1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
|
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xml:id="chap-meta">
<title>Meta-attributes</title>
<para>
Nix packages can declare <emphasis>meta-attributes</emphasis> that contain information about a package such as a description, its homepage, its license, and so on. For instance, the GNU Hello package has a <varname>meta</varname> declaration like this:
<programlisting>
meta = with stdenv.lib; {
description = "A program that produces a familiar, friendly greeting";
longDescription = ''
GNU Hello is a program that prints "Hello, world!" when you run it.
It is fully customizable.
'';
homepage = "https://www.gnu.org/software/hello/manual/";
license = licenses.gpl3Plus;
maintainers = [ maintainers.eelco ];
platforms = platforms.all;
};
</programlisting>
</para>
<para>
Meta-attributes are not passed to the builder of the package. Thus, a change to a meta-attribute doesn’t trigger a recompilation of the package. The value of a meta-attribute must be a string.
</para>
<para>
The meta-attributes of a package can be queried from the command-line using <command>nix-env</command>:
<screen>
<prompt>$ </prompt>nix-env -qa hello --json
{
"hello": {
"meta": {
"description": "A program that produces a familiar, friendly greeting",
"homepage": "https://www.gnu.org/software/hello/manual/",
"license": {
"fullName": "GNU General Public License version 3 or later",
"shortName": "GPLv3+",
"url": "http://www.fsf.org/licensing/licenses/gpl.html"
},
"longDescription": "GNU Hello is a program that prints \"Hello, world!\" when you run it.\nIt is fully customizable.\n",
"maintainers": [
"Ludovic Court\u00e8s <ludo@gnu.org>"
],
"platforms": [
"i686-linux",
"x86_64-linux",
"armv5tel-linux",
"armv7l-linux",
"mips32-linux",
"x86_64-darwin",
"i686-cygwin",
"i686-freebsd",
"x86_64-freebsd",
"i686-openbsd",
"x86_64-openbsd"
],
"position": "/home/user/dev/nixpkgs/pkgs/applications/misc/hello/default.nix:14"
},
"name": "hello-2.9",
"system": "x86_64-linux"
}
}
</screen>
<command>nix-env</command> knows about the <varname>description</varname> field specifically:
<screen>
<prompt>$ </prompt>nix-env -qa hello --description
hello-2.3 A program that produces a familiar, friendly greeting
</screen>
</para>
<section xml:id="sec-standard-meta-attributes">
<title>Standard meta-attributes</title>
<para>
It is expected that each meta-attribute is one of the following:
</para>
<variablelist>
<varlistentry>
<term>
<varname>description</varname>
</term>
<listitem>
<para>
A short (one-line) description of the package. This is shown by <command>nix-env -q --description</command> and also on the Nixpkgs release pages.
</para>
<para>
Don’t include a period at the end. Don’t include newline characters. Capitalise the first character. For brevity, don’t repeat the name of package — just describe what it does.
</para>
<para>
Wrong: <literal>"libpng is a library that allows you to decode PNG images."</literal>
</para>
<para>
Right: <literal>"A library for decoding PNG images"</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>longDescription</varname>
</term>
<listitem>
<para>
An arbitrarily long description of the package.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>branch</varname>
</term>
<listitem>
<para>
Release branch. Used to specify that a package is not going to receive updates that are not in this branch; for example, Linux kernel 3.0 is supposed to be updated to 3.0.X, not 3.1.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>homepage</varname>
</term>
<listitem>
<para>
The package’s homepage. Example: <literal>https://www.gnu.org/software/hello/manual/</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>downloadPage</varname>
</term>
<listitem>
<para>
The page where a link to the current version can be found. Example: <literal>https://ftp.gnu.org/gnu/hello/</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>changelog</varname>
</term>
<listitem>
<para>
A link or a list of links to the location of Changelog for a package. A link may use expansion to refer to the correct changelog version. Example: <literal>"https://git.savannah.gnu.org/cgit/hello.git/plain/NEWS?h=v${version}"</literal>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>license</varname>
</term>
<listitem>
<para>
The license, or licenses, for the package. One from the attribute set defined in <link
xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/licenses.nix"> <filename>nixpkgs/lib/licenses.nix</filename></link>. At this moment using both a list of licenses and a single license is valid. If the license field is in the form of a list representation, then it means that parts of the package are licensed differently. Each license should preferably be referenced by their attribute. The non-list attribute value can also be a space delimited string representation of the contained attribute shortNames or spdxIds. The following are all valid examples:
<itemizedlist>
<listitem>
<para>
Single license referenced by attribute (preferred) <literal>stdenv.lib.licenses.gpl3Only</literal>.
</para>
</listitem>
<listitem>
<para>
Single license referenced by its attribute shortName (frowned upon) <literal>"gpl3Only"</literal>.
</para>
</listitem>
<listitem>
<para>
Single license referenced by its attribute spdxId (frowned upon) <literal>"GPL-3.0-only"</literal>.
</para>
</listitem>
<listitem>
<para>
Multiple licenses referenced by attribute (preferred) <literal>with stdenv.lib.licenses; [ asl20 free ofl ]</literal>.
</para>
</listitem>
<listitem>
<para>
Multiple licenses referenced as a space delimited string of attribute shortNames (frowned upon) <literal>"asl20 free ofl"</literal>.
</para>
</listitem>
</itemizedlist>
For details, see <xref linkend='sec-meta-license'/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>maintainers</varname>
</term>
<listitem>
<para>
A list of the maintainers of this Nix expression. Maintainers are defined in <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/maintainers/maintainer-list.nix"><filename>nixpkgs/maintainers/maintainer-list.nix</filename></link>. There is no restriction to becoming a maintainer, just add yourself to that list in a separate commit titled 'maintainers: add alice', and reference maintainers with <literal>maintainers = with lib.maintainers; [ alice bob ]</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>priority</varname>
</term>
<listitem>
<para>
The <emphasis>priority</emphasis> of the package, used by <command>nix-env</command> to resolve file name conflicts between packages. See the Nix manual page for <command>nix-env</command> for details. Example: <literal>"10"</literal> (a low-priority package).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>platforms</varname>
</term>
<listitem>
<para>
The list of Nix platform types on which the package is supported. Hydra builds packages according to the platform specified. If no platform is specified, the package does not have prebuilt binaries. An example is:
<programlisting>
meta.platforms = stdenv.lib.platforms.linux;
</programlisting>
Attribute Set <varname>stdenv.lib.platforms</varname> defines <link xlink:href="https://github.com/NixOS/nixpkgs/blob/master/lib/systems/doubles.nix"> various common lists</link> of platforms types.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>tests</varname>
</term>
<listitem>
<warning>
<para>
This attribute is special in that it is not actually under the <literal>meta</literal> attribute set but rather under the <literal>passthru</literal> attribute set. This is due to how <literal>meta</literal> attributes work, and the fact that they are supposed to contain only metadata, not derivations.
</para>
</warning>
<para>
An attribute set with as values tests. A test is a derivation, which builds successfully when the test passes, and fails to build otherwise. A derivation that is a test needs to have <literal>meta.timeout</literal> defined.
</para>
<para>
The NixOS tests are available as <literal>nixosTests</literal> in parameters of derivations. For instance, the OpenSMTPD derivation includes lines similar to:
<programlisting>
{ /* ... */, nixosTests }:
{
# ...
passthru.tests = {
basic-functionality-and-dovecot-integration = nixosTests.opensmtpd;
};
}
</programlisting>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>timeout</varname>
</term>
<listitem>
<para>
A timeout (in seconds) for building the derivation. If the derivation takes longer than this time to build, it can fail due to breaking the timeout. However, all computers do not have the same computing power, hence some builders may decide to apply a multiplicative factor to this value. When filling this value in, try to keep it approximately consistent with other values already present in <literal>nixpkgs</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
<varname>hydraPlatforms</varname>
</term>
<listitem>
<para>
The list of Nix platform
|