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The use of "he/she" and "his/her" isn't recommended. It's ugly and better ways
are known such as the use of "they" and "their" (even if it's not plural). Okay,
English is a weird language, but I'm learning :)

Thanks to Xavier for the information

1 swift 1.7 <?xml version='1.0' encoding='UTF-8'?>
2     <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3    
4 swift 1.1 <!-- 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 swift 1.11 <!-- $Header: /home/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.10 2004/04/15 07:06:36 swift Exp $ -->
8 swift 1.1
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 swift 1.2 <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 swift 1.5 with KDE-support if those packages work flawlessly without?
29 swift 1.2 </p>
30    
31     <p>
32     To help users in deciding what to install/activate and what not, we wanted the
33 swift 1.10 user to specify his/her environment in an easy way. This forces the user into
34 swift 1.11 deciding what they really want and eases the process for Portage, our package
35 swift 1.5 managment system, to make useful decisions.
36 swift 1.2 </p>
37    
38 swift 1.1 </body>
39     </subsection>
40     <subsection>
41     <title>Definition of a USE-flag</title>
42     <body>
43    
44 swift 1.2 <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 swift 1.3 Portage will know that you want support for the chosen keyword. Of course
48 swift 1.2 this also alters the dependency information for a package.
49     </p>
50    
51     <p>
52 swift 1.6 Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
53 swift 1.2 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 swift 1.1 </body>
67     </subsection>
68     <subsection>
69     <title>What USE-flags exist?</title>
70     <body>
71    
72 swift 1.2 <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 swift 1.8 A <e>local</e> USE-flag is used by a single package to make package-specific
83 swift 1.2 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 swift 1.1 </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 swift 1.2 <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 swift 1.1 </body>
159     </subsection>
160     <subsection>
161     <title>Declare temporary USE-flags</title>
162     <body>
163    
164 swift 1.2 <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 swift 1.1 </body>
185     </subsection>
186     <subsection>
187     <title>Inheriting USE-flags</title>
188     <body>
189    
190 swift 1.2 <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 swift 1.3 Of course there is a certain precendence on what setting has priority over the
213 swift 1.2 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 swift 1.4
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 swift 1.2
244 swift 1.1 </body>
245     </subsection>
246     </section>
247     <section>
248     <title>Package specific USE-flags</title>
249     <subsection>
250 swift 1.2 <title>Viewing available USE-flags</title>
251 swift 1.1 <body>
252 swift 1.2
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 swift 1.1
304     </body>
305     </subsection>
306     </section>
307     </sections>

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