mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-24 16:03:23 +00:00
f5dfe78a1e
This patch add a new argument to Nixpkgs default expression named "overlays".
By default, the value of the argument is either taken from the environment variable `NIXPKGS_OVERLAYS`,
or from the directory `~/.nixpkgs/overlays/`. If the environment variable does not name a valid directory
then this mechanism would fallback on the home directory. If the home directory does not exists it will
fallback on an empty list of overlays.
The overlays directory should contain the list of extra Nixpkgs stages which would be used to extend the
content of Nixpkgs, with additional set of packages. The overlays, i-e directory, files, symbolic links
are used in alphabetical order.
The simplest overlay which extends Nixpkgs with nothing looks like:
```nix
self: super: {
}
```
More refined overlays can use `super` as the basis for building new packages, and `self` as a way to query
the final result of the fix-point.
An example of overlay which extends Nixpkgs with a small set of packages can be found at:
https://github.com/nbp/nixpkgs-mozilla/blob/nixpkgs-overlay/moz-overlay.nix
To use this file, checkout the repository and add a symbolic link to
the `moz-overlay.nix` file in `~/.nixpkgs/overlays` directory.
691 lines
23 KiB
XML
691 lines
23 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>~/.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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|
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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>
|
||
|
||
<calloutlist>
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||
<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>
|
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<varname>tag</varname> specifies the tag of the resulting image.
|
||
By default it's <literal>latest</literal>.
|
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</para>
|
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</callout>
|
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|
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<callout arearefs='ex-dockerTools-buildImage-3'>
|
||
<para>
|
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<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>.
|
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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>.
|
||
</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/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>
|
||
|
||
</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>
|