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1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/1.0 -->
6
7 <!-- $Header: /home/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.6 2004/01/06 10:08:38 swift Exp $ -->
8
9 <sections>
10 <section>
11 <title>What are USE-flags?</title>
12 <subsection>
13 <title>The ideas behind USE-flags</title>
14 <body>
15
16 <p>
17 When you are installing Gentoo (or any other distribution, or even operating
18 system for that matter) you make choices depending on the environment you are
19 working with. A setup for a server differs from a setup for a workstation.
20 A gaming workstation differs from a 3D rendering workstation.
21 </p>
22
23 <p>
24 This is not only true for choosing what packages you want to install, but also
25 what features a certain package should support. If you don't need OpenGL, why
26 would you bother installing OpenGL and build OpenGL support in most of your
27 packages? If you don't want to use KDE, why would you bother compiling packages
28 with KDE-support if those packages work flawlessly without?
29 </p>
30
31 <p>
32 To help users in deciding what to install/activate and what not, we wanted the
33 user to specify his environment in an easy way. This forces the user into
34 deciding what he really wants and eases the process for Portage, our package
35 managment system, to make useful decisions.
36 </p>
37
38 </body>
39 </subsection>
40 <subsection>
41 <title>Definition of a USE-flag</title>
42 <body>
43
44 <p>
45 Enter the USE-flags. Such a flag is a keyword that embodies support and
46 dependency-information for a certain concept. If you define a certain USE-flag,
47 Portage will know that you want support for the chosen keyword. Of course
48 this also alters the dependency information for a package.
49 </p>
50
51 <p>
52 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
53 have 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
55 packages 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
57 the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
58 support, and the KDE libraries will be installed as dependency.
59 </p>
60
61 <p>
62 By correctly defining the keywords you will receive a system tailored
63 specifically to your needs.
64 </p>
65
66 </body>
67 </subsection>
68 <subsection>
69 <title>What USE-flags exist?</title>
70 <body>
71
72 <p>
73 There 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-fag is used by a single package to make package-specific
83 decisions.
84 </li>
85 </ul>
86
87 <p>
88 A list of available global USE-flags can be found <uri
89 link="/dyn/use-index.xml">online</uri> or locally in
90 <path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
91 snippet:
92 </p>
93
94 <pre caption="A short snippet of available USE-flags">
95 gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
96 gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
97 gtkhtml - Adds support for gnome-extra/gtkhtml
98 guile - Adds support for dev-util/guile (interpreter for Scheme)
99 icc - Use the Intel C++ Compiler if the package supports it
100 icc-pgo - Enable PGO data generation or use when use icc.
101 imap - Adds support for IMAP
102 </pre>
103
104 </body>
105 </subsection>
106 </section>
107 <section>
108 <title>Using USE-flags</title>
109 <subsection>
110 <title>Declare permanent USE-flags</title>
111 <body>
112
113 <p>
114 In the hope you are convinced of the importance of USE-flags we will now inform
115 you how to declare USE-flags.
116 </p>
117
118 <p>
119 As previously mentioned, all USE-flags are declared inside the <c>USE</c>
120 variable. To make it easy for users to search and pick USE-flags, we already
121 provide a <e>default</e> USE setting. This setting is a collection of USE-flags
122 we think are commonly used by the Gentoo users. This default setting is declared
123 in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
124 this default setting:
125 </p>
126
127 <pre caption="/etc/make.profile/make.defaults USE variable">
128 USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm gtk
129 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses nls
130 oggvorbis opengl pam pdflib png python qt quicktime readline sdl slang
131 spell ssl svga tcpd truetype X xml2 xmms xv zlib"
132 </pre>
133
134 <p>
135 As 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
137 the <c>USE</c> variable to your needs: changes in this file will be undone when
138 you update Portage!
139 </p>
140
141 <p>
142 To 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
144 in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
145 require, or remove the USE-flags you don't want. This latter is done by
146 prefixing the keyword with the minus-sign ("-").
147 </p>
148
149 <p>
150 For instance, to remove support for KDE and QT but add support for ldap, the
151 following <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">
155 USE="-kde -qt ldap"
156 </pre>
157
158 </body>
159 </subsection>
160 <subsection>
161 <title>Declare temporary USE-flags</title>
162 <body>
163
164 <p>
165 Sometimes 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
167 declare the USE-variable as environment variable.
168 </p>
169
170 <p>
171 As an example we will temporarily remove java from the USE-setting
172 during the installation of mozilla.
173 </p>
174
175 <note>
176 The <c>emerge</c> command will be discussed more thoroughly in <uri
177 link="?part=2&amp;chap=2">Portage and Software</uri>.
178 </note>
179
180 <pre caption="Using USE as evironment variable">
181 # <i>USE="-java" emerge mozilla</i>
182 </pre>
183
184 </body>
185 </subsection>
186 <subsection>
187 <title>Inheriting USE-flags</title>
188 <body>
189
190 <p>
191 Some packages don't only listen to USE-flags, but also provide USE-flags. When
192 you install such a package, the USE-flag they provide is added to your USE
193 setting. 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">
198 gnome gnome-base/gnome
199 gtk x11-libs/gtk+
200 qt x11-libs/qt
201 kde kde-base/kdebase
202 motif x11-libs/openmotif
203 </pre>
204
205 </body>
206 </subsection>
207 <subsection>
208 <title>Precendence</title>
209 <body>
210
211 <p>
212 Of course there is a certain precendence on what setting has priority over the
213 USE 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
215 by 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>
235 To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
236 This will list all relevant variables (including the <c>USE</c> variable) with
237 the 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 </section>
247 <section>
248 <title>Package specific USE-flags</title>
249 <subsection>
250 <title>Viewing available USE-flags</title>
251 <body>
252
253 <p>
254 In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
255 we will explain how to manage your installed software and how to work with
256 <c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
257 you how to view what USE-flags a package uses.
258 </p>
259
260 <p>
261 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
262 find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
263 anything) and <c>--verbose</c> (give more output) options:
264 </p>
265
266 <pre caption="Viewing the used USE-flags">
267 # <i>emerge --pretend --verbose mozilla</i>
268 These are the packages that I would merge, in order:
269
270 Calculating dependencies ...done!
271 [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
272 +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
273 -moznocompose -moznoxft
274 </pre>
275
276 <p>
277 <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
278 dedicated to package information called <c>etcat</c> which resides in the
279 <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
280 </p>
281
282 <pre caption="Installing gentoolkit">
283 # <i>emerge --usepkg gentoolkit</i>
284 </pre>
285
286 <p>
287 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
288 certain package. For instance, for the <c>gnumeric</c> package:
289 </p>
290
291 <pre caption="Using etcat to view used USE-flags">
292 # <i>etcat uses gnumeric</i>
293 [ Colour Code : <i>set</i> <comment>unset</comment> ]
294 [ Legend : (U) Col 1 - Current USE flags ]
295 [ : (I) Col 2 - Installed With USE flags ]
296
297 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
298 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
299 - - <comment>gnomedb</comment> : unknown
300 + + <i>python</i> : Adds support/bindings for the Python language
301 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
302 </pre>
303
304 </body>
305 </subsection>
306 </section>
307 </sections>

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