<para>
      This chapter explains how to install Hydra on your own build farm server.
    </para>

	            <listitem><para>Nix</para></listitem>
	            <listitem><para>PostgreSQL</para></listitem>

	            <listitem>Nix</listitem>
	            <listitem>either PostgreSQL or SQLite</listitem>
		    <listitem>many Perl packages, notably Catalyst,
		    EmailSender, and NixPerl (see the <link
		    xlink:href="https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/development/tools/misc/hydra/default.nix">Hydra
		    expression in Nixpkgs</link> for the complete
		    list).</listitem>

	        At the moment, Hydra runs only on 32 bit and 64 bit Linux (<emphasis>i686-linux</emphasis> and <emphasis>x86_64_linux</emphasis>).

	        At the moment, Hydra runs only on GNU/Linux
	        (<emphasis>i686-linux</emphasis> and
	        <emphasis>x86_64_linux</emphasis>).

	<para>
	  For small projects, Hydra can be run on any reasonably
	  modern machine. For individual projects you can even run
	  Hydra on a laptop. However, the charm of a buildfarm server
	  is usually that it operates without disturbing the
	  developer's working environment and can serve releases over
	  the internet. In conjunction you should typically have your
	  source code administered in a version management system,
	  such as subversion. Therefore, you will probably want to
	  install a server that is connected to the internet. To scale
	  up to large and/or many projects, you will need at least a
	  considerable amount of diskspace to store builds. Since
	  Hydra can schedule multiple simultaneous build jobs, it can
	  be useful to have a multi-core machine, and/or attach
	  multiple build machines in a network to the central Hydra
	  server.
	</para>
	<para>
	  Of course we think it is a good idea to use the <a
	  href="http://nixos.org/nixos">NixOS</a> GNU/Linux
	  distribution for your buildfarm server. But this is not a
	  requirement.  The Nix software deployment system can be
	  installed on any GNU/Linux distribution in parallel to the
	  regular package management system. Thus, you can use Hydra
	  on a Debian, Fedora, SuSE, or Ubuntu system.
	</para>

    </section>
    <section>
      <title>Getting Nix</title>
      <para>
	If your server runs NixOS you are all set to continue with
	installation of Hydra. Otherwise you first need to install
	Nix.  The latest stable version can be found one <link
	xlink:href="http://nixos.org/nix/download.html">the Nix web
	site</link>, along with a manual, which includes installation
	instructions.
      </para>

	<para>
	  Hydra can be installed using Nixpkgs:
	  <screen>
	    nix-env -Ai hydra -f /path/to/nixpkgs</screen>
	  This makes the tools available in your Nix user environment,
	  <literal>$HOME/.nix-profile</literal> by default.
	</para>

            Hydra can be installed by visiting the URL, 
<screen>
http://hydra.nixos.org/view/hydra/unstable</screen>
            and use the one-click install available at one of the build pages. You could also  

            Alternatively, the latest development snapshot can be
            installed by visiting the URL
	    <link xlink:href="http://hydra.nixos.org/view/hydra/unstable"><literal>http://hydra.nixos.org/view/hydra/unstable</literal></link>
            and use the one-click install available at one of the build pages. You can also  

        </para>
	<para>
	  Command completion should reveal a number of command-line tools from Hydra:

        </para>

	  <screen>
hydra_build.pl            hydra_eval_jobs           hydra_server.pl
hydra_control.sh          hydra_evaluator.pl        hydra_update_gc_roots.pl
hydra_create.pl           hydra_queue_runner.pl     </screen>
	</para>