en/handbook/hb-working-use.xml

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE sections SYSTEM "/dtd/book.dtd">

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<!-- $Header: /home/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.13 2004/05/07 07:42:53 swift Exp $ -->

<sections>
<section>
<title>What are USE-flags?</title>
<subsection>
<title>The ideas behind USE-flags</title>
<body>

<p>
When you are installing Gentoo (or any other distribution, or even operating
system for that matter) you make choices depending on the environment you are 
working with. A setup for a server differs from a setup for a workstation.
A gaming workstation differs from a 3D rendering workstation.
</p>

<p>
This is not only true for choosing what packages you want to install, but also
what features a certain package should support. If you don't need OpenGL, why
would you bother installing OpenGL and build OpenGL support in most of your
packages? If you don't want to use KDE, why would you bother compiling packages
with KDE-support if those packages work flawlessly without?
</p>

<p>
To help users in deciding what to install/activate and what not, we wanted the
user to specify his/her environment in an easy way. This forces the user into
deciding what they really want and eases the process for Portage, our package
managment system, to make useful decisions.
</p>

</body>
</subsection>
<subsection>
<title>Definition of a USE-flag</title>
<body>

<p>
Enter the USE-flags. Such a flag is a keyword that embodies support and
dependency-information for a certain concept. If you define a certain USE-flag, 
Portage will know that you want support for the chosen keyword. Of course
this also alters the dependency information for a package.
</p>

<p>
Let us take a look at a specific example: the <c>kde</c> keyword. If you do not
have this keyword in your <c>USE</c> variable, all packages that have
<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All
packages that have an <e>optional</e> KDE dependency will be installed
<e>without</e> installing the KDE libraries (as dependency). If you have defined
the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE
support, and the KDE libraries will be installed as dependency.
</p>

<p>
By correctly defining the keywords you will receive a system tailored
specifically to your needs.
</p>

</body>
</subsection>
<subsection>
<title>What USE-flags exist?</title>
<body>

<p>
There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags.
</p>

<ul>
  <li>
    A <e>global</e> USE-flag is used by several packages, system-wide. This is 
    what most people see as USE-flags.
  </li>
  <li>
    A <e>local</e> USE-flag is used by a single package to make package-specific
    decisions.
  </li>
</ul>

<p>
A list of available global USE-flags can be found <uri
link="/dyn/use-index.xml">online</uri> or locally in
<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete)
snippet:
</p>

<pre caption="A short snippet of available USE-flags">
gtk     - Adds support for x11-libs/gtk+ (The GIMP Toolkit)
gtk2    - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both.
gtkhtml - Adds support for gnome-extra/gtkhtml
guile   - Adds support for dev-util/guile (interpreter for Scheme)
icc     - Use the Intel C++ Compiler if the package supports it
icc-pgo - Enable PGO data generation or use when use icc.
imap    - Adds support for IMAP
</pre>

</body>
</subsection>
</section>
<section>
<title>Using USE-flags</title>
<subsection>
<title>Declare permanent USE-flags</title>
<body>

<p>
In the hope you are convinced of the importance of USE-flags we will now inform
you how to declare USE-flags.
</p>

<p>
As previously mentioned, all USE-flags are declared inside the <c>USE</c>
variable. To make it easy for users to search and pick USE-flags, we already
provide a <e>default</e> USE setting. This setting is a collection of USE-flags
we think are commonly used by the Gentoo users. This default setting is declared
in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at
this default setting:
</p>

<pre caption="/etc/make.profile/make.defaults USE variable on an x86 system">
USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm
     gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses
     nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl
     slang spell ssl svga tcpd truetype X xml2 xmms xv zlib"
</pre>

<p>
As you can see, this variable already contains quite a lot of keywords. Do
<b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor
the <c>USE</c> variable to your needs: changes in this file will be undone when
you update Portage!
</p>

<p>
To change this default setting, you need to add or remove keywords to the
<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable 
in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you
require, or remove the USE-flags you don't want. This latter is done by
prefixing the keyword with the minus-sign ("-").
</p>

<p>
For instance, to remove support for KDE and QT but add support for ldap, the
following <c>USE</c> can be defined in <path>/etc/make.conf</path>:
</p>

<pre caption="An example USE setting in /etc/make.conf">
USE="-kde -qt ldap"
</pre>

</body>
</subsection>
<subsection>
<title>Declare temporary USE-flags</title>
<body>

<p>
Sometimes you want to set a certain USE-setting only once. Instead of editing
<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just 
declare the USE-variable as environment variable.
</p>

<p>
As an example we will temporarily remove java from the USE-setting
during the installation of mozilla.
</p>

<note>
The <c>emerge</c> command will be discussed more thoroughly in <uri
link="?part=2&amp;chap=2">Portage and Software</uri>.
</note>

<pre caption="Using USE as environment variable">
# <i>USE="-java" emerge mozilla</i>
</pre>

</body>
</subsection>
<subsection>
<title>Inheriting USE-flags</title>
<body>

<p>
Some packages don't only listen to USE-flags, but also provide USE-flags. When
you install such a package, the USE-flag they provide is added to your USE
setting. To view the list of packages that provide a USE-flag, check
<path>/etc/make.profile/use.defaults</path>:
</p>

<pre caption="A snippet from /etc/make.profile/use.defaults">
gnome           gnome-base/gnome
gtk             x11-libs/gtk+
qt              x11-libs/qt
kde             kde-base/kdebase
motif           x11-libs/openmotif
</pre>

</body>
</subsection>
<subsection>
<title>Precendence</title>
<body>

<p>
Of course there is a certain precendence on what setting has priority over the
USE setting. You don't want to declare <c>USE="-java"</c> only to see that
<c>java</c> is declared anyway. The precedence for the USE setting is, ordered
by priority (first has lowest priority):
</p>

<ol>
  <li>
    Default USE setting declared in <path>/etc/make.profile/make.defaults</path>
  </li>
  <li>
    Inherited USE setting if a package from
    <path>/etc/make.profile/use.defaults</path> is installed
  </li>
  <li>
    User-defined USE setting in <path>/etc/make.conf</path>
  </li>
  <li>
    User-defined USE setting as environment variable
  </li>
</ol>

<p>
To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>.
This will list all relevant variables (including the <c>USE</c> variable) with
the content used by Portage.
</p>

<pre caption="Running emerge info">
# <i>emerge info</i>
</pre>

</body>
</subsection>
<subsection>
<title>Adapting your Entire System to New USE Flags</title>
<body>

<p>
If you have altered your USE flags and you wish to update your entire system to
use the new USE flags, you can try following the next steps to accomplish this.
Note however that these steps will take a long time to finish and that work is
on the way to adjust Portage to handle this behaviour quicker and automatically.
</p>

<p>
First of all, rebuild your entire system using the new USE flags:
</p>

<pre caption="Rebuilding your entire system">
# <i>emerge --emptytree world</i>
</pre>

<p>
Next, run Portage' depclean to remove the conditional dependencies that
were emerged on your "old" system but that have been obsoleted by the new USE
flags. 
</p>

<warn>
Running <c>emerge depclean</c> is a dangerous operation and should be handled
with care. Double-check the provided list of "obsoleted" packages to make sure
it doesn't remove packages you need. In the following example we add the
<c>-p</c> switch to have depclean only list the packages without removing them.
</warn>

<pre caption="Removing obsoleted packages">
# <i>emerge -p depclean</i>
</pre>

<p>
When depclean has finished, your system is using the new USE flag settings.
</p>

</body>
</subsection>
</section>
<section>
<title>Package specific USE-flags</title>
<subsection>
<title>Viewing available USE-flags</title>
<body>

<p>
In the next chapter on <uri link="?part=2&amp;chap=2">Portage and Software</uri>
we will explain how to manage your installed software and how to work with 
<c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing
you how to view what USE-flags a package uses.
</p>

<p>
Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To
find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do
anything) and <c>--verbose</c> (give more output) options:
</p>

<pre caption="Viewing the used USE-flags">
# <i>emerge --pretend --verbose mozilla</i>
These are the packages that I would merge, in order:

Calculating dependencies ...done!
[ebuild  N    ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap 
+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail
-moznocompose -moznoxft 
</pre>

<p>
<c>emerge</c> isn't the only tool for this job. In fact, we have a tool
dedicated to package information called <c>etcat</c> which resides in the
<c>gentoolkit</c> package. First, install <c>gentoolkit</c>:
</p>

<pre caption="Installing gentoolkit">
# <i>emerge --usepkg gentoolkit</i>
</pre>

<p>
Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a
certain package. For instance, for the <c>gnumeric</c> package:
</p>

<pre caption="Using etcat to view used USE-flags">
# <i>etcat uses gnumeric</i>
[ Colour Code : <i>set</i> <comment>unset</comment> ]
[ Legend      : (U) Col 1 - Current USE flags        ]
[             : (I) Col 2 - Installed With USE flags ]

 U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ]
 - - <comment>libgda</comment>  : Adds GNU Data Access (CORBA wrapper) support for gnumeric
 - - <comment>gnomedb</comment> : unknown
 + + <i>python</i>  : Adds support/bindings for the Python language
 + + <i>bonobo</i>  : Adds support for gnome-base/bonobo (Gnome CORBA interfaces)
</pre>

</body>
</subsection>
</section>
</sections>
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: /home/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.13 2004/05/07 07:42:53 swift 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&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>Precendence</title>
209	<body>
210
211	<p>
212	Of course there is a certain precendence 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&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>