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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 1.51 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.50 2010/06/07 09:20:00 nightmorph Exp $ -->
8 swift 1.1
9     <sections>
10 swift 1.22
11 neysx 1.44 <abstract>
12 nightmorph 1.46 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 neysx 1.44 </abstract>
15    
16 nightmorph 1.51 <version>2</version>
17     <date>2012-07-08</date>
18 swift 1.22
19 swift 1.1 <section>
20 nightmorph 1.46 <title>What are USE flags?</title>
21 swift 1.1 <subsection>
22 nightmorph 1.46 <title>The ideas behind USE flags</title>
23 swift 1.1 <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 nightmorph 1.46 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 nightmorph 1.46 <title>Definition of a USE flag</title>
51 swift 1.1 <body>
52    
53 swift 1.2 <p>
54 nightmorph 1.46 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 nightmorph 1.46 <title>What USE flags exist?</title>
79 swift 1.1 <body>
80    
81 swift 1.2 <p>
82 nightmorph 1.46 There are two types of USE flags: <e>global</e> and <e>local</e> USE flags.
83 swift 1.2 </p>
84    
85     <ul>
86     <li>
87 nightmorph 1.46 A <e>global</e> USE flag is used by several packages, system-wide. This is
88     what most people see as USE flags.
89 swift 1.2 </li>
90     <li>
91 nightmorph 1.46 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 nightmorph 1.46 A list of available global USE flags can be found <uri
98 swift 1.2 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 nightmorph 1.46 A list of available local USE flags can be found locally in
104 swift 1.18 <path>/usr/portage/profiles/use.local.desc</path>.
105     </p>
106    
107 swift 1.1 </body>
108     </subsection>
109     </section>
110     <section>
111 nightmorph 1.46 <title>Using USE flags</title>
112 swift 1.1 <subsection>
113 nightmorph 1.46 <title>Declare permanent USE flags</title>
114 swift 1.1 <body>
115    
116 swift 1.2 <p>
117 nightmorph 1.46 In the hope you are convinced of the importance of USE flags we will now inform
118     you how to declare USE flags.
119 swift 1.2 </p>
120    
121     <p>
122 nightmorph 1.46 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 swift 1.2 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 nightmorph 1.50 Let us take a look at this default setting for the 10.0 profile:
139 swift 1.28 </p>
140    
141 nightmorph 1.50 <pre caption="Cumulative make.defaults USE variable for the 10.0 profile">
142     <comment>(This example is the sum of the settings in base, default/linux,
143     default/linux/x86 and default/linux/x86/10.0/)</comment>
144     USE="a52 aac acpi alsa branding cairo cdr dbus dts dvd dvdr emboss encode exif
145     fam firefox flac gif gpm gtk hal jpeg lcms ldap libnotify mad mikmod mng mp3
146     mp4 mpeg ogg opengl pango pdf png ppds qt3support qt4 sdl spell
147 nightmorph 1.51 startup-notification svg tiff truetype vorbis unicode usb X xcb x264 xml xv
148     xvid"
149 swift 1.2 </pre>
150    
151     <p>
152     As you can see, this variable already contains quite a lot of keywords. Do
153 swift 1.25 <b>not</b> alter any <path>make.defaults</path> file to tailor
154 swift 1.2 the <c>USE</c> variable to your needs: changes in this file will be undone when
155     you update Portage!
156     </p>
157    
158     <p>
159     To change this default setting, you need to add or remove keywords to the
160     <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
161 nightmorph 1.46 in <path>/etc/make.conf</path>. In this variable you add the extra USE flags you
162     require, or remove the USE flags you don't want. This latter is done by
163 swift 1.2 prefixing the keyword with the minus-sign ("-").
164     </p>
165    
166     <p>
167     For instance, to remove support for KDE and QT but add support for ldap, the
168     following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
169     </p>
170    
171     <pre caption="An example USE setting in /etc/make.conf">
172 nightmorph 1.50 USE="-kde -qt4 ldap"
173 swift 1.2 </pre>
174    
175 swift 1.19 </body>
176     </subsection>
177     <subsection>
178     <title>Declaring USE flags for individual packages</title>
179     <body>
180    
181 swift 1.17 <p>
182     Sometimes you want to declare a certain USE flag for one (or a couple) of
183     applications but not system-wide. To accomplish this, you will need to create
184     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
185 nightmorph 1.49 <path>/etc/portage/package.use</path>. This is usually a single file, but can
186     also be a directory; see <c>man portage</c> for more information. The following
187     examples assume <path>package.use</path> is a single file.
188 swift 1.17 </p>
189    
190     <p>
191     For instance, if you don't want <c>berkdb</c> support globally but you do want
192     it for <c>mysql</c>, you would add:
193     </p>
194    
195     <pre caption="/etc/portage/package.use example">
196     dev-db/mysql berkdb
197     </pre>
198    
199     <p>
200     You can of course also explicitly <e>disable</e> USE flags for a certain
201     application. For instance, if you don't want <c>java</c> support in PHP:
202     </p>
203    
204     <pre caption="/etc/portage/package.use 2nd example">
205     dev-php/php -java
206     </pre>
207    
208 swift 1.1 </body>
209     </subsection>
210     <subsection>
211 nightmorph 1.46 <title>Declare temporary USE flags</title>
212 swift 1.1 <body>
213    
214 swift 1.2 <p>
215 nightmorph 1.46 Sometimes you want to set a certain USE setting only once. Instead of editing
216     <path>/etc/make.conf</path> twice (to do and undo the USE changes) you can just
217     declare the USE variable as environment variable. Remember that, when you
218 swift 1.17 re-emerge or update this application (either explicitly or as part of a system
219     update) your changes will be lost!
220 swift 1.2 </p>
221    
222     <p>
223 nightmorph 1.46 As an example we will temporarily remove java from the USE setting
224 nightmorph 1.45 during the installation of seamonkey.
225 swift 1.2 </p>
226    
227 swift 1.13 <pre caption="Using USE as environment variable">
228 nightmorph 1.45 # <i>USE="-java" emerge seamonkey</i>
229 swift 1.2 </pre>
230    
231 swift 1.1 </body>
232     </subsection>
233     <subsection>
234 swift 1.15 <title>Precedence</title>
235 swift 1.2 <body>
236    
237     <p>
238 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
239 swift 1.32 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
240     <c>java</c> is still used due to a setting that has a higher priority.
241     The precedence for the USE setting is, ordered
242 swift 1.2 by priority (first has lowest priority):
243     </p>
244    
245     <ol>
246     <li>
247 swift 1.25 Default USE setting declared in the <path>make.defaults</path> files part of
248     your profile
249 swift 1.2 </li>
250     <li>
251     User-defined USE setting in <path>/etc/make.conf</path>
252     </li>
253     <li>
254 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
255     </li>
256     <li>
257 swift 1.2 User-defined USE setting as environment variable
258     </li>
259     </ol>
260 swift 1.4
261     <p>
262 cam 1.27 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
263     --info</c>. This will list all relevant variables (including the <c>USE</c>
264     variable) with the content used by Portage.
265 swift 1.4 </p>
266    
267 cam 1.27 <pre caption="Running emerge --info">
268     # <i>emerge --info</i>
269 swift 1.4 </pre>
270 swift 1.2
271 swift 1.1 </body>
272     </subsection>
273 swift 1.12 <subsection>
274     <title>Adapting your Entire System to New USE Flags</title>
275     <body>
276    
277     <p>
278     If you have altered your USE flags and you wish to update your entire system to
279 swift 1.21 use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
280 swift 1.12 </p>
281    
282     <pre caption="Rebuilding your entire system">
283 swift 1.21 # <i>emerge --update --deep --newuse world</i>
284 swift 1.12 </pre>
285    
286     <p>
287 swift 1.20 Next, run Portage's depclean to remove the conditional dependencies that
288 swift 1.12 were emerged on your "old" system but that have been obsoleted by the new USE
289     flags.
290     </p>
291    
292     <warn>
293 cam 1.27 Running <c>emerge --depclean</c> is a dangerous operation and should be handled
294 swift 1.12 with care. Double-check the provided list of "obsoleted" packages to make sure
295     it doesn't remove packages you need. In the following example we add the
296     <c>-p</c> switch to have depclean only list the packages without removing them.
297     </warn>
298    
299     <pre caption="Removing obsoleted packages">
300 cam 1.27 # <i>emerge -p --depclean</i>
301 swift 1.12 </pre>
302    
303     <p>
304 swift 1.21 When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
305     applications that are dynamically linked against shared objects provided by
306     possibly removed packages. <c>revdep-rebuild</c> is part of the
307     <c>gentoolkit</c> package; don't forget to emerge it first.
308     </p>
309    
310     <pre caption="Running revdep-rebuild">
311     # <i>revdep-rebuild</i>
312     </pre>
313    
314     <p>
315     When all this is accomplished, your system is using the new USE flag settings.
316 swift 1.12 </p>
317    
318     </body>
319     </subsection>
320 swift 1.1 </section>
321     <section>
322 nightmorph 1.46 <title>Package specific USE flags</title>
323 swift 1.1 <subsection>
324 nightmorph 1.46 <title>Viewing available USE flags</title>
325 swift 1.1 <body>
326 swift 1.2
327     <p>
328 nightmorph 1.46 Let us take the example of <c>seamonkey</c>: what USE flags does it listen to? To
329 swift 1.21 find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
330     options:
331 swift 1.2 </p>
332    
333 nightmorph 1.46 <pre caption="Viewing the used USE flags">
334 nightmorph 1.45 # <i>emerge --pretend --verbose seamonkey</i>
335 swift 1.2 These are the packages that I would merge, in order:
336    
337     Calculating dependencies ...done!
338 nightmorph 1.45 [ebuild R ] www-client/seamonkey-1.0.7 USE="crypt gnome java -debug -ipv6
339     -ldap -mozcalendar -mozdevelop -moznocompose -moznoirc -moznomail -moznopango
340     -moznoroaming -postgres -xinerama -xprint" 0 kB
341 swift 1.2 </pre>
342    
343     <p>
344     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
345 swift 1.30 dedicated to package information called <c>equery</c> which resides in the
346 swift 1.2 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
347     </p>
348    
349     <pre caption="Installing gentoolkit">
350 swift 1.21 # <i>emerge gentoolkit</i>
351 swift 1.2 </pre>
352    
353     <p>
354 nightmorph 1.46 Now run <c>equery</c> with the <c>uses</c> argument to view the USE flags of a
355 swift 1.2 certain package. For instance, for the <c>gnumeric</c> package:
356     </p>
357    
358 nightmorph 1.46 <pre caption="Using equery to view used USE flags">
359 neysx 1.48 # <i>equery --nocolor uses =gnumeric-1.6.3 -a</i>
360 rane 1.42 [ Searching for packages matching =gnumeric-1.6.3... ]
361 neysx 1.48 [ Colour Code : set unset ]
362     [ Legend : Left column (U) - USE flags from make.conf ]
363     [ : Right column (I) - USE flags packages was installed with ]
364 rane 1.42 [ Found these USE variables for app-office/gnumeric-1.6.3 ]
365     U I
366 neysx 1.48 - - debug : Enable extra debug codepaths, like asserts and extra output.
367     If you want to get meaningful backtraces see
368     http://www.gentoo.org/proj/en/qa/backtraces.xml .
369     + + gnome : Adds GNOME support
370     + + python : Adds support/bindings for the Python language
371     - - static : !!do not set this during bootstrap!! Causes binaries to be
372     statically linked instead of dynamically
373 swift 1.2 </pre>
374 swift 1.1
375     </body>
376     </subsection>
377     </section>
378     </sections>

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