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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 1.26 2004/12/28 20:01:06 cam Exp $ -->
8
9 <sections>
10
11 <version>1.24</version>
12 <date>2005-01-22</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>make.defaults</path> files part of your profile. Let us take a
133 look at this default setting:
134 </p>
135
136 <pre caption="/usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
137 <comment>(This is an example and might have changed since it was taken)</comment>
138 USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
139 foomaticdb gdbm gif gpm gtk gtk2 imlib jpeg kde gnome libg++ libwww mad
140 mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
141 quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
142 </pre>
143
144 <p>
145 As you can see, this variable already contains quite a lot of keywords. Do
146 <b>not</b> alter any <path>make.defaults</path> file to tailor
147 the <c>USE</c> variable to your needs: changes in this file will be undone when
148 you update Portage!
149 </p>
150
151 <p>
152 To change this default setting, you need to add or remove keywords to the
153 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
154 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
155 require, or remove the USE-flags you don't want. This latter is done by
156 prefixing the keyword with the minus-sign ("-").
157 </p>
158
159 <p>
160 For instance, to remove support for KDE and QT but add support for ldap, the
161 following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
162 </p>
163
164 <pre caption="An example USE setting in /etc/make.conf">
165 USE="-kde -qt ldap"
166 </pre>
167
168 </body>
169 </subsection>
170 <subsection>
171 <title>Declaring USE flags for individual packages</title>
172 <body>
173
174 <p>
175 Sometimes you want to declare a certain USE flag for one (or a couple) of
176 applications but not system-wide. To accomplish this, you will need to create
177 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
178 <path>/etc/portage/package.use</path>.
179 </p>
180
181 <p>
182 For instance, if you don't want <c>berkdb</c> support globally but you do want
183 it for <c>mysql</c>, you would add:
184 </p>
185
186 <pre caption="/etc/portage/package.use example">
187 dev-db/mysql berkdb
188 </pre>
189
190 <p>
191 You can of course also explicitly <e>disable</e> USE flags for a certain
192 application. For instance, if you don't want <c>java</c> support in PHP:
193 </p>
194
195 <pre caption="/etc/portage/package.use 2nd example">
196 dev-php/php -java
197 </pre>
198
199 </body>
200 </subsection>
201 <subsection>
202 <title>Declare temporary USE-flags</title>
203 <body>
204
205 <p>
206 Sometimes you want to set a certain USE-setting only once. Instead of editing
207 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
208 declare the USE-variable as environment variable. Remember that, when you
209 re-emerge or update this application (either explicitly or as part of a system
210 update) your changes will be lost!
211 </p>
212
213 <p>
214 As an example we will temporarily remove java from the USE-setting
215 during the installation of mozilla.
216 </p>
217
218 <pre caption="Using USE as environment variable">
219 # <i>USE="-java" emerge mozilla</i>
220 </pre>
221
222 </body>
223 </subsection>
224 <subsection>
225 <title>Inheriting USE-flags</title>
226 <body>
227
228 <p>
229 Some packages don't only listen to USE-flags, but also provide USE-flags. When
230 you install such a package, the USE-flag they provide is added to your USE
231 setting. To view the list of packages that provide a USE-flag, check
232 <path>/etc/make.profile/use.defaults</path>:
233 </p>
234
235 <pre caption="A snippet from /etc/make.profile/use.defaults">
236 gnome gnome-base/gnome
237 gtk x11-libs/gtk+
238 qt x11-libs/qt
239 kde kde-base/kdebase
240 motif x11-libs/openmotif
241 </pre>
242
243 </body>
244 </subsection>
245 <subsection>
246 <title>Precedence</title>
247 <body>
248
249 <p>
250 Of course there is a certain precedence on what setting has priority over the
251 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
252 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
253 by priority (first has lowest priority):
254 </p>
255
256 <ol>
257 <li>
258 Default USE setting declared in the <path>make.defaults</path> files part of
259 your profile
260 </li>
261 <li>
262 Inherited USE setting if a package from
263 <path>/etc/make.profile/use.defaults</path> is installed
264 </li>
265 <li>
266 User-defined USE setting in <path>/etc/make.conf</path>
267 </li>
268 <li>
269 User-defined USE setting in <path>/etc/portage/package.use</path>
270 </li>
271 <li>
272 User-defined USE setting as environment variable
273 </li>
274 </ol>
275
276 <p>
277 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
278 --info</c>. This will list all relevant variables (including the <c>USE</c>
279 variable) with the content used by Portage.
280 </p>
281
282 <pre caption="Running emerge --info">
283 # <i>emerge --info</i>
284 </pre>
285
286 </body>
287 </subsection>
288 <subsection>
289 <title>Adapting your Entire System to New USE Flags</title>
290 <body>
291
292 <p>
293 If you have altered your USE flags and you wish to update your entire system to
294 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
295 </p>
296
297 <pre caption="Rebuilding your entire system">
298 # <i>emerge --update --deep --newuse world</i>
299 </pre>
300
301 <p>
302 Next, run Portage's depclean to remove the conditional dependencies that
303 were emerged on your "old" system but that have been obsoleted by the new USE
304 flags.
305 </p>
306
307 <warn>
308 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
309 with care. Double-check the provided list of "obsoleted" packages to make sure
310 it doesn't remove packages you need. In the following example we add the
311 <c>-p</c> switch to have depclean only list the packages without removing them.
312 </warn>
313
314 <pre caption="Removing obsoleted packages">
315 # <i>emerge -p --depclean</i>
316 </pre>
317
318 <p>
319 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
320 applications that are dynamically linked against shared objects provided by
321 possibly removed packages. <c>revdep-rebuild</c> is part of the
322 <c>gentoolkit</c> package; don't forget to emerge it first.
323 </p>
324
325 <pre caption="Running revdep-rebuild">
326 # <i>revdep-rebuild</i>
327 </pre>
328
329 <p>
330 When all this is accomplished, your system is using the new USE flag settings.
331 </p>
332
333 </body>
334 </subsection>
335 </section>
336 <section>
337 <title>Package specific USE-flags</title>
338 <subsection>
339 <title>Viewing available USE-flags</title>
340 <body>
341
342 <p>
343 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
344 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
345 options:
346 </p>
347
348 <pre caption="Viewing the used USE-flags">
349 # <i>emerge --pretend --verbose mozilla</i>
350 These are the packages that I would merge, in order:
351
352 Calculating dependencies ...done!
353 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
354 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
355 -moznocompose -moznoxft
356 </pre>
357
358 <p>
359 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
360 dedicated to package information called <c>etcat</c> which resides in the
361 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
362 </p>
363
364 <pre caption="Installing gentoolkit">
365 # <i>emerge gentoolkit</i>
366 </pre>
367
368 <p>
369 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
370 certain package. For instance, for the <c>gnumeric</c> package:
371 </p>
372
373 <pre caption="Using etcat to view used USE-flags">
374 # <i>etcat uses gnumeric</i>
375 [ Colour Code : <i>set</i> <comment>unset</comment> ]
376 [ Legend : (U) Col 1 - Current USE flags ]
377 [ : (I) Col 2 - Installed With USE flags ]
378
379 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
380 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
381 - - <comment>gnomedb</comment> : unknown
382 + + <i>python</i> : Adds support/bindings for the Python language
383 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
384 </pre>
385
386 </body>
387 </subsection>
388 </section>
389 </sections>

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