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#65107 - Added Portage-specific part to the Gentoo Handbook now that .51 is official; major version bump to 3.0

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/draft/hb-working-use.xml,v 1.12 2004/10/10 11:09:40 swift Exp $ -->
8
9 <sections>
10 <section>
11 <title>What are USE-flags?</title>
12 <subsection>
13 <title>The ideas behind USE-flags</title>
14 <body>
15
16 <p>
17 When you are installing Gentoo (or any other distribution, or even operating
18 system for that matter) you make choices depending on the environment you are
19 working with. A setup for a server differs from a setup for a workstation.
20 A gaming workstation differs from a 3D rendering workstation.
21 </p>
22
23 <p>
24 This is not only true for choosing what packages you want to install, but also
25 what features a certain package should support. If you don't need OpenGL, why
26 would you bother installing OpenGL and build OpenGL support in most of your
27 packages? If you don't want to use KDE, why would you bother compiling packages
28 with KDE-support if those packages work flawlessly without?
29 </p>
30
31 <p>
32 To help users in deciding what to install/activate and what not, we wanted the
33 user to specify his/her environment in an easy way. This forces the user into
34 deciding what they really want and eases the process for Portage, our package
35 managment system, to make useful decisions.
36 </p>
37
38 </body>
39 </subsection>
40 <subsection>
41 <title>Definition of a USE-flag</title>
42 <body>
43
44 <p>
45 Enter the USE-flags. Such a flag is a keyword that embodies support and
46 dependency-information for a certain concept. If you define a certain USE-flag,
47 Portage will know that you want support for the chosen keyword. Of course
48 this also alters the dependency information for a package.
49 </p>
50
51 <p>
52 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
53 have this keyword in your <c>USE</c> variable, all packages that have
54 <e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
55 packages that have an <e>optional</e> KDE dependency will be installed
56 <e>without</e> installing the KDE libraries (as dependency). If you have defined
57 the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
58 support, and the KDE libraries will be installed as dependency.
59 </p>
60
61 <p>
62 By correctly defining the keywords you will receive a system tailored
63 specifically to your needs.
64 </p>
65
66 </body>
67 </subsection>
68 <subsection>
69 <title>What USE-flags exist?</title>
70 <body>
71
72 <p>
73 There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
74 </p>
75
76 <ul>
77 <li>
78 A <e>global</e> USE-flag is used by several packages, system-wide. This is
79 what most people see as USE-flags.
80 </li>
81 <li>
82 A <e>local</e> USE-flag is used by a single package to make package-specific
83 decisions.
84 </li>
85 </ul>
86
87 <p>
88 A list of available global USE-flags can be found <uri
89 link="/dyn/use-index.xml">online</uri> or locally in
90 <path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
91 snippet:
92 </p>
93
94 <pre caption="A short snippet of available USE-flags">
95 gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
96 gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
97 gtkhtml - Adds support for gnome-extra/gtkhtml
98 guile - Adds support for dev-util/guile (interpreter for Scheme)
99 icc - Use the Intel C++ Compiler if the package supports it
100 icc-pgo - Enable PGO data generation or use when use icc.
101 imap - Adds support for IMAP
102 </pre>
103
104 <p>
105 A list of available local USE-flags can be found locally in
106 <path>/usr/portage/profiles/use.local.desc</path>.
107 </p>
108
109 </body>
110 </subsection>
111 </section>
112 <section>
113 <title>Using USE-flags</title>
114 <subsection>
115 <title>Declare permanent USE-flags</title>
116 <body>
117
118 <p>
119 In the hope you are convinced of the importance of USE-flags we will now inform
120 you how to declare USE-flags.
121 </p>
122
123 <p>
124 As previously mentioned, all USE-flags are declared inside the <c>USE</c>
125 variable. To make it easy for users to search and pick USE-flags, we already
126 provide a <e>default</e> USE setting. This setting is a collection of USE-flags
127 we think are commonly used by the Gentoo users. This default setting is declared
128 in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
129 this default setting:
130 </p>
131
132 <pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
133 USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
134 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
135 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
136 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
137 </pre>
138
139 <p>
140 As you can see, this variable already contains quite a lot of keywords. Do
141 <b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
142 the <c>USE</c> variable to your needs: changes in this file will be undone when
143 you update Portage!
144 </p>
145
146 <p>
147 To change this default setting, you need to add or remove keywords to the
148 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
149 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
150 require, or remove the USE-flags you don't want. This latter is done by
151 prefixing the keyword with the minus-sign ("-").
152 </p>
153
154 <p>
155 For instance, to remove support for KDE and QT but add support for ldap, the
156 following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
157 </p>
158
159 <pre caption="An example USE setting in /etc/make.conf">
160 USE="-kde -qt ldap"
161 </pre>
162
163 </body>
164 </subsection>
165 <subsection>
166 <title>Declaring USE flags for individual packages</title>
167 <body>
168
169 <p>
170 Sometimes you want to declare a certain USE flag for one (or a couple) of
171 applications but not system-wide. To accomplish this, you will need to create
172 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
173 <path>/etc/portage/package.use</path>.
174 </p>
175
176 <p>
177 For instance, if you don't want <c>berkdb</c> support globally but you do want
178 it for <c>mysql</c>, you would add:
179 </p>
180
181 <pre caption="/etc/portage/package.use example">
182 dev-db/mysql berkdb
183 </pre>
184
185 <p>
186 You can of course also explicitly <e>disable</e> USE flags for a certain
187 application. For instance, if you don't want <c>java</c> support in PHP:
188 </p>
189
190 <pre caption="/etc/portage/package.use 2nd example">
191 dev-php/php -java
192 </pre>
193
194 </body>
195 </subsection>
196 <subsection>
197 <title>Declare temporary USE-flags</title>
198 <body>
199
200 <p>
201 Sometimes you want to set a certain USE-setting only once. Instead of editing
202 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
203 declare the USE-variable as environment variable. Remember that, when you
204 re-emerge or update this application (either explicitly or as part of a system
205 update) your changes will be lost!
206 </p>
207
208 <p>
209 As an example we will temporarily remove java from the USE-setting
210 during the installation of mozilla.
211 </p>
212
213 <pre caption="Using USE as environment variable">
214 # <i>USE="-java" emerge mozilla</i>
215 </pre>
216
217 </body>
218 </subsection>
219 <subsection>
220 <title>Inheriting USE-flags</title>
221 <body>
222
223 <p>
224 Some packages don't only listen to USE-flags, but also provide USE-flags. When
225 you install such a package, the USE-flag they provide is added to your USE
226 setting. To view the list of packages that provide a USE-flag, check
227 <path>/etc/make.profile/use.defaults</path>:
228 </p>
229
230 <pre caption="A snippet from /etc/make.profile/use.defaults">
231 gnome gnome-base/gnome
232 gtk x11-libs/gtk+
233 qt x11-libs/qt
234 kde kde-base/kdebase
235 motif x11-libs/openmotif
236 </pre>
237
238 </body>
239 </subsection>
240 <subsection>
241 <title>Precedence</title>
242 <body>
243
244 <p>
245 Of course there is a certain precedence on what setting has priority over the
246 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
247 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
248 by priority (first has lowest priority):
249 </p>
250
251 <ol>
252 <li>
253 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
254 </li>
255 <li>
256 Inherited USE setting if a package from
257 <path>/etc/make.profile/use.defaults</path> is installed
258 </li>
259 <li>
260 User-defined USE setting in <path>/etc/make.conf</path>
261 </li>
262 <li>
263 User-defined USE setting in <path>/etc/portage/package.use</path>
264 </li>
265 <li>
266 User-defined USE setting as environment variable
267 </li>
268 </ol>
269
270 <p>
271 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
272 This will list all relevant variables (including the <c>USE</c> variable) with
273 the content used by Portage.
274 </p>
275
276 <pre caption="Running emerge info">
277 # <i>emerge info</i>
278 </pre>
279
280 </body>
281 </subsection>
282 <subsection>
283 <title>Adapting your Entire System to New USE Flags</title>
284 <body>
285
286 <p>
287 If you have altered your USE flags and you wish to update your entire system to
288 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
289 </p>
290
291 <pre caption="Rebuilding your entire system">
292 # <i>emerge --update --deep --newuse world</i>
293 </pre>
294
295 <p>
296 Next, run Portage's depclean to remove the conditional dependencies that
297 were emerged on your "old" system but that have been obsoleted by the new USE
298 flags.
299 </p>
300
301 <warn>
302 Running <c>emerge depclean</c> is a dangerous operation and should be handled
303 with care. Double-check the provided list of "obsoleted" packages to make sure
304 it doesn't remove packages you need. In the following example we add the
305 <c>-p</c> switch to have depclean only list the packages without removing them.
306 </warn>
307
308 <pre caption="Removing obsoleted packages">
309 # <i>emerge -p depclean</i>
310 </pre>
311
312 <p>
313 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
314 applications that are dynamically linked against shared objects provided by
315 possibly removed packages. <c>revdep-rebuild</c> is part of the
316 <c>gentoolkit</c> package; don't forget to emerge it first.
317 </p>
318
319 <pre caption="Running revdep-rebuild">
320 # <i>revdep-rebuild</i>
321 </pre>
322
323 <p>
324 When all this is accomplished, your system is using the new USE flag settings.
325 </p>
326
327 </body>
328 </subsection>
329 </section>
330 <section>
331 <title>Package specific USE-flags</title>
332 <subsection>
333 <title>Viewing available USE-flags</title>
334 <body>
335
336 <p>
337 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
338 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
339 options:
340 </p>
341
342 <pre caption="Viewing the used USE-flags">
343 # <i>emerge --pretend --verbose mozilla</i>
344 These are the packages that I would merge, in order:
345
346 Calculating dependencies ...done!
347 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
348 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
349 -moznocompose -moznoxft
350 </pre>
351
352 <p>
353 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
354 dedicated to package information called <c>etcat</c> which resides in the
355 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
356 </p>
357
358 <pre caption="Installing gentoolkit">
359 # <i>emerge gentoolkit</i>
360 </pre>
361
362 <p>
363 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
364 certain package. For instance, for the <c>gnumeric</c> package:
365 </p>
366
367 <pre caption="Using etcat to view used USE-flags">
368 # <i>etcat uses gnumeric</i>
369 [ Colour Code : <i>set</i> <comment>unset</comment> ]
370 [ Legend : (U) Col 1 - Current USE flags ]
371 [ : (I) Col 2 - Installed With USE flags ]
372
373 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
374 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
375 - - <comment>gnomedb</comment> : unknown
376 + + <i>python</i> : Adds support/bindings for the Python language
377 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
378 </pre>
379
380 </body>
381 </subsection>
382 </section>
383 </sections>

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