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In the new cross-compilation approach, the $PATH in chroot does not contain '/tools/bin'. So "+h" is useless in chroot as the newly installed tools always replace the temporary counterpart at the same location. "+h" in chapter4/settingenviron.xml is kept deliberately. Currently $LFS/tools/bin only contains programs prefixed with "x86_64-lfs-linux-gnu-", and it's highly unlikely that any distro will ever ship a program named with such prefix. So it may seems that we can remove this "+h" as well. However, the situation may change in future and we can take this oppertunity to teach the advantage and disvantage of bash hash feature.
203 lines
8.7 KiB
XML
203 lines
8.7 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % general-entities SYSTEM "../general.ent">
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%general-entities;
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]>
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<sect1 id="ch-preps-settingenviron">
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<?dbhtml filename="settingenvironment.html"?>
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<title>Setting Up the Environment</title>
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<para>Set up a good working environment by creating two new startup files
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for the <command>bash</command> shell. While logged in as user
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<systemitem class="username">lfs</systemitem>, issue the following command
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to create a new <filename>.bash_profile</filename>:</para>
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<screen><userinput>cat > ~/.bash_profile << "EOF"
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<literal>exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash</literal>
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EOF</userinput></screen>
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<para>When logged on as user <systemitem class="username">lfs</systemitem>,
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the initial shell is usually a <emphasis>login</emphasis> shell which reads
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the <filename>/etc/profile</filename> of the host (probably containing some
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settings and environment variables) and then <filename>.bash_profile</filename>.
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The <command>exec env -i.../bin/bash</command> command in the
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<filename>.bash_profile</filename> file replaces the running shell with a new
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one with a completely empty environment, except for the <envar>HOME</envar>,
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<envar>TERM</envar>, and <envar>PS1</envar> variables. This ensures that no
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unwanted and potentially hazardous environment variables from the host system
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leak into the build environment. The technique used here achieves the goal of
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ensuring a clean environment.</para>
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<para>The new instance of the shell is a <emphasis>non-login</emphasis>
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shell, which does not read, and execute, the contents of <filename>/etc/profile</filename> or
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<filename>.bash_profile</filename> files, but rather reads, and executes, the
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<filename>.bashrc</filename> file instead. Create the
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<filename>.bashrc</filename> file now:</para>
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<screen><userinput>cat > ~/.bashrc << "EOF"
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<literal>set +h
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umask 022
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LFS=/mnt/lfs
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LC_ALL=POSIX
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LFS_TGT=$(uname -m)-lfs-linux-gnu
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PATH=/usr/bin
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if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
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PATH=$LFS/tools/bin:$PATH
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CONFIG_SITE=$LFS/usr/share/config.site
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export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
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EOF</userinput></screen>
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<variablelist>
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<title>The meaning of the settings in <filename>.bashrc</filename></title>
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<varlistentry>
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<term><parameter>set +h</parameter></term>
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<listitem>
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<para>The <command>set +h</command> command turns off
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<command>bash</command>'s hash function. Hashing is ordinarily a useful
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feature—<command>bash</command> uses a hash table to remember the
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full path of executable files to avoid searching the <envar>PATH</envar>
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time and again to find the same executable. However, the new tools should
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be used as soon as they are installed. By switching off the hash function,
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the shell will always search the <envar>PATH</envar> when a program is to
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be run. As such, the shell will find the newly compiled tools in
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<filename class="directory">$LFS/tools/bin</filename> as soon as they are
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available without remembering a previous version of the same program
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provided by the host distro, in
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<filename class='directory'>/usr/bin</filename> or
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<filename class='directory'>/bin</filename>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>umask 022</parameter></term>
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<listitem>
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<para>Setting the user file-creation mask (umask) to 022 ensures that newly
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created files and directories are only writable by their owner, but are
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readable and executable by anyone (assuming default modes are used by the
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<function>open(2)</function> system call, new files will end up with permission
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mode 644 and directories with mode 755).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LFS=/mnt/lfs</parameter></term>
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<listitem>
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<para>The <envar>LFS</envar> variable should be set to the chosen mount
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point.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LC_ALL=POSIX</parameter></term>
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<listitem>
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<para>The <envar>LC_ALL</envar> variable controls the localization of certain
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programs, making their messages follow the conventions of a specified country.
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Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
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(the two are equivalent) ensures that everything will work as expected in
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the chroot environment.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
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<listitem>
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<para>The <envar>LFS_TGT</envar> variable sets a non-default, but compatible machine
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description for use when building our cross compiler and linker and when cross
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compiling our temporary toolchain. More information is contained in
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<xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>PATH=/usr/bin</parameter></term>
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<listitem>
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<para>Many modern linux distributions have merged <filename
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class="directory">/bin</filename> and <filename
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class="directory">/usr/bin</filename>. When this is the case, the standard
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<envar>PATH</envar> variable needs just to be set to <filename
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class="directory">/usr/bin/</filename> for the <xref
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linkend="chapter-temporary-tools"/> environment. When this is not the
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case, the following line adds <filename class="directory">/bin</filename>
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to the path.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
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<listitem>
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<para>If <filename class="directory">/bin</filename> is not a symbolic
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link, then it has to be added to the <envar>PATH</envar> variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
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<listitem>
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<para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
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standard <envar>PATH</envar>, the cross-compiler installed at the beginning
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of <xref linkend="chapter-cross-tools"/> is picked up by the shell
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immediately after its installation. This, combined with turning off hashing,
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limits the risk that the compiler from the host be used instead of the
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cross-compiler.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
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<listitem>
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<para>In <xref linkend="chapter-cross-tools"/> and
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<xref linkend="chapter-temporary-tools"/>, if this variable is not set,
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<command>configure</command> scripts
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may attempt to load configuration items specific to some distributions from
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<filename>/usr/share/config.site</filename> on the host system. Override
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it to prevent potential contamination from the host.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>export ...</parameter></term>
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<listitem>
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<para>While the above commands have set some variables, in order
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to make them visible within any sub-shells, we export them.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<important>
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<para>Several commercial distributions add a non-documented instantiation
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of <filename>/etc/bash.bashrc</filename> to the initialization of
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<command>bash</command>. This file has the potential to modify the
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<systemitem class="username">lfs</systemitem>
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user's environment in ways that can affect the building of critical LFS
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packages. To make sure the <systemitem class="username">lfs</systemitem>
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user's environment is clean, check for the
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presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
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out of the way. As the <systemitem class="username">root</systemitem>
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user, run:</para>
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<screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
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<para>After use of the <systemitem class="username">lfs</systemitem>
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user is finished at the beginning of <xref
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linkend="chapter-chroot-temporary-tools"/>, you can restore
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<filename>/etc/bash.bashrc</filename> (if desired).</para>
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<para>Note that the LFS Bash package we will build in
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<xref linkend="ch-system-bash"/> is not configured to load or execute
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<filename>/etc/bash.bashrc</filename>, so this file is useless on a
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completed LFS system.</para>
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</important>
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<para>Finally, to have the environment fully prepared for building the
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temporary tools, source the just-created user profile:</para>
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<screen><userinput>source ~/.bash_profile</userinput></screen>
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</sect1>
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