mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-12-22 21:53:32 +00:00
777 lines
26 KiB
XML
777 lines
26 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
|
||
xmlns:xlink="http://www.w3.org/1999/xlink"
|
||
xml:id="chap-functions">
|
||
<title>Functions reference</title>
|
||
<para>
|
||
The nixpkgs repository has several utility functions to manipulate Nix
|
||
expressions.
|
||
</para>
|
||
<section xml:id="sec-overrides">
|
||
<title>Overriding</title>
|
||
|
||
<para>
|
||
Sometimes one wants to override parts of <literal>nixpkgs</literal>, e.g.
|
||
derivation attributes, the results of derivations or even the whole package
|
||
set.
|
||
</para>
|
||
|
||
<section xml:id="sec-pkg-override">
|
||
<title><pkg>.override</title>
|
||
|
||
<para>
|
||
The function <varname>override</varname> is usually available for all the
|
||
derivations in the nixpkgs expression (<varname>pkgs</varname>).
|
||
</para>
|
||
|
||
<para>
|
||
It is used to override the arguments passed to a function.
|
||
</para>
|
||
|
||
<para>
|
||
Example usages:
|
||
<programlisting>pkgs.foo.override { arg1 = val1; arg2 = val2; ... }</programlisting>
|
||
<programlisting>import pkgs.path { overlays = [ (self: super: {
|
||
foo = super.foo.override { barSupport = true ; };
|
||
})]};</programlisting>
|
||
<programlisting>mypkg = pkgs.callPackage ./mypkg.nix {
|
||
mydep = pkgs.mydep.override { ... };
|
||
}</programlisting>
|
||
</para>
|
||
|
||
<para>
|
||
In the first example, <varname>pkgs.foo</varname> is the result of a
|
||
function call with some default arguments, usually a derivation. Using
|
||
<varname>pkgs.foo.override</varname> will call the same function with the
|
||
given new arguments.
|
||
</para>
|
||
</section>
|
||
|
||
<section xml:id="sec-pkg-overrideAttrs">
|
||
<title><pkg>.overrideAttrs</title>
|
||
|
||
<para>
|
||
The function <varname>overrideAttrs</varname> allows overriding the
|
||
attribute set passed to a <varname>stdenv.mkDerivation</varname> call,
|
||
producing a new derivation based on the original one. This function is
|
||
available on all derivations produced by the
|
||
<varname>stdenv.mkDerivation</varname> function, which is most packages in
|
||
the nixpkgs expression <varname>pkgs</varname>.
|
||
</para>
|
||
|
||
<para>
|
||
Example usage:
|
||
<programlisting>helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
|
||
separateDebugInfo = true;
|
||
});</programlisting>
|
||
</para>
|
||
|
||
<para>
|
||
In the above example, the <varname>separateDebugInfo</varname> attribute is
|
||
overridden to be true, thus building debug info for
|
||
<varname>helloWithDebug</varname>, while all other attributes will be
|
||
retained from the original <varname>hello</varname> package.
|
||
</para>
|
||
|
||
<para>
|
||
The argument <varname>oldAttrs</varname> is conventionally used to refer to
|
||
the attr set originally passed to <varname>stdenv.mkDerivation</varname>.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
Note that <varname>separateDebugInfo</varname> is processed only by the
|
||
<varname>stdenv.mkDerivation</varname> function, not the generated, raw
|
||
Nix derivation. Thus, using <varname>overrideDerivation</varname> will not
|
||
work in this case, as it overrides only the attributes of the final
|
||
derivation. It is for this reason that <varname>overrideAttrs</varname>
|
||
should be preferred in (almost) all cases to
|
||
<varname>overrideDerivation</varname>, i.e. to allow using
|
||
<varname>sdenv.mkDerivation</varname> to process input arguments, as well
|
||
as the fact that it is easier to use (you can use the same attribute names
|
||
you see in your Nix code, instead of the ones generated (e.g.
|
||
<varname>buildInputs</varname> vs <varname>nativeBuildInputs</varname>,
|
||
and involves less typing.
|
||
</para>
|
||
</note>
|
||
</section>
|
||
|
||
<section xml:id="sec-pkg-overrideDerivation">
|
||
<title><pkg>.overrideDerivation</title>
|
||
|
||
<warning>
|
||
<para>
|
||
You should prefer <varname>overrideAttrs</varname> in almost all cases,
|
||
see its documentation for the reasons why.
|
||
<varname>overrideDerivation</varname> is not deprecated and will continue
|
||
to work, but is less nice to use and does not have as many abilities as
|
||
<varname>overrideAttrs</varname>.
|
||
</para>
|
||
</warning>
|
||
|
||
<warning>
|
||
<para>
|
||
Do not use this function in Nixpkgs as it evaluates a Derivation before
|
||
modifying it, which breaks package abstraction and removes error-checking
|
||
of function arguments. In addition, this evaluation-per-function
|
||
application incurs a performance penalty, which can become a problem if
|
||
many overrides are used. It is only intended for ad-hoc customisation,
|
||
such as in <filename>~/.config/nixpkgs/config.nix</filename>.
|
||
</para>
|
||
</warning>
|
||
|
||
<para>
|
||
The function <varname>overrideDerivation</varname> creates a new derivation
|
||
based on an existing one by overriding the original's attributes with the
|
||
attribute set produced by the specified function. This function is
|
||
available on all derivations defined using the
|
||
<varname>makeOverridable</varname> function. Most standard
|
||
derivation-producing functions, such as
|
||
<varname>stdenv.mkDerivation</varname>, are defined using this function,
|
||
which means most packages in the nixpkgs expression,
|
||
<varname>pkgs</varname>, have this function.
|
||
</para>
|
||
|
||
<para>
|
||
Example usage:
|
||
<programlisting>mySed = pkgs.gnused.overrideDerivation (oldAttrs: {
|
||
name = "sed-4.2.2-pre";
|
||
src = fetchurl {
|
||
url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
|
||
sha256 = "11nq06d131y4wmf3drm0yk502d2xc6n5qy82cg88rb9nqd2lj41k";
|
||
};
|
||
patches = [];
|
||
});</programlisting>
|
||
</para>
|
||
|
||
<para>
|
||
In the above example, the <varname>name</varname>, <varname>src</varname>,
|
||
and <varname>patches</varname> of the derivation will be overridden, while
|
||
all other attributes will be retained from the original derivation.
|
||
</para>
|
||
|
||
<para>
|
||
The argument <varname>oldAttrs</varname> is used to refer to the attribute
|
||
set of the original derivation.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
A package's attributes are evaluated *before* being modified by the
|
||
<varname>overrideDerivation</varname> function. For example, the
|
||
<varname>name</varname> attribute reference in <varname>url =
|
||
"mirror://gnu/hello/${name}.tar.gz";</varname> is filled-in *before* the
|
||
<varname>overrideDerivation</varname> function modifies the attribute set.
|
||
This means that overriding the <varname>name</varname> attribute, in this
|
||
example, *will not* change the value of the <varname>url</varname>
|
||
attribute. Instead, we need to override both the <varname>name</varname>
|
||
*and* <varname>url</varname> attributes.
|
||
</para>
|
||
</note>
|
||
</section>
|
||
|
||
<section xml:id="sec-lib-makeOverridable">
|
||
<title>lib.makeOverridable</title>
|
||
|
||
<para>
|
||
The function <varname>lib.makeOverridable</varname> is used to make the
|
||
result of a function easily customizable. This utility only makes sense for
|
||
functions that accept an argument set and return an attribute set.
|
||
</para>
|
||
|
||
<para>
|
||
Example usage:
|
||
<programlisting>f = { a, b }: { result = a+b; }
|
||
c = lib.makeOverridable f { a = 1; b = 2; }</programlisting>
|
||
</para>
|
||
|
||
<para>
|
||
The variable <varname>c</varname> is the value of the <varname>f</varname>
|
||
function applied with some default arguments. Hence the value of
|
||
<varname>c.result</varname> is <literal>3</literal>, in this example.
|
||
</para>
|
||
|
||
<para>
|
||
The variable <varname>c</varname> however also has some additional
|
||
functions, like <link linkend="sec-pkg-override">c.override</link> which
|
||
can be used to override the default arguments. In this example the value of
|
||
<varname>(c.override { a = 4; }).result</varname> is 6.
|
||
</para>
|
||
</section>
|
||
</section>
|
||
<section xml:id="sec-generators">
|
||
<title>Generators</title>
|
||
|
||
<para>
|
||
Generators are functions that create file formats from nix data structures,
|
||
e. g. for configuration files. There are generators available for:
|
||
<literal>INI</literal>, <literal>JSON</literal> and <literal>YAML</literal>
|
||
</para>
|
||
|
||
<para>
|
||
All generators follow a similar call interface: <code>generatorName
|
||
configFunctions data</code>, where <literal>configFunctions</literal> is an
|
||
attrset of user-defined functions that format nested parts of the content.
|
||
They each have common defaults, so often they do not need to be set
|
||
manually. An example is <code>mkSectionName ? (name: libStr.escape [ "[" "]"
|
||
] name)</code> from the <literal>INI</literal> generator. It receives the
|
||
name of a section and sanitizes it. The default
|
||
<literal>mkSectionName</literal> escapes <literal>[</literal> and
|
||
<literal>]</literal> with a backslash.
|
||
</para>
|
||
|
||
<para>
|
||
Generators can be fine-tuned to produce exactly the file format required by
|
||
your application/service. One example is an INI-file format which uses
|
||
<literal>: </literal> as separator, the strings
|
||
<literal>"yes"</literal>/<literal>"no"</literal> as boolean values and
|
||
requires all string values to be quoted:
|
||
</para>
|
||
|
||
<programlisting>
|
||
with lib;
|
||
let
|
||
customToINI = generators.toINI {
|
||
# specifies how to format a key/value pair
|
||
mkKeyValue = generators.mkKeyValueDefault {
|
||
# specifies the generated string for a subset of nix values
|
||
mkValueString = v:
|
||
if v == true then ''"yes"''
|
||
else if v == false then ''"no"''
|
||
else if isString v then ''"${v}"''
|
||
# and delegats all other values to the default generator
|
||
else generators.mkValueStringDefault {} v;
|
||
} ":";
|
||
};
|
||
|
||
# the INI file can now be given as plain old nix values
|
||
in customToINI {
|
||
main = {
|
||
pushinfo = true;
|
||
autopush = false;
|
||
host = "localhost";
|
||
port = 42;
|
||
};
|
||
mergetool = {
|
||
merge = "diff3";
|
||
};
|
||
}
|
||
</programlisting>
|
||
|
||
<para>
|
||
This will produce the following INI file as nix string:
|
||
</para>
|
||
|
||
<programlisting>
|
||
[main]
|
||
autopush:"no"
|
||
host:"localhost"
|
||
port:42
|
||
pushinfo:"yes"
|
||
str\:ange:"very::strange"
|
||
|
||
[mergetool]
|
||
merge:"diff3"
|
||
</programlisting>
|
||
|
||
<note>
|
||
<para>
|
||
Nix store paths can be converted to strings by enclosing a derivation
|
||
attribute like so: <code>"${drv}"</code>.
|
||
</para>
|
||
</note>
|
||
|
||
<para>
|
||
Detailed documentation for each generator can be found in
|
||
<literal>lib/generators.nix</literal>.
|
||
</para>
|
||
</section>
|
||
<section xml:id="sec-debug">
|
||
<title>Debugging Nix Expressions</title>
|
||
|
||
<para>
|
||
Nix is a unityped, dynamic language, this means every value can potentially
|
||
appear anywhere. Since it is also non-strict, evaluation order and what
|
||
ultimately is evaluated might surprise you. Therefore it is important to be
|
||
able to debug nix expressions.
|
||
</para>
|
||
|
||
<para>
|
||
In the <literal>lib/debug.nix</literal> file you will find a number of
|
||
functions that help (pretty-)printing values while evaluation is runnnig.
|
||
You can even specify how deep these values should be printed recursively,
|
||
and transform them on the fly. Please consult the docstrings in
|
||
<literal>lib/debug.nix</literal> for usage information.
|
||
</para>
|
||
</section>
|
||
<section xml:id="sec-fhs-environments">
|
||
<title>buildFHSUserEnv</title>
|
||
|
||
<para>
|
||
<function>buildFHSUserEnv</function> provides a way to build and run
|
||
FHS-compatible lightweight sandboxes. It creates an isolated root with bound
|
||
<filename>/nix/store</filename>, so its footprint in terms of disk space
|
||
needed is quite small. This allows one to run software which is hard or
|
||
unfeasible to patch for NixOS -- 3rd-party source trees with FHS
|
||
assumptions, games distributed as tarballs, software with integrity checking
|
||
and/or external self-updated binaries. It uses Linux namespaces feature to
|
||
create temporary lightweight environments which are destroyed after all
|
||
child processes exit, without root user rights requirement. Accepted
|
||
arguments are:
|
||
</para>
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>name</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Environment name.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>targetPkgs</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Packages to be installed for the main host's architecture (i.e. x86_64 on
|
||
x86_64 installations). Along with libraries binaries are also installed.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>multiPkgs</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Packages to be installed for all architectures supported by a host (i.e.
|
||
i686 and x86_64 on x86_64 installations). Only libraries are installed by
|
||
default.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>extraBuildCommands</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Additional commands to be executed for finalizing the directory
|
||
structure.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>extraBuildCommandsMulti</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Like <literal>extraBuildCommands</literal>, but executed only on multilib
|
||
architectures.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>extraOutputsToInstall</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Additional derivation outputs to be linked for both target and
|
||
multi-architecture packages.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>extraInstallCommands</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
Additional commands to be executed for finalizing the derivation with
|
||
runner script.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
<varlistentry>
|
||
<term>
|
||
<literal>runScript</literal>
|
||
</term>
|
||
<listitem>
|
||
<para>
|
||
A command that would be executed inside the sandbox and passed all the
|
||
command line arguments. It defaults to <literal>bash</literal>.
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>
|
||
One can create a simple environment using a <literal>shell.nix</literal>
|
||
like that:
|
||
</para>
|
||
|
||
<programlisting><![CDATA[
|
||
{ pkgs ? import <nixpkgs> {} }:
|
||
|
||
(pkgs.buildFHSUserEnv {
|
||
name = "simple-x11-env";
|
||
targetPkgs = pkgs: (with pkgs;
|
||
[ udev
|
||
alsaLib
|
||
]) ++ (with pkgs.xorg;
|
||
[ libX11
|
||
libXcursor
|
||
libXrandr
|
||
]);
|
||
multiPkgs = pkgs: (with pkgs;
|
||
[ udev
|
||
alsaLib
|
||
]);
|
||
runScript = "bash";
|
||
}).env
|
||
]]></programlisting>
|
||
|
||
<para>
|
||
Running <literal>nix-shell</literal> would then drop you into a shell with
|
||
these libraries and binaries available. You can use this to run
|
||
closed-source applications which expect FHS structure without hassles:
|
||
simply change <literal>runScript</literal> to the application path, e.g.
|
||
<filename>./bin/start.sh</filename> -- relative paths are supported.
|
||
</para>
|
||
</section>
|
||
<section xml:id="sec-pkgs-dockerTools">
|
||
<title>pkgs.dockerTools</title>
|
||
|
||
<para>
|
||
<varname>pkgs.dockerTools</varname> is a set of functions for creating and
|
||
manipulating Docker images according to the
|
||
<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#docker-image-specification-v120">
|
||
Docker Image Specification v1.2.0 </link>. Docker itself is not used to
|
||
perform any of the operations done by these functions.
|
||
</para>
|
||
|
||
<warning>
|
||
<para>
|
||
The <varname>dockerTools</varname> API is unstable and may be subject to
|
||
backwards-incompatible changes in the future.
|
||
</para>
|
||
</warning>
|
||
|
||
<section xml:id="ssec-pkgs-dockerTools-buildImage">
|
||
<title>buildImage</title>
|
||
|
||
<para>
|
||
This function is analogous to the <command>docker build</command> command,
|
||
in that can used to build a Docker-compatible repository tarball containing
|
||
a single image with one or multiple layers. As such, the result is suitable
|
||
for being loaded in Docker with <command>docker load</command>.
|
||
</para>
|
||
|
||
<para>
|
||
The parameters of <varname>buildImage</varname> with relative example
|
||
values are described below:
|
||
</para>
|
||
|
||
<example xml:id='ex-dockerTools-buildImage'>
|
||
<title>Docker build</title>
|
||
<programlisting>
|
||
buildImage {
|
||
name = "redis"; <co xml:id='ex-dockerTools-buildImage-1' />
|
||
tag = "latest"; <co xml:id='ex-dockerTools-buildImage-2' />
|
||
|
||
fromImage = someBaseImage; <co xml:id='ex-dockerTools-buildImage-3' />
|
||
fromImageName = null; <co xml:id='ex-dockerTools-buildImage-4' />
|
||
fromImageTag = "latest"; <co xml:id='ex-dockerTools-buildImage-5' />
|
||
|
||
contents = pkgs.redis; <co xml:id='ex-dockerTools-buildImage-6' />
|
||
runAsRoot = '' <co xml:id='ex-dockerTools-buildImage-runAsRoot' />
|
||
#!${stdenv.shell}
|
||
mkdir -p /data
|
||
'';
|
||
|
||
config = { <co xml:id='ex-dockerTools-buildImage-8' />
|
||
Cmd = [ "/bin/redis-server" ];
|
||
WorkingDir = "/data";
|
||
Volumes = {
|
||
"/data" = {};
|
||
};
|
||
};
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<para>
|
||
The above example will build a Docker image <literal>redis/latest</literal>
|
||
from the given base image. Loading and running this image in Docker results
|
||
in <literal>redis-server</literal> being started automatically.
|
||
</para>
|
||
|
||
<calloutlist>
|
||
<callout arearefs='ex-dockerTools-buildImage-1'>
|
||
<para>
|
||
<varname>name</varname> specifies the name of the resulting image. This
|
||
is the only required argument for <varname>buildImage</varname>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-2'>
|
||
<para>
|
||
<varname>tag</varname> specifies the tag of the resulting image. By
|
||
default it's <literal>latest</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-3'>
|
||
<para>
|
||
<varname>fromImage</varname> is the repository tarball containing the
|
||
base image. It must be a valid Docker image, such as exported by
|
||
<command>docker save</command>. By default it's <literal>null</literal>,
|
||
which can be seen as equivalent to <literal>FROM scratch</literal> of a
|
||
<filename>Dockerfile</filename>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-4'>
|
||
<para>
|
||
<varname>fromImageName</varname> can be used to further specify the base
|
||
image within the repository, in case it contains multiple images. By
|
||
default it's <literal>null</literal>, in which case
|
||
<varname>buildImage</varname> will peek the first image available in the
|
||
repository.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-5'>
|
||
<para>
|
||
<varname>fromImageTag</varname> can be used to further specify the tag of
|
||
the base image within the repository, in case an image contains multiple
|
||
tags. By default it's <literal>null</literal>, in which case
|
||
<varname>buildImage</varname> will peek the first tag available for the
|
||
base image.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-6'>
|
||
<para>
|
||
<varname>contents</varname> is a derivation that will be copied in the
|
||
new layer of the resulting image. This can be similarly seen as
|
||
<command>ADD contents/ /</command> in a <filename>Dockerfile</filename>.
|
||
By default it's <literal>null</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-runAsRoot'>
|
||
<para>
|
||
<varname>runAsRoot</varname> is a bash script that will run as root in an
|
||
environment that overlays the existing layers of the base image with the
|
||
new resulting layer, including the previously copied
|
||
<varname>contents</varname> derivation. This can be similarly seen as
|
||
<command>RUN ...</command> in a <filename>Dockerfile</filename>.
|
||
<note>
|
||
<para>
|
||
Using this parameter requires the <literal>kvm</literal> device to be
|
||
available.
|
||
</para>
|
||
</note>
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-buildImage-8'>
|
||
<para>
|
||
<varname>config</varname> is used to specify the configuration of the
|
||
containers that will be started off the built image in Docker. The
|
||
available options are listed in the
|
||
<link xlink:href="https://github.com/moby/moby/blob/master/image/spec/v1.2.md#image-json-field-descriptions">
|
||
Docker Image Specification v1.2.0 </link>.
|
||
</para>
|
||
</callout>
|
||
</calloutlist>
|
||
|
||
<para>
|
||
After the new layer has been created, its closure (to which
|
||
<varname>contents</varname>, <varname>config</varname> and
|
||
<varname>runAsRoot</varname> contribute) will be copied in the layer
|
||
itself. Only new dependencies that are not already in the existing layers
|
||
will be copied.
|
||
</para>
|
||
|
||
<para>
|
||
At the end of the process, only one new single layer will be produced and
|
||
added to the resulting image.
|
||
</para>
|
||
|
||
<para>
|
||
The resulting repository will only list the single image
|
||
<varname>image/tag</varname>. In the case of
|
||
<xref linkend='ex-dockerTools-buildImage'/> it would be
|
||
<varname>redis/latest</varname>.
|
||
</para>
|
||
|
||
<para>
|
||
It is possible to inspect the arguments with which an image was built using
|
||
its <varname>buildArgs</varname> attribute.
|
||
</para>
|
||
|
||
<note>
|
||
<para>
|
||
If you see errors similar to <literal>getProtocolByName: does not exist
|
||
(no such protocol name: tcp)</literal> you may need to add
|
||
<literal>pkgs.iana-etc</literal> to <varname>contents</varname>.
|
||
</para>
|
||
</note>
|
||
|
||
<note>
|
||
<para>
|
||
If you see errors similar to <literal>Error_Protocol ("certificate has
|
||
unknown CA",True,UnknownCa)</literal> you may need to add
|
||
<literal>pkgs.cacert</literal> to <varname>contents</varname>.
|
||
</para>
|
||
</note>
|
||
</section>
|
||
|
||
<section xml:id="ssec-pkgs-dockerTools-fetchFromRegistry">
|
||
<title>pullImage</title>
|
||
|
||
<para>
|
||
This function is analogous to the <command>docker pull</command> command,
|
||
in that can be used to pull a Docker image from a Docker registry. By
|
||
default <link xlink:href="https://hub.docker.com/">Docker Hub</link> is
|
||
used to pull images.
|
||
</para>
|
||
|
||
<para>
|
||
Its parameters are described in the example below:
|
||
</para>
|
||
|
||
<example xml:id='ex-dockerTools-pullImage'>
|
||
<title>Docker pull</title>
|
||
<programlisting>
|
||
pullImage {
|
||
imageName = "nixos/nix"; <co xml:id='ex-dockerTools-pullImage-1' />
|
||
imageDigest = "sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b"; <co xml:id='ex-dockerTools-pullImage-2' />
|
||
finalImageTag = "1.11"; <co xml:id='ex-dockerTools-pullImage-3' />
|
||
sha256 = "0mqjy3zq2v6rrhizgb9nvhczl87lcfphq9601wcprdika2jz7qh8"; <co xml:id='ex-dockerTools-pullImage-4' />
|
||
}
|
||
</programlisting>
|
||
</example>
|
||
|
||
<calloutlist>
|
||
<callout arearefs='ex-dockerTools-pullImage-1'>
|
||
<para>
|
||
<varname>imageName</varname> specifies the name of the image to be
|
||
downloaded, which can also include the registry namespace (e.g.
|
||
<literal>nixos</literal>). This argument is required.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-2'>
|
||
<para>
|
||
<varname>imageDigest</varname> specifies the digest of the image to be
|
||
downloaded. Skopeo can be used to get the digest of an image
|
||
<programlisting>
|
||
$ skopeo inspect docker://docker.io/nixos/nix:1.11 | jq -r '.Digest'
|
||
sha256:20d9485b25ecfd89204e843a962c1bd70e9cc6858d65d7f5fadc340246e2116b
|
||
</programlisting>
|
||
This argument is required.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-3'>
|
||
<para>
|
||
<varname>finalImageTag</varname>, if specified, this is the tag of the
|
||
image to be created. Note it is never used to fetch the image since we
|
||
prefer to rely on the immutable digest ID. By default it's
|
||
<literal>latest</literal>.
|
||
</para>
|
||
</callout>
|
||
<callout arearefs='ex-dockerTools-pullImage-4'>
|
||
<para>
|
||
<varname>sha256</varname> is the checksum of the whole fetched image.
|
||
This argument is required.
|
||
</para>
|
||
</callout>
|
||
</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>
|