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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/1.0 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.21 2004/10/21 10:31:20 swift Exp $ -->
8
9 <sections>
10
11 <version>1.21</version>
12 <date>October 21, 2004</date>
13
14 <section>
15 <title>What are USE-flags?</title>
16 <subsection>
17 <title>The ideas behind USE-flags</title>
18 <body>
19
20 <p>
21 When you are installing Gentoo (or any other distribution, or even operating
22 system for that matter) you make choices depending on the environment you are
23 working with. A setup for a server differs from a setup for a workstation.
24 A gaming workstation differs from a 3D rendering workstation.
25 </p>
26
27 <p>
28 This is not only true for choosing what packages you want to install, but also
29 what features a certain package should support. If you don't need OpenGL, why
30 would you bother installing OpenGL and build OpenGL support in most of your
31 packages? If you don't want to use KDE, why would you bother compiling packages
32 with KDE-support if those packages work flawlessly without?
33 </p>
34
35 <p>
36 To help users in deciding what to install/activate and what not, we wanted the
37 user to specify his/her environment in an easy way. This forces the user into
38 deciding what they really want and eases the process for Portage, our package
39 managment system, to make useful decisions.
40 </p>
41
42 </body>
43 </subsection>
44 <subsection>
45 <title>Definition of a USE-flag</title>
46 <body>
47
48 <p>
49 Enter the USE-flags. Such a flag is a keyword that embodies support and
50 dependency-information for a certain concept. If you define a certain USE-flag,
51 Portage will know that you want support for the chosen keyword. Of course
52 this also alters the dependency information for a package.
53 </p>
54
55 <p>
56 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
57 have this keyword in your <c>USE</c> variable, all packages that have
58 <e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
59 packages that have an <e>optional</e> KDE dependency will be installed
60 <e>without</e> installing the KDE libraries (as dependency). If you have defined
61 the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
62 support, and the KDE libraries will be installed as dependency.
63 </p>
64
65 <p>
66 By correctly defining the keywords you will receive a system tailored
67 specifically to your needs.
68 </p>
69
70 </body>
71 </subsection>
72 <subsection>
73 <title>What USE-flags exist?</title>
74 <body>
75
76 <p>
77 There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
78 </p>
79
80 <ul>
81 <li>
82 A <e>global</e> USE-flag is used by several packages, system-wide. This is
83 what most people see as USE-flags.
84 </li>
85 <li>
86 A <e>local</e> USE-flag is used by a single package to make package-specific
87 decisions.
88 </li>
89 </ul>
90
91 <p>
92 A list of available global USE-flags can be found <uri
93 link="/dyn/use-index.xml">online</uri> or locally in
94 <path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
95 snippet:
96 </p>
97
98 <pre caption="A short snippet of available USE-flags">
99 gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
100 gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
101 gtkhtml - Adds support for gnome-extra/gtkhtml
102 guile - Adds support for dev-util/guile (interpreter for Scheme)
103 icc - Use the Intel C++ Compiler if the package supports it
104 icc-pgo - Enable PGO data generation or use when use icc.
105 imap - Adds support for IMAP
106 </pre>
107
108 <p>
109 A list of available local USE-flags can be found locally in
110 <path>/usr/portage/profiles/use.local.desc</path>.
111 </p>
112
113 </body>
114 </subsection>
115 </section>
116 <section>
117 <title>Using USE-flags</title>
118 <subsection>
119 <title>Declare permanent USE-flags</title>
120 <body>
121
122 <p>
123 In the hope you are convinced of the importance of USE-flags we will now inform
124 you how to declare USE-flags.
125 </p>
126
127 <p>
128 As previously mentioned, all USE-flags are declared inside the <c>USE</c>
129 variable. To make it easy for users to search and pick USE-flags, we already
130 provide a <e>default</e> USE setting. This setting is a collection of USE-flags
131 we think are commonly used by the Gentoo users. This default setting is declared
132 in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
133 this default setting:
134 </p>
135
136 <pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
137 USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
138 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
139 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
140 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
141 </pre>
142
143 <p>
144 As you can see, this variable already contains quite a lot of keywords. Do
145 <b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
146 the <c>USE</c> variable to your needs: changes in this file will be undone when
147 you update Portage!
148 </p>
149
150 <p>
151 To change this default setting, you need to add or remove keywords to the
152 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
153 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
154 require, or remove the USE-flags you don't want. This latter is done by
155 prefixing the keyword with the minus-sign ("-").
156 </p>
157
158 <p>
159 For instance, to remove support for KDE and QT but add support for ldap, the
160 following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
161 </p>
162
163 <pre caption="An example USE setting in /etc/make.conf">
164 USE="-kde -qt ldap"
165 </pre>
166
167 </body>
168 </subsection>
169 <subsection>
170 <title>Declaring USE flags for individual packages</title>
171 <body>
172
173 <p>
174 Sometimes you want to declare a certain USE flag for one (or a couple) of
175 applications but not system-wide. To accomplish this, you will need to create
176 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
177 <path>/etc/portage/package.use</path>.
178 </p>
179
180 <p>
181 For instance, if you don't want <c>berkdb</c> support globally but you do want
182 it for <c>mysql</c>, you would add:
183 </p>
184
185 <pre caption="/etc/portage/package.use example">
186 dev-db/mysql berkdb
187 </pre>
188
189 <p>
190 You can of course also explicitly <e>disable</e> USE flags for a certain
191 application. For instance, if you don't want <c>java</c> support in PHP:
192 </p>
193
194 <pre caption="/etc/portage/package.use 2nd example">
195 dev-php/php -java
196 </pre>
197
198 </body>
199 </subsection>
200 <subsection>
201 <title>Declare temporary USE-flags</title>
202 <body>
203
204 <p>
205 Sometimes you want to set a certain USE-setting only once. Instead of editing
206 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
207 declare the USE-variable as environment variable. Remember that, when you
208 re-emerge or update this application (either explicitly or as part of a system
209 update) your changes will be lost!
210 </p>
211
212 <p>
213 As an example we will temporarily remove java from the USE-setting
214 during the installation of mozilla.
215 </p>
216
217 <pre caption="Using USE as environment variable">
218 # <i>USE="-java" emerge mozilla</i>
219 </pre>
220
221 </body>
222 </subsection>
223 <subsection>
224 <title>Inheriting USE-flags</title>
225 <body>
226
227 <p>
228 Some packages don't only listen to USE-flags, but also provide USE-flags. When
229 you install such a package, the USE-flag they provide is added to your USE
230 setting. To view the list of packages that provide a USE-flag, check
231 <path>/etc/make.profile/use.defaults</path>:
232 </p>
233
234 <pre caption="A snippet from /etc/make.profile/use.defaults">
235 gnome gnome-base/gnome
236 gtk x11-libs/gtk+
237 qt x11-libs/qt
238 kde kde-base/kdebase
239 motif x11-libs/openmotif
240 </pre>
241
242 </body>
243 </subsection>
244 <subsection>
245 <title>Precedence</title>
246 <body>
247
248 <p>
249 Of course there is a certain precedence on what setting has priority over the
250 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
251 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
252 by priority (first has lowest priority):
253 </p>
254
255 <ol>
256 <li>
257 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
258 </li>
259 <li>
260 Inherited USE setting if a package from
261 <path>/etc/make.profile/use.defaults</path> is installed
262 </li>
263 <li>
264 User-defined USE setting in <path>/etc/make.conf</path>
265 </li>
266 <li>
267 User-defined USE setting in <path>/etc/portage/package.use</path>
268 </li>
269 <li>
270 User-defined USE setting as environment variable
271 </li>
272 </ol>
273
274 <p>
275 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
276 This will list all relevant variables (including the <c>USE</c> variable) with
277 the content used by Portage.
278 </p>
279
280 <pre caption="Running emerge info">
281 # <i>emerge info</i>
282 </pre>
283
284 </body>
285 </subsection>
286 <subsection>
287 <title>Adapting your Entire System to New USE Flags</title>
288 <body>
289
290 <p>
291 If you have altered your USE flags and you wish to update your entire system to
292 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
293 </p>
294
295 <pre caption="Rebuilding your entire system">
296 # <i>emerge --update --deep --newuse world</i>
297 </pre>
298
299 <p>
300 Next, run Portage's depclean to remove the conditional dependencies that
301 were emerged on your "old" system but that have been obsoleted by the new USE
302 flags.
303 </p>
304
305 <warn>
306 Running <c>emerge depclean</c> is a dangerous operation and should be handled
307 with care. Double-check the provided list of "obsoleted" packages to make sure
308 it doesn't remove packages you need. In the following example we add the
309 <c>-p</c> switch to have depclean only list the packages without removing them.
310 </warn>
311
312 <pre caption="Removing obsoleted packages">
313 # <i>emerge -p depclean</i>
314 </pre>
315
316 <p>
317 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
318 applications that are dynamically linked against shared objects provided by
319 possibly removed packages. <c>revdep-rebuild</c> is part of the
320 <c>gentoolkit</c> package; don't forget to emerge it first.
321 </p>
322
323 <pre caption="Running revdep-rebuild">
324 # <i>revdep-rebuild</i>
325 </pre>
326
327 <p>
328 When all this is accomplished, your system is using the new USE flag settings.
329 </p>
330
331 </body>
332 </subsection>
333 </section>
334 <section>
335 <title>Package specific USE-flags</title>
336 <subsection>
337 <title>Viewing available USE-flags</title>
338 <body>
339
340 <p>
341 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
342 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
343 options:
344 </p>
345
346 <pre caption="Viewing the used USE-flags">
347 # <i>emerge --pretend --verbose mozilla</i>
348 These are the packages that I would merge, in order:
349
350 Calculating dependencies ...done!
351 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
352 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
353 -moznocompose -moznoxft
354 </pre>
355
356 <p>
357 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
358 dedicated to package information called <c>etcat</c> which resides in the
359 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
360 </p>
361
362 <pre caption="Installing gentoolkit">
363 # <i>emerge gentoolkit</i>
364 </pre>
365
366 <p>
367 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
368 certain package. For instance, for the <c>gnumeric</c> package:
369 </p>
370
371 <pre caption="Using etcat to view used USE-flags">
372 # <i>etcat uses gnumeric</i>
373 [ Colour Code : <i>set</i> <comment>unset</comment> ]
374 [ Legend : (U) Col 1 - Current USE flags ]
375 [ : (I) Col 2 - Installed With USE flags ]
376
377 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
378 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
379 - - <comment>gnomedb</comment> : unknown
380 + + <i>python</i> : Adds support/bindings for the Python language
381 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
382 </pre>
383
384 </body>
385 </subsection>
386 </section>
387 </sections>

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