mirror of
https://git.linuxfromscratch.org/lfs.git
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205 lines
8.8 KiB
XML
205 lines
8.8 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-preps-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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or when switched to the &lfs-user; user using an <command>su</command> command
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with the <quote><parameter>-</parameter></quote> option,
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the initial shell is 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.</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, and execute, the contents of the <filename>/etc/profile</filename> or
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<filename>.bash_profile</filename> files, but rather reads, and executes, 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=$(uname -m)-lfs-linux-gnu
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PATH=/usr/bin
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if [ ! -L /bin ]; then PATH=/bin:$PATH; fi
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PATH=$LFS/tools/bin:$PATH
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CONFIG_SITE=$LFS/usr/share/config.site
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export LFS LC_ALL LFS_TGT PATH CONFIG_SITE</literal>
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EOF</userinput></screen>
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<variablelist>
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<title>The meaning of the settings in <filename>.bashrc</filename></title>
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<varlistentry>
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<term><parameter>set +h</parameter></term>
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<listitem>
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<para>The <command>set +h</command> command turns off
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<command>bash</command>'s hash function. Hashing is ordinarily a useful
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feature—<command>bash</command> uses a hash table to remember the
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full path to executable files to avoid searching the <envar>PATH</envar>
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time and again to find the same executable. However, the new tools should
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be used as soon as they are installed. Switching off the hash function forces
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the shell to search the <envar>PATH</envar> whenever a program is to
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be run. As such, the shell will find the newly compiled tools in
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<filename class="directory">$LFS/tools/bin</filename> as soon as they are
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available without remembering a previous version of the same program
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provided by the host distro, in
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<filename class='directory'>/usr/bin</filename> or
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<filename class='directory'>/bin</filename>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>umask 022</parameter></term>
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<listitem>
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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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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LFS=/mnt/lfs</parameter></term>
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<listitem>
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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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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LC_ALL=POSIX</parameter></term>
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<listitem>
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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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Setting <envar>LC_ALL</envar> to <quote>POSIX</quote> or <quote>C</quote>
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(the two are equivalent) ensures that everything will work as expected in
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the cross-compilation environment.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>LFS_TGT=(uname -m)-lfs-linux-gnu</parameter></term>
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<listitem>
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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
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cross-compiling our temporary toolchain. More information is provided by
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<xref linkend="ch-tools-toolchaintechnotes" role=""/>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>PATH=/usr/bin</parameter></term>
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<listitem>
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<para>Many modern Linux distributions have merged <filename
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class="directory">/bin</filename> and <filename
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class="directory">/usr/bin</filename>. When this is the case, the standard
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<envar>PATH</envar> variable should be set to <filename
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class="directory">/usr/bin/</filename> for the <xref
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linkend="chapter-temporary-tools"/> environment. When this is not the
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case, the following line adds <filename class="directory">/bin</filename>
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to the path.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>if [ ! -L /bin ]; then PATH=/bin:$PATH; fi</parameter></term>
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<listitem>
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<para>If <filename class="directory">/bin</filename> is not a symbolic
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link, it must be added to the <envar>PATH</envar> variable.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>PATH=$LFS/tools/bin:$PATH</parameter></term>
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<listitem>
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<para>By putting <filename class="directory">$LFS/tools/bin</filename> ahead of the
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standard <envar>PATH</envar>, the cross-compiler installed at the beginning
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of <xref linkend="chapter-cross-tools"/> is picked up by the shell
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immediately after its installation. This, combined with turning off hashing,
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limits the risk that the compiler from the host is used instead of the
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cross-compiler.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>CONFIG_SITE=$LFS/usr/share/config.site</parameter></term>
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<listitem>
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<para>In <xref linkend="chapter-cross-tools"/> and
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<xref linkend="chapter-temporary-tools"/>, if this variable is not set,
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<command>configure</command> scripts
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may attempt to load configuration items specific to some distributions from
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<filename>/usr/share/config.site</filename> on the host system. Override
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it to prevent potential contamination from the host.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>export ...</parameter></term>
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<listitem>
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<para>While the preceding commands have set some variables, in order
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to make them visible within any sub-shells, we export them.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<important>
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<para>Several commercial distributions add an undocumented instantiation
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of <filename>/etc/bash.bashrc</filename> to the initialization of
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<command>bash</command>. This file has the potential to modify the
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<systemitem class="username">lfs</systemitem>
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user's environment in ways that can affect the building of critical LFS
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packages. To make sure the <systemitem class="username">lfs</systemitem>
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user's environment is clean, check for the
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presence of <filename>/etc/bash.bashrc</filename> and, if present, move it
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out of the way. As the <systemitem class="username">root</systemitem>
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user, run:</para>
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<screen role="nodump"><userinput>[ ! -e /etc/bash.bashrc ] || mv -v /etc/bash.bashrc /etc/bash.bashrc.NOUSE</userinput></screen>
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<para>When the <systemitem class="username">lfs</systemitem>
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user is no longer needed (at the beginning of <xref
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linkend="chapter-chroot-temporary-tools"/>), you may safely restore
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<filename>/etc/bash.bashrc</filename> (if desired).</para>
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<para>Note that the LFS Bash package we will build in
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<xref linkend="ch-system-bash"/> is not configured to load or execute
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<filename>/etc/bash.bashrc</filename>, so this file is useless on a
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completed LFS system.</para>
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</important>
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<para>Finally, to ensure the environment is fully prepared for building the
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temporary tools, force the <command>bash</command> shell to read
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the new user profile:</para>
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<screen><userinput>source ~/.bash_profile</userinput></screen>
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</sect1>
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