895516cadf
Motivation: maintain project-level configuration files. Document the whole situation a bit better so that it corresponds to the implementation, and add NIX_USER_CONF_FILES that allows overriding which user files Nix will load during startup.
209 lines
6.8 KiB
XML
209 lines
6.8 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-common-env">
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<title>Common Environment Variables</title>
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<para>Most Nix commands interpret the following environment variables:</para>
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<variablelist xml:id="env-common">
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<varlistentry><term><envar>IN_NIX_SHELL</envar></term>
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<listitem><para>Indicator that tells if the current environment was set up by
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<command>nix-shell</command>. Since Nix 2.0 the values are
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<literal>"pure"</literal> and <literal>"impure"</literal></para></listitem>
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</varlistentry>
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<varlistentry xml:id="env-NIX_PATH"><term><envar>NIX_PATH</envar></term>
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<listitem>
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<para>A colon-separated list of directories used to look up Nix
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expressions enclosed in angle brackets (i.e.,
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<literal><<replaceable>path</replaceable>></literal>). For
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instance, the value
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<screen>
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/home/eelco/Dev:/etc/nixos</screen>
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will cause Nix to look for paths relative to
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<filename>/home/eelco/Dev</filename> and
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<filename>/etc/nixos</filename>, in this order. It is also
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possible to match paths against a prefix. For example, the value
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<screen>
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nixpkgs=/home/eelco/Dev/nixpkgs-branch:/etc/nixos</screen>
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will cause Nix to search for
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<literal><nixpkgs/<replaceable>path</replaceable>></literal> in
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<filename>/home/eelco/Dev/nixpkgs-branch/<replaceable>path</replaceable></filename>
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and
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<filename>/etc/nixos/nixpkgs/<replaceable>path</replaceable></filename>.</para>
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<para>If a path in the Nix search path starts with
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<literal>http://</literal> or <literal>https://</literal>, it is
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interpreted as the URL of a tarball that will be downloaded and
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unpacked to a temporary location. The tarball must consist of a
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single top-level directory. For example, setting
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<envar>NIX_PATH</envar> to
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<screen>
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nixpkgs=https://github.com/NixOS/nixpkgs-channels/archive/nixos-15.09.tar.gz</screen>
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tells Nix to download the latest revision in the Nixpkgs/NixOS
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15.09 channel.</para>
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<para>A following shorthand can be used to refer to the official channels:
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<screen>nixpkgs=channel:nixos-15.09</screen>
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</para>
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<para>The search path can be extended using the <option
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linkend="opt-I">-I</option> option, which takes precedence over
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<envar>NIX_PATH</envar>.</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_IGNORE_SYMLINK_STORE</envar></term>
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<listitem>
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<para>Normally, the Nix store directory (typically
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<filename>/nix/store</filename>) is not allowed to contain any
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symlink components. This is to prevent “impure” builds. Builders
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sometimes “canonicalise” paths by resolving all symlink components.
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Thus, builds on different machines (with
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<filename>/nix/store</filename> resolving to different locations)
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could yield different results. This is generally not a problem,
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except when builds are deployed to machines where
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<filename>/nix/store</filename> resolves differently. If you are
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sure that you’re not going to do that, you can set
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<envar>NIX_IGNORE_SYMLINK_STORE</envar> to <envar>1</envar>.</para>
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<para>Note that if you’re symlinking the Nix store so that you can
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put it on another file system than the root file system, on Linux
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you’re better off using <literal>bind</literal> mount points, e.g.,
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<screen>
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$ mkdir /nix
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$ mount -o bind /mnt/otherdisk/nix /nix</screen>
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Consult the <citerefentry><refentrytitle>mount</refentrytitle>
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<manvolnum>8</manvolnum></citerefentry> manual page for details.</para>
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</listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_STORE_DIR</envar></term>
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<listitem><para>Overrides the location of the Nix store (default
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<filename><replaceable>prefix</replaceable>/store</filename>).</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_DATA_DIR</envar></term>
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<listitem><para>Overrides the location of the Nix static data
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directory (default
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<filename><replaceable>prefix</replaceable>/share</filename>).</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_LOG_DIR</envar></term>
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<listitem><para>Overrides the location of the Nix log directory
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(default <filename><replaceable>prefix</replaceable>/var/log/nix</filename>).</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_STATE_DIR</envar></term>
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<listitem><para>Overrides the location of the Nix state directory
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(default <filename><replaceable>prefix</replaceable>/var/nix</filename>).</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_CONF_DIR</envar></term>
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<listitem><para>Overrides the location of the system Nix configuration
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directory (default
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<filename><replaceable>prefix</replaceable>/etc/nix</filename>).</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_USER_CONF_FILES</envar></term>
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<listitem><para>Overrides the location of the user Nix configuration files
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to load from (defaults to the XDG spec locations). The variable is treated
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as a list separated by the <literal>:</literal> token.</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>TMPDIR</envar></term>
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<listitem><para>Use the specified directory to store temporary
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files. In particular, this includes temporary build directories;
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these can take up substantial amounts of disk space. The default is
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<filename>/tmp</filename>.</para></listitem>
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</varlistentry>
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<varlistentry xml:id="envar-remote"><term><envar>NIX_REMOTE</envar></term>
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<listitem><para>This variable should be set to
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<literal>daemon</literal> if you want to use the Nix daemon to
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execute Nix operations. This is necessary in <link
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linkend="ssec-multi-user">multi-user Nix installations</link>.
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If the Nix daemon's Unix socket is at some non-standard path,
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this variable should be set to <literal>unix://path/to/socket</literal>.
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Otherwise, it should be left unset.</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_SHOW_STATS</envar></term>
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<listitem><para>If set to <literal>1</literal>, Nix will print some
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evaluation statistics, such as the number of values
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allocated.</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>NIX_COUNT_CALLS</envar></term>
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<listitem><para>If set to <literal>1</literal>, Nix will print how
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often functions were called during Nix expression evaluation. This
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is useful for profiling your Nix expressions.</para></listitem>
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</varlistentry>
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<varlistentry><term><envar>GC_INITIAL_HEAP_SIZE</envar></term>
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<listitem><para>If Nix has been configured to use the Boehm garbage
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collector, this variable sets the initial size of the heap in bytes.
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It defaults to 384 MiB. Setting it to a low value reduces memory
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consumption, but will increase runtime due to the overhead of
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garbage collection.</para></listitem>
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</varlistentry>
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</variablelist>
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</chapter>
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