/[gentoo]/xml/htdocs/doc/en/handbook/hb-working-use.xml
Gentoo

Contents of /xml/htdocs/doc/en/handbook/hb-working-use.xml

Parent Directory Parent Directory | Revision Log Revision Log


Revision 1.15 - (show annotations) (download) (as text)
Wed Jul 7 14:01:31 2004 UTC (9 years, 9 months ago) by swift
Branch: MAIN
Changes since 1.14: +3 -3 lines
File MIME type: application/xml
Fix typo s/precendence/precedence/

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: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.14 2004/06/30 21:44:46 neysx 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/her environment in an easy way. This forces the user into
34 deciding what they really want 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-flag 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 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 </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 environment 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>Precedence</title>
209 <body>
210
211 <p>
212 Of course there is a certain precdence 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 <subsection>
247 <title>Adapting your Entire System to New USE Flags</title>
248 <body>
249
250 <p>
251 If you have altered your USE flags and you wish to update your entire system to
252 use the new USE flags, you can try following the next steps to accomplish this.
253 Note however that these steps will take a long time to finish and that work is
254 on the way to adjust Portage to handle this behaviour quicker and automatically.
255 </p>
256
257 <p>
258 First 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>
266 Next, run Portage' depclean to remove the conditional dependencies that
267 were emerged on your "old" system but that have been obsoleted by the new USE
268 flags.
269 </p>
270
271 <warn>
272 Running <c>emerge depclean</c> is a dangerous operation and should be handled
273 with care. Double-check the provided list of "obsoleted" packages to make sure
274 it 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>
283 When depclean has finished, your system is using the new USE flag settings.
284 </p>
285
286 </body>
287 </subsection>
288 </section>
289 <section>
290 <title>Package specific USE-flags</title>
291 <subsection>
292 <title>Viewing available USE-flags</title>
293 <body>
294
295 <p>
296 In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
297 we 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
299 you how to view what USE-flags a package uses.
300 </p>
301
302 <p>
303 Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
304 find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
305 anything) 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>
310 These are the packages that I would merge, in order:
311
312 Calculating 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
320 dedicated 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>
329 Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
330 certain 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>
345
346 </body>
347 </subsection>
348 </section>
349 </sections>

  ViewVC Help
Powered by ViewVC 1.1.20