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Manual: Expand the Development chapter

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nixos/doc/manual/configuration.xml
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@ -1012,7 +1012,7 @@ manpage or the Nix manual.</para>
<!--===============================================================-->
<section><title>User management</title>
<section xml:id="sec-user-management"><title>User management</title>
<para>NixOS supports both declarative and imperative styles of user
management. In the declarative style, users are specified in

806
nixos/doc/manual/development.xml
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@ -76,190 +76,132 @@ in <filename>nixos/</filename> as packages.</para>
<section>
<title>Extending NixOS</title>
<title>Writing NixOS modules</title>
<para>NixOS is based on a modular system for declarative configuration.
This system combines multiple <emphasis>modules</emphasis> to produce one
configuration. One of the module which compose your computer
configuration is <filename>/etc/nixos/configuration.nix</filename>. Other
modules are available under NixOS <filename>modules</filename>
directory</para>
<para>NixOS has a modular system for declarative configuration. This
system combines multiple <emphasis>modules</emphasis> to produce the
full system configuration. One of the modules that constitute the
configuration is <filename>/etc/nixos/configuration.nix</filename>.
Most of the others live in the <link
xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/modules"><filename>nixos/modules</filename></link>
subdirectory of the Nixpkgs tree.</para>
<para>A module is a file which handles one specific part of the
configuration. This part of the configuration could correspond to
hardware, a service, network settings, or preferences. A module
configuration does not have to handle everything from scratch, it can base
its configuration on other configurations provided by other modules. Thus
a module can <emphasis>define</emphasis> options to setup its
configuration, and it can also <emphasis>declare</emphasis> options to be
fed by other modules.</para>
<para>Each NixOS module is a file that handles one logical aspect of
the configuration, such as a specific kind of hardware, a service, or
network settings. A module configuration does not have to handle
everything from scratch; it can use the functionality provided by
other modules for its implementation. Thus a module can
<emphasis>declare</emphasis> options that can be used by other
modules, and conversely can <emphasis>define</emphasis> options
provided by other modules in its own implementation. For example, the
module <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/security/pam.nix"><filename>pam.nix</filename></link>
declares the option <option>security.pam.services</option> that allows
other modules (e.g. <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/networking/ssh/sshd.nix"><filename>sshd.nix</filename></link>)
to define PAM services; and it defines the option
<option>environment.etc</option> (declared by <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/etc/etc.nix"><filename>etc.nix</filename></link>)
to cause files to be created in
<filename>/etc/pam.d</filename>.</para>
<!-- module syntax -->
<para xml:id="para-module-syn">In <xref
linkend="sec-configuration-syntax"/>, we saw the following structure
of NixOS modules:
<para xml:id="para-module-syn">A module is a file which contains a Nix
expression. This expression should be either an expression which gets
evaluated into an attribute set or a function which returns an attribute
set.</para>
<programlisting>
{ config, pkgs, ... }:
<para>When the expression is a function, it should expect only one argument
which is an attribute set containing an attribute
named <varname>config</varname> and another attribute
named <varname>pkgs</varname>. The <varname>config</varname> attribute
contains the result of the merge of all modules. This attribute is
evaluated lazily, such as any Nix expression. For more details on how
options are merged, see the details in <xref linkend="para-opt-decl"/>.
The <varname>pkgs</varname> attribute
contains <emphasis>nixpkgs</emphasis> attribute set of packages. This
attribute is necessary for declaring options.</para>
{ <replaceable>option definitions</replaceable>
}
</programlisting>
<example xml:id='module-syntax'><title>Usual module content</title>
This is actually an <emphasis>abbreviated</emphasis> form of module
that only defines options, but does not declare any. The structure of
full NixOS modules is shown in <xref linkend='ex-module-syntax' />.</para>
<example xml:id='ex-module-syntax'><title>Structure of NixOS modules</title>
<programlisting>
{ config, pkgs, ... }: <co xml:id='module-syntax-1' />
{
imports =
[ <co xml:id='module-syntax-2' />
[ <replaceable>paths of other modules</replaceable> <co xml:id='module-syntax-2' />
];
options = {
<co xml:id='module-syntax-3' />
<replaceable>option declarations</replaceable> <co xml:id='module-syntax-3' />
};
config = {
<co xml:id='module-syntax-4' />
<replaceable>option definitions</replaceable> <co xml:id='module-syntax-4' />
};
}</programlisting>
</example>
<para><xref linkend='module-syntax' /> Illustrates
a <emphasis>module</emphasis> skeleton.
<para>The meaning of each part is as follows.
<calloutlist>
<callout arearefs='module-syntax-1'>
<para>This line makes the current Nix expression a function. This
line can be omitted if there is no reference to <varname>pkgs</varname>
and <varname>config</varname> inside the module.</para>
<para>This line makes the current Nix expression a function. The
variable <varname>pkgs</varname> contains Nixpkgs, while
<varname>config</varname> contains the full system configuration.
This line can be omitted if there is no reference to
<varname>pkgs</varname> and <varname>config</varname> inside the
module.</para>
</callout>
<callout arearefs='module-syntax-2'>
<para>This list is used to enumerate path to other modules which are
declaring options used by the current module. In NixOS, default modules
are listed in the file <filename>modules/module-list.nix</filename>.
The default modules don't need to be added in the import list.</para>
<para>This list enumerates the paths to other NixOS modules that
should be included in the evaluation of the system configuration.
A default set of modules is defined in the file
<filename>modules/module-list.nix</filename>. These don't need to
be added in the import list.</para>
</callout>
<callout arearefs='module-syntax-3'>
<para>This attribute set contains an attribute set of <emphasis>option
declaration</emphasis>.</para>
<para>The attribute <varname>options</varname> is a nested set of
<emphasis>option declarations</emphasis> (described below).</para>
</callout>
<callout arearefs='module-syntax-4'>
<para>This attribute set contains an attribute set of <emphasis>option
definitions</emphasis>. If the module does not have any imported
modules or any option declarations, then this attribute set can be used
in place of its parent attribute set. This is a common case for simple
modules such
as <filename>/etc/nixos/configuration.nix</filename>.</para>
<para>The attribute <varname>config</varname> is a nested set of
<emphasis>option definitions</emphasis> (also described
below).</para>
</callout>
</calloutlist>
</para>
<!-- option definitions -->
<para><xref linkend='locate-example' /> shows a module that handles
the regular update of the “locate” database, an index of all files in
the file system. This module declares two options that can be defined
by other modules (typically the user’s
<filename>configuration.nix</filename>):
<option>services.locate.enable</option> (whether the database should
be updated) and <option>services.locate.period</option> (when the
update should be done). It implements its functionality by defining
two options declared by other modules:
<option>systemd.services</option> (the set of all systemd services)
and <option>services.cron.systemCronJobs</option> (the list of
commands to be executed periodically by <command>cron</command>).</para>
<para xml:id="para-opt-def">A module defines a configuration which would be
interpreted by other modules. To define a configuration, a module needs
to provide option definitions. An option definition is a simple
attribute assignment.</para>
<para>Option definitions are made in a declarative manner. Without
properties, options will always be defined with the same value. To
introduce more flexibility in the system, option definitions are guarded
by <emphasis>properties</emphasis>.</para>
<para>Properties are means to introduce conditional values inside option
definitions. This conditional values can be distinguished in two
categories. The condition which are local to the current configuration
and conditions which are dependent on others configurations. Local
properties are <varname>mkIf</varname>
and <varname>mkAssert</varname>. Global properties
are <varname>mkOverride</varname>, <varname>mkDefault</varname>
and <varname>mkOrder</varname>.</para>
<para><varname>mkIf</varname> is used to remove the option definitions which
are below it if the condition is evaluated to
false. <varname>mkAssert</varname> expects the condition to be evaluated
to true otherwise it raises an error message.</para>
<para><varname>mkOverride</varname> is used to mask previous definitions if
the current value has a lower mask number. The mask value is 100 (default)
for any option definition which does not use this property.
Thus, <varname>mkDefault</varname> is just a short-cut with a higher mask
(1000) than the default mask value. This means that a module can set an
option definition as a preference, and still let another module defining
it with a different value without using any property.</para>
<para><varname>mkOrder</varname> is used to sort definitions based on the
rank number. The rank number will sort all options definitions before
giving the sorted list of option definition to the merge function defined
in the option declaration. A lower rank will move the definition to the
beginning and a higher rank will move the option toward the end. The
default rank is 100.</para>
<!-- option declarations -->
<para xml:id="para-opt-decl">A module may declare options which are used by
other module to change the configuration provided by the current module.
Changes to the option definitions are made with properties which are using
values extracted from the result of the merge of all modules
(the <varname>config</varname> argument).</para>
<para>The <varname>config</varname> argument reproduce the same hierarchy of
all options declared in all modules. For each option, the result of the
option is available, it is either the default value or the merge of all
definitions of the option.</para>
<para>Options are declared with the
function <varname>pkgs.lib.mkOption</varname>. This function expects an
attribute set which at least provides a description. A default value, an
example, a type, a merge function and a post-process function can be
added.</para>
<para>Types are used to provide a merge strategy for options and to ensure
the type of each option definitions. They are defined
in <varname>pkgs.lib.types</varname>.</para>
<para>The merge function expects a list of option definitions and merge
them to obtain one result of the same type.</para>
<para>The post-process function (named <varname>apply</varname>) takes the
result of the merge or of the default value, and produce an output which
could have a different type than the type expected by the option.</para>
<!-- end -->
<example xml:id='locate-example'><title>Locate Module Example</title>
<example xml:id='locate-example'><title>NixOS module for the “locate” service</title>
<programlisting>
{ config, pkgs, ... }:
with pkgs.lib;
let
cfg = config.services.locate;
locatedb = "/var/cache/locatedb";
logfile = "/var/log/updatedb";
cmd =''root updatedb --localuser=nobody --output=${locatedb} > ${logfile}'';
in
let locatedb = "/var/cache/locatedb"; in
{
imports = [ /path/to/nixpkgs/nixos/modules/services/scheduling/cron.nix ];
options = {
services.locate = {
enable = mkOption {
type = types.bool;
default = false;
example = true;
type = with types; bool;
description = ''
If enabled, NixOS will periodically update the database of
files used by the <command>locate</command> command.
@ -267,35 +209,370 @@ in
};
period = mkOption {
default = "15 02 * * *";
type = types.str;
default = "15 02 * * *";
description = ''
This option defines (in the format used by cron) when the
locate database is updated.
The default is to update at 02:15 (at night) every day.
locate database is updated. The default is to update at
02:15 at night every day.
'';
};
};
};
config = mkIf cfg.enable {
services.cron = {
enable = true;
systemCronJobs = "${cfg.period} root ${cmd}";
};
config = {
systemd.services.update-locatedb =
{ description = "Update Locate Database";
path = [ pkgs.su ];
script =
''
mkdir -m 0755 -p $(dirname ${locatedb})
exec updatedb --localuser=nobody --output=${locatedb} --prunepaths='/tmp /var/tmp /media /run'
'';
};
services.cron.systemCronJobs = optional config.services.locate.enable
"${config.services.locate.period} root ${config.systemd.package}/bin/systemctl start update-locatedb.service";
};
}</programlisting>
</example>
<para><xref linkend='locate-example' /> illustrates a module which handles
the regular update of the database which index all files on the file
system. This modules has option definitions to rely on the cron service
to run the command at predefined dates. In addition, this modules
provides option declarations to enable the indexing and to use different
period of time to run the indexing. Properties are used to prevent
ambiguous definitions of option (enable locate service and disable cron
services) and to ensure that no options would be defined if the locate
service is not enabled.</para>
<section><title>Option declarations</title>
<para>An option declaration specifies the name, type and description
of a NixOS configuration option. It is illegal to define an option
that hasn’t been declared in any module. A option declaration
generally looks like this:
<programlisting>
options = {
<replaceable>name</replaceable> = mkOption {
type = <replaceable>type specification</replaceable>;
default = <replaceable>default value</replaceable>;
example = <replaceable>example value</replaceable>;
description = "<replaceable>Description for use in the NixOS manual.</replaceable>";
};
};
</programlisting>
</para>
<para>The function <varname>mkOption</varname> accepts the following arguments.
<variablelist>
<varlistentry>
<term><varname>type</varname></term>
<listitem>
<para>The type of the option (see below). It may be omitted,
but that’s not advisable since it may lead to errors that are
hard to diagnose.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>default</varname></term>
<listitem>
<para>The default value used if no value is defined by any
module. A default is not required; in that case, if the option
value is ever used, an error will be thrown.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>example</varname></term>
<listitem>
<para>An example value that will be shown in the NixOS manual.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>description</varname></term>
<listitem>
<para>A textual description of the option, in DocBook format,
that will be included in the NixOS manual.</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>Here is a non-exhaustive list of option types:
<variablelist>
<varlistentry>
<term><varname>types.bool</varname></term>
<listitem>
<para>A Boolean.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.int</varname></term>
<listitem>
<para>An integer.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.str</varname></term>
<listitem>
<para>A string.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.lines</varname></term>
<listitem>
<para>A string. If there are multiple definitions, they are
concatenated, with newline characters in between.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.path</varname></term>
<listitem>
<para>A path, defined as anything that, when coerced to a
string, starts with a slash. This includes derivations.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.listOf</varname> <replaceable>t</replaceable></term>
<listitem>
<para>A list of elements of type <replaceable>t</replaceable>
(e.g., <literal>types.listOf types.str</literal> is a list of
strings). Multiple definitions are concatenated together.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.attrsOf</varname> <replaceable>t</replaceable></term>
<listitem>
<para>A set of elements of type <replaceable>t</replaceable>
(e.g., <literal>types.attrsOf types.int</literal> is a set of
name/value pairs, the values being integers).</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>types.nullOr</varname> <replaceable>t</replaceable></term>
<listitem>
<para>Either the value <literal>null</literal> or something of
type <replaceable>t</replaceable>.</para>
</listitem>
</varlistentry>
</variablelist>
You can also create new types using the function
<varname>mkOptionType</varname>. See
<filename>lib/types.nix</filename> in Nixpkgs for details.</para>
</section>
<section><title>Option definitions</title>
<para>Option definitions are generally straight-forward bindings of values to option names, like
<programlisting>
config = {
services.httpd.enable = true;
};
</programlisting>
However, sometimes you need to wrap an option definition or set of
option definitions in a <emphasis>property</emphasis> to achieve
certain effects:</para>
<simplesect><title>Delaying conditionals</title>
<para>If a set of option definitions is conditional on the value of
another option, you may need to use <varname>mkIf</varname>.
Consider, for instance:
<programlisting>
config = if config.services.httpd.enable then {
environment.systemPackages = [ <replaceable>...</replaceable> ];
<replaceable>...</replaceable>
} else {};
</programlisting>
This definition will cause Nix to fail with an “infinite recursion”
error. Why? Because the value of
<option>config.services.httpd.enable</option> depends on the value
being constructed here. After all, you could also write the clearly
circular and contradictory:
<programlisting>
config = if config.services.httpd.enable then {
services.httpd.enable = false;
} else {
services.httpd.enable = true;
};
</programlisting>
The solution is to write:
<programlisting>
config = mkIf config.services.httpd.enable {
environment.systemPackages = [ <replaceable>...</replaceable> ];
<replaceable>...</replaceable>
};
</programlisting>
The special function <varname>mkIf</varname> causes the evaluation of
the conditional to be “pushed down” into the individual definitions,
as if you had written:
<programlisting>
config = {
environment.systemPackages = if config.services.httpd.enable then [ <replaceable>...</replaceable> ] else [];
<replaceable>...</replaceable>
};
</programlisting>
</para>
</simplesect>
<simplesect><title>Setting priorities</title>
<para>A module can override the definitions of an option in other
modules by setting a <emphasis>priority</emphasis>. All option
definitions that do not have the lowest priority value are discarded.
By default, option definitions have priority 1000. You can specify an
explicit priority by using <varname>mkOverride</varname>, e.g.
<programlisting>
services.openssh.enable = mkOverride 10 false;
</programlisting>
This definition causes all other definitions with priorities above 10
to be discarded. The function <varname>mkForce</varname> is
equal to <varname>mkOverride 50</varname>.</para>
</simplesect>
<simplesect><title>Merging configurations</title>
<para>In conjunction with <literal>mkIf</literal>, it is sometimes
useful for a module to return multiple sets of option definitions, to
be merged together as if they were declared in separate modules. This
can be done using <varname>mkMerge</varname>:
<programlisting>
config = mkMerge
[ # Unconditional stuff.
{ environment.systemPackages = [ <replaceable>...</replaceable> ];
}
# Conditional stuff.
(mkIf config.services.bla.enable {
environment.systemPackages = [ <replaceable>...</replaceable> ];
})
];
</programlisting>
</para>
</simplesect>
</section>
<section><title>Important options</title>
<para>NixOS has many options, but some are of particular importance to
module writers.</para>
<variablelist>
<varlistentry>
<term><option>etc.environment</option></term>
<listitem>
<para>This set defines files in <filename>/etc</filename>. A
typical use is:
<programlisting>
environment.etc."os-release".text =
''
NAME=NixOS
<replaceable>...</replaceable>
'';
</programlisting>
which causes a file named <filename>/etc/os-release</filename>
to be created with the given contents.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>system.activationScripts</option></term>
<listitem>
<para>A set of shell script fragments that must be executed
whenever the configuration is activated (i.e., at boot time, or
after running <command>nixos-rebuild switch</command>). For instance,
<programlisting>
system.activationScripts.media =
''
mkdir -m 0755 -p /media
'';
</programlisting>
causes the directory <filename>/media</filename> to be created.
Activation scripts must be idempotent. They should not start
background processes such as daemons; use
<option>systemd.services</option> for that.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>systemd.services</option></term>
<listitem>
<para>This is the set of systemd services. Example:
<programlisting>
systemd.services.dhcpcd =
{ description = "DHCP Client";
wantedBy = [ "multi-user.target" ];
after = [ "systemd-udev-settle.service" ];
path = [ dhcpcd pkgs.nettools pkgs.openresolv ];
serviceConfig =
{ Type = "forking";
PIDFile = "/run/dhcpcd.pid";
ExecStart = "${dhcpcd}/sbin/dhcpcd --config ${dhcpcdConf}";
Restart = "always";
};
};
</programlisting>
which creates the systemd unit
<literal>dhcpcd.service</literal>. The option
<option>wantedBy</option> determined which other units pull this
one in; <literal>multi-user.target</literal> is the default
target of the system, so <literal>dhcpcd.service</literal> will
always be started. The option
<option>serviceConfig.ExecStart</option> provides the main
command for the service; it’s also possible to provide pre-start
actions, stop scripts, and so on.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>users.extraUsers</option></term>
<term><option>users.extraGroups</option></term>
<listitem>
<para>If your service requires special UIDs or GIDs, you can
define them with these options. See <xref
linkend="sec-user-management"/> for details.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>
@ -306,48 +583,77 @@ in
<title>Building specific parts of NixOS</title>
<para>
<para>With the command <command>nix-build</command>, you can build
specific parts of your NixOS configuration. This is done as follows:
<screen>
$ nix-build /path/to/nixpkgs/nixos -A <replaceable>attr</replaceable></screen>
$ cd <replaceable>/path/to/nixpkgs/nixos</replaceable>
$ nix-build -A config.<replaceable>option</replaceable></screen>
where <replaceable>attr</replaceable> is an attribute in
<filename>/path/to/nixpkgs/nixos/default.nix</filename>. Attributes of interest include:
where <replaceable>option</replaceable> is a NixOS option with type
“derivation” (i.e. something that can be built). Attributes of
interest include:
<variablelist>
<varlistentry>
<term><varname>config</varname></term>
<listitem><para>The computer configuration generated from
the <envar>NIXOS_CONFIG</envar> environment variable (default
is <filename>/etc/nixos/configuration.nix</filename>) with the NixOS
default set of modules.</para></listitem>
<term><varname>system.build.toplevel</varname></term>
<listitem>
<para>The top-level option that builds the entire NixOS system.
Everything else in your configuration is indirectly pulled in by
this option. This is what <command>nixos-rebuild</command>
builds and what <filename>/run/current-system</filename> points
to afterwards.</para>
<para>A shortcut to build this is:
<screen>
$ nix-build -A system</screen>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>system</varname></term>
<listitem><para>The derivation which build your computer system. It is
built by the command <command>nixos-rebuild
build</command></para></listitem>
<term><varname>system.build.manual.manual</varname></term>
<listitem><para>The NixOS manual.</para></listitem>
</varlistentry>
<varlistentry>
<term><varname>vm</varname></term>
<listitem><para>The derivation which build your computer system inside a
virtual machine. It is built by the command <command>nixos-rebuild
build-vm</command></para></listitem>
<term><varname>system.build.etc</varname></term>
<listitem><para>A tree of symlinks that form the static parts of
<filename>/etc</filename>.</para></listitem>
</varlistentry>
</variablelist>
<varlistentry>
<term><varname>system.build.initialRamdisk</varname></term>
<term><varname>system.build.kernel</varname></term>
<listitem>
<para>The initial ramdisk and kernel of the system. This allows
a quick way to test whether the kernel and the initial ramdisk
boot correctly, by using QEMU’s <option>-kernel</option> and
<option>-initrd</option> options:
<screen>
$ nix-build -A config.system.build.initialRamdisk -o initrd
$ nix-build -A config.system.build.kernel -o kernel
$ qemu-system-x86_64 -kernel ./kernel/bzImage -initrd ./initrd/initrd -hda /dev/null
</screen>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><varname>system.build.nixos-rebuild</varname></term>
<term><varname>system.build.nixos-install</varname></term>
<term><varname>system.build.nixos-generate-config</varname></term>
<listitem>
<para>These build the corresponding NixOS commands.</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Most parts of NixOS can be built through the <varname>config</varname>
attribute set. This attribute set allows you to have a view of the merged
option definitions and all its derivations. Important derivations are store
inside the option <option>system.build</option> and can be listed with the
command <command>nix-instantiate --xml --eval-only /path/to/nixpkgs/nixos -A
config.system.build</command>
</para>
</section>
@ -370,8 +676,7 @@ you have to set <envar>NIXOS_CONFIG</envar> before
running <command>nix-build</command> to build the ISO.
<screen>
$ export NIXOS_CONFIG=/path/to/nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix
$ nix-build /path/to/nixpkgs/nixos -A config.system.build.isoImage</screen>
$ nix-build -A config.system.build.isoImage -I nixos-config=modules/installer/cd-dvd/installation-cd-minimal.nix</screen>
</para>
@ -386,23 +691,6 @@ $ mount -o loop -t iso9660 ./result/iso/cd.iso /mnt/iso</screen>
</section>
<!--===============================================================-->
<section>
<title>Testing/building the NixOS Manual</title>
<para>A quick way to see if your documentation improvements
or option descriptions look good:
<screen>
$ nix-build -A config.system.build.manual</screen>
</para>
</section>
<!--===============================================================-->
<section>
@ -415,8 +703,7 @@ tedious, so here is a quick way to see if the installer works
properly:
<screen>
$ export NIXOS_CONFIG=/path/to/nixpkgs/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix
$ nix-build /path/to/nixpkgs/nixos -A config.system.build.nixos-install
$ nix-build -A config.system.build.nixos-install
$ dd if=/dev/zero of=diskimage seek=2G count=0 bs=1
$ yes | mke2fs -j diskimage
$ mount -o loop diskimage /mnt
@ -430,74 +717,47 @@ $ ./result/bin/nixos-install</screen>
<!--===============================================================-->
<section>
<section><title>Whole-system testing using virtual machines</title>
<title>Testing the <literal>initrd</literal></title>
<para>A quick way to test whether the kernel and the initial ramdisk
boot correctly is to use QEMU’s <option>-kernel</option> and
<option>-initrd</option> options:
<screen>
$ nix-build /path/to/nixpkgs/nixos -A config.system.build.initialRamdisk -o initrd
$ nix-build /path/to/nixpkgs/nixos -A config.system.build.kernel -o kernel
$ qemu-system-x86_64 -kernel ./kernel/bzImage -initrd ./initrd/initrd -hda /dev/null
</screen>
</para>
</section>
<section>
<title>Whole-system testing using virtual machines</title>
<para>
Complete NixOS GNU/Linux systems can be tested in virtual machines
(VMs). This makes it possible to test a system upgrade or
<para>Complete NixOS GNU/Linux systems can be tested in virtual
machines (VMs). This makes it possible to test a system upgrade or
configuration change before rebooting into it, using the
<command>nixos-rebuild build-vm</command> or
<command>nixos-rebuild build-vm-with-bootloader</command> command.
</para>
<command>nixos-rebuild build-vm</command> or <command>nixos-rebuild
build-vm-with-bootloader</command> command.</para>
<para>
<!-- The following is adapted from
http://wiki.nixos.org/wiki/NixOS_VM_tests, by Eelco Dolstra. -->
The <filename>tests/</filename> directory in the NixOS source tree
contains several <emphasis>whole-system unit tests</emphasis>.
<para>The <filename>tests/</filename> directory in the NixOS source
tree contains several <emphasis>whole-system unit tests</emphasis>.
These tests can be run<footnote><para>NixOS tests can be run both from
NixOS and from a non-NixOS GNU/Linux distribution, provided the
Nix package manager is installed.</para></footnote> from the NixOS
source tree as follows:
NixOS and from a non-NixOS GNU/Linux distribution, provided the Nix
package manager is installed.</para></footnote> from the NixOS source
tree as follows:
<screen>
$ nix-build tests/ -A nfs.test
</screen>
This performs an automated test of the NFS client and server
functionality in the Linux kernel, including file locking
semantics (e.g., whether locks are maintained across server
crashes). It will first build or download all the dependencies of
the test (e.g., all packages needed to run a NixOS VM). The test
is defined in <link
functionality in the Linux kernel, including file locking semantics
(e.g., whether locks are maintained across server crashes). It will
first build or download all the dependencies of the test (e.g., all
packages needed to run a NixOS VM). The test is defined in <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
<filename>tests/nfs.nix</filename></link>. If the test succeeds,
<command>nix-build</command> will place a symlink
<filename>./result</filename> in the current directory pointing at
the location in the Nix store of the test results (e.g.,
screenshots, test reports, and so on). In particular, a
pretty-printed log of the test is written to
<filename>log.html</filename>, which can be viewed using a web
browser like this:
<filename>./result</filename> in the current directory pointing at the
location in the Nix store of the test results (e.g., screenshots, test
reports, and so on). In particular, a pretty-printed log of the test
is written to <filename>log.html</filename>, which can be viewed using
a web browser like this:
<screen>
$ firefox result/log.html
</screen>
</para>
<para>
It is also possible to run the test environment interactively,
<para>It is also possible to run the test environment interactively,
allowing you to experiment with the VMs. For example:
<screen>
@ -505,15 +765,12 @@ $ nix-build tests/ -A nfs.driver
$ ./result/bin/nixos-run-vms
</screen>
The script <command>nixos-run-vms</command> starts the three
virtual machines defined in the NFS test using QEMU/KVM. The root
file system of the VMs is created on the fly and kept across VM
restarts in
<filename>./</filename><varname>hostname</varname><filename>.qcow2</filename>.
</para>
The script <command>nixos-run-vms</command> starts the three virtual
machines defined in the NFS test using QEMU/KVM. The root file system
of the VMs is created on the fly and kept across VM restarts in
<filename>./</filename><varname>hostname</varname><filename>.qcow2</filename>.</para>
<para>
Finally, the test itself can be run interactively. This is
<para>Finally, the test itself can be run interactively. This is
particularly useful when developing or debugging a test:
<screen>
@ -523,8 +780,7 @@ starting VDE switch for network 1
&gt;
</screen>
Perl statements can now be typed in to start or manipulate the
VMs:
Perl statements can now be typed in to start or manipulate the VMs:
<screen>
&gt; startAll;
@ -537,36 +793,30 @@ starting VDE switch for network 1
&gt; $client2-&gt;succeed("flock -n -s /data/lock true");
</screen>
The function <command>testScript</command> executes the entire
test script and drops you back into the test driver command line
upon its completion. This allows you to inspect the state of the
VMs after the test (e.g. to debug the test script).
</para>
The function <command>testScript</command> executes the entire test
script and drops you back into the test driver command line upon its
completion. This allows you to inspect the state of the VMs after the
test (e.g. to debug the test script).</para>
<para>
This and other tests are continuously run on <link
<para>This and other tests are continuously run on <link
xlink:href="http://hydra.nixos.org/jobset/nixos/trunk">the Hydra
instance at <literal>nixos.org</literal></link>, which allows
developers to be notified of any regressions introduced by a NixOS
or Nixpkgs change.
</para>
developers to be notified of any regressions introduced by a NixOS or
Nixpkgs change.</para>
<para>
The actual Nix programming interface to VM testing is in NixOS,
<para>The actual Nix programming interface to VM testing is in NixOS,
under <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/lib/testing.nix">
<filename>lib/testing.nix</filename></link>. This file defines a
function which takes an attribute set containing a
<literal>nixpkgs</literal> attribute (the path to a Nixpkgs
checkout), and a <literal>system</literal> attribute (the system
type). It returns an attribute set containing several utility
functions, among which the main entry point is
<literal>makeTest</literal>.
<literal>nixpkgs</literal> attribute (the path to a Nixpkgs checkout),
and a <literal>system</literal> attribute (the system type). It
returns an attribute set containing several utility functions, among
which the main entry point is <literal>makeTest</literal>.
</para>
<para>
The <literal>makeTest</literal> function takes a function similar to
that found in <link
<para>The <literal>makeTest</literal> function takes a function
similar to that found in <link
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
<filename>tests/nfs.nix</filename></link> (discussed above). It
returns an attribute set containing (among others):
@ -575,9 +825,9 @@ starting VDE switch for network 1
<varlistentry>
<term><varname>test</varname></term>
<listitem><para>A derivation containing the test log as an HTML file,
as seen above, suitable for presentation in the Hydra continuous
build system.</para></listitem>
<listitem><para>A derivation containing the test log as an HTML
file, as seen above, suitable for presentation in the Hydra
continuous build system.</para></listitem>
</varlistentry>
<varlistentry>
@ -594,8 +844,10 @@ starting VDE switch for network 1
</varlistentry>
</variablelist>
</para>
</section>
</chapter>

2
nixos/modules/installer/tools/tools.nix
View File

@ -103,7 +103,7 @@ in
];
system.build = {
inherit nixos-install nixos-generate-config nixos-option;
inherit nixos-install nixos-generate-config nixos-option nixos-rebuild;
};
};
}

5
nixos/modules/misc/version.nix
View File

@ -58,8 +58,7 @@ with pkgs.lib;
# Generate /etc/os-release. See
# http://0pointer.de/public/systemd-man/os-release.html for the
# format.
environment.etc = singleton
{ source = pkgs.writeText "os-release"
environment.etc."os-release".text =
''
NAME=NixOS
ID=nixos
@ -68,8 +67,6 @@ with pkgs.lib;
PRETTY_NAME="NixOS ${config.system.nixosVersion} (${config.system.nixosCodeName})"
HOME_URL="http://nixos.org/"
'';
target = "os-release";
};
};