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<?xml version='1.0' encoding='UTF-8'?> |
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<!DOCTYPE sections SYSTEM "/dtd/book.dtd"> |
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<!-- The content of this document is licensed under the CC-BY-SA license --> |
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<!-- See http://creativecommons.org/licenses/by-sa/1.0 --> |
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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 $ --> |
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<sections> |
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<section> |
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<title>What are USE-flags?</title> |
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<subsection> |
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<title>The ideas behind USE-flags</title> |
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<body> |
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|
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<p> |
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When you are installing Gentoo (or any other distribution, or even operating |
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system for that matter) you make choices depending on the environment you are |
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working with. A setup for a server differs from a setup for a workstation. |
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A gaming workstation differs from a 3D rendering workstation. |
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</p> |
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|
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<p> |
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This is not only true for choosing what packages you want to install, but also |
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what features a certain package should support. If you don't need OpenGL, why |
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would you bother installing OpenGL and build OpenGL support in most of your |
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packages? If you don't want to use KDE, why would you bother compiling packages |
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with KDE-support if those packages work flawlessly without? |
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</p> |
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|
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<p> |
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To help users in deciding what to install/activate and what not, we wanted the |
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user to specify his/her environment in an easy way. This forces the user into |
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deciding what they really want and eases the process for Portage, our package |
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managment system, to make useful decisions. |
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</p> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>Definition of a USE-flag</title> |
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<body> |
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|
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<p> |
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Enter the USE-flags. Such a flag is a keyword that embodies support and |
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dependency-information for a certain concept. If you define a certain USE-flag, |
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Portage will know that you want support for the chosen keyword. Of course |
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this also alters the dependency information for a package. |
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</p> |
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|
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<p> |
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Let us take a look at a specific example: the <c>kde</c> keyword. If you do not |
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have this keyword in your <c>USE</c> variable, all packages that have |
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<e>optional</e> KDE support will be compiled <e>without</e> KDE support. All |
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packages that have an <e>optional</e> KDE dependency will be installed |
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<e>without</e> installing the KDE libraries (as dependency). If you have defined |
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the <c>kde</c> keyword, then those packages <e>will</e> be compiled with KDE |
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support, and the KDE libraries will be installed as dependency. |
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</p> |
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|
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<p> |
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By correctly defining the keywords you will receive a system tailored |
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specifically to your needs. |
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</p> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>What USE-flags exist?</title> |
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<body> |
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|
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<p> |
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There are two types of USE-flags: <e>global</e> and <e>local</e> USE-flags. |
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</p> |
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|
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<ul> |
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<li> |
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A <e>global</e> USE-flag is used by several packages, system-wide. This is |
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what most people see as USE-flags. |
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</li> |
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<li> |
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A <e>local</e> USE-flag is used by a single package to make package-specific |
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decisions. |
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</li> |
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</ul> |
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|
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<p> |
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A list of available global USE-flags can be found <uri |
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link="/dyn/use-index.xml">online</uri> or locally in |
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<path>/usr/portage/profiles/use.desc</path>. A short (<e>very</e> incomplete) |
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snippet: |
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</p> |
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|
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<pre caption="A short snippet of available USE-flags"> |
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gtk - Adds support for x11-libs/gtk+ (The GIMP Toolkit) |
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gtk2 - Use gtk+-2.0.0 over gtk+-1.2 in cases where a program supports both. |
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gtkhtml - Adds support for gnome-extra/gtkhtml |
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guile - Adds support for dev-util/guile (interpreter for Scheme) |
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icc - Use the Intel C++ Compiler if the package supports it |
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icc-pgo - Enable PGO data generation or use when use icc. |
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imap - Adds support for IMAP |
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</pre> |
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|
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</body> |
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</subsection> |
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</section> |
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<section> |
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<title>Using USE-flags</title> |
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<subsection> |
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<title>Declare permanent USE-flags</title> |
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<body> |
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|
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<p> |
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In the hope you are convinced of the importance of USE-flags we will now inform |
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you how to declare USE-flags. |
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</p> |
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|
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<p> |
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As previously mentioned, all USE-flags are declared inside the <c>USE</c> |
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variable. To make it easy for users to search and pick USE-flags, we already |
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provide a <e>default</e> USE setting. This setting is a collection of USE-flags |
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we think are commonly used by the Gentoo users. This default setting is declared |
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in the <path>/etc/make.profile/make.defaults</path> file. Let us take a look at |
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this default setting: |
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</p> |
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|
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<pre caption="/etc/make.profile/make.defaults USE variable on an x86 system"> |
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USE="x86 oss apm arts avi berkdb crypt cups encode foomaticdb gdbm gif gpm |
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gtk gtk2 imlib jpeg kde gnome libg++ libwww mad mikmod motif mpeg ncurses |
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nls oggvorbis opengl pam pdflib png python qt quicktime readline sdl |
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slang spell ssl svga tcpd truetype X xml2 xmms xv zlib" |
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</pre> |
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|
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<p> |
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As you can see, this variable already contains quite a lot of keywords. Do |
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<b>not</b> alter the <path>/etc/make.profile/make.defaults</path> file to tailor |
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the <c>USE</c> variable to your needs: changes in this file will be undone when |
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you update Portage! |
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</p> |
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|
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<p> |
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To change this default setting, you need to add or remove keywords to the |
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<c>USE</c> variable. This is done globally by defining the <c>USE</c> variable |
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in <path>/etc/make.conf</path>. In this variable you add the extra USE-flags you |
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require, or remove the USE-flags you don't want. This latter is done by |
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prefixing the keyword with the minus-sign ("-"). |
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</p> |
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|
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<p> |
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For instance, to remove support for KDE and QT but add support for ldap, the |
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following <c>USE</c> can be defined in <path>/etc/make.conf</path>: |
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</p> |
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|
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<pre caption="An example USE setting in /etc/make.conf"> |
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USE="-kde -qt ldap" |
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</pre> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>Declare temporary USE-flags</title> |
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<body> |
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|
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<p> |
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Sometimes you want to set a certain USE-setting only once. Instead of editing |
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<path>/etc/make.conf</path> twice (to do and undo the USE-changes) you can just |
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declare the USE-variable as environment variable. |
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</p> |
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|
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<p> |
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As an example we will temporarily remove java from the USE-setting |
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during the installation of mozilla. |
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</p> |
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|
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<note> |
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The <c>emerge</c> command will be discussed more thoroughly in <uri |
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link="?part=2&chap=2">Portage and Software</uri>. |
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</note> |
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|
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<pre caption="Using USE as environment variable"> |
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# <i>USE="-java" emerge mozilla</i> |
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</pre> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>Inheriting USE-flags</title> |
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<body> |
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|
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<p> |
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Some packages don't only listen to USE-flags, but also provide USE-flags. When |
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you install such a package, the USE-flag they provide is added to your USE |
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setting. To view the list of packages that provide a USE-flag, check |
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<path>/etc/make.profile/use.defaults</path>: |
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</p> |
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|
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<pre caption="A snippet from /etc/make.profile/use.defaults"> |
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gnome gnome-base/gnome |
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gtk x11-libs/gtk+ |
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qt x11-libs/qt |
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kde kde-base/kdebase |
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motif x11-libs/openmotif |
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</pre> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>Precendence</title> |
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<body> |
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|
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<p> |
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Of course there is a certain precendence on what setting has priority over the |
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USE setting. You don't want to declare <c>USE="-java"</c> only to see that |
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<c>java</c> is declared anyway. The precedence for the USE setting is, ordered |
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by priority (first has lowest priority): |
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</p> |
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|
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<ol> |
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<li> |
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Default USE setting declared in <path>/etc/make.profile/make.defaults</path> |
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</li> |
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<li> |
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Inherited USE setting if a package from |
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<path>/etc/make.profile/use.defaults</path> is installed |
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</li> |
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<li> |
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User-defined USE setting in <path>/etc/make.conf</path> |
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</li> |
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<li> |
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User-defined USE setting as environment variable |
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</li> |
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</ol> |
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|
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<p> |
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To view the final <c>USE</c> setting as seen by Portage, run <c>emerge info</c>. |
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This will list all relevant variables (including the <c>USE</c> variable) with |
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the content used by Portage. |
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</p> |
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|
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<pre caption="Running emerge info"> |
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# <i>emerge info</i> |
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</pre> |
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|
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</body> |
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</subsection> |
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<subsection> |
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<title>Adapting your Entire System to New USE Flags</title> |
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<body> |
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|
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<p> |
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If you have altered your USE flags and you wish to update your entire system to |
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use the new USE flags, you can try following the next steps to accomplish this. |
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Note however that these steps will take a long time to finish and that work is |
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on the way to adjust Portage to handle this behaviour quicker and automatically. |
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</p> |
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|
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<p> |
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First of all, rebuild your entire system using the new USE flags: |
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</p> |
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|
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<pre caption="Rebuilding your entire system"> |
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# <i>emerge --emptytree world</i> |
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</pre> |
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|
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<p> |
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Next, run Portage' depclean to remove the conditional dependencies that |
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were emerged on your "old" system but that have been obsoleted by the new USE |
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flags. |
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</p> |
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|
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<warn> |
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Running <c>emerge depclean</c> is a dangerous operation and should be handled |
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with care. Double-check the provided list of "obsoleted" packages to make sure |
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it doesn't remove packages you need. In the following example we add the |
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<c>-p</c> switch to have depclean only list the packages without removing them. |
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</warn> |
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|
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<pre caption="Removing obsoleted packages"> |
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# <i>emerge -p depclean</i> |
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</pre> |
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|
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<p> |
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When depclean has finished, your system is using the new USE flag settings. |
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</p> |
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|
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</body> |
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</subsection> |
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</section> |
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<section> |
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<title>Package specific USE-flags</title> |
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<subsection> |
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<title>Viewing available USE-flags</title> |
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<body> |
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|
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<p> |
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In the next chapter on <uri link="?part=2&chap=2">Portage and Software</uri> |
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we will explain how to manage your installed software and how to work with |
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<c>emerge</c>. However, we will give you a primer on <c>emerge</c> by showing |
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you how to view what USE-flags a package uses. |
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</p> |
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|
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<p> |
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Let us take the example of <c>mozilla</c>: what USE-flags does it listen to? To |
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find out, we use <c>emerge</c> with the <c>--pretend</c> (don't really do |
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anything) and <c>--verbose</c> (give more output) options: |
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</p> |
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|
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<pre caption="Viewing the used USE-flags"> |
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# <i>emerge --pretend --verbose mozilla</i> |
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These are the packages that I would merge, in order: |
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|
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Calculating dependencies ...done! |
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[ebuild N ] net-www/mozilla-1.5-r1 +java +crypt -ipv6 -gtk2 +ssl +ldap |
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+gnome -debug +mozcalendar -mozaccess -mozxmlterm -moznoirc -moznomail |
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-moznocompose -moznoxft |
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</pre> |
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|
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<p> |
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<c>emerge</c> isn't the only tool for this job. In fact, we have a tool |
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dedicated to package information called <c>etcat</c> which resides in the |
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<c>gentoolkit</c> package. First, install <c>gentoolkit</c>: |
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</p> |
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|
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<pre caption="Installing gentoolkit"> |
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# <i>emerge --usepkg gentoolkit</i> |
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</pre> |
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|
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<p> |
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Now run <c>etcat</c> with the <c>uses</c> argument to view the USE-flags of a |
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certain package. For instance, for the <c>gnumeric</c> package: |
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</p> |
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|
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<pre caption="Using etcat to view used USE-flags"> |
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# <i>etcat uses gnumeric</i> |
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[ Colour Code : <i>set</i> <comment>unset</comment> ] |
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[ Legend : (U) Col 1 - Current USE flags ] |
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[ : (I) Col 2 - Installed With USE flags ] |
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|
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U I [ Found these USE variables in : app-office/gnumeric-1.2.0 ] |
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- - <comment>libgda</comment> : Adds GNU Data Access (CORBA wrapper) support for gnumeric |
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- - <comment>gnomedb</comment> : unknown |
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+ + <i>python</i> : Adds support/bindings for the Python language |
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+ + <i>bonobo</i> : Adds support for gnome-base/bonobo (Gnome CORBA interfaces) |
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</pre> |
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|
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</body> |
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</subsection> |
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</section> |
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</sections> |
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