707 lines
24 KiB
XML
707 lines
24 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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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 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
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<literal>nixpkgs</literal>, e.g. derivation attributes, the results of
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derivations or even the whole package 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 function call
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with some default arguments, usually a derivation.
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Using <varname>pkgs.foo.override</varname> will call the same function with
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the 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.
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This function is available on all derivations produced by the
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<varname>stdenv.mkDerivation</varname> function, which is most packages
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in 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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overriden 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
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not 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
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names 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>You should prefer <varname>overrideAttrs</varname> in almost all
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cases, 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>Do not use this function in Nixpkgs as it evaluates a Derivation
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before modifying it, which breaks package abstraction and removes
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error-checking of function arguments. In addition, this
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evaluation-per-function application incurs a performance penalty,
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which can become a problem if many overrides are used.
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It is only intended for ad-hoc customisation, such as in
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<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
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the attribute set produced by the specified function.
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This function is available on all
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derivations defined using the <varname>makeOverridable</varname> function.
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Most standard derivation-producing functions, such as
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<varname>stdenv.mkDerivation</varname>, are defined using this
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function, 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 set of
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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
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the <varname>overrideDerivation</varname> function.
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For example, the <varname>name</varname> attribute reference
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in <varname>url = "mirror://gnu/hello/${name}.tar.gz";</varname>
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is filled-in *before* the <varname>overrideDerivation</varname> function
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modifies the attribute set. This means that overriding the
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<varname>name</varname> attribute, in this example, *will not* change the
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value of the <varname>url</varname> attribute. Instead, we need to override
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both the <varname>name</varname> *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 result
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of a function easily customizable. This utility only makes sense for functions
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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> function
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applied with some default arguments. Hence the value of <varname>c.result</varname>
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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 functions, like
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<link linkend="sec-pkg-override">c.override</link> which can be used to
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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
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data structures, e. g. for configuration files.
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There are generators available for: <literal>INI</literal>,
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<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 a
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set of user-defined functions that format variable 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 gets the name
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of a section and returns a sanitized name. 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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<note><para>Nix store paths can be converted to strings by enclosing a
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derivation attribute like so: <code>"${drv}"</code>.</para></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-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
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bound <filename>/nix/store</filename>, so its footprint in terms of disk
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space 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 assumptions,
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games distributed as tarballs, software with integrity checking and/or external
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self-updated binaries. It uses Linux namespaces feature to create
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temporary lightweight environments which are destroyed after all child
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processes exit, without root user rights requirement. Accepted arguments are:
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</para>
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<variablelist>
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<varlistentry>
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<term><literal>name</literal></term>
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<listitem><para>Environment name.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>targetPkgs</literal></term>
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<listitem><para>Packages to be installed for the main host's architecture
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(i.e. x86_64 on x86_64 installations). Along with libraries binaries are also
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installed.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>multiPkgs</literal></term>
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<listitem><para>Packages to be installed for all architectures supported by
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a host (i.e. i686 and x86_64 on x86_64 installations). Only libraries are
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installed by default.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>extraBuildCommands</literal></term>
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<listitem><para>Additional commands to be executed for finalizing the
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directory structure.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>extraBuildCommandsMulti</literal></term>
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<listitem><para>Like <literal>extraBuildCommands</literal>, but
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executed only on multilib architectures.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>extraOutputsToInstall</literal></term>
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<listitem><para>Additional derivation outputs to be linked for both
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target and multi-architecture packages.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>extraInstallCommands</literal></term>
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<listitem><para>Additional commands to be executed for finalizing the
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derivation with runner script.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><literal>runScript</literal></term>
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<listitem><para>A command that would be executed inside the sandbox and
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passed all the command line arguments. It defaults to
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<literal>bash</literal>.</para></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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<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,
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e.g. <filename>./bin/start.sh</filename> -- relative paths are supported.
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</para>
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</section>
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<section xml:id="sec-pkgs-dockerTools">
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<title>pkgs.dockerTools</title>
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<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/docker/docker/blob/master/image/spec/v1.md#docker-image-specification-v100">
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Docker Image Specification v1.0.0
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</link>. Docker itself is not used to perform any of the operations done by these
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functions.
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</para>
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<warning>
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<para>
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The <varname>dockerTools</varname> API is unstable and may be subject to
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backwards-incompatible changes in the future.
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</para>
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</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
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is suitable for being loaded in Docker with <command>docker load</command>.
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</para>
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<para>
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The parameters of <varname>buildImage</varname> with relative example values are
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described below:
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</para>
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<example xml:id='ex-dockerTools-buildImage'><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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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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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" = {};
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};
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};
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}
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</programlisting>
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</example>
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<para>The above example will build a Docker image <literal>redis/latest</literal>
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from the given base image. Loading and running this image in Docker results in
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<literal>redis-server</literal> being started automatically.
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</para>
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<calloutlist>
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<callout arearefs='ex-dockerTools-buildImage-1'>
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<para>
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<varname>name</varname> specifies the name of the resulting image.
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This is the only required argument for <varname>buildImage</varname>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-2'>
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<para>
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<varname>tag</varname> specifies the tag of the resulting image.
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By default it's <literal>latest</literal>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-3'>
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<para>
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<varname>fromImage</varname> is the repository tarball containing the base image.
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It must be a valid Docker image, such as exported by <command>docker save</command>.
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By default it's <literal>null</literal>, which can be seen as equivalent
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to <literal>FROM scratch</literal> of a <filename>Dockerfile</filename>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-4'>
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<para>
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<varname>fromImageName</varname> can be used to further specify
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the base image within the repository, in case it contains multiple images.
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By default it's <literal>null</literal>, in which case
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<varname>buildImage</varname> will peek the first image available
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in the repository.
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</para>
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</callout>
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|
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<callout arearefs='ex-dockerTools-buildImage-5'>
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<para>
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<varname>fromImageTag</varname> can be used to further specify the tag
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of the base image within the repository, in case an image contains multiple tags.
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By default it's <literal>null</literal>, in which case
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<varname>buildImage</varname> will peek the first tag available for the base image.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-6'>
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<para>
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<varname>contents</varname> is a derivation that will be copied in the new
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layer of the resulting image. This can be similarly seen as
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<command>ADD contents/ /</command> in a <filename>Dockerfile</filename>.
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By default it's <literal>null</literal>.
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-runAsRoot'>
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<para>
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<varname>runAsRoot</varname> is a bash script that will run as root
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in an environment that overlays the existing layers of the base image with
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the new resulting layer, including the previously copied
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<varname>contents</varname> derivation.
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This can be similarly seen as
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<command>RUN ...</command> in a <filename>Dockerfile</filename>.
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<note>
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<para>
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Using this parameter requires the <literal>kvm</literal>
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device to be available.
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</para>
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</note>
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</para>
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</callout>
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<callout arearefs='ex-dockerTools-buildImage-8'>
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<para>
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<varname>config</varname> is used to specify the configuration of the
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containers that will be started off the built image in Docker.
|
||
The available options are listed in the
|
||
<link xlink:href="https://github.com/docker/docker/blob/master/image/spec/v1.md#container-runconfig-field-descriptions">
|
||
Docker Image Specification v1.0.0
|
||
</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 fetch a Docker image from a Docker registry.
|
||
Currently only registry <literal>v1</literal> is supported.
|
||
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 = "debian"; <co xml:id='ex-dockerTools-pullImage-1' />
|
||
imageTag = "jessie"; <co xml:id='ex-dockerTools-pullImage-2' />
|
||
imageId = null; <co xml:id='ex-dockerTools-pullImage-3' />
|
||
sha256 = "1bhw5hkz6chrnrih0ymjbmn69hyfriza2lr550xyvpdrnbzr4gk2"; <co xml:id='ex-dockerTools-pullImage-4' />
|
||
|
||
indexUrl = "https://index.docker.io"; <co xml:id='ex-dockerTools-pullImage-5' />
|
||
registryVersion = "v1";
|
||
}
|
||
</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>library/debian</literal>).
|
||
This argument is required.
|
||
</para>
|
||
</callout>
|
||
|
||
<callout arearefs='ex-dockerTools-pullImage-2'>
|
||
<para>
|
||
<varname>imageTag</varname> specifies the tag of the image to be downloaded.
|
||
By default it's <literal>latest</literal>.
|
||
</para>
|
||
</callout>
|
||
|
||
<callout arearefs='ex-dockerTools-pullImage-3'>
|
||
<para>
|
||
<varname>imageId</varname>, if specified this exact image will be fetched, instead
|
||
of <varname>imageName/imageTag</varname>. However, the resulting repository
|
||
will still be named <varname>imageName/imageTag</varname>.
|
||
By default it's <literal>null</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>
|
||
|
||
<note>
|
||
<para>The checksum is computed on the unpacked directory, not on the final tarball.</para>
|
||
</note>
|
||
|
||
</callout>
|
||
|
||
<callout arearefs='ex-dockerTools-pullImage-5'>
|
||
<para>
|
||
In the above example the default values are shown for the variables
|
||
<varname>indexUrl</varname> and <varname>registryVersion</varname>.
|
||
Hence by default the Docker.io registry is used to pull the images.
|
||
</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>
|