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1<?xml version='1.0' encoding='UTF-8'?>
2<!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
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4<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.1 2003/11/20 10:52:35 swift Exp $ --> 7<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.36 2005/10/26 14:37:18 rane Exp $ -->
5 8
6<sections> 9<sections>
10
11<version>1.31</version>
12<date>2005-10-26</date>
13
7<section> 14<section>
8<title>What are USE-flags?</title> 15<title>What are USE-flags?</title>
9<subsection> 16<subsection>
10<title>The ideas behind USE-flags</title> 17<title>The ideas behind USE-flags</title>
11<body> 18<body>
12 19
20<p>
21When you are installing Gentoo (or any other distribution, or even operating
22system for that matter) you make choices depending on the environment you are
23working with. A setup for a server differs from a setup for a workstation.
24A gaming workstation differs from a 3D rendering workstation.
25</p>
26
27<p>
28This is not only true for choosing what packages you want to install, but also
29what features a certain package should support. If you don't need OpenGL, why
30would you bother installing OpenGL and build OpenGL support in most of your
31packages? If you don't want to use KDE, why would you bother compiling packages
32with KDE-support if those packages work flawlessly without?
33</p>
34
35<p>
36To help users in deciding what to install/activate and what not, we wanted the
37user to specify his/her environment in an easy way. This forces the user into
38deciding what they really want and eases the process for Portage, our package
39managment system, to make useful decisions.
40</p>
41
13</body> 42</body>
14</subsection> 43</subsection>
15<subsection> 44<subsection>
16<title>Definition of a USE-flag</title> 45<title>Definition of a USE-flag</title>
17<body> 46<body>
18 47
48<p>
49Enter the USE-flags. Such a flag is a keyword that embodies support and
50dependency-information for a certain concept. If you define a certain USE-flag,
51Portage will know that you want support for the chosen keyword. Of course
52this also alters the dependency information for a package.
53</p>
54
55<p>
56Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
57have this keyword in your <c>USE</c> variable, all packages that have
58<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
59packages that have an <e>optional</e> KDE dependency will be installed
60<e>without</e> installing the KDE libraries (as dependency). If you have defined
61the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
62support, and the KDE libraries will be installed as dependency.
63</p>
64
65<p>
66By correctly defining the keywords you will receive a system tailored
67specifically to your needs.
68</p>
69
19</body> 70</body>
20</subsection> 71</subsection>
21<subsection> 72<subsection>
22<title>What USE-flags exist?</title> 73<title>What USE-flags exist?</title>
23<body> 74<body>
75
76<p>
77There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
78</p>
79
80<ul>
81 <li>
82 A <e>global</e> USE-flag is used by several packages, system-wide. This is
83 what most people see as USE-flags.
84 </li>
85 <li>
86 A <e>local</e> USE-flag is used by a single package to make package-specific
87 decisions.
88 </li>
89</ul>
90
91<p>
92A list of available global USE-flags can be found <uri
93link="/dyn/use-index.xml">online</uri> or locally in
94<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
95snippet:
96</p>
97
98<pre caption="A short snippet of available USE-flags">
99gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
100gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
101gtkhtml - Adds support for gnome-extra/gtkhtml
102guile - Adds support for dev-util/guile (interpreter for Scheme)
103icc - Use the Intel C++ Compiler if the package supports it
104icc-pgo - Enable PGO data generation or use when use icc.
105imap - Adds support for IMAP
106</pre>
107
108<p>
109A list of available local USE-flags can be found locally in
110<path>/usr/portage/profiles/use.local.desc</path>.
111</p>
24 112
25</body> 113</body>
26</subsection> 114</subsection>
27</section> 115</section>
28<section> 116<section>
29<title>Using USE-flags</title> 117<title>Using USE-flags</title>
30<subsection> 118<subsection>
31<title>Declare permanent USE-flags</title> 119<title>Declare permanent USE-flags</title>
32<body> 120<body>
33 121
122<p>
123In the hope you are convinced of the importance of USE-flags we will now inform
124you how to declare USE-flags.
125</p>
126
127<p>
128As previously mentioned, all USE-flags are declared inside the <c>USE</c>
129variable. To make it easy for users to search and pick USE-flags, we already
130provide a <e>default</e> USE setting. This setting is a collection of USE-flags
131we think are commonly used by the Gentoo users. This default setting is declared
132in the <path>make.defaults</path> files part of your profile.
133</p>
134
135<p>
136The profile your system listens to is pointed to by the
137<path>/etc/make.profile</path> symlink. Each profile works on top of another,
138larger profile, the end result is therefore the sum of all profiles. The top
139profile is the <path>base</path> profile
140(<path>/usr/portage/profiles/base</path>).
141</p>
142
143<p>
144Let us take a look at this default setting for the 2004.3 profile:
145</p>
146
147<pre caption="Cumulative make.defaults USE variable for the 2004.3 profile">
148<comment>(This example is the sum of the settings in base, default-linux,
149 default-linux/x86 and default-linux/x86/2004.3)</comment>
150USE="x86 oss apm arts avi berkdb bitmap-fonts crypt cups encode fortran f77
151 foomaticdb gdbm gif gpm gtk gtk2 imlib jpeg kde gnome libg++ libwww mad
152 mikmod motif mpeg ncurses nls oggvorbis opengl pam pdflib png python qt
153 quicktime readline sdl spell ssl svga tcpd truetype X xml2 xmms xv zlib"
154</pre>
155
156<p>
157As you can see, this variable already contains quite a lot of keywords. Do
158<b>not</b> alter any <path>make.defaults</path> file to tailor
159the <c>USE</c> variable to your needs: changes in this file will be undone when
160you update Portage!
161</p>
162
163<p>
164To change this default setting, you need to add or remove keywords to the
165<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable
166in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
167require, or remove the USE-flags you don't want. This latter is done by
168prefixing the keyword with the minus-sign ("-").
169</p>
170
171<p>
172For instance, to remove support for KDE and QT but add support for ldap, the
173following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
174</p>
175
176<pre caption="An example USE setting in /etc/make.conf">
177USE="-kde -qt ldap"
178</pre>
179
180</body>
181</subsection>
182<subsection>
183<title>Declaring USE flags for individual packages</title>
184<body>
185
186<p>
187Sometimes you want to declare a certain USE flag for one (or a couple) of
188applications but not system-wide. To accomplish this, you will need to create
189the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit
190<path>/etc/portage/package.use</path>.
191</p>
192
193<p>
194For instance, if you don't want <c>berkdb</c> support globally but you do want
195it for <c>mysql</c>, you would add:
196</p>
197
198<pre caption="/etc/portage/package.use example">
199dev-db/mysql berkdb
200</pre>
201
202<p>
203You can of course also explicitly <e>disable</e> USE flags for a certain
204application. For instance, if you don't want <c>java</c> support in PHP:
205</p>
206
207<pre caption="/etc/portage/package.use 2nd example">
208dev-php/php -java
209</pre>
210
34</body> 211</body>
35</subsection> 212</subsection>
36<subsection> 213<subsection>
37<title>Declare temporary USE-flags</title> 214<title>Declare temporary USE-flags</title>
38<body> 215<body>
39 216
217<p>
218Sometimes you want to set a certain USE-setting only once. Instead of editing
219<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just
220declare the USE-variable as environment variable. Remember that, when you
221re-emerge or update this application (either explicitly or as part of a system
222update) your changes will be lost!
223</p>
224
225<p>
226As an example we will temporarily remove java from the USE-setting
227during the installation of mozilla.
228</p>
229
230<pre caption="Using USE as environment variable">
231# <i>USE="-java" emerge mozilla</i>
232</pre>
233
40</body> 234</body>
41</subsection>
42<subsection> 235</subsection>
43<title>Inheriting USE-flags</title> 236<subsection>
237<title>Automatic USE Flags</title>
238<body>
239
240<p>
241After certain packages are installed, additional USE flags will automatically
242be enabled for you if you do not explicitly disable them. To view the list
243of packages that trigger automatic USE-flags, check
244<path>/etc/make.profile/use.defaults</path> and the <path>use.defaults</path>
245files of the parent profiles.
246</p>
247
248<pre caption="A snippet from /etc/make.profile/use.defaults">
249gnome gnome-base/gnome
250gtk x11-libs/gtk+
251qt x11-libs/qt
252kde kde-base/kdebase
253motif x11-libs/openmotif
254</pre>
255
44<body> 256</body>
257</subsection>
258<subsection>
259<title>Precedence</title>
260<body>
261
262<p>
263Of course there is a certain precedence on what setting has priority over the
264USE setting. You don't want to declare <c>USE="-java"</c> only to see that
265<c>java</c> is still used due to a setting that has a higher priority.
266The precedence for the USE setting is, ordered
267by priority (first has lowest priority):
268</p>
269
270<ol>
271 <li>
272 Default USE setting declared in the <path>make.defaults</path> files part of
273 your profile
274 </li>
275 <li>
276 Inherited USE setting if a package from profile <path>use.defaults</path> is installed
277 </li>
278 <li>
279 User-defined USE setting in <path>/etc/make.conf</path>
280 </li>
281 <li>
282 User-defined USE setting in <path>/etc/portage/package.use</path>
283 </li>
284 <li>
285 User-defined USE setting as environment variable
286 </li>
287</ol>
288
289<p>
290To view the final <c>USE</c> setting as seen by Portage, run <c>emerge
291--info</c>. This will list all relevant variables (including the <c>USE</c>
292variable) with the content used by Portage.
293</p>
294
295<pre caption="Running emerge --info">
296# <i>emerge --info</i>
297</pre>
298
299</body>
300</subsection>
301<subsection>
302<title>Adapting your Entire System to New USE Flags</title>
303<body>
304
305<p>
306If you have altered your USE flags and you wish to update your entire system to
307use the new USE flags, use <c>emerge</c>'s <c>--newuse</c> option:
308</p>
309
310<pre caption="Rebuilding your entire system">
311# <i>emerge --update --deep --newuse world</i>
312</pre>
313
314<p>
315Next, run Portage's depclean to remove the conditional dependencies that
316were emerged on your "old" system but that have been obsoleted by the new USE
317flags.
318</p>
319
320<warn>
321Running <c>emerge --depclean</c> is a dangerous operation and should be handled
322with care. Double-check the provided list of "obsoleted" packages to make sure
323it doesn't remove packages you need. In the following example we add the
324<c>-p</c> switch to have depclean only list the packages without removing them.
325</warn>
326
327<pre caption="Removing obsoleted packages">
328# <i>emerge -p --depclean</i>
329</pre>
330
331<p>
332When depclean has finished, run <c>revdep-rebuild</c> to rebuild the
333applications that are dynamically linked against shared objects provided by
334possibly removed packages. <c>revdep-rebuild</c> is part of the
335<c>gentoolkit</c> package; don't forget to emerge it first.
336</p>
337
338<pre caption="Running revdep-rebuild">
339# <i>revdep-rebuild</i>
340</pre>
341
342<p>
343When all this is accomplished, your system is using the new USE flag settings.
344</p>
45 345
46</body> 346</body>
47</subsection> 347</subsection>
48</section> 348</section>
49<section> 349<section>
50<title>Package specific USE-flags</title> 350<title>Package specific USE-flags</title>
51<subsection> 351<subsection>
52<title>Viewing used USE-flags</title> 352<title>Viewing available USE-flags</title>
53<body> 353<body>
354
355<p>
356Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
357find out, we use <c>emerge</c> with the <c>--pretend</c> and <c>--verbose</c>
358options:
359</p>
360
361<pre caption="Viewing the used USE-flags">
362# <i>emerge --pretend --verbose mozilla</i>
363These are the packages that I would merge, in order:
364
365Calculating dependencies ...done!
366[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap
367+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
368-moznocompose -moznoxft
369</pre>
370
371<p>
372<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
373dedicated to package information called <c>equery</c> which resides in the
374<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
375</p>
376
377<pre caption="Installing gentoolkit">
378# <i>emerge gentoolkit</i>
379</pre>
380
381<p>
382Now run <c>equery</c> with the <c>uses</c> argument to view the USE-flags of a
383certain package. For instance, for the <c>gnumeric</c> package:
384</p>
385
386<pre caption="Using equery to view used USE-flags">
387# <i>equery uses gnumeric</i>
388[ Colour Code : <i>set</i> <comment>unset</comment> ]
389[ Legend : (U) Col 1 - Current USE flags ]
390[ : (I) Col 2 - Installed With USE flags ]
391
392 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
393 - - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric
394 - - <comment>gnomedb</comment> : unknown
395 + + <i>python</i> : Adds support/bindings for the Python language
396 + + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
397</pre>
54 398
55</body> 399</body>
56</subsection> 400</subsection>
57</section> 401</section>
58</sections> 402</sections>

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