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git-svn-id: http://svn.linuxfromscratch.org/LFS/branches/testing/BOOK@3998 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689
94 lines
4.3 KiB
XML
94 lines
4.3 KiB
XML
<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN" "http://www.oasis-open.org/docbook/xml/4.3/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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<title>Setting up the environment</title>
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<?dbhtml filename="settingenvironment.html"?>
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<para>Set up a good working environment by creating two new startup
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files for the <command>bash</command> shell. While logged in as user
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<emphasis>lfs</emphasis>, issue the
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following command to create a new <filename>.bash_profile</filename>:</para>
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<screen><userinput>cat > ~/.bash_profile << "EOF"
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exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash
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EOF</userinput></screen>
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<para>Normally when logged on as user <emphasis>lfs</emphasis>, the
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initial shell is a <emphasis>login</emphasis> shell which reads the
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<filename>/etc/profile</filename> of your host (probably containing
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some settings and environment variables) and then
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<filename>.bash_profile</filename>. The <command>exec env
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-i.../bin/bash</command> command in the
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<filename>.bash_profile</filename> file replaces the running shell
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with a new one with a completely empty environment, except for the
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<emphasis>HOME</emphasis>, <emphasis>TERM</emphasis>, and
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<emphasis>PS1</emphasis> variables. This ensures that no unwanted and
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potentially hazardous environment variables from the host system leak
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into the build environment. The technique used here achieves the goal
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of enforcing 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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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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PATH=/tools/bin:/bin:/usr/bin
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export LFS LC_ALL PATH
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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
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ordinarily a useful feature -- bash uses a hash table to remember the
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full pathnames of executable files to avoid searching the PATH time
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and time again to find the same executable. However, the new tools
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should be used as soon as they are installed. By switching off the
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hash function, the shell will always search the PATH when a program is
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requested to be run. As such, the shell will find our newly compiled
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tools in <filename class="directory">$LFS/tools</filename> as soon as
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they are available without remembering a previous version of the same
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program (name wise) in a 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
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are readable and executable by anyone (assuming default modes are used
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by the open(2) system call, new files will end up with permission mode
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644 and directories with mode 755).</para>
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<para>The <emphasis>LFS</emphasis> variable should be set to the
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chosen mount point.</para>
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<para>The <emphasis>LC_ALL</emphasis> variable controls the
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localization of certain programs, making their messages follow the
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conventions of a specified country. If the host system uses a version
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of Glibc older than 2.2.4, having LC_ALL set to something other than
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<quote>POSIX</quote> or <quote>C</quote> (during this chapter) may
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cause issues if you exit the chroot environment and wish to return
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later. By setting <emphasis>LC_ALL</emphasis> to <quote>POSIX</quote>
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or <quote>C</quote> (the two are equivalent), we ensure that
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everything will work as expected in the chroot environment.</para>
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<para>By putting <filename class="directory">/tools/bin</filename>
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ahead of the standard PATH, all the programs installed in <xref
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linkend="chapter-temporary-tools"/> are picked up by the shell
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imemdiately after their installation. This coupled with the fact that
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hashing has been turned off, there is no risk that old programs from
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the host are being used when they should not be used any
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longer.</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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