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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-tools-settingenviron">
<?dbhtml filename="settingenvironment.html"?>
<title>Setting Up the Environment</title>
<para>Set up a good working environment by creating two new startup files
for the <command>bash</command> shell. While logged in as user
<systemitem class="username">lfs</systemitem>, 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 <systemitem class="username">lfs</systemitem>,
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
LFS=/mnt/lfs
LC_ALL=POSIX
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
<function>open(2)</function> 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 are used from the host when the same programs are available in
the chapter 5 environment.</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>
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