source: chapter04/settingenviron.xml@ 78349b7

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<sect1 id="ch-tools-settingenviron">
<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 &gt; ~/.bash_profile &lt;&lt; "EOF"
exec env -i HOME=$HOME TERM=$TERM PS1='\u:\w\$ ' /bin/bash
EOF</userinput></screen>

<para>Normally when logged on as user <emphasis>lfs</emphasis>, the
initial shell is a <emphasis>login</emphasis> shell which reads the
<filename>/etc/profile</filename> of your 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
<emphasis>HOME</emphasis>, <emphasis>TERM</emphasis>, and
<emphasis>PS1</emphasis> 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 enforcing 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 &gt; ~/.bashrc &lt;&lt; "EOF"
set +h
umask 022
LFS=/mnt/lfs
LC_ALL=POSIX
PATH=/tools/bin:/bin:/usr/bin
export LFS LC_ALL PATH
EOF</userinput></screen>

<para>The <command>set +h</command> command turns off
<command>bash</command>'s hash function. Hashing is
ordinarily a useful feature -- bash uses a hash table to remember the
full pathnames of executable files to avoid searching the PATH time
and time 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 PATH when a program is
requested to be run. As such, the shell will find our 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 (name wise) 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 <emphasis>LFS</emphasis> variable should be set to the
chosen mount point.</para>

<para>The <emphasis>LC_ALL</emphasis> 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 LC_ALL 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. By setting <emphasis>LC_ALL</emphasis> to <quote>POSIX</quote>
or <quote>C</quote> (the two are equivalent), we ensure that
everything will work as expected in the chroot environment.</para>

<para>By putting <filename class="directory">/tools/bin</filename>
ahead of the standard PATH, all the programs installed in <xref
linkend="chapter-temporary-tools"/> are picked up by the shell
imemdiately after their installation. This coupled with the fact that
hashing has been turned off, there is no 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>