<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 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>
     For a more useful example, try the following. This configuration
     only allows unfree packages named flash player and visual studio
     code:
<programlisting>
{
  allowUnfreePredicate = (pkg: builtins.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 returns a
   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>
