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diff --git a/chapter04/settingenviron.xml b/chapter04/settingenviron.xml index ea2672707..247b55e96 100644 --- a/chapter04/settingenviron.xml +++ b/chapter04/settingenviron.xml @@ -7,10 +7,35 @@ <title>Setting Up the Environment</title> <?dbhtml filename="settingenvironment.html"?> +<para>Set up a good working environment by creating two new startup +files for the <command>bash</command> shell. While logged in as user +<emphasis>lfs</emphasis>, issue the +following command to create a new <filename>.bash_profile</filename>:</para> + <screen><userinput>cat > ~/.bash_profile << "EOF" <literal>exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash</literal> EOF</userinput></screen> +<para>When logged on as user <emphasis>lfs</emphasis>, the +initial shell is usually a <emphasis>login</emphasis> shell which reads the +<filename>/etc/profile</filename> of the host (probably containing +some settings and environment variables) and then +<filename>.bash_profile</filename>. The <command>exec env +-i.../bin/bash</command> command in the +<filename>.bash_profile</filename> file replaces the running shell +with a new one with a completely empty environment, except for the +<envar>HOME</envar>, <envar>TERM</envar>, and +<envar>PS1</envar> variables. This ensures that no unwanted and +potentially hazardous environment variables from the host system leak +into the build environment. The technique used here achieves the goal +of ensuring a clean environment.</para> + +<para>The new instance of the shell is a <emphasis>non-login</emphasis> +shell, which does not read the <filename>/etc/profile</filename> or +<filename>.bash_profile</filename> files, but rather reads the +<filename>.bashrc</filename> file instead. Create the +<filename>.bashrc</filename> file now:</para> + <screen><userinput>cat > ~/.bashrc << "EOF" <literal>set +h umask 022 @@ -20,6 +45,49 @@ PATH=/tools/bin:/bin:/usr/bin export LFS LC_ALL PATH</literal> EOF</userinput></screen> +<para>The <command>set +h</command> command turns off +<command>bash</command>'s hash function. Hashing is ordinarily a useful +feature—<command>bash</command> uses a hash table to remember the +full path of executable files to avoid searching the <envar>PATH</envar> time +and again to find the same executable. However, the new tools +should be used as soon as they are installed. By switching off the +hash function, the shell will always search the <envar>PATH</envar> when a program is +to be run. As such, the shell will find the newly compiled +tools in <filename class="directory">$LFS/tools</filename> as soon as +they are available without remembering a previous version of the same +program in a different location.</para> + +<para>Setting the user file-creation mask (umask) to 022 ensures that newly +created files and directories are only writable by their owner, but +are readable and executable by anyone (assuming default modes are used +by the open(2) system call, new files will end up with permission mode +644 and directories with mode 755).</para> + +<para>The <envar>LFS</envar> variable should be set to the +chosen mount point.</para> + +<para>The <envar>LC_ALL</envar> variable controls the +localization of certain programs, making their messages follow the +conventions of a specified country. If the host system uses a version +of Glibc older than 2.2.4, having <envar>LC_ALL</envar> set to something other than +<quote>POSIX</quote> or <quote>C</quote> (during this chapter) may +cause issues if you exit the chroot environment and wish to return +later. Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> +or <quote>C</quote> (the two are equivalent) ensures that +everything will work as expected in the chroot environment.</para> + +<para>By putting <filename class="directory">/tools/bin</filename> +ahead of the standard <envar>PATH</envar>, all the programs installed in <xref +linkend="chapter-temporary-tools"/> are picked up by the shell +immediately after their installation. This, combined with turning off +hashing, limits the risk that old programs from +the host are being used when they should not be used any +longer.</para> + +<para>Finally, to have the environment fully prepared for building the +temporary tools, source the just-created user profile:</para> + <screen><userinput>source ~/.bash_profile</userinput></screen> </sect1> + |