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#94049 - Improve wording on USE precendence

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     <!-- See http://creativecommons.org/licenses/by-sa/1.0 -->
6    
7 swift 1.32 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.31 2005/05/05 00:47:58 vapier Exp $ -->
8 swift 1.1
9     <sections>
10 swift 1.22
11 swift 1.32 <version>1.29</version>
12     <date>2005-05-27</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 swift 1.5 managment 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     <path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
95     snippet:
96     </p>
97    
98     <pre caption="A short snippet of available USE-flags">
99     gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
100     gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
101     gtkhtml - Adds support for gnome-extra/gtkhtml
102     guile - Adds support for dev-util/guile (interpreter for Scheme)
103     icc - Use the Intel C++ Compiler if the package supports it
104     icc-pgo - Enable PGO data generation or use when use icc.
105     imap - Adds support for IMAP
106     </pre>
107    
108 swift 1.18 <p>
109     A list of available local USE-flags can be found locally in
110     <path>/usr/portage/profiles/use.local.desc</path>.
111     </p>
112    
113 swift 1.1 </body>
114     </subsection>
115     </section>
116     <section>
117     <title>Using USE-flags</title>
118     <subsection>
119     <title>Declare permanent USE-flags</title>
120     <body>
121    
122 swift 1.2 <p>
123     In the hope you are convinced of the importance of USE-flags we will now inform
124     you how to declare USE-flags.
125     </p>
126    
127     <p>
128     As previously mentioned, all USE-flags are declared inside the <c>USE</c>
129     variable. To make it easy for users to search and pick USE-flags, we already
130     provide a <e>default</e> USE setting. This setting is a collection of USE-flags
131     we think are commonly used by the Gentoo users. This default setting is declared
132 swift 1.28 in the <path>make.defaults</path> files part of your profile.
133 swift 1.2 </p>
134    
135 swift 1.28 <p>
136     The profile your system listens to is pointed to by the
137     <path>/etc/make.profile</path> symlink. Each profile works on top of another,
138     larger profile, the end result is therefore the sum of all profiles. The top
139     profile is the <path>base</path> profile
140     (<path>/usr/portage/profiles/base</path>).
141     </p>
142    
143     <p>
144     Let us take a look at this default setting:
145     </p>
146    
147     <pre caption="Cumulated /usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
148     <comment>(This example is the sum of the settings in base, default-linux,
149     default-linux/x86 and default-linux/x86/2004.3)</comment>
150 cam 1.26 USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
151     foomaticdb gdbm gif gpm gtk gtk2 imlib jpeg kde gnome libg++ libwww mad
152     mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
153     quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
154 swift 1.2 </pre>
155    
156     <p>
157     As you can see, this variable already contains quite a lot of keywords. Do
158 swift 1.25 <b>not</b> alter any <path>make.defaults</path> file to tailor
159 swift 1.2 the <c>USE</c> variable to your needs: changes in this file will be undone when
160     you update Portage!
161     </p>
162    
163     <p>
164     To change this default setting, you need to add or remove keywords to the
165     <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
166     in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
167     require, or remove the USE-flags you don't want. This latter is done by
168     prefixing the keyword with the minus-sign ("-").
169     </p>
170    
171     <p>
172     For instance, to remove support for KDE and QT but add support for ldap, the
173     following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
174     </p>
175    
176     <pre caption="An example USE setting in /etc/make.conf">
177     USE="-kde -qt ldap"
178     </pre>
179    
180 swift 1.19 </body>
181     </subsection>
182     <subsection>
183     <title>Declaring USE flags for individual packages</title>
184     <body>
185    
186 swift 1.17 <p>
187     Sometimes you want to declare a certain USE flag for one (or a couple) of
188     applications but not system-wide. To accomplish this, you will need to create
189     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
190     <path>/etc/portage/package.use</path>.
191     </p>
192    
193     <p>
194     For instance, if you don't want <c>berkdb</c> support globally but you do want
195     it for <c>mysql</c>, you would add:
196     </p>
197    
198     <pre caption="/etc/portage/package.use example">
199     dev-db/mysql berkdb
200     </pre>
201    
202     <p>
203     You can of course also explicitly <e>disable</e> USE flags for a certain
204     application. For instance, if you don't want <c>java</c> support in PHP:
205     </p>
206    
207     <pre caption="/etc/portage/package.use 2nd example">
208     dev-php/php -java
209     </pre>
210    
211 swift 1.1 </body>
212     </subsection>
213     <subsection>
214     <title>Declare temporary USE-flags</title>
215     <body>
216    
217 swift 1.2 <p>
218     Sometimes you want to set a certain USE-setting only once. Instead of editing
219     <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
220 swift 1.17 declare the USE-variable as environment variable. Remember that, when you
221     re-emerge or update this application (either explicitly or as part of a system
222     update) your changes will be lost!
223 swift 1.2 </p>
224    
225     <p>
226     As an example we will temporarily remove java from the USE-setting
227     during the installation of mozilla.
228     </p>
229    
230 swift 1.13 <pre caption="Using USE as environment variable">
231 swift 1.2 # <i>USE="-java" emerge mozilla</i>
232     </pre>
233    
234 swift 1.1 </body>
235     </subsection>
236     <subsection>
237 vapier 1.31 <title>Automatic USE Flags</title>
238 swift 1.1 <body>
239    
240 swift 1.2 <p>
241 vapier 1.31 After certain packages are installed, additional USE flags will automatically
242     be enabled for you if you do not explicitly disable them. To view the list
243     of packages that trigger automatic USE-flags, check
244     <path>/etc/make.profile/use.defaults</path> and the <path>use.defaults</path>
245 swift 1.29 files of the parent profiles.
246 swift 1.2 </p>
247    
248     <pre caption="A snippet from /etc/make.profile/use.defaults">
249     gnome gnome-base/gnome
250     gtk x11-libs/gtk+
251     qt x11-libs/qt
252     kde kde-base/kdebase
253     motif x11-libs/openmotif
254     </pre>
255    
256     </body>
257     </subsection>
258     <subsection>
259 swift 1.15 <title>Precedence</title>
260 swift 1.2 <body>
261    
262     <p>
263 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
264 swift 1.32 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
265     <c>java</c> is still used due to a setting that has a higher priority.
266     The precedence for the USE setting is, ordered
267 swift 1.2 by priority (first has lowest priority):
268     </p>
269    
270     <ol>
271     <li>
272 swift 1.25 Default USE setting declared in the <path>make.defaults</path> files part of
273     your profile
274 swift 1.2 </li>
275     <li>
276     Inherited USE setting if a package from
277     <path>/etc/make.profile/use.defaults</path> is installed
278     </li>
279     <li>
280     User-defined USE setting in <path>/etc/make.conf</path>
281     </li>
282     <li>
283 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
284     </li>
285     <li>
286 swift 1.2 User-defined USE setting as environment variable
287     </li>
288     </ol>
289 swift 1.4
290     <p>
291 cam 1.27 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
292     --info</c>. This will list all relevant variables (including the <c>USE</c>
293     variable) with the content used by Portage.
294 swift 1.4 </p>
295    
296 cam 1.27 <pre caption="Running emerge --info">
297     # <i>emerge --info</i>
298 swift 1.4 </pre>
299 swift 1.2
300 swift 1.1 </body>
301     </subsection>
302 swift 1.12 <subsection>
303     <title>Adapting your Entire System to New USE Flags</title>
304     <body>
305    
306     <p>
307     If you have altered your USE flags and you wish to update your entire system to
308 swift 1.21 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
309 swift 1.12 </p>
310    
311     <pre caption="Rebuilding your entire system">
312 swift 1.21 # <i>emerge --update --deep --newuse world</i>
313 swift 1.12 </pre>
314    
315     <p>
316 swift 1.20 Next, run Portage's depclean to remove the conditional dependencies that
317 swift 1.12 were emerged on your "old" system but that have been obsoleted by the new USE
318     flags.
319     </p>
320    
321     <warn>
322 cam 1.27 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
323 swift 1.12 with care. Double-check the provided list of "obsoleted" packages to make sure
324     it doesn't remove packages you need. In the following example we add the
325     <c>-p</c> switch to have depclean only list the packages without removing them.
326     </warn>
327    
328     <pre caption="Removing obsoleted packages">
329 cam 1.27 # <i>emerge -p --depclean</i>
330 swift 1.12 </pre>
331    
332     <p>
333 swift 1.21 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
334     applications that are dynamically linked against shared objects provided by
335     possibly removed packages. <c>revdep-rebuild</c> is part of the
336     <c>gentoolkit</c> package; don't forget to emerge it first.
337     </p>
338    
339     <pre caption="Running revdep-rebuild">
340     # <i>revdep-rebuild</i>
341     </pre>
342    
343     <p>
344     When all this is accomplished, your system is using the new USE flag settings.
345 swift 1.12 </p>
346    
347     </body>
348     </subsection>
349 swift 1.1 </section>
350     <section>
351     <title>Package specific USE-flags</title>
352     <subsection>
353 swift 1.2 <title>Viewing available USE-flags</title>
354 swift 1.1 <body>
355 swift 1.2
356     <p>
357     Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
358 swift 1.21 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
359     options:
360 swift 1.2 </p>
361    
362     <pre caption="Viewing the used USE-flags">
363     # <i>emerge --pretend --verbose mozilla</i>
364     These are the packages that I would merge, in order:
365    
366     Calculating dependencies ...done!
367     [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
368     +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
369     -moznocompose -moznoxft
370     </pre>
371    
372     <p>
373     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
374 swift 1.30 dedicated to package information called <c>equery</c> which resides in the
375 swift 1.2 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
376     </p>
377    
378     <pre caption="Installing gentoolkit">
379 swift 1.21 # <i>emerge gentoolkit</i>
380 swift 1.2 </pre>
381    
382     <p>
383 swift 1.30 Now run <c>equery</c> with the <c>uses</c> argument to view the USE-flags of a
384 swift 1.2 certain package. For instance, for the <c>gnumeric</c> package:
385     </p>
386    
387 swift 1.30 <pre caption="Using equery to view used USE-flags">
388     # <i>equery uses gnumeric</i>
389 swift 1.2 [ Colour Code : <i>set</i> <comment>unset</comment> ]
390     [ Legend : (U) Col 1 - Current USE flags ]
391     [ : (I) Col 2 - Installed With USE flags ]
392    
393     U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
394     - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
395     - - <comment>gnomedb</comment> : unknown
396     + + <i>python</i> : Adds support/bindings for the Python language
397     + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
398     </pre>
399 swift 1.1
400     </body>
401     </subsection>
402     </section>
403     </sections>

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