636 lines
21 KiB
XML
636 lines
21 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-pkgs-overridePackages">
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<title>pkgs.overridePackages</title>
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<para>
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This function inside the nixpkgs expression (<varname>pkgs</varname>)
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can be used to override the set of packages itself.
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</para>
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<para>
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Warning: this function is expensive and must not be used from within
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the nixpkgs repository.
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</para>
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<para>
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Example usage:
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<programlisting>let
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pkgs = import <nixpkgs> {};
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newpkgs = pkgs.overridePackages (self: super: {
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foo = super.foo.override { ... };
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};
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in ...</programlisting>
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</para>
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<para>
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The resulting <varname>newpkgs</varname> will have the new <varname>foo</varname>
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expression, and all other expressions depending on <varname>foo</varname> will also
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use the new <varname>foo</varname> expression.
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</para>
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<para>
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The behavior of this function is similar to <link
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linkend="sec-modify-via-packageOverrides">config.packageOverrides</link>.
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</para>
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<para>
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The <varname>self</varname> parameter refers to the final package set with the
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applied overrides. Using this parameter may lead to infinite recursion if not
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used consciously.
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</para>
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<para>
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The <varname>super</varname> parameter refers to the old package set.
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It's equivalent to <varname>pkgs</varname> in the above example.
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</para>
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</section>
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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>pkgs.overridePackages (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-overrideDerivation">
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<title><pkg>.overrideDerivation</title>
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<warning>
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<para>Do not use this function in Nixpkgs. Because it breaks
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package abstraction and doesn’t provide error checking for
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function arguments, it is only intended for ad-hoc customisation
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(such as in <filename>~/.nixpkgs/config.nix</filename>).
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</para>
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<para>
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Additionally, <varname>overrideDerivation</varname> forces an evaluation
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of the Derivation which can be quite a performance penalty if there are many
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overrides used.
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</para>
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</warning>
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<para>
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The function <varname>overrideDerivation</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 create a new derivation by overriding the attributes of
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the original derivation according to the given 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 name, src and patches of the derivation
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will be overridden, while all other attributes will be retained from the
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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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</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 xml:id="sec-fhs-environments">
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<title>buildFHSChrootEnv/buildFHSUserEnv</title>
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<para>
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<function>buildFHSChrootEnv</function> and
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<function>buildFHSUserEnv</function> provide a way to build and run
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FHS-compatible lightweight sandboxes. They get their own isolated root with
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binded <filename>/nix/store</filename>, so their 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.
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</para>
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<para>
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<function>buildFHSChrootEnv</function> allows to create persistent
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environments, which can be constructed, deconstructed and entered by
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multiple users at once. A downside is that it requires
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<literal>root</literal> access for both those who create and destroy and
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those who enter it. It can be useful to create environments for daemons that
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one can enter and observe.
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</para>
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<para>
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<function>buildFHSUserEnv</function> 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. It does not require root access, and can be useful to create
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sandboxes and wrap applications.
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</para>
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<para>
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Those functions both rely on <function>buildFHSEnv</function>, which creates
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an actual directory structure given a list of necessary packages and extra
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build commands.
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<function>buildFHSChrootEnv</function> and <function>buildFHSUserEnv</function>
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both accept those arguments which are passed to
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<function>buildFHSEnv</function>:
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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).</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).</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>extraBuildCommandsMulti</literal>, but
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executed only on multilib architectures.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>
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Additionally, <function>buildFHSUserEnv</function> accepts
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<literal>runScript</literal> parameter, which is a command that would be
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executed inside the sandbox and passed all the command line arguments. It
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default to <literal>bash</literal>.
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</para>
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<para>
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It also uses <literal>CHROOTENV_EXTRA_BINDS</literal> environment variable
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for binding extra directories in the sandbox to outside places. The format of
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the variable is <literal>/mnt=test-mnt:/data</literal>, where
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<literal>/mnt</literal> would be mounted as <literal>/test-mnt</literal>
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and <literal>/data</literal> would be mounted as <literal>/data</literal>.
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<literal>extraBindMounts</literal> array argument to
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<function>buildFHSUserEnv</function> function is prepended to this variable.
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Latter entries take priority if defined several times -- i.e. in case of
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<literal>/data=data1:/data=data2</literal> the actual bind path would be
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<literal>/data2</literal>.
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</para>
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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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<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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|
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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.
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The available options are listed in the
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<link xlink:href="https://github.com/docker/docker/blob/master/image/spec/v1.md#container-runconfig-field-descriptions">
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Docker Image Specification v1.0.0
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</link>.
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</para>
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</callout>
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</calloutlist>
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<para>
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After the new layer has been created, its closure
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(to which <varname>contents</varname>, <varname>config</varname> and
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<varname>runAsRoot</varname> contribute) will be copied in the layer itself.
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Only new dependencies that are not already in the existing layers will be copied.
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</para>
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<para>
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At the end of the process, only one new single layer will be produced and
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added to the resulting image.
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</para>
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|
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<para>
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The resulting repository will only list the single image
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<varname>image/tag</varname>. In the case of <xref linkend='ex-dockerTools-buildImage'/>
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it would be <varname>redis/latest</varname>.
|
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</para>
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|
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<para>
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It is possible to inspect the arguments with which an image was built
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using its <varname>buildArgs</varname> attribute.
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</para>
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||
</section>
|
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|
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<section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
|
||
<title>pullImage</title>
|
||
|
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<para>
|
||
This function is analogous to the <command>docker pull</command> command,
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in that can be used to fetch a Docker image from a Docker registry.
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Currently only registry <literal>v1</literal> is supported.
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By default <link xlink:href="https://hub.docker.com/">Docker Hub</link>
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||
is used to pull images.
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</para>
|
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|
||
<para>
|
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Its parameters are described in the example below:
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</para>
|
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|
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<example xml:id='ex-dockerTools-pullImage'><title>Docker pull</title>
|
||
<programlisting>
|
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pullImage {
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imageName = "debian"; <co xml:id='ex-dockerTools-pullImage-1' />
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imageTag = "jessie"; <co xml:id='ex-dockerTools-pullImage-2' />
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imageId = null; <co xml:id='ex-dockerTools-pullImage-3' />
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sha256 = "1bhw5hkz6chrnrih0ymjbmn69hyfriza2lr550xyvpdrnbzr4gk2"; <co xml:id='ex-dockerTools-pullImage-4' />
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|
||
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>
|