<chapter id='chap-installation'><title>Installation</title>
<sect1><title>Obtaining Nix</title>
<para>The easiest way to obtain Nix is to download a <ulink
url='http://www.cs.uu.nl/groups/ST/Trace/Nix'>source
distribution</ulink>. RPMs for Red Hat 9 are also available. These
distributions are generated automatically.</para>
<para>Alternatively, the most recent sources of Nix can be obtained
from its <ulink
url='https://svn.cs.uu.nl:12443/repos/trace/nix/trunk'>Subversion
repository</ulink>. For example, the following command will check out
the latest revision into a directory called <filename>nix</filename>:</para>
<screen>
$ svn checkout https://svn.cs.uu.nl:12443/repos/trace/nix/trunk nix</screen>
<para>Likewise, specific releases can be obtained from the <ulink
url='https://svn.cs.uu.nl:12443/repos/trace/nix/tags'>tags
directory</ulink> of the repository. If you don't have Subversion,
you can also download an automatically generated <ulink
url='https://svn.cs.uu.nl:12443/dist/trace/'>compressed
tar-file</ulink> of the head revision of the trunk.</para>
</sect1>
<sect1><title>Prerequisites</title>
<para>The following prerequisites only apply when you build from
source. Binary releases (e.g., RPMs) have no prerequisites.</para>
<para>A fairly recent version of GCC/G++ is required. Version 2.95
and higher should work.</para>
<para>To build this manual and the man-pages you need the
<command>xmllint</command> and <command>xsltproc</command> programs,
which are part of the <literal>libxml2</literal> and
<literal>libxslt</literal> packages, respectively. You also need the
<ulink url='http://docbook.sourceforge.net/projects/xsl/'>DocBook XSL
stylesheets</ulink> and optionally the <ulink
url='http://www.oasis-open.org/docbook/xml/4.2/docbook-xml-4.2.zip'>
DocBook XML 4.2 DTD</ulink>. Note that these are only required if you
modify the manual sources or when you are building from the Subversion
repository.</para>
<para>To build the parser, very <emphasis>recent</emphasis> versions
of Bison and Flex are required. (This is because Nix needs GLR
support in Bison and reentrancy support in Flex.) For Bison, you need
version 1.875c or higher (1.875 does <emphasis>not</emphasis> work),
which can be obtained from the <ulink
url='ftp://alpha.gnu.org/pub/gnu/bison'>GNU FTP server</ulink>. For
Flex, you need version 2.5.31, which is available on <ulink
url='http://lex.sourceforge.net/'>SourceForge</ulink>. Slightly older
versions may also work, but ancient versions like the ubiquitous
2.5.4a won't. Note that these are only required if you modify the
parser or when you are building from the Subversion repository.</para>
<para>Nix uses Sleepycat's Berkeley DB and CWI's ATerm library. These
are included in the Nix source distribution. If you build from the
Subversion repository, you must download them yourself and place them
in the <filename>externals/</filename> directory. See
<filename>externals/Makefile.am</filename> for the precise URLs of
these packages. Alternatively, if you already have them installed,
you can use <command>configure</command>'s <option>--with-bdb</option>
and <option>--with-aterm</option> options to point to their respective
locations. Note that Berkeley DB <emphasis>must</emphasis> be version
4.2; other versions may not have compatible database formats.</para>
</sect1>
<sect1><title>Building Nix from source</title>
<para>After unpacking or checking out the Nix sources, issue the
following commands:
</para>
<screen>
$ ./configure <replaceable>options...</replaceable>
$ make
$ make install</screen>
<para>When building from the Subversion repository, these should be
preceded by the command:
</para>
<screen>
$ autoreconf -i</screen>
<para>The installation path can be specified by passing the
<option>--prefix=<replaceable>prefix</replaceable></option> to
<command>configure</command>. The default installation directory is
<filename>/nix</filename>. You can change this to any location you
like. You must have write permission to the
<replaceable>prefix</replaceable> path.</para>
<warning><para>It is advisable <emphasis>not</emphasis> to change the
installation prefix from its default, since doing so will in all
likelihood make it impossible to use derivations built on other
systems.</para></warning>
<para>If you want to rebuilt the documentation, pass the full path to
the DocBook XML catalog file (<filename>docbook.cat</filename>) and to
the DocBook XSL stylesheets using the
<option>--with-docbook-catalog=<replaceable>path</replaceable></option>
and
<option>--with-docbook-xsl=<replaceable>path</replaceable></option>
options.</para>
</sect1>
<sect1><title>Installing from RPMs</title>
<para>RPM packages of Nix can be downloaded from <ulink
url='http://www.cs.uu.nl/groups/ST/Trace/Nix' />. These RPMs should
work for most fairly recent releases of SuSE and Red Hat Linux. They
have been known to work work on SuSE Linux 8.1 and 9.0, and Red Hat
9.0. In fact, it should work on any RPM-based Linux distribution
based on <literal>glibc</literal> 2.3 or later.</para>
<para>Once downloaded, the RPMs can be installed or upgraded using
<command>rpm -U</command>. For example,</para>
<screen>
$ rpm -U nix-0.5pre664-1.i386.rpm</screen>
<para>The RPMs install into the directory <filename>/nix</filename>.
Nix can be uninstalled using <command>rpm -e nix</command>. After
this it will be necessary to manually remove the Nix store and other
auxiliary data:</para>
<screen>
$ rm -rf /nix/store
$ rm -rf /nix/var</screen>
</sect1>
<sect1><title>Permissions</title>
<para>All Nix operations must be performed under the user ID that owns
the Nix store and database
(<filename><replaceable>prefix</replaceable>/store</filename> and
<filename><replaceable>prefix</replaceable>/var/nix/db</filename>,
respectively). When installed from the RPM packages, these
directories are owned by <systemitem
class='username'>root</systemitem>.</para>
<sect2><title>Setuid installation</title>
<para>As a somewhat <emphasis>ad hoc</emphasis> hack, you can also
install the Nix binaries <quote>setuid</quote> so that a Nix store can
be shared among several users. To do this, configure Nix with the
<emphasis>--enable-setuid</emphasis> option. Nix will be installed as
owned by a user and group specified by the
<option>--with-nix-user=<parameter>user</parameter></option> and
<option>--with-nix-group=<parameter>group</parameter></option>
options. E.g.,
<screen>
$ ./configure --enable-setuid --with-nix-user=my_nix_user --with-nix-group=my_nix_group</screen>
The user and group default to <literal>nix</literal>. You should make
sure that both the user and the group exist. Any <quote>real</quote>
users that you want to allow access should be added to the Nix
group.</para>
<warning><para>A setuid installation should only by used if the users
in the Nix group are mutually trusted, since any user in that group
has the ability to change anything in the Nix store or database. For
instance, they could install a trojan horse in executables used by
other users.</para></warning>
<warning><para>On some platforms, the Nix binaries will be installed
as setuid <literal>root</literal>. They drop root privileges
immediately after startup and switch to the Nix user. The reason for
this is that both the real and effective user must be set to the Nix
user, and POSIX has no system call to do this. This is not the case
on systems that have the <function>setresuid()</function> system call
(such as Linux and FreeBSD), so on those systems the binaries are
simply owned by the Nix user.</para></warning>
</sect2>
</sect1>
<sect1><title>Using Nix</title>
<para>To use Nix, some environment variables should be set. In
particular, <envar>PATH</envar> should contain the directories
<filename><replaceable>prefix</replaceable>/bin</filename> and
<filename>~/.nix-profile/bin</filename>. The first directory contains
the Nix tools themselves, while <filename>~/.nix-profile</filename> is
a symbolic link to the current <emphasis>user environment</emphasis>
(an automatically generated package consisting of symlinks to
installed packages). The simplest way to set the required environment
variables is to include the file
<filename><replaceable>prefix</replaceable>/etc/profile.d/nix.sh</filename>
in your <filename>~/.bashrc</filename> (or similar), like this:</para>
<screen>
. <replaceable>prefix</replaceable>/etc/profile.d/nix.sh</screen>
</sect1>
</chapter>
