path: root/doc/manual/env-common.xml

<sect1 id="sec-common-env"><title>Common environment variables</title>

<para>Most Nix commands interpret the following environment variables:</para>

<variablelist>

  
<varlistentry><term><envar>NIX_ROOT</envar></term>

  <listitem><para>If <envar>NIX_ROOT</envar> is set, the Nix command
  will on startup perform a <function>chroot()</function> to the
  specified directory.  This is useful in certain bootstrapping
  situations (e.g., when installing a Nix installation onto a hard
  disk from CD-ROM).</para></listitem>

</varlistentry>

  
<varlistentry><term><envar>NIX_IGNORE_SYMLINK_STORE</envar></term>

  <listitem>

  <para>Normally, the Nix store directory (typically
  <filename>/nix/store</filename>) is not allowed to contain any
  symlink components.  This is to prevent “impure” builds.  Builders
  sometimes “canonicalise” paths by resolving all symlink components.
  Thus, builds on different machines (with
  <filename>/nix/store</filename> resolving to different locations)
  could yield different results.  This is generally not a problem,
  except when builds are deployed to machines where
  <filename>/nix/store</filename> resolves differently.  If you are
  sure that you’re not going to do that, you can set
  <envar>NIX_IGNORE_SYMLINK_STORE</envar> to <envar>1</envar>.</para>

  <para>Note that if you’re symlinking the Nix store so that you can
  put it on another file system than the root file system, on Linux
  you’re better off using <literal>bind</literal> mount points, e.g.,

  <screen>
$ mkdir /nix   
$ mount -o bind /mnt/otherdisk/nix /nix</screen>

  Consult the <citerefentry><refentrytitle>mount</refentrytitle>
  <manvolnum>8</manvolnum></citerefentry> manual page for details.</para>

  </listitem>

</varlistentry>


<varlistentry><term><envar>NIX_STORE_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix store (default
  <filename><replaceable>prefix</replaceable>/store</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_DATA_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix static data
  directory (default
  <filename><replaceable>prefix</replaceable>/share</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_LOG_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix log directory
  (default <filename><replaceable>prefix</replaceable>/log/nix</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_STATE_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix state directory
  (default <filename><replaceable>prefix</replaceable>/var/nix</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_DB_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix database (default
  <filename><replaceable>$NIX_STATE_DIR</replaceable>/db</filename>, i.e.,
  <filename><replaceable>prefix</replaceable>/var/nix/db</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_CONF_DIR</envar></term>

  <listitem><para>Overrides the location of the Nix configuration
  directory (default
  <filename><replaceable>prefix</replaceable>/etc/nix</filename>).</para></listitem>
  
</varlistentry>


<varlistentry><term><envar>NIX_LOG_TYPE</envar></term>

  <listitem><para>Equivalent to the <link
  linkend="opt-log-type"><option>--log-type</option>
  option</link>.</para></listitem>

</varlistentry>
  

<varlistentry><term><envar>TMPDIR</envar></term>

  <listitem><para>Use the specified directory to store temporary
  files.  In particular, this includes temporary build directories;
  these can take up substantial amounts of disk space.  The default is
  <filename>/tmp</filename>.</para></listitem>
  
</varlistentry>


</variablelist>

</sect1>