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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 1.17 2004/08/01 13:08:35 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 <p>
164 Sometimes you want to declare a certain USE flag for one (or a couple) of
165 applications but not system-wide. To accomplish this, you will need to create
166 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
167 <path>/etc/portage/package.use</path>.
168 </p>
169
170 <p>
171 For instance, if you don't want <c>berkdb</c> support globally but you do want
172 it for <c>mysql</c>, you would add:
173 </p>
174
175 <pre caption="/etc/portage/package.use example">
176 dev-db/mysql berkdb
177 </pre>
178
179 <p>
180 You can of course also explicitly <e>disable</e> USE flags for a certain
181 application. For instance, if you don't want <c>java</c> support in PHP:
182 </p>
183
184 <pre caption="/etc/portage/package.use 2nd example">
185 dev-php/php -java
186 </pre>
187
188 </body>
189 </subsection>
190 <subsection>
191 <title>Declare temporary USE-flags</title>
192 <body>
193
194 <p>
195 Sometimes you want to set a certain USE-setting only once. Instead of editing
196 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
197 declare the USE-variable as environment variable. Remember that, when you
198 re-emerge or update this application (either explicitly or as part of a system
199 update) your changes will be lost!
200 </p>
201
202 <p>
203 As an example we will temporarily remove java from the USE-setting
204 during the installation of mozilla.
205 </p>
206
207 <note>
208 The <c>emerge</c> command will be discussed more thoroughly in <uri
209 link="?part=2&amp;chap=2">Portage and Software</uri>.
210 </note>
211
212 <pre caption="Using USE as environment variable">
213 # <i>USE="-java" emerge mozilla</i>
214 </pre>
215
216 </body>
217 </subsection>
218 <subsection>
219 <title>Inheriting USE-flags</title>
220 <body>
221
222 <p>
223 Some packages don't only listen to USE-flags, but also provide USE-flags. When
224 you install such a package, the USE-flag they provide is added to your USE
225 setting. To view the list of packages that provide a USE-flag, check
226 <path>/etc/make.profile/use.defaults</path>:
227 </p>
228
229 <pre caption="A snippet from /etc/make.profile/use.defaults">
230 gnome gnome-base/gnome
231 gtk x11-libs/gtk+
232 qt x11-libs/qt
233 kde kde-base/kdebase
234 motif x11-libs/openmotif
235 </pre>
236
237 </body>
238 </subsection>
239 <subsection>
240 <title>Precedence</title>
241 <body>
242
243 <p>
244 Of course there is a certain precedence on what setting has priority over the
245 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
246 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
247 by priority (first has lowest priority):
248 </p>
249
250 <ol>
251 <li>
252 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
253 </li>
254 <li>
255 Inherited USE setting if a package from
256 <path>/etc/make.profile/use.defaults</path> is installed
257 </li>
258 <li>
259 User-defined USE setting in <path>/etc/make.conf</path>
260 </li>
261 <li>
262 User-defined USE setting in <path>/etc/portage/package.use</path>
263 </li>
264 <li>
265 User-defined USE setting as environment variable
266 </li>
267 </ol>
268
269 <p>
270 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
271 This will list all relevant variables (including the <c>USE</c> variable) with
272 the content used by Portage.
273 </p>
274
275 <pre caption="Running emerge info">
276 # <i>emerge info</i>
277 </pre>
278
279 </body>
280 </subsection>
281 <subsection>
282 <title>Adapting your Entire System to New USE Flags</title>
283 <body>
284
285 <p>
286 If you have altered your USE flags and you wish to update your entire system to
287 use the new USE flags, you can try following the next steps to accomplish this.
288 Note however that these steps will take a long time to finish and that work is
289 on the way to adjust Portage to handle this behaviour quicker and automatically.
290 </p>
291
292 <p>
293 First of all, rebuild your entire system using the new USE flags:
294 </p>
295
296 <pre caption="Rebuilding your entire system">
297 # <i>emerge --emptytree world</i>
298 </pre>
299
300 <p>
301 Next, run Portage' depclean to remove the conditional dependencies that
302 were emerged on your "old" system but that have been obsoleted by the new USE
303 flags.
304 </p>
305
306 <warn>
307 Running <c>emerge depclean</c> is a dangerous operation and should be handled
308 with care. Double-check the provided list of "obsoleted" packages to make sure
309 it doesn't remove packages you need. In the following example we add the
310 <c>-p</c> switch to have depclean only list the packages without removing them.
311 </warn>
312
313 <pre caption="Removing obsoleted packages">
314 # <i>emerge -p depclean</i>
315 </pre>
316
317 <p>
318 When depclean has finished, your system is using the new USE flag settings.
319 </p>
320
321 </body>
322 </subsection>
323 </section>
324 <section>
325 <title>Package specific USE-flags</title>
326 <subsection>
327 <title>Viewing available USE-flags</title>
328 <body>
329
330 <p>
331 In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
332 we will explain how to manage your installed software and how to work with
333 <c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
334 you how to view what USE-flags a package uses.
335 </p>
336
337 <p>
338 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
339 find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
340 anything) and <c>--verbose</c> (give more output) options:
341 </p>
342
343 <pre caption="Viewing the used USE-flags">
344 # <i>emerge --pretend --verbose mozilla</i>
345 These are the packages that I would merge, in order:
346
347 Calculating dependencies ...done!
348 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
349 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
350 -moznocompose -moznoxft
351 </pre>
352
353 <p>
354 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
355 dedicated to package information called <c>etcat</c> which resides in the
356 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
357 </p>
358
359 <pre caption="Installing gentoolkit">
360 # <i>emerge --usepkg gentoolkit</i>
361 </pre>
362
363 <p>
364 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
365 certain package. For instance, for the <c>gnumeric</c> package:
366 </p>
367
368 <pre caption="Using etcat to view used USE-flags">
369 # <i>etcat uses gnumeric</i>
370 [ Colour Code : <i>set</i> <comment>unset</comment> ]
371 [ Legend : (U) Col 1 - Current USE flags ]
372 [ : (I) Col 2 - Installed With USE flags ]
373
374 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
375 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
376 - - <comment>gnomedb</comment> : unknown
377 + + <i>python</i> : Adds support/bindings for the Python language
378 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
379 </pre>
380
381 </body>
382 </subsection>
383 </section>
384 </sections>

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