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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 neysx 1.44 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.43 2006/10/08 19:38:11 nightmorph Exp $ -->
8 swift 1.1
9     <sections>
10 swift 1.22
11 neysx 1.44 <abstract>
12     USE-flags are a very important aspect of Gentoo. In this chapter, you learn to
13     work with USE-flags and understand how USE-flags interact with your system.
14     </abstract>
15    
16 nightmorph 1.43 <version>1.35</version>
17     <date>2006-10-08</date>
18 swift 1.22
19 swift 1.1 <section>
20     <title>What are USE-flags?</title>
21     <subsection>
22     <title>The ideas behind USE-flags</title>
23     <body>
24    
25 swift 1.2 <p>
26     When you are installing Gentoo (or any other distribution, or even operating
27     system for that matter) you make choices depending on the environment you are
28     working with. A setup for a server differs from a setup for a workstation.
29     A gaming workstation differs from a 3D rendering workstation.
30     </p>
31    
32     <p>
33     This is not only true for choosing what packages you want to install, but also
34     what features a certain package should support. If you don't need OpenGL, why
35     would you bother installing OpenGL and build OpenGL support in most of your
36     packages? If you don't want to use KDE, why would you bother compiling packages
37 swift 1.5 with KDE-support if those packages work flawlessly without?
38 swift 1.2 </p>
39    
40     <p>
41     To help users in deciding what to install/activate and what not, we wanted the
42 swift 1.10 user to specify his/her environment in an easy way. This forces the user into
43 swift 1.11 deciding what they really want and eases the process for Portage, our package
44 nightmorph 1.40 management system, to make useful decisions.
45 swift 1.2 </p>
46    
47 swift 1.1 </body>
48     </subsection>
49     <subsection>
50     <title>Definition of a USE-flag</title>
51     <body>
52    
53 swift 1.2 <p>
54     Enter the USE-flags. Such a flag is a keyword that embodies support and
55     dependency-information for a certain concept. If you define a certain USE-flag,
56 swift 1.3 Portage will know that you want support for the chosen keyword. Of course
57 swift 1.2 this also alters the dependency information for a package.
58     </p>
59    
60     <p>
61 swift 1.6 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
62 swift 1.2 have this keyword in your <c>USE</c> variable, all packages that have
63     <e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
64     packages that have an <e>optional</e> KDE dependency will be installed
65     <e>without</e> installing the KDE libraries (as dependency). If you have defined
66     the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
67     support, and the KDE libraries will be installed as dependency.
68     </p>
69    
70     <p>
71     By correctly defining the keywords you will receive a system tailored
72     specifically to your needs.
73     </p>
74    
75 swift 1.1 </body>
76     </subsection>
77     <subsection>
78     <title>What USE-flags exist?</title>
79     <body>
80    
81 swift 1.2 <p>
82     There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
83     </p>
84    
85     <ul>
86     <li>
87     A <e>global</e> USE-flag is used by several packages, system-wide. This is
88     what most people see as USE-flags.
89     </li>
90     <li>
91 swift 1.8 A <e>local</e> USE-flag is used by a single package to make package-specific
92 swift 1.2 decisions.
93     </li>
94     </ul>
95    
96     <p>
97     A list of available global USE-flags can be found <uri
98     link="/dyn/use-index.xml">online</uri> or locally in
99 neysx 1.38 <path>/usr/portage/profiles/use.desc</path>.
100 swift 1.2 </p>
101    
102 swift 1.18 <p>
103     A list of available local USE-flags can be found locally in
104     <path>/usr/portage/profiles/use.local.desc</path>.
105     </p>
106    
107 swift 1.1 </body>
108     </subsection>
109     </section>
110     <section>
111     <title>Using USE-flags</title>
112     <subsection>
113     <title>Declare permanent USE-flags</title>
114     <body>
115    
116 swift 1.2 <p>
117     In the hope you are convinced of the importance of USE-flags we will now inform
118     you how to declare USE-flags.
119     </p>
120    
121     <p>
122     As previously mentioned, all USE-flags are declared inside the <c>USE</c>
123     variable. To make it easy for users to search and pick USE-flags, we already
124     provide a <e>default</e> USE setting. This setting is a collection of USE-flags
125     we think are commonly used by the Gentoo users. This default setting is declared
126 swift 1.28 in the <path>make.defaults</path> files part of your profile.
127 swift 1.2 </p>
128    
129 swift 1.28 <p>
130     The profile your system listens to is pointed to by the
131     <path>/etc/make.profile</path> symlink. Each profile works on top of another,
132     larger profile, the end result is therefore the sum of all profiles. The top
133     profile is the <path>base</path> profile
134     (<path>/usr/portage/profiles/base</path>).
135     </p>
136    
137     <p>
138 vapier 1.33 Let us take a look at this default setting for the 2004.3 profile:
139 swift 1.28 </p>
140    
141 vapier 1.33 <pre caption="Cumulative make.defaults USE variable for the 2004.3 profile">
142 swift 1.28 <comment>(This example is the sum of the settings in base, default-linux,
143     default-linux/x86 and default-linux/x86/2004.3)</comment>
144 cam 1.26 USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
145 neysx 1.38 foomaticdb gdbm gif gpm gtk imlib jpeg kde gnome libg++ libwww mad
146 cam 1.26 mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
147     quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
148 swift 1.2 </pre>
149    
150     <p>
151     As you can see, this variable already contains quite a lot of keywords. Do
152 swift 1.25 <b>not</b> alter any <path>make.defaults</path> file to tailor
153 swift 1.2 the <c>USE</c> variable to your needs: changes in this file will be undone when
154     you update Portage!
155     </p>
156    
157     <p>
158     To change this default setting, you need to add or remove keywords to the
159     <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
160     in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
161     require, or remove the USE-flags you don't want. This latter is done by
162     prefixing the keyword with the minus-sign ("-").
163     </p>
164    
165     <p>
166     For instance, to remove support for KDE and QT but add support for ldap, the
167     following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
168     </p>
169    
170     <pre caption="An example USE setting in /etc/make.conf">
171 nightmorph 1.43 USE="-kde -qt3 -qt4 ldap"
172 swift 1.2 </pre>
173    
174 swift 1.19 </body>
175     </subsection>
176     <subsection>
177     <title>Declaring USE flags for individual packages</title>
178     <body>
179    
180 swift 1.17 <p>
181     Sometimes you want to declare a certain USE flag for one (or a couple) of
182     applications but not system-wide. To accomplish this, you will need to create
183     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
184     <path>/etc/portage/package.use</path>.
185     </p>
186    
187     <p>
188     For instance, if you don't want <c>berkdb</c> support globally but you do want
189     it for <c>mysql</c>, you would add:
190     </p>
191    
192     <pre caption="/etc/portage/package.use example">
193     dev-db/mysql berkdb
194     </pre>
195    
196     <p>
197     You can of course also explicitly <e>disable</e> USE flags for a certain
198     application. For instance, if you don't want <c>java</c> support in PHP:
199     </p>
200    
201     <pre caption="/etc/portage/package.use 2nd example">
202     dev-php/php -java
203     </pre>
204    
205 swift 1.1 </body>
206     </subsection>
207     <subsection>
208     <title>Declare temporary USE-flags</title>
209     <body>
210    
211 swift 1.2 <p>
212     Sometimes you want to set a certain USE-setting only once. Instead of editing
213     <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
214 swift 1.17 declare the USE-variable as environment variable. Remember that, when you
215     re-emerge or update this application (either explicitly or as part of a system
216     update) your changes will be lost!
217 swift 1.2 </p>
218    
219     <p>
220     As an example we will temporarily remove java from the USE-setting
221     during the installation of mozilla.
222     </p>
223    
224 swift 1.13 <pre caption="Using USE as environment variable">
225 swift 1.2 # <i>USE="-java" emerge mozilla</i>
226     </pre>
227    
228 swift 1.1 </body>
229     </subsection>
230     <subsection>
231 swift 1.15 <title>Precedence</title>
232 swift 1.2 <body>
233    
234     <p>
235 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
236 swift 1.32 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
237     <c>java</c> is still used due to a setting that has a higher priority.
238     The precedence for the USE setting is, ordered
239 swift 1.2 by priority (first has lowest priority):
240     </p>
241    
242     <ol>
243     <li>
244 swift 1.25 Default USE setting declared in the <path>make.defaults</path> files part of
245     your profile
246 swift 1.2 </li>
247     <li>
248     User-defined USE setting in <path>/etc/make.conf</path>
249     </li>
250     <li>
251 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
252     </li>
253     <li>
254 swift 1.2 User-defined USE setting as environment variable
255     </li>
256     </ol>
257 swift 1.4
258     <p>
259 cam 1.27 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
260     --info</c>. This will list all relevant variables (including the <c>USE</c>
261     variable) with the content used by Portage.
262 swift 1.4 </p>
263    
264 cam 1.27 <pre caption="Running emerge --info">
265     # <i>emerge --info</i>
266 swift 1.4 </pre>
267 swift 1.2
268 swift 1.1 </body>
269     </subsection>
270 swift 1.12 <subsection>
271     <title>Adapting your Entire System to New USE Flags</title>
272     <body>
273    
274     <p>
275     If you have altered your USE flags and you wish to update your entire system to
276 swift 1.21 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
277 swift 1.12 </p>
278    
279     <pre caption="Rebuilding your entire system">
280 swift 1.21 # <i>emerge --update --deep --newuse world</i>
281 swift 1.12 </pre>
282    
283     <p>
284 swift 1.20 Next, run Portage's depclean to remove the conditional dependencies that
285 swift 1.12 were emerged on your "old" system but that have been obsoleted by the new USE
286     flags.
287     </p>
288    
289     <warn>
290 cam 1.27 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
291 swift 1.12 with care. Double-check the provided list of "obsoleted" packages to make sure
292     it doesn't remove packages you need. In the following example we add the
293     <c>-p</c> switch to have depclean only list the packages without removing them.
294     </warn>
295    
296     <pre caption="Removing obsoleted packages">
297 cam 1.27 # <i>emerge -p --depclean</i>
298 swift 1.12 </pre>
299    
300     <p>
301 swift 1.21 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
302     applications that are dynamically linked against shared objects provided by
303     possibly removed packages. <c>revdep-rebuild</c> is part of the
304     <c>gentoolkit</c> package; don't forget to emerge it first.
305     </p>
306    
307     <pre caption="Running revdep-rebuild">
308     # <i>revdep-rebuild</i>
309     </pre>
310    
311     <p>
312     When all this is accomplished, your system is using the new USE flag settings.
313 swift 1.12 </p>
314    
315     </body>
316     </subsection>
317 swift 1.1 </section>
318     <section>
319     <title>Package specific USE-flags</title>
320     <subsection>
321 swift 1.2 <title>Viewing available USE-flags</title>
322 swift 1.1 <body>
323 swift 1.2
324     <p>
325     Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
326 swift 1.21 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
327     options:
328 swift 1.2 </p>
329    
330     <pre caption="Viewing the used USE-flags">
331     # <i>emerge --pretend --verbose mozilla</i>
332     These are the packages that I would merge, in order:
333    
334     Calculating dependencies ...done!
335 neysx 1.38 [ebuild R ] www-client/mozilla-1.7.12-r2 USE="crypt gnome java mozsvg ssl
336     truetype xprint -debug -ipv6 -ldap -mozcalendar -mozdevelop -moznocompose
337     -moznoirc -moznomail -moznoxft -postgres -xinerama" 0 kB
338 swift 1.2 </pre>
339    
340     <p>
341     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
342 swift 1.30 dedicated to package information called <c>equery</c> which resides in the
343 swift 1.2 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
344     </p>
345    
346     <pre caption="Installing gentoolkit">
347 swift 1.21 # <i>emerge gentoolkit</i>
348 swift 1.2 </pre>
349    
350     <p>
351 swift 1.30 Now run <c>equery</c> with the <c>uses</c> argument to view the USE-flags of a
352 swift 1.2 certain package. For instance, for the <c>gnumeric</c> package:
353     </p>
354    
355 swift 1.30 <pre caption="Using equery to view used USE-flags">
356 rane 1.42 # <i>equery uses =gnumeric-1.6.3 -a</i>
357     [ Searching for packages matching =gnumeric-1.6.3... ]
358     [ Colour Code : <comment>set</comment> <i>unset</i> ]
359     [ Legend : Left column (U) - USE flags from make.conf ]
360     [ : Right column (I) - USE flags packages was installed with ]
361     [ Found these USE variables for app-office/gnumeric-1.6.3 ]
362     U I
363     - - <i>debug</i> : Tells configure and the makefiles to build for debugging.
364     Effects vary across packages, but generally it will at
365     least add -g to CFLAGS. Remember to set FEATURES=nostrip too
366     - - <i>gnome</i> : Adds GNOME support
367     + + <comment>python</comment> : Adds support/bindings for the Python language
368     - - <i>static</i> : !!do not set this during bootstrap!! Causes binaries to be
369     statically linked instead of dynamically
370 swift 1.2 </pre>
371 swift 1.1
372     </body>
373     </subsection>
374     </section>
375     </sections>

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