package-notes.xml

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

<title>Package Notes</title>

<para>This chapter contains information about how to use and maintain
the Nix expressions for a number of specific packages, such as the
Linux kernel or X.org.</para>


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

<section xml:id="sec-linux-kernel">

<title>Linux kernel</title>

<para>The Nix expressions to build the Linux kernel are in <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/os-specific/linux/kernel"><filename>pkgs/os-specific/linux/kernel</filename></link>.</para>

<para>The function that builds the kernel has an argument
<varname>kernelPatches</varname> which should be a list of
<literal>{name, patch, extraConfig}</literal> attribute sets, where
<varname>name</varname> is the name of the patch (which is included in
the kernel’s <varname>meta.description</varname> attribute),
<varname>patch</varname> is the patch itself (possibly compressed),
and <varname>extraConfig</varname> (optional) is a string specifying
extra options to be concatenated to the kernel configuration file
(<filename>.config</filename>).</para>

<para>The kernel derivation exports an attribute
<varname>features</varname> specifying whether optional functionality
is or isn’t enabled.  This is used in NixOS to implement
kernel-specific behaviour.  For instance, if the kernel has the
<varname>iwlwifi</varname> feature (i.e. has built-in support for
Intel wireless chipsets), then NixOS doesn’t have to build the
external <varname>iwlwifi</varname> package:

<programlisting>
modulesTree = [kernel]
  ++ pkgs.lib.optional (!kernel.features ? iwlwifi) kernelPackages.iwlwifi
  ++ ...;
</programlisting>

</para>

<para>How to add a new (major) version of the Linux kernel to Nixpkgs:

<orderedlist>

  <listitem>
    <para>Copy the old Nix expression
    (e.g. <filename>linux-2.6.21.nix</filename>) to the new one
    (e.g. <filename>linux-2.6.22.nix</filename>) and update it.</para>
  </listitem>

  <listitem>
    <para>Add the new kernel to <filename>all-packages.nix</filename>
    (e.g., create an attribute
    <varname>kernel_2_6_22</varname>).</para>
  </listitem>

  <listitem>
    <para>Now we’re going to update the kernel configuration.  First
    unpack the kernel.  Then for each supported platform
    (<literal>i686</literal>, <literal>x86_64</literal>,
    <literal>uml</literal>) do the following:

      <orderedlist>

        <listitem>
          <para>Make an copy from the old
          config (e.g. <filename>config-2.6.21-i686-smp</filename>) to
          the new one
          (e.g. <filename>config-2.6.22-i686-smp</filename>).</para>
        </listitem>

        <listitem>
          <para>Copy the config file for this platform
          (e.g. <filename>config-2.6.22-i686-smp</filename>) to
          <filename>.config</filename> in the kernel source tree.
          </para>
        </listitem>

        <listitem>
          <para>Run <literal>make oldconfig
          ARCH=<replaceable>{i386,x86_64,um}</replaceable></literal>
          and answer all questions.  (For the uml configuration, also
          add <literal>SHELL=bash</literal>.)  Make sure to keep the
          configuration consistent between platforms (i.e. don’t
          enable some feature on <literal>i686</literal> and disable
          it on <literal>x86_64</literal>).
          </para>
        </listitem>

        <listitem>
          <para>If needed you can also run <literal>make
          menuconfig</literal>:

            <screen>
$ nix-env -i ncurses
$ export NIX_CFLAGS_LINK=-lncurses
$ make menuconfig ARCH=<replaceable>arch</replaceable></screen>

          </para>
        </listitem>

        <listitem>
          <para>Copy <filename>.config</filename> over the new config
          file (e.g. <filename>config-2.6.22-i686-smp</filename>).</para>
        </listitem>

      </orderedlist>

    </para>

  </listitem>

  <listitem>
    <para>Test building the kernel: <literal>nix-build -A
    kernel_2_6_22</literal>.  If it compiles, ship it!  For extra
    credit, try booting NixOS with it.</para>
  </listitem>

  <listitem>
    <para>It may be that the new kernel requires updating the external
    kernel modules and kernel-dependent packages listed in the
    <varname>linuxPackagesFor</varname> function in
    <filename>all-packages.nix</filename> (such as the NVIDIA drivers,
    AUFS, etc.).  If the updated packages aren’t backwards compatible
    with older kernels, you may need to keep the older versions
    around.</para>
  </listitem>

</orderedlist>

</para>

</section>


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

<section xml:id="sec-xorg">

<title>X.org</title>

<para>The Nix expressions for the X.org packages reside in
<filename>pkgs/servers/x11/xorg/default.nix</filename>.  This file is
automatically generated from lists of tarballs in an X.org release.
As such it should not be modified directly; rather, you should modify
the lists, the generator script or the file
<filename>pkgs/servers/x11/xorg/overrides.nix</filename>, in which you
can override or add to the derivations produced by the
generator.</para>

<para>The generator is invoked as follows:

<screen>
$ cd pkgs/servers/x11/xorg
$ cat tarballs-7.5.list extra.list old.list \
  | perl ./generate-expr-from-tarballs.pl
</screen>

For each of the tarballs in the <filename>.list</filename> files, the
script downloads it, unpacks it, and searches its
<filename>configure.ac</filename> and <filename>*.pc.in</filename>
files for dependencies.  This information is used to generate
<filename>default.nix</filename>.  The generator caches downloaded
tarballs between runs.  Pay close attention to the <literal>NOT FOUND:
<replaceable>name</replaceable></literal> messages at the end of the
run, since they may indicate missing dependencies.  (Some might be
optional dependencies, however.)</para>

<para>A file like <filename>tarballs-7.5.list</filename> contains all
tarballs in a X.org release.  It can be generated like this:

<screen>
$ export i="mirror://xorg/X11R7.4/src/everything/"
$ cat $(PRINT_PATH=1 nix-prefetch-url $i | tail -n 1) \
  | perl -e 'while (&lt;>) { if (/(href|HREF)="([^"]*.bz2)"/) { print "$ENV{'i'}$2\n"; }; }' \
  | sort > tarballs-7.4.list
</screen>

<filename>extra.list</filename> contains libraries that aren’t part of
X.org proper, but are closely related to it, such as
<literal>libxcb</literal>.  <filename>old.list</filename> contains
some packages that were removed from X.org, but are still needed by
some people or by other packages (such as
<varname>imake</varname>).</para>

<para>If the expression for a package requires derivation attributes
that the generator cannot figure out automatically (say,
<varname>patches</varname> or a <varname>postInstall</varname> hook),
you should modify
<filename>pkgs/servers/x11/xorg/overrides.nix</filename>.</para>

</section>



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

<!--
<section>
  <title>Gnome</title>
  <para>* Expression is auto-generated</para>
  <para>* How to update</para>
</section>
-->


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

<!--
<section>
  <title>GCC</title>
  <para>…</para>
</section>
-->

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

<section xml:id="sec-eclipse">

  <title>Eclipse</title>

  <para>
    The Nix expressions related to the Eclipse platform and IDE are in
    <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/editors/eclipse"><filename>pkgs/applications/editors/eclipse</filename></link>.
  </para>

  <para>
    Nixpkgs provides a number of packages that will install Eclipse in
    its various forms, these range from the bare-bones Eclipse
    Platform to the more fully featured Eclipse SDK or Scala-IDE
    packages and multiple version are often available. It is possible
    to list available Eclipse packages by issuing the command:

<screen>
$ nix-env -f '&lt;nixpkgs&gt;' -qaP -A eclipses --description
</screen>

    Once an Eclipse variant is installed it can be run using the
    <command>eclipse</command> command, as expected. From within
    Eclipse it is then possible to install plugins in the usual manner
    by either manually specifying an Eclipse update site or by
    installing the Marketplace Client plugin and using it to discover
    and install other plugins. This installation method provides an
    Eclipse installation that closely resemble a manually installed
    Eclipse.
  </para>

  <para>
    If you prefer to install plugins in a more declarative manner then
    Nixpkgs also offer a number of Eclipse plugins that can be
    installed in an <emphasis>Eclipse environment</emphasis>. This
    type of environment is created using the function
    <varname>eclipseWithPlugins</varname> found inside the
    <varname>nixpkgs.eclipses</varname> attribute set. This function
    takes as argument <literal>{ eclipse, plugins ? [], jvmArgs ? []
    }</literal> where <varname>eclipse</varname> is a one of the
    Eclipse packages described above, <varname>plugins</varname> is a
    list of plugin derivations, and <varname>jvmArgs</varname> is a
    list of arguments given to the JVM running the Eclipse. For
    example, say you wish to install the latest Eclipse Platform with
    the popular Eclipse Color Theme plugin and also allow Eclipse to
    use more RAM. You could then add

<screen>
packageOverrides = pkgs: {
  myEclipse = with pkgs.eclipses; eclipseWithPlugins {
    eclipse = eclipse-platform;
    jvmArgs = [ "-Xmx2048m" ];
    plugins = [ plugins.color-theme ];
  };
}
</screen>

    to your Nixpkgs configuration
    (<filename>~/.config/nixpkgs/config.nix</filename>) and install it by
    running <command>nix-env -f '&lt;nixpkgs&gt;' -iA
    myEclipse</command> and afterward run Eclipse as usual. It is
    possible to find out which plugins are available for installation
    using <varname>eclipseWithPlugins</varname> by running

<screen>
$ nix-env -f '&lt;nixpkgs&gt;' -qaP -A eclipses.plugins --description
</screen>
  </para>

  <para>
    If there is a need to install plugins that are not available in
    Nixpkgs then it may be possible to define these plugins outside
    Nixpkgs using the <varname>buildEclipseUpdateSite</varname> and
    <varname>buildEclipsePlugin</varname> functions found in the
    <varname>nixpkgs.eclipses.plugins</varname> attribute set. Use the
    <varname>buildEclipseUpdateSite</varname> function to install a
    plugin distributed as an Eclipse update site. This function takes
    <literal>{ name, src }</literal> as argument where
    <literal>src</literal> indicates the Eclipse update site archive.
    All Eclipse features and plugins within the downloaded update site
    will be installed. When an update site archive is not available
    then the <varname>buildEclipsePlugin</varname> function can be
    used to install a plugin that consists of a pair of feature and
    plugin JARs. This function takes an argument <literal>{ name,
    srcFeature, srcPlugin }</literal> where
    <literal>srcFeature</literal> and <literal>srcPlugin</literal> are
    the feature and plugin JARs, respectively.
  </para>

  <para>
    Expanding the previous example with two plugins using the above
    functions we have
<screen>
packageOverrides = pkgs: {
  myEclipse = with pkgs.eclipses; eclipseWithPlugins {
    eclipse = eclipse-platform;
    jvmArgs = [ "-Xmx2048m" ];
    plugins = [
      plugins.color-theme
      (plugins.buildEclipsePlugin {
        name = "myplugin1-1.0";
        srcFeature = fetchurl {
          url = "http://…/features/myplugin1.jar";
          sha256 = "123…";
        };
        srcPlugin = fetchurl {
          url = "http://…/plugins/myplugin1.jar";
          sha256 = "123…";
        };
      });
      (plugins.buildEclipseUpdateSite {
        name = "myplugin2-1.0";
        src = fetchurl {
          stripRoot = false;
          url = "http://…/myplugin2.zip";
          sha256 = "123…";
        };
      });
    ];
  };
}
</screen>
  </para>

</section>

<section xml:id="sec-elm">

<title>Elm</title>

<para>
The Nix expressions for Elm reside in
<filename>pkgs/development/compilers/elm</filename>. They are generated
automatically by <command>update-elm.rb</command> script. One should
specify versions of Elm packages inside the script, clear the
<filename>packages</filename> directory and run the script from inside it.
<literal>elm-reactor</literal> is special because it also has Elm package
dependencies. The process is not automated very much for now -- you should
get the <literal>elm-reactor</literal> source tree (e.g. with
<command>nix-shell</command>) and run <command>elm2nix.rb</command> inside
it. Place the resulting <filename>package.nix</filename> file into
<filename>packages/elm-reactor-elm.nix</filename>.
</para>

</section>

<section xml:id="sec-shell-helpers">

<title>Interactive shell helpers</title>

<para>
  Some packages provide the shell integration to be more useful. But
  unlike other systems, nix doesn't have a standard share directory
  location. This is why a bunch <command>PACKAGE-share</command>
  scripts are shipped that print the location of the corresponding
  shared folder.

  Current list of such packages is as following:

  <itemizedlist>
    <listitem>
      <para>
        <literal>autojump</literal>: <command>autojump-share</command>
      </para>
    </listitem>
    <listitem>
      <para>
        <literal>fzf</literal>: <command>fzf-share</command>
      </para>
    </listitem>
  </itemizedlist>

  E.g. <literal>autojump</literal> can then used in the .bashrc like this:
<screen>
  source "$(autojump-share)/autojump.bash"
</screen>
</para>

</section>

<section xml:id="sec-steam">

<title>Steam</title>

<section xml:id="sec-steam-nix">

<title>Steam in Nix</title>

<para>
  Steam is distributed as a <filename>.deb</filename> file, for now only
  as an i686 package (the amd64 package only has documentation).
  When unpacked, it has a script called <filename>steam</filename> that
  in ubuntu (their target distro) would go to <filename>/usr/bin
  </filename>. When run for the first time, this script copies some
  files to the user's home, which include another script that is the
  ultimate responsible for launching the steam binary, which is also
  in $HOME.
</para>
<para>
  Nix problems and constraints:
<itemizedlist>
  <listitem><para>We don't have <filename>/bin/bash</filename> and many
  scripts point there. Similarly for <filename>/usr/bin/python</filename>
  .</para></listitem>
  <listitem><para>We don't have the dynamic loader in <filename>/lib
  </filename>.</para></listitem>
  <listitem><para>The <filename>steam.sh</filename> script in $HOME can
  not be patched, as it is checked and rewritten by steam.</para></listitem>
  <listitem><para>The steam binary cannot be patched, it's also checked.</para></listitem>
</itemizedlist>
</para>
<para>
  The current approach to deploy Steam in NixOS is composing a FHS-compatible
  chroot environment, as documented
  <link xlink:href="http://sandervanderburg.blogspot.nl/2013/09/composing-fhs-compatible-chroot.html">here</link>.
  This allows us to have binaries in the expected paths without disrupting the system,
  and to avoid patching them to work in a non FHS environment.
</para>

</section>

<section xml:id="sec-steam-play">

<title>How to play</title>

<para>
  For 64-bit systems it's important to have
  <programlisting>hardware.opengl.driSupport32Bit = true;</programlisting>
  in your <filename>/etc/nixos/configuration.nix</filename>. You'll also need
  <programlisting>hardware.pulseaudio.support32Bit = true;</programlisting>
  if you are using PulseAudio - this will enable 32bit ALSA apps integration.
  To use the Steam controller, you need to add
  <programlisting>services.udev.extraRules = ''
    SUBSYSTEM=="usb", ATTRS{idVendor}=="28de", MODE="0666"
    KERNEL=="uinput", MODE="0660", GROUP="users", OPTIONS+="static_node=uinput"
  '';</programlisting>
  to your configuration.
</para>

</section>

<section xml:id="sec-steam-troub">

<title>Troubleshooting</title>

<para>
<variablelist>

  <varlistentry>
    <term>Steam fails to start. What do I do?</term>
    <listitem><para>Try to run
    <programlisting>strace steam</programlisting>
    to see what is causing steam to fail.</para></listitem>
  </varlistentry>

  <varlistentry>
  <term>Using the FOSS Radeon or nouveau (nvidia) drivers</term>
  <listitem><itemizedlist>
    <listitem><para>The <literal>newStdcpp</literal> parameter
    was removed since NixOS 17.09 and should not be needed anymore.
    </para></listitem>

    <listitem><para>
    Steam ships statically linked with a version of libcrypto that
    conflics with the one dynamically loaded by radeonsi_dri.so.
    If you get the error
    <programlisting>steam.sh: line 713: 7842 Segmentation fault (core dumped)</programlisting>
    have a look at <link xlink:href="https://github.com/NixOS/nixpkgs/pull/20269">this pull request</link>.
    </para></listitem>

  </itemizedlist></listitem></varlistentry>

  <varlistentry>
  <term>Java</term>
  <listitem><orderedlist>
  <listitem><para>
  There is no java in steam chrootenv by default. If you get a message like
  <programlisting>/home/foo/.local/share/Steam/SteamApps/common/towns/towns.sh: line 1: java: command not found</programlisting>
  You need to add
  <programlisting> steam.override { withJava = true; };</programlisting>
  to your configuration.
  </para></listitem>
  </orderedlist></listitem></varlistentry>

</variablelist>
</para>

</section>

<section xml:id="sec-steam-run">

<title>steam-run</title>
<para>
The FHS-compatible chroot used for steam can also be used to run
other linux games that expect a FHS environment.
To do it, add
<programlisting>pkgs.(steam.override {
          nativeOnly = true;
          newStdcpp = true;
        }).run</programlisting>
to your configuration, rebuild, and run the game with
<programlisting>steam-run ./foo</programlisting>
</para>

</section>

</section>

<section xml:id="sec-emacs">

<title>Emacs</title>

<section xml:id="sec-emacs-config">

<title>Configuring Emacs</title>

<para>
  The Emacs package comes with some extra helpers to make it easier to
  configure. <varname>emacsWithPackages</varname> allows you to manage
  packages from ELPA. This means that you will not have to install
  that packages from within Emacs. For instance, if you wanted to use
  <literal>company</literal>, <literal>counsel</literal>,
  <literal>flycheck</literal>, <literal>ivy</literal>,
  <literal>magit</literal>, <literal>projectile</literal>, and
  <literal>use-package</literal> you could use this as a
  <filename>~/.config/nixpkgs/config.nix</filename> override:
</para>

<screen>
{
  packageOverrides = pkgs: with pkgs; {
    myEmacs = emacsWithPackages (epkgs: (with epkgs.melpaStablePackages; [
      company
      counsel
      flycheck
      ivy
      magit
      projectile
      use-package
    ]));
  }
}
</screen>

<para>
  You can install it like any other packages via <command>nix-env -iA
  myEmacs</command>. However, this will only install those packages.
  It will not <literal>configure</literal> them for us. To do this, we
  need to provide a configuration file. Luckily, it is possible to do
  this from within Nix! By modifying the above example, we can make
  Emacs load a custom config file. The key is to create a package that
  provide a <filename>default.el</filename> file in
  <filename>/share/emacs/site-start/</filename>. Emacs knows to load
  this file automatically when it starts.
</para>

<screen>
{
  packageOverrides = pkgs: with pkgs; rec {
    myEmacsConfig = writeText "default.el" ''
;; initialize package

(require 'package)
(package-initialize 'noactivate)
(eval-when-compile
  (require 'use-package))

;; load some packages

(use-package company
  :bind ("&lt;C-tab&gt;" . company-complete)
  :diminish company-mode
  :commands (company-mode global-company-mode)
  :defer 1
  :config
  (global-company-mode))

(use-package counsel
  :commands (counsel-descbinds)
  :bind (([remap execute-extended-command] . counsel-M-x)
         ("C-x C-f" . counsel-find-file)
         ("C-c g" . counsel-git)
         ("C-c j" . counsel-git-grep)
         ("C-c k" . counsel-ag)
         ("C-x l" . counsel-locate)
         ("M-y" . counsel-yank-pop)))

(use-package flycheck
  :defer 2
  :config (global-flycheck-mode))

(use-package ivy
  :defer 1
  :bind (("C-c C-r" . ivy-resume)
         ("C-x C-b" . ivy-switch-buffer)
         :map ivy-minibuffer-map
         ("C-j" . ivy-call))
  :diminish ivy-mode
  :commands ivy-mode
  :config
  (ivy-mode 1))

(use-package magit
  :defer
  :if (executable-find "git")
  :bind (("C-x g" . magit-status)
         ("C-x G" . magit-dispatch-popup))
  :init
  (setq magit-completing-read-function 'ivy-completing-read))

(use-package projectile
  :commands projectile-mode
  :bind-keymap ("C-c p" . projectile-command-map)
  :defer 5
  :config
  (projectile-global-mode))
    '';
    myEmacs = emacsWithPackages (epkgs: (with epkgs.melpaStablePackages; [
      (runCommand "default.el" {} ''
mkdir -p $out/share/emacs/site-lisp
cp ${myEmacsConfig} $out/share/emacs/site-lisp/default.el
'')
      company
      counsel
      flycheck
      ivy
      magit
      projectile
      use-package
    ]));
  };
}
</screen>

<para>
  This provides a fairly full Emacs start file. It will load in
  addition to the user's presonal config. You can always disable it by
  passing <command>-q</command> to the Emacs command.
</para>

</section>

</section>

<section xml:id="sec-weechat">
<title>Weechat</title>
<para>
Weechat can currently be configured to include your choice of plugins.
To make use of this functionality, install an expression that overrides its configuration such as
<programlisting>weechat.override {configure = {availablePlugins, ...}: {
        plugins = with availablePlugins; [ python perl ];
    }
}</programlisting>
</para>
<para>
The plugins currently available are <literal>python</literal>,
<literal>perl</literal>, <literal>ruby</literal>, <literal>guile</literal>,
<literal>tcl</literal> and <literal>lua</literal>.
</para>
<para>
The python plugin allows the addition of extra libraries. For instance,
the <literal>inotify.py</literal> script in weechat-scripts requires
D-Bus or libnotify, and the <literal>fish.py</literal> script requires
pycrypto. To use these scripts, use the <literal>python</literal>
plugin's <literal>withPackages</literal> attribute:
<programlisting>weechat.override {configure = {availablePlugins, ...}: {
    plugins = with availablePlugins; [
            (python.withPackages (ps: with ps; [ pycrypto python-dbus ]))
        ];
    }
}
</programlisting>
</para>
</section>
</chapter>