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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/2.5 --> |
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-working-use.xml,v 1.52 2012/07/24 12:12:52 swift Exp $ --> |
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<sections> |
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|
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<abstract> |
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USE flags are a very important aspect of Gentoo. In this chapter, you learn to |
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work with USE flags and understand how USE flags interact with your system. |
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</abstract> |
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|
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<version>4</version> |
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<date>2013-02-09</date> |
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|
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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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management 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>. |
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</p> |
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|
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<p> |
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A list of available local USE flags can be found locally in |
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<path>/usr/portage/profiles/use.local.desc</path>. |
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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>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>make.defaults</path> files part of your profile. |
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</p> |
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|
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<p> |
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The profile your system listens to is pointed to by the |
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<path>/etc/portage/make.profile</path> symlink. Each profile works on top of |
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another, larger profile, the end result is therefore the sum of all profiles. |
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The top profile is the <path>base</path> profile |
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(<path>/usr/portage/profiles/base</path>). |
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</p> |
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|
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<p> |
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Let us take a look at this default setting for the 13.0 profile: |
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</p> |
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|
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<pre caption="Cumulative make.defaults USE variable for the 13.0 profile"> |
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<comment>(This example is the sum of the settings in base, default/linux, |
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default/linux/x86 and default/linux/x86/13.0/)</comment> |
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USE="a52 aac acpi alsa branding cairo cdr dbus dts dvd dvdr emboss encode exif |
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fam firefox flac gif gpm gtk hal jpeg lcms ldap libnotify mad mikmod mng mp3 |
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mp4 mpeg ogg opengl pango pdf png ppds qt3support qt4 sdl spell |
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startup-notification svg tiff truetype vorbis unicode usb X xcb x264 xml xv |
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xvid" |
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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 any <path>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/portage/make.conf</path>. In this variable you add the extra USE |
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flags you require, or remove the USE flags you don't want. This latter is done |
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by 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/portage/make.conf</path>: |
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</p> |
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|
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<pre caption="An example USE setting in /etc/portage/make.conf"> |
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USE="-kde -qt4 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>Declaring USE flags for individual packages</title> |
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<body> |
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|
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<p> |
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Sometimes you want to declare a certain USE flag for one (or a couple) of |
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applications but not system-wide. To accomplish this, you will need to create |
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the <path>/etc/portage</path> directory (if it doesn't exist yet) and edit |
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<path>/etc/portage/package.use</path>. This is usually a single file, but can |
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also be a directory; see <c>man portage</c> for more information. The following |
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examples assume <path>package.use</path> is a single file. |
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</p> |
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|
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<p> |
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For instance, if you don't want <c>berkdb</c> support globally but you do want |
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it for <c>mysql</c>, you would add: |
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</p> |
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|
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<pre caption="/etc/portage/package.use example"> |
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dev-db/mysql berkdb |
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</pre> |
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|
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<p> |
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You can of course also explicitly <e>disable</e> USE flags for a certain |
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application. For instance, if you don't want <c>java</c> support in PHP: |
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</p> |
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|
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<pre caption="/etc/portage/package.use 2nd example"> |
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dev-php/php -java |
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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/portage/make.conf</path> twice (to do and undo the USE changes) you |
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can just declare the USE variable as environment variable. Remember that, when |
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you re-emerge or update this application (either explicitly or as part of a |
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system update) your changes will be lost! |
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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 seamonkey. |
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</p> |
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|
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<pre caption="Using USE as environment variable"> |
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# <i>USE="-java" emerge seamonkey</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>Precedence</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 precedence 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 still used due to a setting that has a higher priority. |
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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 the <path>make.defaults</path> files part of |
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your profile |
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</li> |
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<li> |
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User-defined USE setting in <path>/etc/portage/make.conf</path> |
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</li> |
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<li> |
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User-defined USE setting in <path>/etc/portage/package.use</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 |
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--info</c>. This will list all relevant variables (including the <c>USE</c> |
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variable) with 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, use <c>emerge</c>'s <c>--newuse</c> option: |
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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 --update --deep --newuse world</i> |
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</pre> |
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|
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<p> |
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Next, run Portage's 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, run <c>revdep-rebuild</c> to rebuild the |
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applications that are dynamically linked against shared objects provided by |
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possibly removed packages. <c>revdep-rebuild</c> is part of the |
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<c>gentoolkit</c> package; don't forget to emerge it first. |
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</p> |
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|
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<pre caption="Running revdep-rebuild"> |
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# <i>revdep-rebuild</i> |
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</pre> |
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|
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<p> |
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When all this is accomplished, 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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Let us take the example of <c>seamonkey</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> and <c>--verbose</c> |
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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 seamonkey</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 R ] www-client/seamonkey-1.0.7 USE="crypt gnome java -debug -ipv6 |
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-ldap -mozcalendar -mozdevelop -moznocompose -moznoirc -moznomail -moznopango |
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-moznoroaming -postgres -xinerama -xprint" 0 kB |
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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>equery</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 gentoolkit</i> |
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</pre> |
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|
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<p> |
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Now run <c>equery</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 equery to view used USE flags"> |
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# <i>equery --nocolor uses =gnumeric-1.6.3 -a</i> |
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[ Searching for packages matching =gnumeric-1.6.3... ] |
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[ Colour Code : set unset ] |
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[ Legend : Left column (U) - USE flags from make.conf ] |
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[ : Right column (I) - USE flags packages was installed with ] |
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[ Found these USE variables for app-office/gnumeric-1.6.3 ] |
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U I |
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- - debug : Enable extra debug codepaths, like asserts and extra output. |
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If you want to get meaningful backtraces see |
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http://www.gentoo.org/proj/en/qa/backtraces.xml . |
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+ + gnome : Adds GNOME support |
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+ + python : Adds support/bindings for the Python language |
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- - static : !!do not set this during bootstrap!! Causes binaries to be |
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statically linked instead of dynamically |
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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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