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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 1.27 2005/01/22 01:24:31 cam Exp $ -->
8
9 <sections>
10
11 <version>1.25</version>
12 <date>2005-01-23</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.
133 </p>
134
135 <p>
136 The profile your system listens to is pointed to by the
137 <path>/etc/make.profile</path> symlink. Each profile works on top of another,
138 larger profile, the end result is therefore the sum of all profiles. The top
139 profile is the <path>base</path> profile
140 (<path>/usr/portage/profiles/base</path>).
141 </p>
142
143 <p>
144 Let us take a look at this default setting:
145 </p>
146
147 <pre caption="Cumulated /usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
148 <comment>(This example is the sum of the settings in base, default-linux,
149 default-linux/x86 and default-linux/x86/2004.3)</comment>
150 USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
151 foomaticdb gdbm gif gpm gtk gtk2 imlib jpeg kde gnome libg++ libwww mad
152 mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
153 quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
154 </pre>
155
156 <p>
157 As you can see, this variable already contains quite a lot of keywords. Do
158 <b>not</b> alter any <path>make.defaults</path> file to tailor
159 the <c>USE</c> variable to your needs: changes in this file will be undone when
160 you update Portage!
161 </p>
162
163 <p>
164 To change this default setting, you need to add or remove keywords to the
165 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
166 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
167 require, or remove the USE-flags you don't want. This latter is done by
168 prefixing the keyword with the minus-sign ("-").
169 </p>
170
171 <p>
172 For instance, to remove support for KDE and QT but add support for ldap, the
173 following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
174 </p>
175
176 <pre caption="An example USE setting in /etc/make.conf">
177 USE="-kde -qt ldap"
178 </pre>
179
180 </body>
181 </subsection>
182 <subsection>
183 <title>Declaring USE flags for individual packages</title>
184 <body>
185
186 <p>
187 Sometimes you want to declare a certain USE flag for one (or a couple) of
188 applications but not system-wide. To accomplish this, you will need to create
189 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
190 <path>/etc/portage/package.use</path>.
191 </p>
192
193 <p>
194 For instance, if you don't want <c>berkdb</c> support globally but you do want
195 it for <c>mysql</c>, you would add:
196 </p>
197
198 <pre caption="/etc/portage/package.use example">
199 dev-db/mysql berkdb
200 </pre>
201
202 <p>
203 You can of course also explicitly <e>disable</e> USE flags for a certain
204 application. For instance, if you don't want <c>java</c> support in PHP:
205 </p>
206
207 <pre caption="/etc/portage/package.use 2nd example">
208 dev-php/php -java
209 </pre>
210
211 </body>
212 </subsection>
213 <subsection>
214 <title>Declare temporary USE-flags</title>
215 <body>
216
217 <p>
218 Sometimes you want to set a certain USE-setting only once. Instead of editing
219 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
220 declare the USE-variable as environment variable. Remember that, when you
221 re-emerge or update this application (either explicitly or as part of a system
222 update) your changes will be lost!
223 </p>
224
225 <p>
226 As an example we will temporarily remove java from the USE-setting
227 during the installation of mozilla.
228 </p>
229
230 <pre caption="Using USE as environment variable">
231 # <i>USE="-java" emerge mozilla</i>
232 </pre>
233
234 </body>
235 </subsection>
236 <subsection>
237 <title>Inheriting USE-flags</title>
238 <body>
239
240 <p>
241 Some packages don't only listen to USE-flags, but also provide USE-flags. When
242 you install such a package, the USE-flag they provide is added to your USE
243 setting. To view the list of packages that provide a USE-flag, check
244 <path>/etc/make.profile/use.defaults</path>:
245 </p>
246
247 <pre caption="A snippet from /etc/make.profile/use.defaults">
248 gnome gnome-base/gnome
249 gtk x11-libs/gtk+
250 qt x11-libs/qt
251 kde kde-base/kdebase
252 motif x11-libs/openmotif
253 </pre>
254
255 </body>
256 </subsection>
257 <subsection>
258 <title>Precedence</title>
259 <body>
260
261 <p>
262 Of course there is a certain precedence on what setting has priority over the
263 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
264 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
265 by priority (first has lowest priority):
266 </p>
267
268 <ol>
269 <li>
270 Default USE setting declared in the <path>make.defaults</path> files part of
271 your profile
272 </li>
273 <li>
274 Inherited USE setting if a package from
275 <path>/etc/make.profile/use.defaults</path> is installed
276 </li>
277 <li>
278 User-defined USE setting in <path>/etc/make.conf</path>
279 </li>
280 <li>
281 User-defined USE setting in <path>/etc/portage/package.use</path>
282 </li>
283 <li>
284 User-defined USE setting as environment variable
285 </li>
286 </ol>
287
288 <p>
289 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
290 --info</c>. This will list all relevant variables (including the <c>USE</c>
291 variable) with the content used by Portage.
292 </p>
293
294 <pre caption="Running emerge --info">
295 # <i>emerge --info</i>
296 </pre>
297
298 </body>
299 </subsection>
300 <subsection>
301 <title>Adapting your Entire System to New USE Flags</title>
302 <body>
303
304 <p>
305 If you have altered your USE flags and you wish to update your entire system to
306 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
307 </p>
308
309 <pre caption="Rebuilding your entire system">
310 # <i>emerge --update --deep --newuse world</i>
311 </pre>
312
313 <p>
314 Next, run Portage's depclean to remove the conditional dependencies that
315 were emerged on your "old" system but that have been obsoleted by the new USE
316 flags.
317 </p>
318
319 <warn>
320 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
321 with care. Double-check the provided list of "obsoleted" packages to make sure
322 it doesn't remove packages you need. In the following example we add the
323 <c>-p</c> switch to have depclean only list the packages without removing them.
324 </warn>
325
326 <pre caption="Removing obsoleted packages">
327 # <i>emerge -p --depclean</i>
328 </pre>
329
330 <p>
331 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
332 applications that are dynamically linked against shared objects provided by
333 possibly removed packages. <c>revdep-rebuild</c> is part of the
334 <c>gentoolkit</c> package; don't forget to emerge it first.
335 </p>
336
337 <pre caption="Running revdep-rebuild">
338 # <i>revdep-rebuild</i>
339 </pre>
340
341 <p>
342 When all this is accomplished, your system is using the new USE flag settings.
343 </p>
344
345 </body>
346 </subsection>
347 </section>
348 <section>
349 <title>Package specific USE-flags</title>
350 <subsection>
351 <title>Viewing available USE-flags</title>
352 <body>
353
354 <p>
355 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
356 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
357 options:
358 </p>
359
360 <pre caption="Viewing the used USE-flags">
361 # <i>emerge --pretend --verbose mozilla</i>
362 These are the packages that I would merge, in order:
363
364 Calculating dependencies ...done!
365 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
366 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
367 -moznocompose -moznoxft
368 </pre>
369
370 <p>
371 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
372 dedicated to package information called <c>etcat</c> which resides in the
373 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
374 </p>
375
376 <pre caption="Installing gentoolkit">
377 # <i>emerge gentoolkit</i>
378 </pre>
379
380 <p>
381 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
382 certain package. For instance, for the <c>gnumeric</c> package:
383 </p>
384
385 <pre caption="Using etcat to view used USE-flags">
386 # <i>etcat uses gnumeric</i>
387 [ Colour Code : <i>set</i> <comment>unset</comment> ]
388 [ Legend : (U) Col 1 - Current USE flags ]
389 [ : (I) Col 2 - Installed With USE flags ]
390
391 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
392 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
393 - - <comment>gnomedb</comment> : unknown
394 + + <i>python</i> : Adds support/bindings for the Python language
395 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
396 </pre>
397
398 </body>
399 </subsection>
400 </section>
401 </sections>

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