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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 1.17 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.16 2004/07/07 19:19:26 neysx 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 neysx 1.14 <pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
128     USE="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 swift 1.2 </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 1.17 <p>
159     Sometimes you want to declare a certain USE flag for one (or a couple) of
160     applications but not system-wide. To accomplish this, you will need to create
161     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
162     <path>/etc/portage/package.use</path>.
163     </p>
164    
165     <p>
166     For instance, if you don't want <c>berkdb</c> support globally but you do want
167     it for <c>mysql</c>, you would add:
168     </p>
169    
170     <pre caption="/etc/portage/package.use example">
171     dev-db/mysql berkdb
172     </pre>
173    
174     <p>
175     You can of course also explicitly <e>disable</e> USE flags for a certain
176     application. For instance, if you don't want <c>java</c> support in PHP:
177     </p>
178    
179     <pre caption="/etc/portage/package.use 2nd example">
180     dev-php/php -java
181     </pre>
182    
183 swift 1.1 </body>
184     </subsection>
185     <subsection>
186     <title>Declare temporary USE-flags</title>
187     <body>
188    
189 swift 1.2 <p>
190     Sometimes you want to set a certain USE-setting only once. Instead of editing
191     <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
192 swift 1.17 declare the USE-variable as environment variable. Remember that, when you
193     re-emerge or update this application (either explicitly or as part of a system
194     update) your changes will be lost!
195 swift 1.2 </p>
196    
197     <p>
198     As an example we will temporarily remove java from the USE-setting
199     during the installation of mozilla.
200     </p>
201    
202     <note>
203     The <c>emerge</c> command will be discussed more thoroughly in <uri
204     link="?part=2&amp;chap=2">Portage and Software</uri>.
205     </note>
206    
207 swift 1.13 <pre caption="Using USE as environment variable">
208 swift 1.2 # <i>USE="-java" emerge mozilla</i>
209     </pre>
210    
211 swift 1.1 </body>
212     </subsection>
213     <subsection>
214     <title>Inheriting USE-flags</title>
215     <body>
216    
217 swift 1.2 <p>
218     Some packages don't only listen to USE-flags, but also provide USE-flags. When
219     you install such a package, the USE-flag they provide is added to your USE
220     setting. To view the list of packages that provide a USE-flag, check
221     <path>/etc/make.profile/use.defaults</path>:
222     </p>
223    
224     <pre caption="A snippet from /etc/make.profile/use.defaults">
225     gnome gnome-base/gnome
226     gtk x11-libs/gtk+
227     qt x11-libs/qt
228     kde kde-base/kdebase
229     motif x11-libs/openmotif
230     </pre>
231    
232     </body>
233     </subsection>
234     <subsection>
235 swift 1.15 <title>Precedence</title>
236 swift 1.2 <body>
237    
238     <p>
239 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
240 swift 1.2 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
241     <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
242     by priority (first has lowest priority):
243     </p>
244    
245     <ol>
246     <li>
247     Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
248     </li>
249     <li>
250     Inherited USE setting if a package from
251     <path>/etc/make.profile/use.defaults</path> is installed
252     </li>
253     <li>
254     User-defined USE setting in <path>/etc/make.conf</path>
255     </li>
256     <li>
257 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
258     </li>
259     <li>
260 swift 1.2 User-defined USE setting as environment variable
261     </li>
262     </ol>
263 swift 1.4
264     <p>
265     To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
266     This will list all relevant variables (including the <c>USE</c> variable) with
267     the content used by Portage.
268     </p>
269    
270     <pre caption="Running emerge info">
271     # <i>emerge info</i>
272     </pre>
273 swift 1.2
274 swift 1.1 </body>
275     </subsection>
276 swift 1.12 <subsection>
277     <title>Adapting your Entire System to New USE Flags</title>
278     <body>
279    
280     <p>
281     If you have altered your USE flags and you wish to update your entire system to
282     use the new USE flags, you can try following the next steps to accomplish this.
283     Note however that these steps will take a long time to finish and that work is
284     on the way to adjust Portage to handle this behaviour quicker and automatically.
285     </p>
286    
287     <p>
288     First of all, rebuild your entire system using the new USE flags:
289     </p>
290    
291     <pre caption="Rebuilding your entire system">
292     # <i>emerge --emptytree world</i>
293     </pre>
294    
295     <p>
296     Next, run Portage' depclean to remove the conditional dependencies that
297     were emerged on your "old" system but that have been obsoleted by the new USE
298     flags.
299     </p>
300    
301     <warn>
302     Running <c>emerge depclean</c> is a dangerous operation and should be handled
303     with care. Double-check the provided list of "obsoleted" packages to make sure
304     it doesn't remove packages you need. In the following example we add the
305     <c>-p</c> switch to have depclean only list the packages without removing them.
306     </warn>
307    
308     <pre caption="Removing obsoleted packages">
309     # <i>emerge -p depclean</i>
310     </pre>
311    
312     <p>
313     When depclean has finished, your system is using the new USE flag settings.
314     </p>
315    
316     </body>
317     </subsection>
318 swift 1.1 </section>
319     <section>
320     <title>Package specific USE-flags</title>
321     <subsection>
322 swift 1.2 <title>Viewing available USE-flags</title>
323 swift 1.1 <body>
324 swift 1.2
325     <p>
326     In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
327     we will explain how to manage your installed software and how to work with
328     <c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
329     you how to view what USE-flags a package uses.
330     </p>
331    
332     <p>
333     Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
334     find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
335     anything) and <c>--verbose</c> (give more output) options:
336     </p>
337    
338     <pre caption="Viewing the used USE-flags">
339     # <i>emerge --pretend --verbose mozilla</i>
340     These are the packages that I would merge, in order:
341    
342     Calculating dependencies ...done!
343     [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
344     +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
345     -moznocompose -moznoxft
346     </pre>
347    
348     <p>
349     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
350     dedicated to package information called <c>etcat</c> which resides in the
351     <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
352     </p>
353    
354     <pre caption="Installing gentoolkit">
355     # <i>emerge --usepkg gentoolkit</i>
356     </pre>
357    
358     <p>
359     Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
360     certain package. For instance, for the <c>gnumeric</c> package:
361     </p>
362    
363     <pre caption="Using etcat to view used USE-flags">
364     # <i>etcat uses gnumeric</i>
365     [ Colour Code : <i>set</i> <comment>unset</comment> ]
366     [ Legend : (U) Col 1 - Current USE flags ]
367     [ : (I) Col 2 - Installed With USE flags ]
368    
369     U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
370     - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
371     - - <comment>gnomedb</comment> : unknown
372     + + <i>python</i> : Adds support/bindings for the Python language
373     + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
374     </pre>
375 swift 1.1
376     </body>
377     </subsection>
378     </section>
379     </sections>

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