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1 swift 1.7 <?xml version='1.0' encoding='UTF-8'?>
2     <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3    
4 swift 1.1 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 neysx 1.39 <!-- See http://creativecommons.org/licenses/by-sa/2.5 -->
6 swift 1.1
7 nightmorph 1.40 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.39 2006/03/14 19:29:29 neysx Exp $ -->
8 swift 1.1
9     <sections>
10 swift 1.22
11 neysx 1.38 <version>1.32</version>
12     <date>2006-01-13</date>
13 swift 1.22
14 swift 1.1 <section>
15     <title>What are USE-flags?</title>
16     <subsection>
17     <title>The ideas behind USE-flags</title>
18     <body>
19    
20 swift 1.2 <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 swift 1.5 with KDE-support if those packages work flawlessly without?
33 swift 1.2 </p>
34    
35     <p>
36     To help users in deciding what to install/activate and what not, we wanted the
37 swift 1.10 user to specify his/her environment in an easy way. This forces the user into
38 swift 1.11 deciding what they really want and eases the process for Portage, our package
39 nightmorph 1.40 management system, to make useful decisions.
40 swift 1.2 </p>
41    
42 swift 1.1 </body>
43     </subsection>
44     <subsection>
45     <title>Definition of a USE-flag</title>
46     <body>
47    
48 swift 1.2 <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 swift 1.3 Portage will know that you want support for the chosen keyword. Of course
52 swift 1.2 this also alters the dependency information for a package.
53     </p>
54    
55     <p>
56 swift 1.6 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
57 swift 1.2 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 swift 1.1 </body>
71     </subsection>
72     <subsection>
73     <title>What USE-flags exist?</title>
74     <body>
75    
76 swift 1.2 <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 swift 1.8 A <e>local</e> USE-flag is used by a single package to make package-specific
87 swift 1.2 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 neysx 1.38 <path>/usr/portage/profiles/use.desc</path>.
95 swift 1.2 </p>
96    
97 swift 1.18 <p>
98     A list of available local USE-flags can be found locally in
99     <path>/usr/portage/profiles/use.local.desc</path>.
100     </p>
101    
102 swift 1.1 </body>
103     </subsection>
104     </section>
105     <section>
106     <title>Using USE-flags</title>
107     <subsection>
108     <title>Declare permanent USE-flags</title>
109     <body>
110    
111 swift 1.2 <p>
112     In the hope you are convinced of the importance of USE-flags we will now inform
113     you how to declare USE-flags.
114     </p>
115    
116     <p>
117     As previously mentioned, all USE-flags are declared inside the <c>USE</c>
118     variable. To make it easy for users to search and pick USE-flags, we already
119     provide a <e>default</e> USE setting. This setting is a collection of USE-flags
120     we think are commonly used by the Gentoo users. This default setting is declared
121 swift 1.28 in the <path>make.defaults</path> files part of your profile.
122 swift 1.2 </p>
123    
124 swift 1.28 <p>
125     The profile your system listens to is pointed to by the
126     <path>/etc/make.profile</path> symlink. Each profile works on top of another,
127     larger profile, the end result is therefore the sum of all profiles. The top
128     profile is the <path>base</path> profile
129     (<path>/usr/portage/profiles/base</path>).
130     </p>
131    
132     <p>
133 vapier 1.33 Let us take a look at this default setting for the 2004.3 profile:
134 swift 1.28 </p>
135    
136 vapier 1.33 <pre caption="Cumulative make.defaults USE variable for the 2004.3 profile">
137 swift 1.28 <comment>(This example is the sum of the settings in base, default-linux,
138     default-linux/x86 and default-linux/x86/2004.3)</comment>
139 cam 1.26 USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
140 neysx 1.38 foomaticdb gdbm gif gpm gtk imlib jpeg kde gnome libg++ libwww mad
141 cam 1.26 mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
142     quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
143 swift 1.2 </pre>
144    
145     <p>
146     As you can see, this variable already contains quite a lot of keywords. Do
147 swift 1.25 <b>not</b> alter any <path>make.defaults</path> file to tailor
148 swift 1.2 the <c>USE</c> variable to your needs: changes in this file will be undone when
149     you update Portage!
150     </p>
151    
152     <p>
153     To change this default setting, you need to add or remove keywords to the
154     <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
155     in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
156     require, or remove the USE-flags you don't want. This latter is done by
157     prefixing the keyword with the minus-sign ("-").
158     </p>
159    
160     <p>
161     For instance, to remove support for KDE and QT but add support for ldap, the
162     following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
163     </p>
164    
165     <pre caption="An example USE setting in /etc/make.conf">
166     USE="-kde -qt ldap"
167     </pre>
168    
169 swift 1.19 </body>
170     </subsection>
171     <subsection>
172     <title>Declaring USE flags for individual packages</title>
173     <body>
174    
175 swift 1.17 <p>
176     Sometimes you want to declare a certain USE flag for one (or a couple) of
177     applications but not system-wide. To accomplish this, you will need to create
178     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
179     <path>/etc/portage/package.use</path>.
180     </p>
181    
182     <p>
183     For instance, if you don't want <c>berkdb</c> support globally but you do want
184     it for <c>mysql</c>, you would add:
185     </p>
186    
187     <pre caption="/etc/portage/package.use example">
188     dev-db/mysql berkdb
189     </pre>
190    
191     <p>
192     You can of course also explicitly <e>disable</e> USE flags for a certain
193     application. For instance, if you don't want <c>java</c> support in PHP:
194     </p>
195    
196     <pre caption="/etc/portage/package.use 2nd example">
197     dev-php/php -java
198     </pre>
199    
200 swift 1.1 </body>
201     </subsection>
202     <subsection>
203     <title>Declare temporary USE-flags</title>
204     <body>
205    
206 swift 1.2 <p>
207     Sometimes you want to set a certain USE-setting only once. Instead of editing
208     <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
209 swift 1.17 declare the USE-variable as environment variable. Remember that, when you
210     re-emerge or update this application (either explicitly or as part of a system
211     update) your changes will be lost!
212 swift 1.2 </p>
213    
214     <p>
215     As an example we will temporarily remove java from the USE-setting
216     during the installation of mozilla.
217     </p>
218    
219 swift 1.13 <pre caption="Using USE as environment variable">
220 swift 1.2 # <i>USE="-java" emerge mozilla</i>
221     </pre>
222    
223 swift 1.1 </body>
224     </subsection>
225     <subsection>
226 vapier 1.31 <title>Automatic USE Flags</title>
227 swift 1.1 <body>
228    
229 swift 1.2 <p>
230 vapier 1.31 After certain packages are installed, additional USE flags will automatically
231     be enabled for you if you do not explicitly disable them. To view the list
232     of packages that trigger automatic USE-flags, check
233     <path>/etc/make.profile/use.defaults</path> and the <path>use.defaults</path>
234 swift 1.29 files of the parent profiles.
235 swift 1.2 </p>
236    
237     <pre caption="A snippet from /etc/make.profile/use.defaults">
238     gnome gnome-base/gnome
239     gtk x11-libs/gtk+
240     qt x11-libs/qt
241     kde kde-base/kdebase
242     motif x11-libs/openmotif
243     </pre>
244    
245     </body>
246     </subsection>
247     <subsection>
248 swift 1.15 <title>Precedence</title>
249 swift 1.2 <body>
250    
251     <p>
252 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
253 swift 1.32 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
254     <c>java</c> is still used due to a setting that has a higher priority.
255     The precedence for the USE setting is, ordered
256 swift 1.2 by priority (first has lowest priority):
257     </p>
258    
259     <ol>
260     <li>
261 swift 1.25 Default USE setting declared in the <path>make.defaults</path> files part of
262     your profile
263 swift 1.2 </li>
264     <li>
265 swift 1.37 Inherited USE setting if a package from profile <path>use.defaults</path>
266     is installed
267 swift 1.2 </li>
268     <li>
269     User-defined USE setting in <path>/etc/make.conf</path>
270     </li>
271     <li>
272 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
273     </li>
274     <li>
275 swift 1.2 User-defined USE setting as environment variable
276     </li>
277     </ol>
278 swift 1.4
279     <p>
280 cam 1.27 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
281     --info</c>. This will list all relevant variables (including the <c>USE</c>
282     variable) with the content used by Portage.
283 swift 1.4 </p>
284    
285 cam 1.27 <pre caption="Running emerge --info">
286     # <i>emerge --info</i>
287 swift 1.4 </pre>
288 swift 1.2
289 swift 1.1 </body>
290     </subsection>
291 swift 1.12 <subsection>
292     <title>Adapting your Entire System to New USE Flags</title>
293     <body>
294    
295     <p>
296     If you have altered your USE flags and you wish to update your entire system to
297 swift 1.21 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
298 swift 1.12 </p>
299    
300     <pre caption="Rebuilding your entire system">
301 swift 1.21 # <i>emerge --update --deep --newuse world</i>
302 swift 1.12 </pre>
303    
304     <p>
305 swift 1.20 Next, run Portage's depclean to remove the conditional dependencies that
306 swift 1.12 were emerged on your "old" system but that have been obsoleted by the new USE
307     flags.
308     </p>
309    
310     <warn>
311 cam 1.27 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
312 swift 1.12 with care. Double-check the provided list of "obsoleted" packages to make sure
313     it doesn't remove packages you need. In the following example we add the
314     <c>-p</c> switch to have depclean only list the packages without removing them.
315     </warn>
316    
317     <pre caption="Removing obsoleted packages">
318 cam 1.27 # <i>emerge -p --depclean</i>
319 swift 1.12 </pre>
320    
321     <p>
322 swift 1.21 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
323     applications that are dynamically linked against shared objects provided by
324     possibly removed packages. <c>revdep-rebuild</c> is part of the
325     <c>gentoolkit</c> package; don't forget to emerge it first.
326     </p>
327    
328     <pre caption="Running revdep-rebuild">
329     # <i>revdep-rebuild</i>
330     </pre>
331    
332     <p>
333     When all this is accomplished, your system is using the new USE flag settings.
334 swift 1.12 </p>
335    
336     </body>
337     </subsection>
338 swift 1.1 </section>
339     <section>
340     <title>Package specific USE-flags</title>
341     <subsection>
342 swift 1.2 <title>Viewing available USE-flags</title>
343 swift 1.1 <body>
344 swift 1.2
345     <p>
346     Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
347 swift 1.21 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
348     options:
349 swift 1.2 </p>
350    
351     <pre caption="Viewing the used USE-flags">
352     # <i>emerge --pretend --verbose mozilla</i>
353     These are the packages that I would merge, in order:
354    
355     Calculating dependencies ...done!
356 neysx 1.38 [ebuild R ] www-client/mozilla-1.7.12-r2 USE="crypt gnome java mozsvg ssl
357     truetype xprint -debug -ipv6 -ldap -mozcalendar -mozdevelop -moznocompose
358     -moznoirc -moznomail -moznoxft -postgres -xinerama" 0 kB
359 swift 1.2 </pre>
360    
361     <p>
362     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
363 swift 1.30 dedicated to package information called <c>equery</c> which resides in the
364 swift 1.2 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
365     </p>
366    
367     <pre caption="Installing gentoolkit">
368 swift 1.21 # <i>emerge gentoolkit</i>
369 swift 1.2 </pre>
370    
371     <p>
372 swift 1.30 Now run <c>equery</c> with the <c>uses</c> argument to view the USE-flags of a
373 swift 1.2 certain package. For instance, for the <c>gnumeric</c> package:
374     </p>
375    
376 swift 1.30 <pre caption="Using equery to view used USE-flags">
377     # <i>equery uses gnumeric</i>
378 swift 1.2 [ Colour Code : <i>set</i> <comment>unset</comment> ]
379     [ Legend : (U) Col 1 - Current USE flags ]
380     [ : (I) Col 2 - Installed With USE flags ]
381    
382     U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
383     - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
384     - - <comment>gnomedb</comment> : unknown
385     + + <i>python</i> : Adds support/bindings for the Python language
386     + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
387     </pre>
388 swift 1.1
389     </body>
390     </subsection>
391     </section>
392     </sections>

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