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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 1.25 2004/12/26 14:56:32 swift Exp $ -->
5 8
6<sections> 9<sections>
10
11<version>1.22</version>
12<date>2004-12-26</date>
13
7<section> 14<section>
8<title>What are USE-flags?</title> 15<title>What are USE-flags?</title>
9<subsection> 16<subsection>
10<title>The ideas behind USE-flags</title> 17<title>The ideas behind USE-flags</title>
11<body> 18<body>
12 19
20<p>
21When you are installing Gentoo (or any other distribution, or even operating
22system for that matter) you make choices depending on the environment you are
23working with. A setup for a server differs from a setup for a workstation.
24A gaming workstation differs from a 3D rendering workstation.
25</p>
26
27<p>
28This is not only true for choosing what packages you want to install, but also
29what features a certain package should support. If you don't need OpenGL, why
30would you bother installing OpenGL and build OpenGL support in most of your
31packages? If you don't want to use KDE, why would you bother compiling packages
32with KDE-support if those packages work flawlessly without?
33</p>
34
35<p>
36To help users in deciding what to install/activate and what not, we wanted the
37user to specify his/her environment in an easy way. This forces the user into
38deciding what they really want and eases the process for Portage, our package
39managment system, to make useful decisions.
40</p>
41
13</body> 42</body>
14</subsection> 43</subsection>
15<subsection> 44<subsection>
16<title>Definition of a USE-flag</title> 45<title>Definition of a USE-flag</title>
17<body> 46<body>
18 47
48<p>
49Enter the USE-flags. Such a flag is a keyword that embodies support and
50dependency-information for a certain concept. If you define a certain USE-flag,
51Portage will know that you want support for the chosen keyword. Of course
52this also alters the dependency information for a package.
53</p>
54
55<p>
56Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
57have 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
59packages 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
61the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
62support, and the KDE libraries will be installed as dependency.
63</p>
64
65<p>
66By correctly defining the keywords you will receive a system tailored
67specifically to your needs.
68</p>
69
19</body> 70</body>
20</subsection> 71</subsection>
21<subsection> 72<subsection>
22<title>What USE-flags exist?</title> 73<title>What USE-flags exist?</title>
23<body> 74<body>
75
76<p>
77There 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 A <e>local</e> USE-flag is used by a single package to make package-specific
87 decisions.
88 </li>
89</ul>
90
91<p>
92A list of available global USE-flags can be found <uri
93link="/dyn/use-index.xml">online</uri> or locally in
94<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
95snippet:
96</p>
97
98<pre caption="A short snippet of available USE-flags">
99gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
100gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
101gtkhtml - Adds support for gnome-extra/gtkhtml
102guile - Adds support for dev-util/guile (interpreter for Scheme)
103icc - Use the Intel C++ Compiler if the package supports it
104icc-pgo - Enable PGO data generation or use when use icc.
105imap - Adds support for IMAP
106</pre>
107
108<p>
109A list of available local USE-flags can be found locally in
110<path>/usr/portage/profiles/use.local.desc</path>.
111</p>
24 112
25</body> 113</body>
26</subsection> 114</subsection>
27</section> 115</section>
28<section> 116<section>
29<title>Using USE-flags</title> 117<title>Using USE-flags</title>
30<subsection> 118<subsection>
31<title>Declare permanent USE-flags</title> 119<title>Declare permanent USE-flags</title>
32<body> 120<body>
33 121
122<p>
123In the hope you are convinced of the importance of USE-flags we will now inform
124you how to declare USE-flags.
125</p>
126
127<p>
128As previously mentioned, all USE-flags are declared inside the <c>USE</c>
129variable. To make it easy for users to search and pick USE-flags, we already
130provide a <e>default</e> USE setting. This setting is a collection of USE-flags
131we think are commonly used by the Gentoo users. This default setting is declared
132in the <path>make.defaults</path> files part of your profile. Let us take a
133look at this default setting:
134</p>
135
136<pre caption="/usr/portage/profiles/default-linux/x86/2004.3/make.defaults USE variable">
137<comment>(This is an example and might have changed since it was taken)</comment>
138USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
139 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
140 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
141 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
142</pre>
143
144<p>
145As you can see, this variable already contains quite a lot of keywords. Do
146<b>not</b> alter any <path>make.defaults</path> file to tailor
147the <c>USE</c> variable to your needs: changes in this file will be undone when
148you update Portage!
149</p>
150
151<p>
152To change this default setting, you need to add or remove keywords to the
153<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
154in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
155require, or remove the USE-flags you don't want. This latter is done by
156prefixing the keyword with the minus-sign ("-").
157</p>
158
159<p>
160For instance, to remove support for KDE and QT but add support for ldap, the
161following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
162</p>
163
164<pre caption="An example USE setting in /etc/make.conf">
165USE="-kde -qt ldap"
166</pre>
167
168</body>
169</subsection>
170<subsection>
171<title>Declaring USE flags for individual packages</title>
172<body>
173
174<p>
175Sometimes you want to declare a certain USE flag for one (or a couple) of
176applications but not system-wide. To accomplish this, you will need to create
177the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
178<path>/etc/portage/package.use</path>.
179</p>
180
181<p>
182For instance, if you don't want <c>berkdb</c> support globally but you do want
183it for <c>mysql</c>, you would add:
184</p>
185
186<pre caption="/etc/portage/package.use example">
187dev-db/mysql berkdb
188</pre>
189
190<p>
191You can of course also explicitly <e>disable</e> USE flags for a certain
192application. For instance, if you don't want <c>java</c> support in PHP:
193</p>
194
195<pre caption="/etc/portage/package.use 2nd example">
196dev-php/php -java
197</pre>
198
34</body> 199</body>
35</subsection> 200</subsection>
36<subsection> 201<subsection>
37<title>Declare temporary USE-flags</title> 202<title>Declare temporary USE-flags</title>
38<body> 203<body>
39 204
205<p>
206Sometimes you want to set a certain USE-setting only once. Instead of editing
207<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
208declare the USE-variable as environment variable. Remember that, when you
209re-emerge or update this application (either explicitly or as part of a system
210update) your changes will be lost!
211</p>
212
213<p>
214As an example we will temporarily remove java from the USE-setting
215during the installation of mozilla.
216</p>
217
218<pre caption="Using USE as environment variable">
219# <i>USE="-java" emerge mozilla</i>
220</pre>
221
40</body> 222</body>
41</subsection> 223</subsection>
42<subsection> 224<subsection>
43<title>Inheriting USE-flags</title> 225<title>Inheriting USE-flags</title>
44<body> 226<body>
227
228<p>
229Some packages don't only listen to USE-flags, but also provide USE-flags. When
230you install such a package, the USE-flag they provide is added to your USE
231setting. To view the list of packages that provide a USE-flag, check
232<path>/etc/make.profile/use.defaults</path>:
233</p>
234
235<pre caption="A snippet from /etc/make.profile/use.defaults">
236gnome gnome-base/gnome
237gtk x11-libs/gtk+
238qt x11-libs/qt
239kde kde-base/kdebase
240motif x11-libs/openmotif
241</pre>
242
243</body>
244</subsection>
245<subsection>
246<title>Precedence</title>
247<body>
248
249<p>
250Of course there is a certain precedence on what setting has priority over the
251USE setting. You don't want to declare <c>USE="-java"</c> only to see that
252<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
253by priority (first has lowest priority):
254</p>
255
256<ol>
257 <li>
258 Default USE setting declared in the <path>make.defaults</path> files part of
259 your profile
260 </li>
261 <li>
262 Inherited USE setting if a package from
263 <path>/etc/make.profile/use.defaults</path> is installed
264 </li>
265 <li>
266 User-defined USE setting in <path>/etc/make.conf</path>
267 </li>
268 <li>
269 User-defined USE setting in <path>/etc/portage/package.use</path>
270 </li>
271 <li>
272 User-defined USE setting as environment variable
273 </li>
274</ol>
275
276<p>
277To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
278This will list all relevant variables (including the <c>USE</c> variable) with
279the content used by Portage.
280</p>
281
282<pre caption="Running emerge info">
283# <i>emerge info</i>
284</pre>
285
286</body>
287</subsection>
288<subsection>
289<title>Adapting your Entire System to New USE Flags</title>
290<body>
291
292<p>
293If you have altered your USE flags and you wish to update your entire system to
294use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
295</p>
296
297<pre caption="Rebuilding your entire system">
298# <i>emerge --update --deep --newuse world</i>
299</pre>
300
301<p>
302Next, run Portage's depclean to remove the conditional dependencies that
303were emerged on your "old" system but that have been obsoleted by the new USE
304flags.
305</p>
306
307<warn>
308Running <c>emerge depclean</c> is a dangerous operation and should be handled
309with care. Double-check the provided list of "obsoleted" packages to make sure
310it doesn't remove packages you need. In the following example we add the
311<c>-p</c> switch to have depclean only list the packages without removing them.
312</warn>
313
314<pre caption="Removing obsoleted packages">
315# <i>emerge -p depclean</i>
316</pre>
317
318<p>
319When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
320applications that are dynamically linked against shared objects provided by
321possibly removed packages. <c>revdep-rebuild</c> is part of the
322<c>gentoolkit</c> package; don't forget to emerge it first.
323</p>
324
325<pre caption="Running revdep-rebuild">
326# <i>revdep-rebuild</i>
327</pre>
328
329<p>
330When all this is accomplished, your system is using the new USE flag settings.
331</p>
45 332
46</body> 333</body>
47</subsection> 334</subsection>
48</section> 335</section>
49<section> 336<section>
50<title>Package specific USE-flags</title> 337<title>Package specific USE-flags</title>
51<subsection> 338<subsection>
52<title>Viewing used USE-flags</title> 339<title>Viewing available USE-flags</title>
53<body> 340<body>
341
342<p>
343Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
344find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
345options:
346</p>
347
348<pre caption="Viewing the used USE-flags">
349# <i>emerge --pretend --verbose mozilla</i>
350These are the packages that I would merge, in order:
351
352Calculating dependencies ...done!
353[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
354+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
355-moznocompose -moznoxft
356</pre>
357
358<p>
359<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
360dedicated to package information called <c>etcat</c> which resides in the
361<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
362</p>
363
364<pre caption="Installing gentoolkit">
365# <i>emerge gentoolkit</i>
366</pre>
367
368<p>
369Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
370certain package. For instance, for the <c>gnumeric</c> package:
371</p>
372
373<pre caption="Using etcat to view used USE-flags">
374# <i>etcat uses gnumeric</i>
375[ Colour Code : <i>set</i> <comment>unset</comment> ]
376[ Legend : (U) Col 1 - Current USE flags ]
377[ : (I) Col 2 - Installed With USE flags ]
378
379 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
380 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
381 - - <comment>gnomedb</comment> : unknown
382 + + <i>python</i> : Adds support/bindings for the Python language
383 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
384</pre>
54 385
55</body> 386</body>
56</subsection> 387</subsection>
57</section> 388</section>
58</sections> 389</sections>

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