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1<?xml version='1.0' encoding='UTF-8'?>
2<!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
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3 6
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 1.14 2004/06/30 21:44:46 neysx Exp $ -->
5 8
6<sections> 9<sections>
7<section> 10<section>
8<title>What are USE-flags?</title> 11<title>What are USE-flags?</title>
9<subsection> 12<subsection>
10<title>The ideas behind USE-flags</title> 13<title>The ideas behind USE-flags</title>
11<body> 14<body>
12 15
16<p>
17When you are installing Gentoo (or any other distribution, or even operating
18system for that matter) you make choices depending on the environment you are
19working with. A setup for a server differs from a setup for a workstation.
20A gaming workstation differs from a 3D rendering workstation.
21</p>
22
23<p>
24This is not only true for choosing what packages you want to install, but also
25what features a certain package should support. If you don't need OpenGL, why
26would you bother installing OpenGL and build OpenGL support in most of your
27packages? If you don't want to use KDE, why would you bother compiling packages
28with KDE-support if those packages work flawlessly without?
29</p>
30
31<p>
32To help users in deciding what to install/activate and what not, we wanted the
33user to specify his/her environment in an easy way. This forces the user into
34deciding what they really want and eases the process for Portage, our package
35managment system, to make useful decisions.
36</p>
37
13</body> 38</body>
14</subsection> 39</subsection>
15<subsection> 40<subsection>
16<title>Definition of a USE-flag</title> 41<title>Definition of a USE-flag</title>
17<body> 42<body>
18 43
44<p>
45Enter the USE-flags. Such a flag is a keyword that embodies support and
46dependency-information for a certain concept. If you define a certain USE-flag,
47Portage will know that you want support for the chosen keyword. Of course
48this also alters the dependency information for a package.
49</p>
50
51<p>
52Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
53have this keyword in your <c>USE</c> variable, all packages that have
54<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
55packages that have an <e>optional</e> KDE dependency will be installed
56<e>without</e> installing the KDE libraries (as dependency). If you have defined
57the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
58support, and the KDE libraries will be installed as dependency.
59</p>
60
61<p>
62By correctly defining the keywords you will receive a system tailored
63specifically to your needs.
64</p>
65
19</body> 66</body>
20</subsection> 67</subsection>
21<subsection> 68<subsection>
22<title>What USE-flags exist?</title> 69<title>What USE-flags exist?</title>
23<body> 70<body>
71
72<p>
73There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
74</p>
75
76<ul>
77 <li>
78 A <e>global</e> USE-flag is used by several packages, system-wide. This is
79 what most people see as USE-flags.
80 </li>
81 <li>
82 A <e>local</e> USE-flag is used by a single package to make package-specific
83 decisions.
84 </li>
85</ul>
86
87<p>
88A list of available global USE-flags can be found <uri
89link="/dyn/use-index.xml">online</uri> or locally in
90<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
91snippet:
92</p>
93
94<pre caption="A short snippet of available USE-flags">
95gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
96gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
97gtkhtml - Adds support for gnome-extra/gtkhtml
98guile - Adds support for dev-util/guile (interpreter for Scheme)
99icc - Use the Intel C++ Compiler if the package supports it
100icc-pgo - Enable PGO data generation or use when use icc.
101imap - Adds support for IMAP
102</pre>
24 103
25</body> 104</body>
26</subsection> 105</subsection>
27</section> 106</section>
28<section> 107<section>
29<title>Using USE-flags</title> 108<title>Using USE-flags</title>
30<subsection> 109<subsection>
31<title>Declare permanent USE-flags</title> 110<title>Declare permanent USE-flags</title>
32<body> 111<body>
33 112
113<p>
114In the hope you are convinced of the importance of USE-flags we will now inform
115you how to declare USE-flags.
116</p>
117
118<p>
119As previously mentioned, all USE-flags are declared inside the <c>USE</c>
120variable. To make it easy for users to search and pick USE-flags, we already
121provide a <e>default</e> USE setting. This setting is a collection of USE-flags
122we think are commonly used by the Gentoo users. This default setting is declared
123in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
124this default setting:
125</p>
126
127<pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
128USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
129 gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
130 nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
131 slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
132</pre>
133
134<p>
135As you can see, this variable already contains quite a lot of keywords. Do
136<b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
137the <c>USE</c> variable to your needs: changes in this file will be undone when
138you update Portage!
139</p>
140
141<p>
142To change this default setting, you need to add or remove keywords to the
143<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
144in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
145require, or remove the USE-flags you don't want. This latter is done by
146prefixing the keyword with the minus-sign ("-").
147</p>
148
149<p>
150For instance, to remove support for KDE and QT but add support for ldap, the
151following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
152</p>
153
154<pre caption="An example USE setting in /etc/make.conf">
155USE="-kde -qt ldap"
156</pre>
157
34</body> 158</body>
35</subsection> 159</subsection>
36<subsection> 160<subsection>
37<title>Declare temporary USE-flags</title> 161<title>Declare temporary USE-flags</title>
38<body> 162<body>
39 163
164<p>
165Sometimes you want to set a certain USE-setting only once. Instead of editing
166<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
167declare the USE-variable as environment variable.
168</p>
169
170<p>
171As an example we will temporarily remove java from the USE-setting
172during the installation of mozilla.
173</p>
174
175<note>
176The <c>emerge</c> command will be discussed more thoroughly in <uri
177link="?part=2&amp;chap=2">Portage and Software</uri>.
178</note>
179
180<pre caption="Using USE as environment variable">
181# <i>USE="-java" emerge mozilla</i>
182</pre>
183
40</body> 184</body>
41</subsection> 185</subsection>
42<subsection> 186<subsection>
43<title>Inheriting USE-flags</title> 187<title>Inheriting USE-flags</title>
44<body> 188<body>
189
190<p>
191Some packages don't only listen to USE-flags, but also provide USE-flags. When
192you install such a package, the USE-flag they provide is added to your USE
193setting. To view the list of packages that provide a USE-flag, check
194<path>/etc/make.profile/use.defaults</path>:
195</p>
196
197<pre caption="A snippet from /etc/make.profile/use.defaults">
198gnome gnome-base/gnome
199gtk x11-libs/gtk+
200qt x11-libs/qt
201kde kde-base/kdebase
202motif x11-libs/openmotif
203</pre>
204
205</body>
206</subsection>
207<subsection>
208<title>Precendence</title>
209<body>
210
211<p>
212Of course there is a certain precendence on what setting has priority over the
213USE setting. You don't want to declare <c>USE="-java"</c> only to see that
214<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
215by priority (first has lowest priority):
216</p>
217
218<ol>
219 <li>
220 Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
221 </li>
222 <li>
223 Inherited USE setting if a package from
224 <path>/etc/make.profile/use.defaults</path> is installed
225 </li>
226 <li>
227 User-defined USE setting in <path>/etc/make.conf</path>
228 </li>
229 <li>
230 User-defined USE setting as environment variable
231 </li>
232</ol>
233
234<p>
235To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
236This will list all relevant variables (including the <c>USE</c> variable) with
237the content used by Portage.
238</p>
239
240<pre caption="Running emerge info">
241# <i>emerge info</i>
242</pre>
243
244</body>
245</subsection>
246<subsection>
247<title>Adapting your Entire System to New USE Flags</title>
248<body>
249
250<p>
251If you have altered your USE flags and you wish to update your entire system to
252use the new USE flags, you can try following the next steps to accomplish this.
253Note however that these steps will take a long time to finish and that work is
254on the way to adjust Portage to handle this behaviour quicker and automatically.
255</p>
256
257<p>
258First of all, rebuild your entire system using the new USE flags:
259</p>
260
261<pre caption="Rebuilding your entire system">
262# <i>emerge --emptytree world</i>
263</pre>
264
265<p>
266Next, run Portage' depclean to remove the conditional dependencies that
267were emerged on your "old" system but that have been obsoleted by the new USE
268flags.
269</p>
270
271<warn>
272Running <c>emerge depclean</c> is a dangerous operation and should be handled
273with care. Double-check the provided list of "obsoleted" packages to make sure
274it doesn't remove packages you need. In the following example we add the
275<c>-p</c> switch to have depclean only list the packages without removing them.
276</warn>
277
278<pre caption="Removing obsoleted packages">
279# <i>emerge -p depclean</i>
280</pre>
281
282<p>
283When depclean has finished, your system is using the new USE flag settings.
284</p>
45 285
46</body> 286</body>
47</subsection> 287</subsection>
48</section> 288</section>
49<section> 289<section>
50<title>Package specific USE-flags</title> 290<title>Package specific USE-flags</title>
51<subsection> 291<subsection>
52<title>Viewing used USE-flags</title> 292<title>Viewing available USE-flags</title>
53<body> 293<body>
294
295<p>
296In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
297we will explain how to manage your installed software and how to work with
298<c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
299you how to view what USE-flags a package uses.
300</p>
301
302<p>
303Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
304find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
305anything) and <c>--verbose</c> (give more output) options:
306</p>
307
308<pre caption="Viewing the used USE-flags">
309# <i>emerge --pretend --verbose mozilla</i>
310These are the packages that I would merge, in order:
311
312Calculating dependencies ...done!
313[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
314+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
315-moznocompose -moznoxft
316</pre>
317
318<p>
319<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
320dedicated to package information called <c>etcat</c> which resides in the
321<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
322</p>
323
324<pre caption="Installing gentoolkit">
325# <i>emerge --usepkg gentoolkit</i>
326</pre>
327
328<p>
329Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
330certain package. For instance, for the <c>gnumeric</c> package:
331</p>
332
333<pre caption="Using etcat to view used USE-flags">
334# <i>etcat uses gnumeric</i>
335[ Colour Code : <i>set</i> <comment>unset</comment> ]
336[ Legend : (U) Col 1 - Current USE flags ]
337[ : (I) Col 2 - Installed With USE flags ]
338
339 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
340 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
341 - - <comment>gnomedb</comment> : unknown
342 + + <i>python</i> : Adds support/bindings for the Python language
343 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
344</pre>
54 345
55</body> 346</body>
56</subsection> 347</subsection>
57</section> 348</section>
58</sections> 349</sections>

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