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1<?xml version='1.0' encoding='UTF-8'?>
2<!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
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4<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.1 2003/11/20 10:52:35 swift Exp $ --> 7<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.53 2013/02/09 08:46:08 swift Exp $ -->
5 8
6<sections> 9<sections>
10
11<abstract>
12USE flags are a very important aspect of Gentoo. In this chapter, you learn to
13work with USE flags and understand how USE flags interact with your system.
14</abstract>
15
16<version>4</version>
17<date>2013-02-09</date>
18
7<section> 19<section>
8<title>What are USE-flags?</title> 20<title>What are USE flags?</title>
9<subsection> 21<subsection>
10<title>The ideas behind USE-flags</title> 22<title>The ideas behind USE flags</title>
11<body>
12
13</body> 23<body>
14</subsection> 24
25<p>
26When you are installing Gentoo (or any other distribution, or even operating
27system for that matter) you make choices depending on the environment you are
28working with. A setup for a server differs from a setup for a workstation.
29A gaming workstation differs from a 3D rendering workstation.
30</p>
31
32<p>
33This is not only true for choosing what packages you want to install, but also
34what features a certain package should support. If you don't need OpenGL, why
35would you bother installing OpenGL and build OpenGL support in most of your
36packages? If you don't want to use KDE, why would you bother compiling packages
37with KDE support if those packages work flawlessly without?
38</p>
39
40<p>
41To help users in deciding what to install/activate and what not, we wanted the
42user to specify his/her environment in an easy way. This forces the user into
43deciding what they really want and eases the process for Portage, our package
44management system, to make useful decisions.
45</p>
46
47</body>
15<subsection> 48</subsection>
49<subsection>
16<title>Definition of a USE-flag</title> 50<title>Definition of a USE flag</title>
17<body>
18
19</body> 51<body>
20</subsection> 52
53<p>
54Enter the USE flags. Such a flag is a keyword that embodies support and
55dependency-information for a certain concept. If you define a certain USE flag,
56Portage will know that you want support for the chosen keyword. Of course
57this also alters the dependency information for a package.
58</p>
59
60<p>
61Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
62have 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
64packages 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
66the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
67support, and the KDE libraries will be installed as dependency.
68</p>
69
70<p>
71By correctly defining the keywords you will receive a system tailored
72specifically to your needs.
73</p>
74
75</body>
21<subsection> 76</subsection>
77<subsection>
22<title>What USE-flags exist?</title> 78<title>What USE flags exist?</title>
23<body> 79<body>
80
81<p>
82There 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 A <e>local</e> USE flag is used by a single package to make package-specific
92 decisions.
93 </li>
94</ul>
95
96<p>
97A list of available global USE flags can be found <uri
98link="/dyn/use-index.xml">online</uri> or locally in
99<path>/usr/portage/profiles/use.desc</path>.
100</p>
101
102<p>
103A list of available local USE flags can be found locally in
104<path>/usr/portage/profiles/use.local.desc</path>.
105</p>
24 106
25</body> 107</body>
26</subsection> 108</subsection>
27</section> 109</section>
28<section> 110<section>
29<title>Using USE-flags</title> 111<title>Using USE flags</title>
30<subsection> 112<subsection>
31<title>Declare permanent USE-flags</title> 113<title>Declare permanent USE flags</title>
32<body>
33
34</body> 114<body>
35</subsection> 115
116<p>
117In the hope you are convinced of the importance of USE flags we will now inform
118you how to declare USE flags.
119</p>
120
121<p>
122As previously mentioned, all USE flags are declared inside the <c>USE</c>
123variable. To make it easy for users to search and pick USE flags, we already
124provide a <e>default</e> USE setting. This setting is a collection of USE flags
125we think are commonly used by the Gentoo users. This default setting is declared
126in the <path>make.defaults</path> files part of your profile.
127</p>
128
129<p>
130The profile your system listens to is pointed to by the
131<path>/etc/portage/make.profile</path> symlink. Each profile works on top of
132another, larger profile, the end result is therefore the sum of all profiles.
133The top profile is the <path>base</path> profile
134(<path>/usr/portage/profiles/base</path>).
135</p>
136
137<p>
138Let us take a look at this default setting for the 13.0 profile:
139</p>
140
141<pre caption="Cumulative make.defaults USE variable for the 13.0 profile">
142<comment>(This example is the sum of the settings in base, default/linux,
143 default/linux/x86 and default/linux/x86/13.0/)</comment>
144USE="a52 aac acpi alsa branding cairo cdr dbus dts dvd dvdr emboss encode exif
145fam firefox flac gif gpm gtk hal jpeg lcms ldap libnotify mad mikmod mng mp3
146mp4 mpeg ogg opengl pango pdf png ppds qt3support qt4 sdl spell
147startup-notification svg tiff truetype vorbis unicode usb X xcb x264 xml xv
148xvid"
149</pre>
150
151<p>
152As you can see, this variable already contains quite a lot of keywords. Do
153<b>not</b> alter any <path>make.defaults</path> file to tailor
154the <c>USE</c> variable to your needs: changes in this file will be undone when
155you update Portage!
156</p>
157
158<p>
159To 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
161in <path>/etc/portage/make.conf</path>. In this variable you add the extra USE
162flags you require, or remove the USE flags you don't want. This latter is done
163by prefixing the keyword with the minus-sign ("-").
164</p>
165
166<p>
167For instance, to remove support for KDE and QT but add support for ldap, the
168following <c>USE</c> can be defined in <path>/etc/portage/make.conf</path>:
169</p>
170
171<pre caption="An example USE setting in /etc/portage/make.conf">
172USE="-kde -qt4 ldap"
173</pre>
174
175</body>
36<subsection> 176</subsection>
177<subsection>
178<title>Declaring USE flags for individual packages</title>
179<body>
180
181<p>
182Sometimes you want to declare a certain USE flag for one (or a couple) of
183applications but not system-wide. To accomplish this, you will need to create
184the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
185<path>/etc/portage/package.use</path>. This is usually a single file, but can
186also be a directory; see <c>man portage</c> for more information. The following
187examples assume <path>package.use</path> is a single file.
188</p>
189
190<p>
191For instance, if you don't want <c>berkdb</c> support globally but you do want
192it for <c>mysql</c>, you would add:
193</p>
194
195<pre caption="/etc/portage/package.use example">
196dev-db/mysql berkdb
197</pre>
198
199<p>
200You can of course also explicitly <e>disable</e> USE flags for a certain
201application. 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">
205dev-php/php -java
206</pre>
207
208</body>
209</subsection>
210<subsection>
37<title>Declare temporary USE-flags</title> 211<title>Declare temporary USE flags</title>
38<body>
39
40</body> 212<body>
41</subsection> 213
214<p>
215Sometimes you want to set a certain USE setting only once. Instead of editing
216<path>/etc/portage/make.conf</path> twice (to do and undo the USE changes) you
217can just declare the USE variable as environment variable. Remember that, when
218you re-emerge or update this application (either explicitly or as part of a
219system update) your changes will be lost!
220</p>
221
222<p>
223As an example we will temporarily remove java from the USE setting
224during the installation of seamonkey.
225</p>
226
227<pre caption="Using USE as environment variable">
228# <i>USE="-java" emerge seamonkey</i>
229</pre>
230
231</body>
42<subsection> 232</subsection>
43<title>Inheriting USE-flags</title> 233<subsection>
234<title>Precedence</title>
235<body>
236
237<p>
238Of course there is a certain precedence on what setting has priority over the
239USE 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.
241The precedence for the USE setting is, ordered
242by priority (first has lowest priority):
243</p>
244
245<ol>
246 <li>
247 Default USE setting declared in the <path>make.defaults</path> files part of
248 your profile
249 </li>
250 <li>
251 User-defined USE setting in <path>/etc/portage/make.conf</path>
252 </li>
253 <li>
254 User-defined USE setting in <path>/etc/portage/package.use</path>
255 </li>
256 <li>
257 User-defined USE setting as environment variable
258 </li>
259</ol>
260
261<p>
262To 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>
264variable) with the content used by Portage.
265</p>
266
267<pre caption="Running emerge --info">
268# <i>emerge --info</i>
269</pre>
270
44<body> 271</body>
272</subsection>
273<subsection>
274<title>Adapting your Entire System to New USE Flags</title>
275<body>
276
277<p>
278If you have altered your USE flags and you wish to update your entire system to
279use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
280</p>
281
282<pre caption="Rebuilding your entire system">
283# <i>emerge --update --deep --newuse world</i>
284</pre>
285
286<p>
287Next, run Portage's depclean to remove the conditional dependencies that
288were emerged on your "old" system but that have been obsoleted by the new USE
289flags.
290</p>
291
292<warn>
293Running <c>emerge --depclean</c> is a dangerous operation and should be handled
294with care. Double-check the provided list of "obsoleted" packages to make sure
295it 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# <i>emerge -p --depclean</i>
301</pre>
302
303<p>
304When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
305applications that are dynamically linked against shared objects provided by
306possibly 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>
315When all this is accomplished, your system is using the new USE flag settings.
316</p>
45 317
46</body> 318</body>
47</subsection> 319</subsection>
48</section> 320</section>
49<section> 321<section>
50<title>Package specific USE-flags</title> 322<title>Package specific USE flags</title>
51<subsection> 323<subsection>
52<title>Viewing used USE-flags</title> 324<title>Viewing available USE flags</title>
53<body> 325<body>
326
327<p>
328Let us take the example of <c>seamonkey</c>: what USE flags does it listen to? To
329find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
330options:
331</p>
332
333<pre caption="Viewing the used USE flags">
334# <i>emerge --pretend --verbose seamonkey</i>
335These are the packages that I would merge, in order:
336
337Calculating dependencies ...done!
338[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</pre>
342
343<p>
344<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
345dedicated to package information called <c>equery</c> which resides in the
346<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
347</p>
348
349<pre caption="Installing gentoolkit">
350# <i>emerge gentoolkit</i>
351</pre>
352
353<p>
354Now run <c>equery</c> with the <c>uses</c> argument to view the USE flags of a
355certain package. For instance, for the <c>gnumeric</c> package:
356</p>
357
358<pre caption="Using equery to view used USE flags">
359# <i>equery --nocolor uses =gnumeric-1.6.3 -a</i>
360[ Searching for packages matching =gnumeric-1.6.3... ]
361[ 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[ Found these USE variables for app-office/gnumeric-1.6.3 ]
365 U I
366 - - 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</pre>
54 374
55</body> 375</body>
56</subsection> 376</subsection>
57</section> 377</section>
58</sections> 378</sections>

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