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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 1.18 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.17 2004/08/01 13:08:35 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 1.18 <p>
105     A list of available local USE-flags can be found locally in
106     <path>/usr/portage/profiles/use.local.desc</path>.
107     </p>
108    
109 swift 1.1 </body>
110     </subsection>
111     </section>
112     <section>
113     <title>Using USE-flags</title>
114     <subsection>
115     <title>Declare permanent USE-flags</title>
116     <body>
117    
118 swift 1.2 <p>
119     In the hope you are convinced of the importance of USE-flags we will now inform
120     you how to declare USE-flags.
121     </p>
122    
123     <p>
124     As previously mentioned, all USE-flags are declared inside the <c>USE</c>
125     variable. To make it easy for users to search and pick USE-flags, we already
126     provide a <e>default</e> USE setting. This setting is a collection of USE-flags
127     we think are commonly used by the Gentoo users. This default setting is declared
128     in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
129     this default setting:
130     </p>
131    
132 neysx 1.14 <pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
133     USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
134     gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
135     nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
136     slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
137 swift 1.2 </pre>
138    
139     <p>
140     As you can see, this variable already contains quite a lot of keywords. Do
141     <b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
142     the <c>USE</c> variable to your needs: changes in this file will be undone when
143     you update Portage!
144     </p>
145    
146     <p>
147     To change this default setting, you need to add or remove keywords to the
148     <c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
149     in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
150     require, or remove the USE-flags you don't want. This latter is done by
151     prefixing the keyword with the minus-sign ("-").
152     </p>
153    
154     <p>
155     For instance, to remove support for KDE and QT but add support for ldap, the
156     following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
157     </p>
158    
159     <pre caption="An example USE setting in /etc/make.conf">
160     USE="-kde -qt ldap"
161     </pre>
162    
163 swift 1.17 <p>
164     Sometimes you want to declare a certain USE flag for one (or a couple) of
165     applications but not system-wide. To accomplish this, you will need to create
166     the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
167     <path>/etc/portage/package.use</path>.
168     </p>
169    
170     <p>
171     For instance, if you don't want <c>berkdb</c> support globally but you do want
172     it for <c>mysql</c>, you would add:
173     </p>
174    
175     <pre caption="/etc/portage/package.use example">
176     dev-db/mysql berkdb
177     </pre>
178    
179     <p>
180     You can of course also explicitly <e>disable</e> USE flags for a certain
181     application. For instance, if you don't want <c>java</c> support in PHP:
182     </p>
183    
184     <pre caption="/etc/portage/package.use 2nd example">
185     dev-php/php -java
186     </pre>
187    
188 swift 1.1 </body>
189     </subsection>
190     <subsection>
191     <title>Declare temporary USE-flags</title>
192     <body>
193    
194 swift 1.2 <p>
195     Sometimes you want to set a certain USE-setting only once. Instead of editing
196     <path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
197 swift 1.17 declare the USE-variable as environment variable. Remember that, when you
198     re-emerge or update this application (either explicitly or as part of a system
199     update) your changes will be lost!
200 swift 1.2 </p>
201    
202     <p>
203     As an example we will temporarily remove java from the USE-setting
204     during the installation of mozilla.
205     </p>
206    
207     <note>
208     The <c>emerge</c> command will be discussed more thoroughly in <uri
209     link="?part=2&amp;chap=2">Portage and Software</uri>.
210     </note>
211    
212 swift 1.13 <pre caption="Using USE as environment variable">
213 swift 1.2 # <i>USE="-java" emerge mozilla</i>
214     </pre>
215    
216 swift 1.1 </body>
217     </subsection>
218     <subsection>
219     <title>Inheriting USE-flags</title>
220     <body>
221    
222 swift 1.2 <p>
223     Some packages don't only listen to USE-flags, but also provide USE-flags. When
224     you install such a package, the USE-flag they provide is added to your USE
225     setting. To view the list of packages that provide a USE-flag, check
226     <path>/etc/make.profile/use.defaults</path>:
227     </p>
228    
229     <pre caption="A snippet from /etc/make.profile/use.defaults">
230     gnome gnome-base/gnome
231     gtk x11-libs/gtk+
232     qt x11-libs/qt
233     kde kde-base/kdebase
234     motif x11-libs/openmotif
235     </pre>
236    
237     </body>
238     </subsection>
239     <subsection>
240 swift 1.15 <title>Precedence</title>
241 swift 1.2 <body>
242    
243     <p>
244 neysx 1.16 Of course there is a certain precedence on what setting has priority over the
245 swift 1.2 USE setting. You don't want to declare <c>USE="-java"</c> only to see that
246     <c>java</c> is declared anyway. The precedence for the USE setting is, ordered
247     by priority (first has lowest priority):
248     </p>
249    
250     <ol>
251     <li>
252     Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
253     </li>
254     <li>
255     Inherited USE setting if a package from
256     <path>/etc/make.profile/use.defaults</path> is installed
257     </li>
258     <li>
259     User-defined USE setting in <path>/etc/make.conf</path>
260     </li>
261     <li>
262 swift 1.17 User-defined USE setting in <path>/etc/portage/package.use</path>
263     </li>
264     <li>
265 swift 1.2 User-defined USE setting as environment variable
266     </li>
267     </ol>
268 swift 1.4
269     <p>
270     To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
271     This will list all relevant variables (including the <c>USE</c> variable) with
272     the content used by Portage.
273     </p>
274    
275     <pre caption="Running emerge info">
276     # <i>emerge info</i>
277     </pre>
278 swift 1.2
279 swift 1.1 </body>
280     </subsection>
281 swift 1.12 <subsection>
282     <title>Adapting your Entire System to New USE Flags</title>
283     <body>
284    
285     <p>
286     If you have altered your USE flags and you wish to update your entire system to
287     use the new USE flags, you can try following the next steps to accomplish this.
288     Note however that these steps will take a long time to finish and that work is
289     on the way to adjust Portage to handle this behaviour quicker and automatically.
290     </p>
291    
292     <p>
293     First of all, rebuild your entire system using the new USE flags:
294     </p>
295    
296     <pre caption="Rebuilding your entire system">
297     # <i>emerge --emptytree world</i>
298     </pre>
299    
300     <p>
301     Next, run Portage' depclean to remove the conditional dependencies that
302     were emerged on your "old" system but that have been obsoleted by the new USE
303     flags.
304     </p>
305    
306     <warn>
307     Running <c>emerge depclean</c> is a dangerous operation and should be handled
308     with care. Double-check the provided list of "obsoleted" packages to make sure
309     it doesn't remove packages you need. In the following example we add the
310     <c>-p</c> switch to have depclean only list the packages without removing them.
311     </warn>
312    
313     <pre caption="Removing obsoleted packages">
314     # <i>emerge -p depclean</i>
315     </pre>
316    
317     <p>
318     When depclean has finished, your system is using the new USE flag settings.
319     </p>
320    
321     </body>
322     </subsection>
323 swift 1.1 </section>
324     <section>
325     <title>Package specific USE-flags</title>
326     <subsection>
327 swift 1.2 <title>Viewing available USE-flags</title>
328 swift 1.1 <body>
329 swift 1.2
330     <p>
331     In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
332     we will explain how to manage your installed software and how to work with
333     <c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
334     you how to view what USE-flags a package uses.
335     </p>
336    
337     <p>
338     Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
339     find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
340     anything) and <c>--verbose</c> (give more output) options:
341     </p>
342    
343     <pre caption="Viewing the used USE-flags">
344     # <i>emerge --pretend --verbose mozilla</i>
345     These are the packages that I would merge, in order:
346    
347     Calculating dependencies ...done!
348     [ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
349     +gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
350     -moznocompose -moznoxft
351     </pre>
352    
353     <p>
354     <c>emerge</c> isn't the only tool for this job. In fact, we have a tool
355     dedicated to package information called <c>etcat</c> which resides in the
356     <c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
357     </p>
358    
359     <pre caption="Installing gentoolkit">
360     # <i>emerge --usepkg gentoolkit</i>
361     </pre>
362    
363     <p>
364     Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
365     certain package. For instance, for the <c>gnumeric</c> package:
366     </p>
367    
368     <pre caption="Using etcat to view used USE-flags">
369     # <i>etcat uses gnumeric</i>
370     [ Colour Code : <i>set</i> <comment>unset</comment> ]
371     [ Legend : (U) Col 1 - Current USE flags ]
372     [ : (I) Col 2 - Installed With USE flags ]
373    
374     U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
375     - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
376     - - <comment>gnomedb</comment> : unknown
377     + + <i>python</i> : Adds support/bindings for the Python language
378     + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
379     </pre>
380 swift 1.1
381     </body>
382     </subsection>
383     </section>
384     </sections>

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