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1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.54 2013/07/23 20:14:45 swift Exp $ -->
8
9 <sections>
10
11 <abstract>
12 USE flags are a very important aspect of Gentoo. In this chapter, you learn to
13 work with USE flags and understand how USE flags interact with your system.
14 </abstract>
15
16 <version>6</version>
17 <date>2013-12-17</date>
18
19 <section>
20 <title>What are USE flags?</title>
21 <subsection>
22 <title>The ideas behind USE flags</title>
23 <body>
24
25 <p>
26 When you are installing Gentoo (or any other distribution, or even operating
27 system for that matter) you make choices depending on the environment you are
28 working with. A setup for a server differs from a setup for a workstation.
29 A gaming workstation differs from a 3D rendering workstation.
30 </p>
31
32 <p>
33 This is not only true for choosing what packages you want to install, but also
34 what features a certain package should support. If you don't need OpenGL, why
35 would you bother installing OpenGL and build OpenGL support in most of your
36 packages? If you don't want to use KDE, why would you bother compiling packages
37 with KDE support if those packages work flawlessly without?
38 </p>
39
40 <p>
41 To help users in deciding what to install/activate and what not, we wanted the
42 user to specify his/her environment in an easy way. This forces the user into
43 deciding what they really want and eases the process for Portage, our package
44 management system, to make useful decisions.
45 </p>
46
47 </body>
48 </subsection>
49 <subsection>
50 <title>Definition of a USE flag</title>
51 <body>
52
53 <p>
54 Enter the USE flags. Such a flag is a keyword that embodies support and
55 dependency-information for a certain concept. If you define a certain USE flag,
56 Portage will know that you want support for the chosen keyword. Of course
57 this also alters the dependency information for a package.
58 </p>
59
60 <p>
61 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
62 have this keyword in your <c>USE</c> variable, all packages that have
63 <e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
64 packages that have an <e>optional</e> KDE dependency will be installed
65 <e>without</e> installing the KDE libraries (as dependency). If you have defined
66 the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
67 support, and the KDE libraries will be installed as dependency.
68 </p>
69
70 <p>
71 By correctly defining the keywords you will receive a system tailored
72 specifically to your needs.
73 </p>
74
75 </body>
76 </subsection>
77 <subsection>
78 <title>What USE flags exist?</title>
79 <body>
80
81 <p>
82 There are two types of USE flags: <e>global</e> and <e>local</e> USE flags.
83 </p>
84
85 <ul>
86 <li>
87 A <e>global</e> USE flag is used by several packages, system-wide. This is
88 what most people see as USE flags.
89 </li>
90 <li>
91 A <e>local</e> USE flag is used by a single package to make package-specific
92 decisions.
93 </li>
94 </ul>
95
96 <p>
97 A list of available global USE flags can be found <uri
98 link="/dyn/use-index.xml#doc_chap1">online</uri> or locally in
99 <path>/usr/portage/profiles/use.desc</path>.
100 </p>
101
102 <p>
103 A list of available local USE flags can be found <uri
104 link="/dyn/use-index.xml#doc_chap2">online</uri> or locally in
105 <path>/usr/portage/profiles/use.local.desc</path>.
106 </p>
107
108 </body>
109 </subsection>
110 </section>
111 <section>
112 <title>Using USE flags</title>
113 <subsection>
114 <title>Declare permanent USE flags</title>
115 <body>
116
117 <p>
118 In the hope you are convinced of the importance of USE flags we will now inform
119 you how to declare USE flags.
120 </p>
121
122 <p>
123 As previously mentioned, all USE flags are declared inside the <c>USE</c>
124 variable. To make it easy for users to search and pick USE flags, we already
125 provide a <e>default</e> USE setting. This setting is a collection of USE flags
126 we think are commonly used by the Gentoo users. This default setting is declared
127 in the <path>make.defaults</path> files part of your profile.
128 </p>
129
130 <p>
131 The profile your system listens to is pointed to by the
132 <path>/etc/portage/make.profile</path> symlink. Each profile works on top of
133 another, larger profile, the end result is therefore the sum of all profiles.
134 The top profile is the <path>base</path> profile
135 (<path>/usr/portage/profiles/base</path>).
136 </p>
137
138 <p>
139 Let us take a look at this default setting for the 13.0 profile:
140 </p>
141
142 <pre caption="Cumulative make.defaults USE variable for the 13.0 profile">
143 <comment>(This example is the sum of the settings in base, default/linux,
144 default/linux/x86 and default/linux/x86/13.0/)</comment>
145 USE="a52 aac acpi alsa branding cairo cdr dbus dts dvd dvdr emboss encode exif
146 fam firefox flac gif gpm gtk hal jpeg lcms ldap libnotify mad mikmod mng mp3
147 mp4 mpeg ogg opengl pango pdf png ppds qt3support qt4 sdl spell
148 startup-notification svg tiff truetype vorbis unicode usb X xcb x264 xml xv
149 xvid"
150 </pre>
151
152 <p>
153 As you can see, this variable already contains quite a lot of keywords. Do
154 <b>not</b> alter any <path>make.defaults</path> file to tailor
155 the <c>USE</c> variable to your needs: changes in this file will be undone when
156 you update Portage!
157 </p>
158
159 <p>
160 To change this default setting, you need to add or remove keywords to the
161 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
162 in <path>/etc/portage/make.conf</path>. In this variable you add the extra USE
163 flags you require, or remove the USE flags you don't want. This latter is done
164 by prefixing the keyword with the minus-sign ("-").
165 </p>
166
167 <p>
168 For instance, to remove support for KDE and QT but add support for ldap, the
169 following <c>USE</c> can be defined in <path>/etc/portage/make.conf</path>:
170 </p>
171
172 <pre caption="An example USE setting in /etc/portage/make.conf">
173 USE="-kde -qt4 ldap"
174 </pre>
175
176 </body>
177 </subsection>
178 <subsection>
179 <title>Declaring USE flags for individual packages</title>
180 <body>
181
182 <p>
183 Sometimes you want to declare a certain USE flag for one (or a couple) of
184 applications but not system-wide. To accomplish this, you will need to create
185 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
186 <path>/etc/portage/package.use</path>. This is usually a single file, but can
187 also be a directory; see <c>man portage</c> for more information. The following
188 examples assume <path>package.use</path> is a single file.
189 </p>
190
191 <p>
192 For instance, if you don't want <c>berkdb</c> support globally but you do want
193 it for <c>mysql</c>, you would add:
194 </p>
195
196 <pre caption="/etc/portage/package.use example">
197 dev-db/mysql berkdb
198 </pre>
199
200 <p>
201 You can of course also explicitly <e>disable</e> USE flags for a certain
202 application. For instance, if you don't want <c>java</c> support in PHP:
203 </p>
204
205 <pre caption="/etc/portage/package.use 2nd example">
206 dev-php/php -java
207 </pre>
208
209 </body>
210 </subsection>
211 <subsection>
212 <title>Declare temporary USE flags</title>
213 <body>
214
215 <p>
216 Sometimes you want to set a certain USE setting only once. Instead of editing
217 <path>/etc/portage/make.conf</path> twice (to do and undo the USE changes) you
218 can just declare the USE variable as environment variable. Remember that, when
219 you re-emerge or update this application (either explicitly or as part of a
220 system update) your changes will be lost!
221 </p>
222
223 <p>
224 As an example we will temporarily remove java from the USE setting
225 during the installation of seamonkey.
226 </p>
227
228 <pre caption="Using USE as environment variable">
229 # <i>USE="-java" emerge seamonkey</i>
230 </pre>
231
232 </body>
233 </subsection>
234 <subsection>
235 <title>Precedence</title>
236 <body>
237
238 <p>
239 Of course there is a certain precedence on what setting has priority over the
240 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
241 <c>java</c> is still used due to a setting that has a higher priority.
242 The precedence for the USE setting is, ordered
243 by priority (first has lowest priority):
244 </p>
245
246 <ol>
247 <li>
248 Default USE setting declared in the <path>make.defaults</path> files part of
249 your profile
250 </li>
251 <li>
252 User-defined USE setting in <path>/etc/portage/make.conf</path>
253 </li>
254 <li>
255 User-defined USE setting in <path>/etc/portage/package.use</path>
256 </li>
257 <li>
258 User-defined USE setting as environment variable
259 </li>
260 </ol>
261
262 <p>
263 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
264 --info</c>. This will list all relevant variables (including the <c>USE</c>
265 variable) with the content used by Portage.
266 </p>
267
268 <pre caption="Running emerge --info">
269 # <i>emerge --info</i>
270 </pre>
271
272 </body>
273 </subsection>
274 <subsection>
275 <title>Adapting your Entire System to New USE Flags</title>
276 <body>
277
278 <p>
279 If you have altered your USE flags and you wish to update your entire system to
280 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
281 </p>
282
283 <pre caption="Rebuilding your entire system">
284 # <i>emerge --update --deep --newuse @world</i>
285 </pre>
286
287 <p>
288 Next, run Portage's depclean to remove the conditional dependencies that
289 were emerged on your "old" system but that have been obsoleted by the new USE
290 flags.
291 </p>
292
293 <warn>
294 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
295 with care. Double-check the provided list of "obsoleted" packages to make sure
296 it doesn't remove packages you need. In the following example we add the
297 <c>-p</c> switch to have depclean only list the packages without removing them.
298 </warn>
299
300 <pre caption="Removing obsoleted packages">
301 # <i>emerge -p --depclean</i>
302 </pre>
303
304 <p>
305 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
306 applications that are dynamically linked against shared objects provided by
307 possibly removed packages. <c>revdep-rebuild</c> is part of the
308 <c>gentoolkit</c> package; don't forget to emerge it first.
309 </p>
310
311 <pre caption="Running revdep-rebuild">
312 # <i>revdep-rebuild</i>
313 </pre>
314
315 <p>
316 When all this is accomplished, your system is using the new USE flag settings.
317 </p>
318
319 </body>
320 </subsection>
321 </section>
322 <section>
323 <title>Package specific USE flags</title>
324 <subsection>
325 <title>Viewing available USE flags</title>
326 <body>
327
328 <p>
329 Let us take the example of <c>seamonkey</c>: what USE flags does it listen to? To
330 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
331 options:
332 </p>
333
334 <pre caption="Viewing the used USE flags">
335 # <i>emerge --pretend --verbose seamonkey</i>
336 These are the packages that I would merge, in order:
337
338 Calculating dependencies ...done!
339 [ebuild R ] www-client/seamonkey-1.0.7 USE="crypt gnome java -debug -ipv6
340 -ldap -mozcalendar -mozdevelop -moznocompose -moznoirc -moznomail -moznopango
341 -moznoroaming -postgres -xinerama -xprint" 0 kB
342 </pre>
343
344 <p>
345 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
346 dedicated to package information called <c>equery</c> which resides in the
347 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
348 </p>
349
350 <pre caption="Installing gentoolkit">
351 # <i>emerge gentoolkit</i>
352 </pre>
353
354 <p>
355 Now run <c>equery</c> with the <c>uses</c> argument to view the USE flags of a
356 certain package. For instance, for the <c>gnumeric</c> package:
357 </p>
358
359 <pre caption="Using equery to view used USE flags">
360 # <i>equery --nocolor uses =gnumeric-1.6.3 -a</i>
361 [ Searching for packages matching =gnumeric-1.6.3... ]
362 [ Colour Code : set unset ]
363 [ Legend : Left column (U) - USE flags from make.conf ]
364 [ : Right column (I) - USE flags packages was installed with ]
365 [ Found these USE variables for app-office/gnumeric-1.6.3 ]
366 U I
367 - - debug : Enable extra debug codepaths, like asserts and extra output.
368 If you want to get meaningful backtraces see
369 http://www.gentoo.org/proj/en/qa/backtraces.xml .
370 + + gnome : Adds GNOME support
371 + + python : Adds support/bindings for the Python language
372 - - static : !!do not set this during bootstrap!! Causes binaries to be
373 statically linked instead of dynamically
374 </pre>
375
376 </body>
377 </subsection>
378 </section>
379 </sections>

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