903129f770
* authorization token is optional * registry url is taken from X-Docker-Endpoints header * pull.sh correctly resumes partial layer downloads * detjson.py does not fail on missing keys
629 lines
20 KiB
XML
629 lines
20 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-pkgs-overridePackages">
|
||
<title>pkgs.overridePackages</title>
|
||
|
||
<para>
|
||
This function inside the nixpkgs expression (<varname>pkgs</varname>)
|
||
can be used to override the set of packages itself.
|
||
</para>
|
||
<para>
|
||
Warning: this function is expensive and must not be used from within
|
||
the nixpkgs repository.
|
||
</para>
|
||
<para>
|
||
Example usage:
|
||
|
||
<programlisting>let
|
||
pkgs = import <nixpkgs> {};
|
||
newpkgs = pkgs.overridePackages (self: super: {
|
||
foo = super.foo.override { ... };
|
||
};
|
||
in ...</programlisting>
|
||
</para>
|
||
|
||
<para>
|
||
The resulting <varname>newpkgs</varname> will have the new <varname>foo</varname>
|
||
expression, and all other expressions depending on <varname>foo</varname> will also
|
||
use the new <varname>foo</varname> expression.
|
||
</para>
|
||
|
||
<para>
|
||
The behavior of this function is similar to <link
|
||
linkend="sec-modify-via-packageOverrides">config.packageOverrides</link>.
|
||
</para>
|
||
|
||
<para>
|
||
The <varname>self</varname> parameter refers to the final package set with the
|
||
applied overrides. Using this parameter may lead to infinite recursion if not
|
||
used consciously.
|
||
</para>
|
||
|
||
<para>
|
||
The <varname>super</varname> parameter refers to the old package set.
|
||
It's equivalent to <varname>pkgs</varname> in the above example.
|
||
</para>
|
||
|
||
</section>
|
||
|
||
<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>pkgs.overridePackages (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-overrideDerivation">
|
||
<title><pkg>.overrideDerivation</title>
|
||
|
||
<warning>
|
||
<para>Do not use this function in Nixpkgs. Because it breaks
|
||
package abstraction and doesn’t provide error checking for
|
||
function arguments, it is only intended for ad-hoc customisation
|
||
(such as in <filename>~/.nixpkgs/config.nix</filename>).</para>
|
||
</warning>
|
||
|
||
<para>
|
||
The function <varname>overrideDerivation</varname> is usually available for all the
|
||
derivations in the nixpkgs expression (<varname>pkgs</varname>).
|
||
</para>
|
||
<para>
|
||
It is used to create a new derivation by overriding the attributes of
|
||
the original derivation according to the given 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 name, src and patches 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>
|
||
|
||
</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 xml:id="sec-fhs-environments">
|
||
<title>buildFHSChrootEnv/buildFHSUserEnv</title>
|
||
|
||
<para>
|
||
<function>buildFHSChrootEnv</function> and
|
||
<function>buildFHSUserEnv</function> provide a way to build and run
|
||
FHS-compatible lightweight sandboxes. They get their own isolated root with
|
||
binded <filename>/nix/store</filename>, so their 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.
|
||
</para>
|
||
|
||
<para>
|
||
<function>buildFHSChrootEnv</function> allows to create persistent
|
||
environments, which can be constructed, deconstructed and entered by
|
||
multiple users at once. A downside is that it requires
|
||
<literal>root</literal> access for both those who create and destroy and
|
||
those who enter it. It can be useful to create environments for daemons that
|
||
one can enter and observe.
|
||
</para>
|
||
|
||
<para>
|
||
<function>buildFHSUserEnv</function> uses Linux namespaces feature to create
|
||
temporary lightweight environments which are destroyed after all child
|
||
processes exit. It does not require root access, and can be useful to create
|
||
sandboxes and wrap applications.
|
||
</para>
|
||
|
||
<para>
|
||
Those functions both rely on <function>buildFHSEnv</function>, which creates
|
||
an actual directory structure given a list of necessary packages and extra
|
||
build commands.
|
||
<function>buildFHSChrootEnv</function> and <function>buildFHSUserEnv</function>
|
||
both accept those arguments which are passed to
|
||
<function>buildFHSEnv</function>:
|
||
</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).</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).</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>extraBuildCommandsMulti</literal>, but
|
||
executed only on multilib architectures.</para></listitem>
|
||
</varlistentry>
|
||
</variablelist>
|
||
|
||
<para>
|
||
Additionally, <function>buildFHSUserEnv</function> accepts
|
||
<literal>runScript</literal> parameter, which is a command that would be
|
||
executed inside the sandbox and passed all the command line arguments. It
|
||
default to <literal>bash</literal>.
|
||
</para>
|
||
<para>
|
||
It also uses <literal>CHROOTENV_EXTRA_BINDS</literal> environment variable
|
||
for binding extra directories in the sandbox to outside places. The format of
|
||
the variable is <literal>/mnt=test-mnt:/data</literal>, where
|
||
<literal>/mnt</literal> would be mounted as <literal>/test-mnt</literal>
|
||
and <literal>/data</literal> would be mounted as <literal>/data</literal>.
|
||
<literal>extraBindMounts</literal> array argument to
|
||
<function>buildFHSUserEnv</function> function is prepended to this variable.
|
||
Latter entries take priority if defined several times -- i.e. in case of
|
||
<literal>/data=data1:/data=data2</literal> the actual bind path would be
|
||
<literal>/data2</literal>.
|
||
</para>
|
||
<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/docker/docker/blob/master/image/spec/v1.md#docker-image-specification-v100">
|
||
Docker Image Specification v1.0.0
|
||
</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/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>
|