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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 1.23 2004/11/15 12:47:47 swift Exp $ -->
5 8
6<sections> 9<sections>
10
11<version>1.21</version>
12<date>October 21, 2004</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>/etc/make.profile/make.defaults</path> file. Let us take a look at
133this default setting:
134</p>
135
136<pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
137USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
138 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
139 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
140 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
141</pre>
142
143<p>
144As you can see, this variable already contains quite a lot of keywords. Do
145<b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
146the <c>USE</c> variable to your needs: changes in this file will be undone when
147you update Portage!
148</p>
149
150<p>
151To change this default setting, you need to add or remove keywords to the
152<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
153in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
154require, or remove the USE-flags you don't want. This latter is done by
155prefixing the keyword with the minus-sign ("-").
156</p>
157
158<p>
159For instance, to remove support for KDE and QT but add support for ldap, the
160following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
161</p>
162
163<pre caption="An example USE setting in /etc/make.conf">
164USE="-kde -qt ldap"
165</pre>
166
167</body>
168</subsection>
169<subsection>
170<title>Declaring USE flags for individual packages</title>
171<body>
172
173<p>
174Sometimes you want to declare a certain USE flag for one (or a couple) of
175applications but not system-wide. To accomplish this, you will need to create
176the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
177<path>/etc/portage/package.use</path>.
178</p>
179
180<p>
181For instance, if you don't want <c>berkdb</c> support globally but you do want
182it for <c>mysql</c>, you would add:
183</p>
184
185<pre caption="/etc/portage/package.use example">
186dev-db/mysql berkdb
187</pre>
188
189<p>
190You can of course also explicitly <e>disable</e> USE flags for a certain
191application. For instance, if you don't want <c>java</c> support in PHP:
192</p>
193
194<pre caption="/etc/portage/package.use 2nd example">
195dev-php/php -java
196</pre>
197
34</body> 198</body>
35</subsection> 199</subsection>
36<subsection> 200<subsection>
37<title>Declare temporary USE-flags</title> 201<title>Declare temporary USE-flags</title>
38<body> 202<body>
39 203
204<p>
205Sometimes you want to set a certain USE-setting only once. Instead of editing
206<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
207declare the USE-variable as environment variable. Remember that, when you
208re-emerge or update this application (either explicitly or as part of a system
209update) your changes will be lost!
210</p>
211
212<p>
213As an example we will temporarily remove java from the USE-setting
214during the installation of mozilla.
215</p>
216
217<pre caption="Using USE as environment variable">
218# <i>USE="-java" emerge mozilla</i>
219</pre>
220
40</body> 221</body>
41</subsection> 222</subsection>
42<subsection> 223<subsection>
43<title>Inheriting USE-flags</title> 224<title>Inheriting USE-flags</title>
44<body> 225<body>
226
227<p>
228Some packages don't only listen to USE-flags, but also provide USE-flags. When
229you install such a package, the USE-flag they provide is added to your USE
230setting. To view the list of packages that provide a USE-flag, check
231<path>/etc/make.profile/use.defaults</path>:
232</p>
233
234<pre caption="A snippet from /etc/make.profile/use.defaults">
235gnome gnome-base/gnome
236gtk x11-libs/gtk+
237qt x11-libs/qt
238kde kde-base/kdebase
239motif x11-libs/openmotif
240</pre>
241
242</body>
243</subsection>
244<subsection>
245<title>Precedence</title>
246<body>
247
248<p>
249Of course there is a certain precedence on what setting has priority over the
250USE setting. You don't want to declare <c>USE="-java"</c> only to see that
251<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
252by priority (first has lowest priority):
253</p>
254
255<ol>
256 <li>
257 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
258 </li>
259 <li>
260 Inherited USE setting if a package from
261 <path>/etc/make.profile/use.defaults</path> is installed
262 </li>
263 <li>
264 User-defined USE setting in <path>/etc/make.conf</path>
265 </li>
266 <li>
267 User-defined USE setting in <path>/etc/portage/package.use</path>
268 </li>
269 <li>
270 User-defined USE setting as environment variable
271 </li>
272</ol>
273
274<p>
275To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
276This will list all relevant variables (including the <c>USE</c> variable) with
277the content used by Portage.
278</p>
279
280<pre caption="Running emerge info">
281# <i>emerge info</i>
282</pre>
283
284</body>
285</subsection>
286<subsection>
287<title>Adapting your Entire System to New USE Flags</title>
288<body>
289
290<p>
291If you have altered your USE flags and you wish to update your entire system to
292use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
293</p>
294
295<pre caption="Rebuilding your entire system">
296# <i>emerge --update --deep --newuse world</i>
297</pre>
298
299<p>
300Next, run Portage's depclean to remove the conditional dependencies that
301were emerged on your "old" system but that have been obsoleted by the new USE
302flags.
303</p>
304
305<warn>
306Running <c>emerge depclean</c> is a dangerous operation and should be handled
307with care. Double-check the provided list of "obsoleted" packages to make sure
308it doesn't remove packages you need. In the following example we add the
309<c>-p</c> switch to have depclean only list the packages without removing them.
310</warn>
311
312<pre caption="Removing obsoleted packages">
313# <i>emerge -p depclean</i>
314</pre>
315
316<p>
317When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
318applications that are dynamically linked against shared objects provided by
319possibly removed packages. <c>revdep-rebuild</c> is part of the
320<c>gentoolkit</c> package; don't forget to emerge it first.
321</p>
322
323<pre caption="Running revdep-rebuild">
324# <i>revdep-rebuild</i>
325</pre>
326
327<p>
328When all this is accomplished, your system is using the new USE flag settings.
329</p>
45 330
46</body> 331</body>
47</subsection> 332</subsection>
48</section> 333</section>
49<section> 334<section>
50<title>Package specific USE-flags</title> 335<title>Package specific USE-flags</title>
51<subsection> 336<subsection>
52<title>Viewing used USE-flags</title> 337<title>Viewing available USE-flags</title>
53<body> 338<body>
339
340<p>
341Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
342find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
343options:
344</p>
345
346<pre caption="Viewing the used USE-flags">
347# <i>emerge --pretend --verbose mozilla</i>
348These are the packages that I would merge, in order:
349
350Calculating dependencies ...done!
351[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
352+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
353-moznocompose -moznoxft
354</pre>
355
356<p>
357<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
358dedicated to package information called <c>etcat</c> which resides in the
359<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
360</p>
361
362<pre caption="Installing gentoolkit">
363# <i>emerge gentoolkit</i>
364</pre>
365
366<p>
367Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
368certain package. For instance, for the <c>gnumeric</c> package:
369</p>
370
371<pre caption="Using etcat to view used USE-flags">
372# <i>etcat uses gnumeric</i>
373[ Colour Code : <i>set</i> <comment>unset</comment> ]
374[ Legend : (U) Col 1 - Current USE flags ]
375[ : (I) Col 2 - Installed With USE flags ]
376
377 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
378 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
379 - - <comment>gnomedb</comment> : unknown
380 + + <i>python</i> : Adds support/bindings for the Python language
381 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
382</pre>
54 383
55</body> 384</body>
56</subsection> 385</subsection>
57</section> 386</section>
58</sections> 387</sections>

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