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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-features.xml,v 1.39 2011/10/27 18:33:42 swift Exp $ -->
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<sections>
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<abstract>
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Discover the features Portage has, such as support for distributed compiling,
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ccache and more.
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</abstract>
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<version>4</version>
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<date>2011-11-27</date>
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<section>
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<title>Portage Features</title>
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<body>
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<p>
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Portage has several additional features that makes your Gentoo experience even
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better. Many of these features rely on certain software tools that improve
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performance, reliability, security, ...
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</p>
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<p>
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To enable or disable certain Portage features you need to edit
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<path>/etc/make.conf</path>'s <c>FEATURES</c> variable which contains the
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various feature keywords, separated by white space. In several cases you
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will also need to install the additional tool on which the feature relies.
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</p>
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<p>
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Not all features that Portage supports are listed here. For a full overview,
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please consult the <path>make.conf</path> man page:
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</p>
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<pre caption="Consulting the make.conf man page">
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$ <i>man make.conf</i>
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</pre>
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<p>
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To find out what FEATURES are default set, run <c>emerge --info</c> and search
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for the FEATURES variable or grep it out:
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</p>
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<pre caption="Finding out the FEATURES that are already set">
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$ <i>emerge --info | grep FEATURES</i>
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</pre>
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</body>
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</section>
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<section>
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<title>Distributed Compiling</title>
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<subsection>
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<title>Using distcc</title>
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<body>
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<p>
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<c>distcc</c> is a program to distribute compilations across several, not
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necessarily identical, machines on a network. The <c>distcc</c> client sends all
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necessary information to the available distcc servers (running <c>distccd</c>)
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so they can compile pieces of source code for the client. The net result is a
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faster compilation time.
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</p>
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<p>
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You can find more information about <c>distcc</c> (and how to have it work
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with Gentoo) in our <uri link="/doc/en/distcc.xml">Gentoo Distcc
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Documentation</uri>.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Installing distcc</title>
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<body>
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<p>
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Distcc ships with a graphical monitor to monitor tasks that your computer is
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sending away for compilation. If you use Gnome then put 'gnome' in your USE
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variable. However, if you don't use Gnome and would still like to have the
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monitor then you should put 'gtk' in your USE variable.
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</p>
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<pre caption="Installing distcc">
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# <i>emerge distcc</i>
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</pre>
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</body>
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</subsection>
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<subsection>
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<title>Activating Portage Support</title>
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<body>
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<p>
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Add <c>distcc</c> to the FEATURES variable inside <path>/etc/make.conf</path>.
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Next, edit the MAKEOPTS variable to your liking. A known guideline is to fill in
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"-jX" with X the number of CPUs that run <c>distccd</c> (including the current
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host) plus one, but you might have better results with other numbers.
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</p>
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<p>
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Now run <c>distcc-config</c> and enter the list of available distcc servers. For
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a simple example we assume that the available DistCC servers are 192.168.1.102
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(the current host), 192.168.1.103 and 192.168.1.104 (two "remote" hosts):
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</p>
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<pre caption="Configuring distcc to use three available distcc servers">
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# <i>distcc-config --set-hosts "192.168.1.102 192.168.1.103 192.168.1.104"</i>
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</pre>
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<p>
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Don't forget to run the <c>distccd</c> daemon as well:
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</p>
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<pre caption="Starting the distccd daemons">
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# <i>rc-update add distccd default</i>
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# <i>/etc/init.d/distccd start</i>
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</pre>
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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>Caching Compilation</title>
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<subsection>
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<title>About ccache</title>
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<body>
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<p>
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<c>ccache</c> is a fast compiler cache. When you compile a program, it will
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cache intermediate results so that, whenever you recompile the same program, the
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compilation time is greatly reduced. The first time you run ccache, it will be
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much slower than a normal compilation. Subsequent recompiles should be faster.
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ccache is only helpful if you will be recompiling the same application many
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times; thus it's mostly only useful for software developers.
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</p>
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<p>
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If you are interested in the ins and outs of ccache, please visit the
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<uri link="http://ccache.samba.org">ccache homepage</uri>.
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</p>
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<warn>
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<c>ccache</c> is known to cause numerous compilation failures. Sometimes ccache
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will retain stale code objects or corrupted files, which can lead to packages
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that cannot be emerged. If this happens (if you receive errors like "File not
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recognized: File truncated"), try recompiling the application with ccache
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disabled (<c>FEATURES="-ccache"</c> in <path>/etc/make.conf</path>)
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<e>before</e> reporting a bug. Unless you are doing development work, <e>do not
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enable ccache</e>.
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</warn>
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</body>
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</subsection>
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<subsection>
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<title>Installing ccache</title>
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<body>
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<p>
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To install <c>ccache</c>, run <c>emerge ccache</c>:
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</p>
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<pre caption="Installing ccache">
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# <i>emerge ccache</i>
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</pre>
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</body>
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</subsection>
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<subsection>
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<title>Activating Portage Support</title>
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<body>
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<p>
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Open <path>/etc/make.conf</path> and add <c>ccache</c> to the FEATURES variable.
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Next, add a new variable called CCACHE_SIZE and set it to "2G":
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</p>
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<pre caption="Editing CCACHE_SIZE in /etc/make.conf">
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CCACHE_SIZE="2G"
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</pre>
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<p>
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To check if ccache functions, ask ccache to provide you with its statistics.
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Because Portage uses a different ccache home directory, you need to set the
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<c>CCACHE_DIR</c> variable as well:
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</p>
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<pre caption="Viewing ccache statistics">
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# <i>CCACHE_DIR="/var/tmp/ccache" ccache -s</i>
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</pre>
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<p>
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The <path>/var/tmp/ccache</path> location is Portage' default ccache home
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directory; if you want to alter this setting you can set the <c>CCACHE_DIR</c>
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variable in <path>/etc/make.conf</path>.
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</p>
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<p>
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However, if you would run <c>ccache</c>, it would use the default location of
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<path>${HOME}/.ccache</path>, which is why you needed to set the
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<c>CCACHE_DIR</c> variable when asking for the (Portage) ccache statistics.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Using ccache for non-Portage C Compiling</title>
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<body>
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<p>
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If you would like to use ccache for non-Portage compilations, add
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<path>/usr/lib/ccache/bin</path> to the beginning of your PATH variable (before
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<path>/usr/bin</path>). This can be accomplished by editing
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<path>.bash_profile</path> in your user's home directory. Using
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<path>.bash_profile</path> is one way to define PATH variables.
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</p>
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<pre caption="Editing .bash_profile">
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PATH="<i>/usr/lib/ccache/bin</i>:/opt/bin:${PATH}"
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</pre>
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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>Binary Package Support</title>
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<subsection>
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<title>Creating Prebuilt Packages</title>
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<body>
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<p>
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Portage supports the installation of prebuilt packages. Even though Gentoo does
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not provide prebuilt packages by itself (except for the GRP snapshots) Portage
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can be made fully aware of prebuilt packages.
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</p>
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<p>
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To create a prebuilt package you can use <c>quickpkg</c> if the package is
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already installed on your system, or <c>emerge</c> with the <c>--buildpkg</c> or
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<c>--buildpkgonly</c> options.
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</p>
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<p>
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If you want Portage to create prebuilt packages of every single package you
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install, add <c>buildpkg</c> to the FEATURES variable.
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</p>
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<p>
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More extended support for creating prebuilt package sets can be obtained with
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<c>catalyst</c>. For more information on catalyst please read the <uri
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link="/proj/en/releng/catalyst/faq.xml">Catalyst Frequently Asked
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Questions</uri>.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Installing Prebuilt Packages</title>
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<body>
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<p>
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Although Gentoo doesn't provide one, you can create a central repository where
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you store prebuilt packages. If you want to use this repository, you need to
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make Portage aware of it by having the PORTAGE_BINHOST variable point to
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it. For instance, if the prebuilt packages are on ftp://buildhost/gentoo:
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</p>
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<pre caption="Setting PORTAGE_BINHOST in /etc/make.conf">
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PORTAGE_BINHOST="ftp://buildhost/gentoo"
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</pre>
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<p>
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When you want to install a prebuilt package, add the <c>--getbinpkg</c> option
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to the emerge command alongside of the <c>--usepkg</c> option. The former tells
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emerge to download the prebuilt package from the previously defined server
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while the latter asks emerge to try to install the prebuilt package first before
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fetching the sources and compiling it.
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</p>
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<p>
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For instance, to install <c>gnumeric</c> with prebuilt packages:
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</p>
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<pre caption="Installing the gnumeric prebuilt package">
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# <i>emerge --usepkg --getbinpkg gnumeric</i>
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</pre>
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<p>
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More information about emerge's prebuilt package options can be found in the
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emerge man page:
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</p>
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<pre caption="Reading the emerge man page">
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$ <i>man emerge</i>
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</pre>
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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>Fetching Files</title>
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<subsection>
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<title>Parallel fetch</title>
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<body>
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<p>
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When you are emerging a series of packages, Portage can fetch the source files
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for the next package in the list even while it is compiling another package,
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thus shortening compile times. To make use of this capability, add
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"parallel-fetch" to your FEATURES.
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</p>
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</body>
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</subsection>
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<subsection>
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<title>Userfetch</title>
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<body>
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<p>
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When Portage is run as root, FEATURES="userfetch" will allow Portage to drop
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root privileges while fetching package sources. This is a small security
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improvement.
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</p>
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</body>
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</subsection>
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</section>
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<section id="webrsync-gpg">
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<title>Pulling Validated Portage Tree Snapshots</title>
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<body>
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<p>
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As an administrator, you can opt to only update your local Portage tree with a
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cryptographically validated Portage tree snapshot as released by the Gentoo
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infrastructure. This ensures that no rogue rsync mirror is adding unwanted code
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or packages in the tree you are downloading.
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</p>
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<p>
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To configure Portage, first create a truststore in which you download and accept
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the keys of the Gentoo Infrastructure responsible for signing the Portage tree
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snapshots. Of course, if you want to, you can validate this GPG key as per the
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<uri link="/doc/en/gnupg-user.xml#doc_chap2_sect4">proper guidelines</uri>
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(like checking the key fingerprint <c>AE54 54F9 67B5 6AB0 9AE1 6064 0838
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C26E 239C 75C4</c> for key <c>0x239C75C4</c> or <c>DCD0 5B71 EAB9 4199 527F 44AC
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DB6B 8C1F 96D8 BF6D</c> for key <c>0x96D8BF6D</c>).
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</p>
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<!-- Key 0x239C75C4 is superceded by 0x96D8BF6D, but keep it in the documents
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for a while to ensure continuity -->
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<pre caption="Creating a truststore for Portage">
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# <i>mkdir -p /etc/portage/gpg</i>
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# <i>chmod 0700 /etc/portage/gpg</i>
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# <i>gpg --homedir /etc/portage/gpg --keyserver subkeys.pgp.net --recv-keys 0x239C75C4 0x96D8BF6D</i>
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# <i>gpg --homedir /etc/portage/gpg --edit-key 0x239C75C4 trust</i>
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# <i>gpg --homedir /etc/portage/gpg --edit-key 0x96D8BF6D trust</i>
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</pre>
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<p>
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Next, edit <path>/etc/make.conf</path> and enable support for validating the
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signed Portage tree snapshots (using <c>FEATURES="webrsync-gpg"</c>) and
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disabling updating the Portage tree using the regular <c>emerge --sync</c>
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method.
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</p>
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<pre caption="Updating Portage for signed tree validation">
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FEATURES="webrsync-gpg"
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PORTAGE_GPG_DIR="/etc/portage/gpg"
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SYNC=""
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</pre>
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<p>
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That's it. Next time you run <c>emerge-webrsync</c>, only the snapshots with
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a valid signature will be expanded on your file system.
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</p>
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</body>
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</section>
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</sections>
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