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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 1.16 2004/07/07 19:19:26 neysx 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 </body>
105 </subsection>
106 </section>
107 <section>
108 <title>Using USE-flags</title>
109 <subsection>
110 <title>Declare permanent USE-flags</title>
111 <body>
112
113 <p>
114 In the hope you are convinced of the importance of USE-flags we will now inform
115 you how to declare USE-flags.
116 </p>
117
118 <p>
119 As previously mentioned, all USE-flags are declared inside the <c>USE</c>
120 variable. To make it easy for users to search and pick USE-flags, we already
121 provide a <e>default</e> USE setting. This setting is a collection of USE-flags
122 we think are commonly used by the Gentoo users. This default setting is declared
123 in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
124 this default setting:
125 </p>
126
127 <pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
128 USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
129 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
130 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
131 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
132 </pre>
133
134 <p>
135 As you can see, this variable already contains quite a lot of keywords. Do
136 <b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
137 the <c>USE</c> variable to your needs: changes in this file will be undone when
138 you update Portage!
139 </p>
140
141 <p>
142 To change this default setting, you need to add or remove keywords to the
143 <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
144 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
145 require, or remove the USE-flags you don't want. This latter is done by
146 prefixing the keyword with the minus-sign ("-").
147 </p>
148
149 <p>
150 For instance, to remove support for KDE and QT but add support for ldap, the
151 following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
152 </p>
153
154 <pre caption="An example USE setting in /etc/make.conf">
155 USE="-kde -qt ldap"
156 </pre>
157
158 <p>
159 Sometimes you want to declare a certain USE flag for one (or a couple) of
160 applications but not system-wide. To accomplish this, you will need to create
161 the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
162 <path>/etc/portage/package.use</path>.
163 </p>
164
165 <p>
166 For instance, if you don't want <c>berkdb</c> support globally but you do want
167 it for <c>mysql</c>, you would add:
168 </p>
169
170 <pre caption="/etc/portage/package.use example">
171 dev-db/mysql berkdb
172 </pre>
173
174 <p>
175 You can of course also explicitly <e>disable</e> USE flags for a certain
176 application. For instance, if you don't want <c>java</c> support in PHP:
177 </p>
178
179 <pre caption="/etc/portage/package.use 2nd example">
180 dev-php/php -java
181 </pre>
182
183 </body>
184 </subsection>
185 <subsection>
186 <title>Declare temporary USE-flags</title>
187 <body>
188
189 <p>
190 Sometimes you want to set a certain USE-setting only once. Instead of editing
191 <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
192 declare the USE-variable as environment variable. Remember that, when you
193 re-emerge or update this application (either explicitly or as part of a system
194 update) your changes will be lost!
195 </p>
196
197 <p>
198 As an example we will temporarily remove java from the USE-setting
199 during the installation of mozilla.
200 </p>
201
202 <note>
203 The <c>emerge</c> command will be discussed more thoroughly in <uri
204 link="?part=2&amp;chap=2">Portage and Software</uri>.
205 </note>
206
207 <pre caption="Using USE as environment variable">
208 # <i>USE="-java" emerge mozilla</i>
209 </pre>
210
211 </body>
212 </subsection>
213 <subsection>
214 <title>Inheriting USE-flags</title>
215 <body>
216
217 <p>
218 Some packages don't only listen to USE-flags, but also provide USE-flags. When
219 you install such a package, the USE-flag they provide is added to your USE
220 setting. To view the list of packages that provide a USE-flag, check
221 <path>/etc/make.profile/use.defaults</path>:
222 </p>
223
224 <pre caption="A snippet from /etc/make.profile/use.defaults">
225 gnome gnome-base/gnome
226 gtk x11-libs/gtk+
227 qt x11-libs/qt
228 kde kde-base/kdebase
229 motif x11-libs/openmotif
230 </pre>
231
232 </body>
233 </subsection>
234 <subsection>
235 <title>Precedence</title>
236 <body>
237
238 <p>
239 Of course there is a certain precedence on what setting has priority over the
240 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
241 <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
242 by priority (first has lowest priority):
243 </p>
244
245 <ol>
246 <li>
247 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
248 </li>
249 <li>
250 Inherited USE setting if a package from
251 <path>/etc/make.profile/use.defaults</path> is installed
252 </li>
253 <li>
254 User-defined USE setting in <path>/etc/make.conf</path>
255 </li>
256 <li>
257 User-defined USE setting in <path>/etc/portage/package.use</path>
258 </li>
259 <li>
260 User-defined USE setting as environment variable
261 </li>
262 </ol>
263
264 <p>
265 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
266 This will list all relevant variables (including the <c>USE</c> variable) with
267 the content used by Portage.
268 </p>
269
270 <pre caption="Running emerge info">
271 # <i>emerge info</i>
272 </pre>
273
274 </body>
275 </subsection>
276 <subsection>
277 <title>Adapting your Entire System to New USE Flags</title>
278 <body>
279
280 <p>
281 If you have altered your USE flags and you wish to update your entire system to
282 use the new USE flags, you can try following the next steps to accomplish this.
283 Note however that these steps will take a long time to finish and that work is
284 on the way to adjust Portage to handle this behaviour quicker and automatically.
285 </p>
286
287 <p>
288 First of all, rebuild your entire system using the new USE flags:
289 </p>
290
291 <pre caption="Rebuilding your entire system">
292 # <i>emerge --emptytree world</i>
293 </pre>
294
295 <p>
296 Next, run Portage' 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, your system is using the new USE flag settings.
314 </p>
315
316 </body>
317 </subsection>
318 </section>
319 <section>
320 <title>Package specific USE-flags</title>
321 <subsection>
322 <title>Viewing available USE-flags</title>
323 <body>
324
325 <p>
326 In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
327 we will explain how to manage your installed software and how to work with
328 <c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
329 you how to view what USE-flags a package uses.
330 </p>
331
332 <p>
333 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
334 find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
335 anything) and <c>--verbose</c> (give more output) options:
336 </p>
337
338 <pre caption="Viewing the used USE-flags">
339 # <i>emerge --pretend --verbose mozilla</i>
340 These are the packages that I would merge, in order:
341
342 Calculating dependencies ...done!
343 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
344 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
345 -moznocompose -moznoxft
346 </pre>
347
348 <p>
349 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
350 dedicated to package information called <c>etcat</c> which resides in the
351 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
352 </p>
353
354 <pre caption="Installing gentoolkit">
355 # <i>emerge --usepkg gentoolkit</i>
356 </pre>
357
358 <p>
359 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
360 certain package. For instance, for the <c>gnumeric</c> package:
361 </p>
362
363 <pre caption="Using etcat to view used USE-flags">
364 # <i>etcat uses gnumeric</i>
365 [ Colour Code : <i>set</i> <comment>unset</comment> ]
366 [ Legend : (U) Col 1 - Current USE flags ]
367 [ : (I) Col 2 - Installed With USE flags ]
368
369 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
370 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
371 - - <comment>gnomedb</comment> : unknown
372 + + <i>python</i> : Adds support/bindings for the Python language
373 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
374 </pre>
375
376 </body>
377 </subsection>
378 </section>
379 </sections>

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