<sect1 id="building-in-jails">

        <title>Building in jails</title>

	<para>Note, that the behavior of <makevar>OSVERSION</makevar> has been

	  changed recently.  Now, it gets the <link

	   linkend="freebsd-versions"><literal>__FreeBSD_version</literal></link>

	  from the userland, since it makes more sense for the ports, than the

	  kernel.  You can still override it, if you really have to get it from

	  the kernel.</para>

      </sect1>

	<para>Firstly, you should completely unerstand what these two

	  variables are for.  <makevar>PREFIX</makevar> determines the

	  location where all ports should install in the current environemt.

	  This is usually <filename>/usr/local</filename>, or

	  <filename>/opt</filename> in other operating systems.   You

	  can set <makevar>PREFIX</makevar> to everything you want, See the

	  <a href="http://www.pathname.com/fhs/2.2/>Filesystem Hierarchy

	  Standard</a> for making a good decision.  <makevar>DESTDIR</makevar>

	  determines the whole environment you want to use the package from.

	  This environment can be a jail, or an installed system mounted

	  elsewhere than <filename>/</filename>.  This means a port will

	  actually install to <makevar>DESTDIR</makevar>/<makevar>PREFIX</makevar>,

	  and registered in the package database of the given environment.

	  It is very important that you write such ports that respect this,

	  thus you can find some guidelines below to do so.</para>

	<para>For writing <makevar>DESTDIR</makevar>-compliant ports, note that

	  <makevar>LOCALBASE</makevar>, <makevar>LINUXBASE</makevar>,

	  <makevar>X11BASE</makevar>, <makevar>DOCSDIR</makevar>,

	  <makevar>EXAMPLESDIR</makevar>, <makevar>DATADIR</makevar>, 

	  <makevar>DESKTOPDIR</makevar> variables already contain

	  <makevar>DESTDIR</makevar>, so

	  <makevar>DESTDIR</makevar>/<makevar>LOCALBASE</makevar> is

	  definitely wrong, but you can use <makevar>LOCALBASE_REL</makevar> if

	  you need a variable relative to <makevar>DESTDIR</makevar>.

	  Similarly, you can use <makevar>LINUXBASE_REL</makevar> and

	  <makevar>X11BASE_REL</makevar> variables as well.

	  <makevar>PREFIX</makevar> is an absolute path. but relative

	  to <makewar>DESTDIR</makevar>.  If you want to refer to the

	  fully qualified destination you can use <makevar>TARGETDIR</makevar>,

	  which resolves to <makevar>DESTDIR</makevar>/<makevar>PREFIX</makevar>.</para>

	<para>You have to use these variables correctly

	  in your ports <filename>Makefile</filename>, esepecially in

	  custom targets, to ensure each files are installed to the

	  corect place.  For dependencies, using <makevar>LOCALBASE</makevar>

	  is still correct, since we want to check for dependencies

	  in <makevar>DESTDIR</makevar>.</para>

	<para>In packing lists, or in <filename>pkg-*</filename> scripts you

	  can still use <literal>%%LOCALBASE%%</literal>,

	  <literal>%%LINUXBASE%%</literal> and <literal>%%X11BASE%%</literal>

	  expansions, since they represent relative paths there.  This ambiguity

	  can be frustrating at first, but this actually simplifies the process

	  of writing <makevar>DESTDIR</makevar>-compliant ports.  We did not use to

	  have <makevar>DESTDIR</makevar> support by our ports infrastructure,

	  and one of the major goals was to avoid modifying a tons of ports,

	  so we just changed <makevar>LOCALBASE</makevar> in the

	  infrastructure instead of changing that in tons of individual ports.

	  With a little workaround, <makevar>LOCALBASE</makevar>,

	  <makevar>LINUXBASE</makevar> and <makevar>X11BASE</makevar>

	  are still overrideable, though.</para>