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git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@8755 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
98 lines
4.8 KiB
XML
98 lines
4.8 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-tools-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 the <filename>/etc/profile</filename> or
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<filename>.bash_profile</filename> files, but rather reads 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=$(uname -m)-lfs-linux-gnu
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PATH=/tools/bin:/bin:/usr/bin
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export LFS LC_ALL LFS_TGT PATH</literal>
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EOF</userinput></screen>
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<para>The <command>set +h</command> command turns off
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<command>bash</command>'s hash function. Hashing is ordinarily a useful
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feature—<command>bash</command> uses a hash table to remember the
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full path of executable files to avoid searching the <envar>PATH</envar>
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time and again to find the same executable. However, the new tools should
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be used as soon as they are installed. By switching off the hash function,
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the shell will always search the <envar>PATH</envar> when a program is to
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be run. As such, the shell will find the newly compiled tools in
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<filename class="directory">$LFS/tools</filename> as soon as they are
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available without remembering a previous version of the same program in a
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different location.</para>
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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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<para>The <envar>LFS</envar> variable should be set to the chosen mount
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point.</para>
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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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If the host system uses a version of Glibc older than 2.2.4, having
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<envar>LC_ALL</envar> set to something other than <quote>POSIX</quote> or
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<quote>C</quote> (during this chapter) may cause issues if you exit the chroot
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environment and wish to return later. Setting <envar>LC_ALL</envar> to
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<quote>POSIX</quote> or <quote>C</quote> (the two are equivalent) ensures that
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everything will work as expected in the chroot environment.</para>
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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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<para>By putting <filename class="directory">/tools/bin</filename> ahead of the
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standard <envar>PATH</envar>, all the programs installed in <xref
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linkend="chapter-temporary-tools"/> are picked up by the shell immediately after
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their installation. This, combined with turning off hashing, limits the risk
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that old programs are used from the host when the same programs are available in
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the chapter 5 environment.</para>
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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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