and returns a boolean. The following example
      configuration accepts a package and always returns false:
<programlisting>
{
  allowUnfreePredicate = (pkg: false);
}
</programlisting>
      </para>

      <para>A more useful example, the following configuration allows
      only allows flash player and visual studio code:

<programlisting>
{
  allowUnfreePredicate = (pkg: elem (builtins.parseDrvName pkg.name).name [ "flashplayer" "vscode" ]);
}
</programlisting>
    </para></listitem>

    <listitem>
      <para>It is also possible to whitelist and blacklist licenses
      that are specifically acceptable or not acceptable, using
      <literal>whitelistedLicenses</literal> and
      <literal>blacklistedLicenses</literal>, respectively.
      </para>

      <para>The following example configuration whitelists the
      licenses <literal>amd</literal> and <literal>wtfpl</literal>:

<programlisting>
{
  whitelistedLicenses = with stdenv.lib.licenses; [ amd wtfpl ];
}
</programlisting>
      </para>

      <para>The following example configuration blacklists the
      <literal>gpl3</literal> and <literal>agpl3</literal> licenses:

<programlisting>
{
  blacklistedLicenses = with stdenv.lib.licenses; [ agpl3 gpl3 ];
}
</programlisting>
      </para>
    </listitem>
  </itemizedlist>

  <para>A complete list of licenses can be found in the file
  <filename>lib/licenses.nix</filename> of the nixpkgs tree.</para>
</section>


<section xml:id="sec-allow-insecure">
  <title>
    Installing insecure packages
  </title>

  <para>There are several ways to tweak how Nix handles a package
  which has been marked as insecure.</para>

  <itemizedlist>
    <listitem><para>
      To temporarily allow all insecure packages, you can use an
      environment variable for a single invocation of the nix tools:

      <programlisting>$ export NIXPKGS_ALLOW_INSECURE=1</programlisting>
    </para></listitem>

    <listitem><para>
      It is possible to permanently allow individual insecure
      packages, while still blocking other insecure packages by
      default using the <literal>permittedInsecurePackages</literal>
      configuration option in the user configuration file.</para>

      <para>The following example configuration permits the
      installation of the hypothetically insecure package
      <literal>hello</literal>, version <literal>1.2.3</literal>:
<programlisting>
{
  permittedInsecurePackages = [
    "hello-1.2.3"
  ];
}
</programlisting>
      </para>
    </listitem>

    <listitem><para>
      It is also possible to create a custom policy around which
      insecure packages to allow and deny, by overriding the
      <literal>allowInsecurePredicate</literal> configuration
      option.</para>

      <para>The <literal>allowInsecurePredicate</literal> option is a
      function which accepts a package and returns a boolean, much
      like <literal>allowUnfreePredicate</literal>.</para>

      <para>The following configuration example only allows insecure
      packages with very short names:

<programlisting>
{
  allowInsecurePredicate = (pkg: (builtins.stringLength (builtins.parseDrvName pkg.name).name) &lt;= 5);
}
</programlisting>
      </para>

      <para>Note that <literal>permittedInsecurePackages</literal> is
      only checked if <literal>allowInsecurePredicate</literal> is not
      specified.
    </para></listitem>
  </itemizedlist>
</section>

<!--============================================================-->

<section xml:id="sec-modify-via-packageOverrides"><title>Modify
packages via <literal>packageOverrides</literal></title>

<para>You can define a function called
<varname>packageOverrides</varname> in your local
<filename>~/.config/nixpkgs/config.nix</filename> to override nix packages.  It
must be a function that takes pkgs as an argument and return modified
set of packages.

<programlisting>
{
  packageOverrides = pkgs: rec {
    foo = pkgs.foo.override { ... };
  };
}
</programlisting>

</para>

</section>

<section xml:id="sec-declarative-package-management">
  <title>Declarative Package Management</title>

  <section xml:id="sec-building-environment">
    <title>Build an environment</title>

    <para>
      Using <literal>packageOverrides</literal>, it is possible to manage
      packages declaratively. This means that we can list all of our desired
      packages within a declarative Nix expression. For example, to have
      <literal>aspell</literal>, <literal>bc</literal>,
      <literal>ffmpeg</literal>, <literal>coreutils</literal>,
      <literal>gdb</literal>, <literal>nixUnstable</literal>,
      <literal>emscripten</literal>, <literal>jq</literal>,
      <literal>nox</literal>, and <literal>silver-searcher</literal>, we could
      use the following in <filename>~/.config/nixpkgs/config.nix</filename>:
    </para>

    <screen>
{
  packageOverrides = pkgs: with pkgs; {
    myPackages = pkgs.buildEnv {
      name = "my-packages";
      paths = [ aspell bc coreutils gdb ffmpeg nixUnstable emscripten jq nox silver-searcher ];
    };
  };
}
    </screen>

    <para>
      To install it into our environment, you can just run <literal>nix-env -iA
      nixpkgs.myPackages</literal>. If you want to load the packages to be built
      from a working copy of <literal>nixpkgs</literal> you just run
      <literal>nix-env -f. -iA myPackages</literal>. To explore what's been
      installed, just look through <filename>~/.nix-profile/</filename>. You can
      see that a lot of stuff has been installed. Some of this stuff is useful
      some of it isn't. Let's tell Nixpkgs to only link the stuff that we want:
    </para>

    <screen>
{
  packageOverrides = pkgs: with pkgs; {
    myPackages = pkgs.buildEnv {
      name = "my-packages";
      paths = [ aspell bc coreutils gdb ffmpeg nixUnstable emscripten jq nox silver-searcher ];
      pathsToLink = [ "/share" "/bin" ];
    };
  };
}
    </screen>

    <para>
      <literal>pathsToLink</literal> tells Nixpkgs to only link the paths listed
      which gets rid of the extra stuff in the profile.
      <filename>/bin</filename> and <filename>/share</filename> are good
      defaults for a user environment, getting rid of the clutter. If you are
      running on Nix on MacOS, you may want to add another path as well,
      <filename>/Applications</filename>, that makes GUI apps available.
    </para>

  </section>

  <section xml:id="sec-getting-documentation">
    <title>Getting documentation</title>

    <para>
      After building that new environment, look through
      <filename>~/.nix-profile</filename> to make sure everything is there that
      we wanted. Discerning readers will note that some files are missing. Look
      inside <filename>~/.nix-profile/share/man/man1/</filename> to verify this.
      There are no man pages for any of the Nix tools! This is because some
      packages like Nix have multiple outputs for things like documentation (see
      section 4). Let's make Nix install those as well.
    </para>

    <screen>
{
  packageOverrides = pkgs: with pkgs; {
    myPackages = pkgs.buildEnv {
      name = "my-packages";
      paths = [ aspell bc coreutils ffmpeg nixUnstable emscripten jq nox silver-searcher ];
      pathsToLink = [ "/share/man" "/share/doc" /bin" ];
      extraOutputsToInstall = [ "man" "doc" ];
    };
  };
}
    </screen>

    <para>
      This provides us with some useful documentation for using our packages.
      However, if we actually want those manpages to be detected by man, we need
      to set up our environment. This can also be managed within Nix
      expressions.
    </para>

    <screen>
{
  packageOverrides = pkgs: with pkgs; rec {
    myProfile = writeText "my-profile" ''
export PATH=$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:/sbin:/bin:/usr/sbin:/usr/bin
export MANPATH=$HOME/.nix-profile/share/man:/nix/var/nix/profiles/default/share/man:/usr/share/man
    '';
    myPackages = pkgs.buildEnv {
      name = "my-packages";
      paths = [
        (runCommand "profile" {} ''
mkdir -p $out/etc/profile.d
cp ${myProfile} $out/etc/profile.d/my-profile.sh
        '')
        aspell
        bc
        coreutils
        ffmpeg
        man
        nixUnstable
        emscripten
        jq
        nox
        silver-searcher
      ];
      pathsToLink = [ "/share/man" "/share/doc" /bin" "/etc" ];
      extraOutputsToInstall = [ "man" "doc" ];
    };
  };
}
    </screen>

    <para>
      For this to work fully, you must also have this script sourced when you
      are logged in. Try adding something like this to your
      <filename>~/.profile</filename> file:
    </para>

    <screen>
#!/bin/sh
if [ -d $HOME/.nix-profile/etc/profile.d ]; then
  for i in $HOME/.nix-profile/etc/profile.d/*.sh; do
    if [ -r $i ]; then
      . $i
    fi
  done
fi
    </screen>

    <para>
      Now just run <literal>source $HOME/.profile</literal> and you can starting
      loading man pages from your environent.
    </para>

  </section>

  <section xml:id="sec-gnu-info-setup">
    <title>GNU info setup</title>

    <para>
      Configuring GNU info is a little bit trickier than man pages. To work
      correctly, info needs a database to be generated. This can be done with
      some small modifications to our environment scripts.
    </para>

    <screen>
{
  packageOverrides = pkgs: with pkgs; rec {
    myProfile = writeText "my-profile" ''
export PATH=$HOME/.nix-profile/bin:/nix/var/nix/profiles/default/bin:/sbin:/bin:/usr/sbin:/usr/bin
export MANPATH=$HOME/.nix-profile/share/man:/nix/var/nix/profiles/default/share/man:/usr/share/man
export INFOPATH=$HOME/.nix-profile/share/info:/nix/var/nix/profiles/default/share/info:/usr/share/info
    '';
    myPackages = pkgs.buildEnv {
      name = "my-packages";
      paths = [
        (runCommand "profile" {} ''
mkdir -p $out/etc/profile.d
cp ${myProfile} $out/etc/profile.d/my-profile.sh
        '')
        aspell
        bc
        coreutils
        ffmpeg
        man
        nixUnstable
        emscripten
        jq
        nox
        silver-searcher
        texinfoInteractive
      ];
      pathsToLink = [ "/share/man" "/share/doc" "/share/info" "/bin" "/etc" ];
      extraOutputsToInstall = [ "man" "doc" "info" ];
      postBuild = ''
          if [ -x $out/bin/install-info -a -w $out/share/info ]; then
            shopt -s nullglob
            for i in $out/share/info/*.info $out/share/info/*.info.gz; do
                $out/bin/install-info $i $out/share/info/dir
            done
          fi
      '';
    };
  };
}
    </screen>

    <para>
      <literal>postBuild</literal> tells Nixpkgs to run a command after building
      the environment. In this case, <literal>install-info</literal> adds the
      installed info pages to <literal>dir</literal> which is GNU info's default
      root node. Note that <literal>texinfoInteractive</literal> is added to the
      environment to give the <literal>install-info</literal> command.
    </para>

  </section>

</section>

</chapter>