mirror of
https://github.com/NixOS/nixpkgs.git
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800 lines
27 KiB
XML
800 lines
27 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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xml:id="chap-functions">
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<title>Functions reference</title>
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<para>
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The nixpkgs repository has several utility functions to manipulate Nix
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expressions.
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</para>
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<section xml:id="sec-overrides">
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<title>Overriding</title>
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<para>
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Sometimes one wants to override parts of <literal>nixpkgs</literal>, e.g.
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derivation attributes, the results of derivations or even the whole package
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set.
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</para>
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<section xml:id="sec-pkg-override">
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<title><pkg>.override</title>
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<para>
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The function <varname>override</varname> is usually available for all the
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derivations in the nixpkgs expression (<varname>pkgs</varname>).
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</para>
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<para>
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It is used to override the arguments passed to a function.
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</para>
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<para>
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Example usages:
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<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
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<programlisting>import pkgs.path { overlays = [ (self: super: {
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foo = super.foo.override { barSupport = true ; };
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})]};</programlisting>
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<programlisting>mypkg = pkgs.callPackage ./mypkg.nix {
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mydep = pkgs.mydep.override { ... };
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}</programlisting>
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</para>
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<para>
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In the first example, <varname>pkgs.foo</varname> is the result of a
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function call with some default arguments, usually a derivation. Using
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<varname>pkgs.foo.override</varname> will call the same function with the
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given new arguments.
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</para>
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</section>
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<section xml:id="sec-pkg-overrideAttrs">
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<title><pkg>.overrideAttrs</title>
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<para>
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The function <varname>overrideAttrs</varname> allows overriding the
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attribute set passed to a <varname>stdenv.mkDerivation</varname> call,
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producing a new derivation based on the original one. This function is
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available on all derivations produced by the
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<varname>stdenv.mkDerivation</varname> function, which is most packages in
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the nixpkgs expression <varname>pkgs</varname>.
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</para>
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<para>
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Example usage:
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<programlisting>helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
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separateDebugInfo = true;
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});</programlisting>
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</para>
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<para>
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In the above example, the <varname>separateDebugInfo</varname> attribute is
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overridden to be true, thus building debug info for
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<varname>helloWithDebug</varname>, while all other attributes will be
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retained from the original <varname>hello</varname> package.
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</para>
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<para>
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The argument <varname>oldAttrs</varname> is conventionally used to refer to
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the attr set originally passed to <varname>stdenv.mkDerivation</varname>.
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</para>
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<note>
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<para>
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Note that <varname>separateDebugInfo</varname> is processed only by the
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<varname>stdenv.mkDerivation</varname> function, not the generated, raw
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Nix derivation. Thus, using <varname>overrideDerivation</varname> will not
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work in this case, as it overrides only the attributes of the final
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derivation. It is for this reason that <varname>overrideAttrs</varname>
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should be preferred in (almost) all cases to
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<varname>overrideDerivation</varname>, i.e. to allow using
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<varname>sdenv.mkDerivation</varname> to process input arguments, as well
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as the fact that it is easier to use (you can use the same attribute names
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you see in your Nix code, instead of the ones generated (e.g.
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<varname>buildInputs</varname> vs <varname>nativeBuildInputs</varname>,
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and involves less typing.
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</para>
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</note>
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</section>
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<section xml:id="sec-pkg-overrideDerivation">
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<title><pkg>.overrideDerivation</title>
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<warning>
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<para>
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You should prefer <varname>overrideAttrs</varname> in almost all cases,
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see its documentation for the reasons why.
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<varname>overrideDerivation</varname> is not deprecated and will continue
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to work, but is less nice to use and does not have as many abilities as
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<varname>overrideAttrs</varname>.
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</para>
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</warning>
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<warning>
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<para>
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Do not use this function in Nixpkgs as it evaluates a Derivation before
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modifying it, which breaks package abstraction and removes error-checking
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of function arguments. In addition, this evaluation-per-function
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application incurs a performance penalty, which can become a problem if
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many overrides are used. It is only intended for ad-hoc customisation,
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such as in <filename>~/.config/nixpkgs/config.nix</filename>.
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</para>
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</warning>
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<para>
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The function <varname>overrideDerivation</varname> creates a new derivation
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based on an existing one by overriding the original's attributes with the
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attribute set produced by the specified function. This function is
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available on all derivations defined using the
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<varname>makeOverridable</varname> function. Most standard
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derivation-producing functions, such as
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<varname>stdenv.mkDerivation</varname>, are defined using this function,
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which means most packages in the nixpkgs expression,
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<varname>pkgs</varname>, have this function.
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</para>
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<para>
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Example usage:
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<programlisting>mySed = pkgs.gnused.overrideDerivation (oldAttrs: {
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name = "sed-4.2.2-pre";
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src = fetchurl {
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url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
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sha256 = "11nq06d131y4wmf3drm0yk502d2xc6n5qy82cg88rb9nqd2lj41k";
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};
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patches = [];
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});</programlisting>
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</para>
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<para>
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In the above example, the <varname>name</varname>, <varname>src</varname>,
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and <varname>patches</varname> of the derivation will be overridden, while
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all other attributes will be retained from the original derivation.
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</para>
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<para>
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The argument <varname>oldAttrs</varname> is used to refer to the attribute
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set of the original derivation.
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</para>
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<note>
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<para>
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A package's attributes are evaluated *before* being modified by the
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<varname>overrideDerivation</varname> function. For example, the
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<varname>name</varname> attribute reference in <varname>url =
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"mirror://gnu/hello/${name}.tar.gz";</varname> is filled-in *before* the
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<varname>overrideDerivation</varname> function modifies the attribute set.
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This means that overriding the <varname>name</varname> attribute, in this
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example, *will not* change the value of the <varname>url</varname>
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attribute. Instead, we need to override both the <varname>name</varname>
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*and* <varname>url</varname> attributes.
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</para>
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</note>
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</section>
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<section xml:id="sec-lib-makeOverridable">
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<title>lib.makeOverridable</title>
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<para>
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The function <varname>lib.makeOverridable</varname> is used to make the
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result of a function easily customizable. This utility only makes sense for
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functions that accept an argument set and return an attribute set.
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</para>
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<para>
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Example usage:
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<programlisting>f = { a, b }: { result = a+b; }
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c = lib.makeOverridable f { a = 1; b = 2; }</programlisting>
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</para>
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<para>
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The variable <varname>c</varname> is the value of the <varname>f</varname>
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function applied with some default arguments. Hence the value of
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<varname>c.result</varname> is <literal>3</literal>, in this example.
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</para>
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<para>
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The variable <varname>c</varname> however also has some additional
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functions, like <link linkend="sec-pkg-override">c.override</link> which
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can be used to override the default arguments. In this example the value of
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<varname>(c.override { a = 4; }).result</varname> is 6.
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</para>
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</section>
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</section>
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<section xml:id="sec-generators">
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<title>Generators</title>
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<para>
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Generators are functions that create file formats from nix data structures,
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e. g. for configuration files. There are generators available for:
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<literal>INI</literal>, <literal>JSON</literal> and <literal>YAML</literal>
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</para>
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<para>
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All generators follow a similar call interface: <code>generatorName
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configFunctions data</code>, where <literal>configFunctions</literal> is an
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attrset of user-defined functions that format nested parts of the content.
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They each have common defaults, so often they do not need to be set
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manually. An example is <code>mkSectionName ? (name: libStr.escape [ "[" "]"
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] name)</code> from the <literal>INI</literal> generator. It receives the
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name of a section and sanitizes it. The default
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<literal>mkSectionName</literal> escapes <literal>[</literal> and
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<literal>]</literal> with a backslash.
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</para>
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<para>
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Generators can be fine-tuned to produce exactly the file format required by
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your application/service. One example is an INI-file format which uses
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<literal>: </literal> as separator, the strings
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<literal>"yes"</literal>/<literal>"no"</literal> as boolean values and
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requires all string values to be quoted:
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</para>
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<programlisting>
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with lib;
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let
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customToINI = generators.toINI {
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# specifies how to format a key/value pair
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mkKeyValue = generators.mkKeyValueDefault {
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# specifies the generated string for a subset of nix values
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mkValueString = v:
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if v == true then ''"yes"''
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else if v == false then ''"no"''
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else if isString v then ''"${v}"''
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# and delegats all other values to the default generator
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else generators.mkValueStringDefault {} v;
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} ":";
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};
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# the INI file can now be given as plain old nix values
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in customToINI {
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main = {
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pushinfo = true;
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autopush = false;
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host = "localhost";
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port = 42;
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};
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mergetool = {
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merge = "diff3";
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};
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}
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</programlisting>
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<para>
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This will produce the following INI file as nix string:
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</para>
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<programlisting>
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[main]
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autopush:"no"
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host:"localhost"
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port:42
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pushinfo:"yes"
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str\:ange:"very::strange"
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[mergetool]
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merge:"diff3"
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</programlisting>
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<note>
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<para>
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Nix store paths can be converted to strings by enclosing a derivation
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attribute like so: <code>"${drv}"</code>.
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</para>
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</note>
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<para>
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Detailed documentation for each generator can be found in
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<literal>lib/generators.nix</literal>.
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</para>
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</section>
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<section xml:id="sec-debug">
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<title>Debugging Nix Expressions</title>
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<para>
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Nix is a unityped, dynamic language, this means every value can potentially
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appear anywhere. Since it is also non-strict, evaluation order and what
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ultimately is evaluated might surprise you. Therefore it is important to be
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able to debug nix expressions.
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</para>
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<para>
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In the <literal>lib/debug.nix</literal> file you will find a number of
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functions that help (pretty-)printing values while evaluation is runnnig.
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You can even specify how deep these values should be printed recursively,
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and transform them on the fly. Please consult the docstrings in
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<literal>lib/debug.nix</literal> for usage information.
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</para>
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</section>
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<section xml:id="sec-fhs-environments">
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<title>buildFHSUserEnv</title>
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<para>
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<function>buildFHSUserEnv</function> provides a way to build and run
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FHS-compatible lightweight sandboxes. It creates an isolated root with bound
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<filename>/nix/store</filename>, so its footprint in terms of disk space
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needed is quite small. This allows one to run software which is hard or
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unfeasible to patch for NixOS -- 3rd-party source trees with FHS
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assumptions, games distributed as tarballs, software with integrity checking
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and/or external self-updated binaries. It uses Linux namespaces feature to
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create temporary lightweight environments which are destroyed after all
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child processes exit, without root user rights requirement. Accepted
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arguments are:
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</para>
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<variablelist>
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<varlistentry>
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<term>
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<literal>name</literal>
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</term>
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<listitem>
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<para>
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Environment name.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>targetPkgs</literal>
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</term>
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<listitem>
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<para>
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Packages to be installed for the main host's architecture (i.e. x86_64 on
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x86_64 installations). Along with libraries binaries are also installed.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>multiPkgs</literal>
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</term>
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<listitem>
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<para>
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Packages to be installed for all architectures supported by a host (i.e.
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i686 and x86_64 on x86_64 installations). Only libraries are installed by
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default.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>extraBuildCommands</literal>
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</term>
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<listitem>
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<para>
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Additional commands to be executed for finalizing the directory
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structure.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>extraBuildCommandsMulti</literal>
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</term>
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<listitem>
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<para>
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Like <literal>extraBuildCommands</literal>, but executed only on multilib
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architectures.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>extraOutputsToInstall</literal>
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</term>
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<listitem>
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<para>
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Additional derivation outputs to be linked for both target and
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multi-architecture packages.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>extraInstallCommands</literal>
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</term>
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<listitem>
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<para>
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Additional commands to be executed for finalizing the derivation with
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runner script.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<literal>runScript</literal>
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</term>
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<listitem>
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<para>
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A command that would be executed inside the sandbox and passed all the
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command line arguments. It defaults to <literal>bash</literal>.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>
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One can create a simple environment using a <literal>shell.nix</literal>
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like that:
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</para>
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<programlisting><![CDATA[
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{ pkgs ? import <nixpkgs> {} }:
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(pkgs.buildFHSUserEnv {
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name = "simple-x11-env";
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targetPkgs = pkgs: (with pkgs;
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[ udev
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alsaLib
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]) ++ (with pkgs.xorg;
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[ libX11
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libXcursor
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libXrandr
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]);
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multiPkgs = pkgs: (with pkgs;
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[ udev
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alsaLib
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]);
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runScript = "bash";
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}).env
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]]></programlisting>
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|
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<para>
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Running <literal>nix-shell</literal> would then drop you into a shell with
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these libraries and binaries available. You can use this to run
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||
closed-source applications which expect FHS structure without hassles:
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simply change <literal>runScript</literal> to the application path, e.g.
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<filename>./bin/start.sh</filename> -- relative paths are supported.
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</para>
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</section>
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<xi:include href="shell.section.xml" />
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<section xml:id="sec-pkgs-dockerTools">
|
||
<title>pkgs.dockerTools</title>
|
||
|
||
<para>
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||
<varname>pkgs.dockerTools</varname> is a set of functions for creating and
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||
manipulating Docker images according to the
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||
<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#docker-image-specification-v120">
|
||
Docker Image Specification v1.2.0 </link>. Docker itself is not used to
|
||
perform any of the operations done by these functions.
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||
</para>
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||
|
||
<warning>
|
||
<para>
|
||
The <varname>dockerTools</varname> API is unstable and may be subject to
|
||
backwards-incompatible changes in the future.
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||
</para>
|
||
</warning>
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||
|
||
<section xml:id="ssec-pkgs-dockerTools-buildImage">
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||
<title>buildImage</title>
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||
|
||
<para>
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||
This function is analogous to the <command>docker build</command> command,
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in that can used to build a Docker-compatible repository tarball containing
|
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a single image with one or multiple layers. As such, the result is suitable
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||
for being loaded in Docker with <command>docker load</command>.
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||
</para>
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||
|
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<para>
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The parameters of <varname>buildImage</varname> with relative example
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||
values are described below:
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||
</para>
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||
|
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<example xml:id='ex-dockerTools-buildImage'>
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||
<title>Docker build</title>
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<programlisting>
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buildImage {
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name = "redis"; <co xml:id='ex-dockerTools-buildImage-1' />
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tag = "latest"; <co xml:id='ex-dockerTools-buildImage-2' />
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||
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fromImage = someBaseImage; <co xml:id='ex-dockerTools-buildImage-3' />
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fromImageName = null; <co xml:id='ex-dockerTools-buildImage-4' />
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fromImageTag = "latest"; <co xml:id='ex-dockerTools-buildImage-5' />
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|
||
contents = pkgs.redis; <co xml:id='ex-dockerTools-buildImage-6' />
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runAsRoot = '' <co xml:id='ex-dockerTools-buildImage-runAsRoot' />
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#!${stdenv.shell}
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mkdir -p /data
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'';
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||
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config = { <co xml:id='ex-dockerTools-buildImage-8' />
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Cmd = [ "/bin/redis-server" ];
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||
WorkingDir = "/data";
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||
Volumes = {
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||
"/data" = {};
|
||
};
|
||
};
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<para>
|
||
The above example will build a Docker image <literal>redis/latest</literal>
|
||
from the given base image. Loading and running this image in Docker results
|
||
in <literal>redis-server</literal> being started automatically.
|
||
</para>
|
||
|
||
<calloutlist>
|
||
<callout arearefs='ex-dockerTools-buildImage-1'>
|
||
<para>
|
||
<varname>name</varname> specifies the name of the resulting image. This
|
||
is the only required argument for <varname>buildImage</varname>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-2'>
|
||
<para>
|
||
<varname>tag</varname> specifies the tag of the resulting image. By
|
||
default it's <literal>null</literal>, which indicates that the nix output
|
||
hash will be used as tag.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-3'>
|
||
<para>
|
||
<varname>fromImage</varname> is the repository tarball containing the
|
||
base image. It must be a valid Docker image, such as exported by
|
||
<command>docker save</command>. By default it's <literal>null</literal>,
|
||
which can be seen as equivalent to <literal>FROM scratch</literal> of a
|
||
<filename>Dockerfile</filename>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-4'>
|
||
<para>
|
||
<varname>fromImageName</varname> can be used to further specify the base
|
||
image within the repository, in case it contains multiple images. By
|
||
default it's <literal>null</literal>, in which case
|
||
<varname>buildImage</varname> will peek the first image available in the
|
||
repository.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-5'>
|
||
<para>
|
||
<varname>fromImageTag</varname> can be used to further specify the tag of
|
||
the base image within the repository, in case an image contains multiple
|
||
tags. By default it's <literal>null</literal>, in which case
|
||
<varname>buildImage</varname> will peek the first tag available for the
|
||
base image.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-6'>
|
||
<para>
|
||
<varname>contents</varname> is a derivation that will be copied in the
|
||
new layer of the resulting image. This can be similarly seen as
|
||
<command>ADD contents/ /</command> in a <filename>Dockerfile</filename>.
|
||
By default it's <literal>null</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-runAsRoot'>
|
||
<para>
|
||
<varname>runAsRoot</varname> is a bash script that will run as root in an
|
||
environment that overlays the existing layers of the base image with the
|
||
new resulting layer, including the previously copied
|
||
<varname>contents</varname> derivation. This can be similarly seen as
|
||
<command>RUN ...</command> in a <filename>Dockerfile</filename>.
|
||
<note>
|
||
<para>
|
||
Using this parameter requires the <literal>kvm</literal> device to be
|
||
available.
|
||
</para>
|
||
</note>
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-8'>
|
||
<para>
|
||
<varname>config</varname> is used to specify the configuration of the
|
||
containers that will be started off the built image in Docker. The
|
||
available options are listed in the
|
||
<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions">
|
||
Docker Image Specification v1.2.0 </link>.
|
||
</para>
|
||
</callout>
|
||
</calloutlist>
|
||
|
||
<para>
|
||
After the new layer has been created, its closure (to which
|
||
<varname>contents</varname>, <varname>config</varname> and
|
||
<varname>runAsRoot</varname> contribute) will be copied in the layer
|
||
itself. Only new dependencies that are not already in the existing layers
|
||
will be copied.
|
||
</para>
|
||
|
||
<para>
|
||
At the end of the process, only one new single layer will be produced and
|
||
added to the resulting image.
|
||
</para>
|
||
|
||
<para>
|
||
The resulting repository will only list the single image
|
||
<varname>image/tag</varname>. In the case of
|
||
<xref linkend='ex-dockerTools-buildImage'/> it would be
|
||
<varname>redis/latest</varname>.
|
||
</para>
|
||
|
||
<para>
|
||
It is possible to inspect the arguments with which an image was built using
|
||
its <varname>buildArgs</varname> attribute.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
If you see errors similar to <literal>getProtocolByName: does not exist
|
||
(no such protocol name: tcp)</literal> you may need to add
|
||
<literal>pkgs.iana-etc</literal> to <varname>contents</varname>.
|
||
</para>
|
||
</note>
|
||
|
||
<note>
|
||
<para>
|
||
If you see errors similar to <literal>Error_Protocol ("certificate has
|
||
unknown CA",True,UnknownCa)</literal> you may need to add
|
||
<literal>pkgs.cacert</literal> to <varname>contents</varname>.
|
||
</para>
|
||
</note>
|
||
</section>
|
||
|
||
<section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
|
||
<title>pullImage</title>
|
||
|
||
<para>
|
||
This function is analogous to the <command>docker pull</command> command,
|
||
in that can be used to pull a Docker image from a Docker registry. By
|
||
default <link xlink:href="https://hub.docker.com/">Docker Hub</link> is
|
||
used to pull images.
|
||
</para>
|
||
|
||
<para>
|
||
Its parameters are described in the example below:
|
||
</para>
|
||
|
||
<example xml:id='ex-dockerTools-pullImage'>
|
||
<title>Docker pull</title>
|
||
<programlisting>
|
||
pullImage {
|
||
imageName = "nixos/nix"; <co xml:id='ex-dockerTools-pullImage-1' />
|
||
imageDigest = "sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b"; <co xml:id='ex-dockerTools-pullImage-2' />
|
||
finalImageTag = "1.11"; <co xml:id='ex-dockerTools-pullImage-3' />
|
||
sha256 = "0mqjy3zq2v6rrhizgb9nvhczl87lcfphq9601wcprdika2jz7qh8"; <co xml:id='ex-dockerTools-pullImage-4' />
|
||
os = "linux"; <co xml:id='ex-dockerTools-pullImage-5' />
|
||
arch = "x86_64"; <co xml:id='ex-dockerTools-pullImage-6' />
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<calloutlist>
|
||
<callout arearefs='ex-dockerTools-pullImage-1'>
|
||
<para>
|
||
<varname>imageName</varname> specifies the name of the image to be
|
||
downloaded, which can also include the registry namespace (e.g.
|
||
<literal>nixos</literal>). This argument is required.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-2'>
|
||
<para>
|
||
<varname>imageDigest</varname> specifies the digest of the image to be
|
||
downloaded. Skopeo can be used to get the digest of an image, with its
|
||
<varname>inspect</varname> subcommand. Since a given
|
||
<varname>imageName</varname> may transparently refer to a manifest list
|
||
of images which support multiple architectures and/or operating systems,
|
||
supply the `--override-os` and `--override-arch` arguments to specify
|
||
exactly which image you want. By default it will match the OS and
|
||
architecture of the host the command is run on.
|
||
<programlisting>
|
||
$ nix-shell --packages skopeo jq --command "skopeo --override-os linux --override-arch x86_64 inspect docker://docker.io/nixos/nix:1.11 | jq -r '.Digest'"
|
||
sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b
|
||
</programlisting>
|
||
This argument is required.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-3'>
|
||
<para>
|
||
<varname>finalImageTag</varname>, if specified, this is the tag of the
|
||
image to be created. Note it is never used to fetch the image since we
|
||
prefer to rely on the immutable digest ID. By default it's
|
||
<literal>latest</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-4'>
|
||
<para>
|
||
<varname>sha256</varname> is the checksum of the whole fetched image.
|
||
This argument is required.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-5'>
|
||
<para>
|
||
<varname>os</varname>, if specified, is the operating system of the
|
||
fetched image. By default it's <literal>linux</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-6'>
|
||
<para>
|
||
<varname>arch</varname>, if specified, is the cpu architecture of the
|
||
fetched image. By default it's <literal>x86_64</literal>.
|
||
</para>
|
||
</callout>
|
||
</calloutlist>
|
||
</section>
|
||
|
||
<section xml:id="ssec-pkgs-dockerTools-exportImage">
|
||
<title>exportImage</title>
|
||
|
||
<para>
|
||
This function is analogous to the <command>docker export</command> command,
|
||
in that can used to flatten a Docker image that contains multiple layers.
|
||
It is in fact the result of the merge of all the layers of the image. As
|
||
such, the result is suitable for being imported in Docker with
|
||
<command>docker import</command>.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
Using this function requires the <literal>kvm</literal> device to be
|
||
available.
|
||
</para>
|
||
</note>
|
||
|
||
<para>
|
||
The parameters of <varname>exportImage</varname> are the following:
|
||
</para>
|
||
|
||
<example xml:id='ex-dockerTools-exportImage'>
|
||
<title>Docker export</title>
|
||
<programlisting>
|
||
exportImage {
|
||
fromImage = someLayeredImage;
|
||
fromImageName = null;
|
||
fromImageTag = null;
|
||
|
||
name = someLayeredImage.name;
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<para>
|
||
The parameters relative to the base image have the same synopsis as
|
||
described in <xref linkend='ssec-pkgs-dockerTools-buildImage'/>, except
|
||
that <varname>fromImage</varname> is the only required argument in this
|
||
case.
|
||
</para>
|
||
|
||
<para>
|
||
The <varname>name</varname> argument is the name of the derivation output,
|
||
which defaults to <varname>fromImage.name</varname>.
|
||
</para>
|
||
</section>
|
||
|
||
<section xml:id="ssec-pkgs-dockerTools-shadowSetup">
|
||
<title>shadowSetup</title>
|
||
|
||
<para>
|
||
This constant string is a helper for setting up the base files for managing
|
||
users and groups, only if such files don't exist already. It is suitable
|
||
for being used in a <varname>runAsRoot</varname>
|
||
<xref linkend='ex-dockerTools-buildImage-runAsRoot'/> script for cases like
|
||
in the example below:
|
||
</para>
|
||
|
||
<example xml:id='ex-dockerTools-shadowSetup'>
|
||
<title>Shadow base files</title>
|
||
<programlisting>
|
||
buildImage {
|
||
name = "shadow-basic";
|
||
|
||
runAsRoot = ''
|
||
#!${stdenv.shell}
|
||
${shadowSetup}
|
||
groupadd -r redis
|
||
useradd -r -g redis redis
|
||
mkdir /data
|
||
chown redis:redis /data
|
||
'';
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<para>
|
||
Creating base files like <literal>/etc/passwd</literal> or
|
||
<literal>/etc/login.defs</literal> are necessary for shadow-utils to
|
||
manipulate users and groups.
|
||
</para>
|
||
</section>
|
||
</section>
|
||
</chapter>
|